Progressive Crop Consultant - March/April 2018

March/April 2018 Chemically and Biologically-Designed Compost Extract: A Potential Tactic for Biological Control of Weeds Sensors and Controls in Ag Plant Resistance Breaking Tomato Spotted Wilt Virus: What It Is, What Is Known And What We Can Do Monitoring and Treatment of NOW in Walnuts: Research Update Best Practices for California Rice Weed Management

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Volume 3 : Issue 2

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PUBLISHER: Jason Scott Email: jason@jcsmarketinginc.com EDITOR: Kathy Coatney Email: article@jcsmarketinginc.com PRODUCTION: design@jcsmarketinginc.com Phone: 559.352.4456 Fax: 559.472.3113 Web: www.progressivecrop.com

IN THIS ISSUE 4

CONTRIBUTING WRITERS & INDUSTRY SUPPORT Terry Brase Precision Ag Instructor at West Hills College Chuck Burks USDA, Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center Whitney Brim-DeForest UCCE Rice Advisor Julie R. Johnson Contrbuting Writer

Emily Symmes University of California Cooperative Extension Integrated Pest Management Advisor, Sacramento Valley

Chemically and Biologically-Designed Compost Extract: A Potential Tactic for Biological Control of Weeds

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Sensors and Controls in Ag

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Plant Resistance Breaking Tomato Spotted Wilt Virus: What It Is, What Is Known And What We Can Do

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Monitoring and Treatment of NOW in Walnuts: Research Update

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Best Practices for California Rice Weed Management

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The Latest on Bot Control in Walnuts

Thomas Turini University of California Cooperative Extension Vegetable Crops Advisor Dr. Gladis Zinati Associate Research Scientist, Rodale Institute

Jhalendra Rijal University of California Cooperative Extension Integrated Pest Management Advisor, Northern San Joaquin Valley

UC Cooperative Extension Advisory Board Kevin Day

Steven Koike

David Doll

Emily J. Symmes

Dr. Brent Holtz

Kris Tollerup

County Director and UCCE Pomology Farm Advisor, Tulare/Kings County UCCE Farm Advisor, Merced County County Director and UCCE Pomology Farm Advisor, San Joaquin County

UCCE Plant Pathology Farm Advisor, Monterey & Santa Cruz Counties UCCE IPM Advisor, Sacramento Valley UCCE Integrated Pest Management Advisor, Parlier, CA

The articles, research, industry updates, company profiles, and advertisements in this publication are the professional opinions of writers and advertisers. Progressive Crop Consultant does not assume any responsibility for the opinions given in the publication.

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UPCOMING EVENTS: Central Valley Almond Day June 20, 2018 | 7:00AM - 1:30PM - wcngg.com Fresno Fairgrounds

1121 Chance Avenue, Fresno, CA 93702 Join us as we bring together Almond growers in the Central California region. This conference will offer education, networking, and free industry lunch.

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CHEMICALLY AND BIOLOGICALLY-DESIGNED COMPOST EXTRACT:

A POTENTIAL TACTIC FOR BIOLOGICAL CONTROL OF WEEDS Dr. Gladis Zinati | Associate Research Scientist, Rodale Institute

W

eeds can be defined as plants growing out of place and can rapidly populate in ecosystems that do not support their natural enemies. Many methods are being used to keep weeds under control. These include burning them, pulling them out or chopping them down, and treating them with herbicides.

Vegetable growers ranked weeds as number one obstacle to organic crop production. In early stages of crop growth, weeds compete at a faster rate than crop seeds for water, space, and nutrients especially in the first 20-30 days of crop growth. Organic growers have been using mechanical cultivation and hand weeding to control weeds.

However, frequent soil cultivation decreases soil health and disrupts the ecological system; increases fuel and

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labor costs, and brings buried weed seeds to the soil surface. Biological control holds much promise for longterm, economical, and environmentally sensitive weed management.

What is biological control of weeds?

Plants are labeled “weeds” when their natural enemies become ineffective or are nonexistent. In nature, plants are controlled biologically by naturally occurring organisms. Biological control of weeds involves using biological agents that include living organisms, such as insects, nematodes, bacteria, or fungi, to reduce weed populations. By introducing biological control agents, we are attempting to restore or enhance nature’s systems.

March/April 2018

How to introduce biological control agents?

Using compost as soil mulch (4 to 6 inch (10 to 15 cm)) can be most effective in weed suppression. However, composts may vary in their chemical and biological components based on method of preparation and feedstock components. In addition, applications of composts at these quantities can be expensive. As a weed management method, chemically-and biologicallydesigned compost extracts offer an environmentally friendly biological control approach that complements conventional methods. It helps meet the need for new weed management strategies while protecting soil health.

The application of compost extracts that are rich with biological agents on an annual basis will reduce the expression

of weeds by reducing the number of weed seeds stored in the soil.

How to design compost extract for reducing weed expression?

Not all composts are created equally, neither are their extract preparations deemed to be containing the biological control agents that target specific weeds.

Organic growers, whether they grow vegetables, herbs, berries or native crops, are constantly challenged with weeds that grow at a faster rate than their cash crops. These weeds include a pigweed, lambsquarters, hairy galinsoga, and Canadian thistle. In 2015,

nitrogen but with 50 percent brown and 30 percent green of same feedstock components.

The feedstock materials were mixed and layered into 3-foot (91.4 cm) tall compost bins made of 0.5 inch (1.27 cm) mesh galvanized hardware cloth (Photo 1). The piles were turned four times as temperatures increased beyond 131°F (55 °C) and below 170 °F (76.6 °C).

Cured compost piles were then used to prepare compost extracts by bubbling air into containers that contained compost with deionized water at several dilutions for 24 hours before being tested on weed and crop seeds under controlled conditions. Compost extracts

Photo 1. Monitoring temperature in compost pile using REOTEMP thermometer (Photo credit: Gladis Zinati, Rodale Institute).

I prepared compost piles with diverse feedstock components at varying rates to encourage diversity in microbial community and subsequently produce compost extracts that target various weed species. One compost pile (C1) was prepared at 30 percent brown (woodchips and straw), 50 percent green (leaf mulch, tomato leaf and stems), and 20 percent high nitrogen (whole plant sunflower) and the second compost pile (C2) had similar percentages of high

were prepared at 1:2, 1:3, 1:4, 1:5, 1:10, and 1:20 dilutions. Ten seeds per weed species were placed in petri dishes and tested at each dilution in three replications in an incubator at 24°C. Percentages of weed seed germination were assessed five days after initiation of the experiments. Cucumber seeds were used as a model cash crop in these experiments as well.

What did the research show?

Results showed that compost piles while having similar feedstocks their chemical and biological distribution is dictated by the ratio of these feedstocks (Table 1, at bottom of page 5).

Only compost extracts with dilutions at 1:3 (compost to water (volume to volume)) were most effective in reducing pigweed weed seed germination under controlled conditions. Compost extract prepared from C1 pile reduced germination of pigweed by 20 percent compared to deionized water at p=0.0032.

Similarly, percentage of lambsquarter seed germination was lower in C1 and C2 compost extracts (52 percent, and 57 percent, respectively) but not statistically different from deionized water (65 percent). At the 1:3 dilution, cucumber seeds were not affected as those incubated in 1:2 dilutions (showed severe reduction in root elongation).

Results also showed that both C1 and C2 at 1:3 dilutions improved significantly at p= 0.018 cucumber seed germination (100 percent and 87 percent, respectively) when compared to deionized water (43 percent). While these results verified a proof of concept of using chemically-and biologicallydesigned compost extracts to reduce the expression of weeds, it was necessary to take this concept one step further and assess its usefulness under field conditions.

A follow up field trial was conducted in spring 2016 to assess whether the applications of compost extract C1 at 1:3 dilutions will be useful to suppress the expression of weeds when compared to soil cultivation (standard grower’s treatment). In a randomized complete block design (RCBD) with four replications, two compost extract

Continued on Page 6

Table 1. Chemical and biological properties of composts used for preparing compost extracts.

Treatment†

pH

Nitrate-N (mg/kg)

percentP percentK percentCa percentMg Bacterial Biomass (ng/g)

Fungal biomass (ng/g)

Protozoa biomass (#/g)

Nematode (#/g)

C1

7.7

267.5

0.22

0.49

6.60

1.40

2,173

119

2,173

3,586

C2

7.8

202.5

0.29

0.31

7.10

1.50

2,472

152

2,472

4,425

†C1 has 30 percent Browns, 50 percent Greens, and 20 percent Hi N; C2 has 50 percent Browns, 30 percent Greens, and 20 percent Hi N.

March/April 2018

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Continued from Page 5 application treatments were compared to the grower’s standard treatment (cultivation between rows of crop plants). The first compost extract application treatment is referred to as pre- and post-planting (plots received compost extracts before and after planting the cash crop), while the second treatment is referred to as post-planting treatment (compost extract was only applied after the cash crop was planted or seeded). When compost extracts were applied on plots dedicated to compost treatments, the grower’s standard

plots were treated with water. The land was previously cropped to cereal rye cover crop. The soil was cultivated, disked and packed two weeks before planting cabbage. Cabbage ‘Tender Sweet’ seedlings were established in the greenhouse in March 2016. Four-leaf stage seedlings were transplanted into two-row beds, spaced 30 inches (76 cm) between rows and 18 inches (46 cm) spacing within rows on April 19, 2016, five days after bed preparation. Cabbage transplants were covered with row covers for a month. At harvest, cabbage heads were cut at the crown level and yield was recorded.

Results showed that weeds in cabbage beds were dominated by broadleaf weeds than grasses early in the season (Photo 2 below). Broadleaf (BL) weeds included mainly Pennsylvania smartweed, Canadian thistle and ragweed. Other BL weeds such as velvet leaf, henbit, chickweed, clover, alfalfa were of lower densities. Total BL weed density in plots that received pre- and post-planting compost extract applications were 43 percent lower than with cultivation (i.e. the grower’s standard practice (Figure 1.a, at top of page 8).

Photo 2. Weeds in grower’s standard treatment (just before cultivation) plot compared to those in plots that received either preand post-planting or only post-planting compost extract C1 applications. (Photo credit: Gladis Zinati, Rodale Institute, Kutztown, PA, spring 2016).

Chemical and biological properties of composts used for preparing compost extracts.

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Weeds in plots that received two compost extract applications (pre- and post-planting).

March/April 2018

Weeds in plots that received one compost extract application (post-planting).

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Canadian thistle weed density was reduced to 65 percent in plots that received two applications of compost extract (pre- and post-planting) when compared to cultivation (grower’s standard) treatment. Similarly, ragweed density was reduced by 57 percent when plots received two applications versus one application (post-planting) of compost extract. The compost extracts were effective on broadleaf weeds rather than grassy ones.

A month after the first observation and before the second cultivation, broadleaf weed densities were assessed in each treatment. On June 13, 2016, Canadian thistle, ragweed, velvet leaf and pennycress were the major weeds.

Canadian thistle and velvet weed densities were reduced by 93 percent and 73 percent, respectively in plots that received the designed compost extract C1 applications when compared to those in grower’s treatment (Figure 2, at bottom of page 8). The designed compost extract C1 did not reduce seed weed expression and growth of ragweed and pennycress weeds.

In summary, the technology of applying chemically-and biologicallydesigned compost extracts at 1:3

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dilutions during the vegetable growing season can serve as an alternative tactic to cultivation and hand weeding and as a potential biological method for suppressing weed expression without impacting crop yields. Weeds vary in time of emergence, and thus multiple applications will be required throughout the growing season to ensure suppression of weed seeds. Designing and using compost extracts with chemistry and biology in mind, growers

Continued on Page 8

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Cabbage yield was greater in treatments that received pre- and postcompost extract applications, followed by those with post-planting application and significantly different from those produced in grower’s standard treatment (Figure 3, at bottom of page 8).

Bars with same letters are not statistically different p=0.05.

C1 samples was 0.235 mg/g dry weight.

To learn whether the chlorogenic acid may be impacted with heat, samples of autoclaved compost extracts were compared to non-autoclaved ones.

Mean value of chlorogenic acid in nonautoclaved compost extracts was 1.680 mg/g dry weight and not different from those in autoclaved samples (1.623 mg/g).

In another experimental trial the compost extract was assessed for phytochemicals at Dr. T. Casey Barickman’s laboratory at Mississippi State University. The reason behind testing it for phytochemicals is to learn whether the compost extract in question has any chemical that may interfere with weed germination. Results showed that the prepared compost and its extract at 1:3 dilution did not contain any phenolic acids or flavonoids but it only contained chlorogenic acid. Chlorogenic acid is an important intermediary compound in plant metabolism and has a broad range of antimicrobial properties. It is a phytochemical and antioxidant found in high concentrations in coffee and sunflower. The presence of chlorogenic acid in this compost extract can be explained by the inclusion of sunflower plants in the feedstock when the compost pile was prepared. Mean value of chlorogenic acid in compost

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Continued from Page 7 Figure 1. Mean weed densities of broadleaf and grasses in cabbage (1.a) and mean density of major broadleaf weeds (1.b) before first cultivation, Kutztown, PA, 2016

1.a Weed density (#/m2)

can now conserve soil health, minimize crop losses to certain weeds (such as Canadian thistle and velvet leaf), and with time build soil capacity with diverse microorganisms and phytochemicals.

This technology is safe for applicators and consumers. Future research work will expand on identifying the biological communities and learn which major bacterial and fungal organisms are playing the role of suppressing weed germination. In addition, more research is needed to evaluate and validate the use of compost extracts with varying feedstock components for suppression of other annual and perennial broadleaf weeds.

A

50 40

AB

B

30 20 10 0

BL

This material is based upon work supported by Frontier Natural Products Cooperative, a Northeast SARE Partnership Grant, under Grant Agreement Number ONE 16-278, and by Organic Farming Research Foundation (OFRF).

Grasses

Weed density (#/m2)

1.b

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

A

25 20

B

15

B ab

10

b

5 0

a

Pre and post planting

Post planting

Grower

TREATMENT Canadian thistle

8

14 12 10 8 6 4 2 0

A A

Aa

a b

Bb

b

Pre and post planting

Bb

B

Post planting

Thistle

Velvet Leaf

Ragweed

Pennycress

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Grower

March/April 2018

Pennsylvania smartweed

Figure 3. Mean cabbage yield (kg/m2), Kutztown, PA, spring 2016

Yield (kg/m2)

Weed density (#/m2)

Figure 2. Mean density of major broadleaf weeds in cabbage before second cultivation, Kutztown, PA, 2016

Ragweed

2.5 2.0 1.5 1.0 0.5 0.0

A

A B

Pre and post planting

Post planting

TREATMENT

Grower

March/April 2018

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9

SENSORS AND CONTROLS IN AG

By Terry Brase | Precision Ag instructor at West Hills College

F

or many years now growers and farmers have collected data from soil moisture sensors, infrared sensors, SPAD sensors and brix sensors.

The use of sensors in agriculture will continue to grow as the importance of accurate data collection grows. However, though we already hear about how much data producers are flooded with, collection of data is not the only use of sensors. Human involvement is bypassed by using sensors that work directly with control devices for automated functions in agricultural production systems. Control devices use data from the sensors to change or adjust the application of product.

A previous article in this series discussed sensors in remote sensing, which measures the intensity and wavelength of light waves and do not actually contact a surface. Contact sensors are sensors that are in direct contact with an object to measure some condition (and in a simplification I am also including optic sensors which use 10

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light but not for the same as remote sensing). This article will concentrate on contact sensors and how they work with controllers to automate various field activities.

Sensors The basic concept of how a contact sensor works, is in its ability to convert pressure, temperature, speed, flow, proximity to an electrical value. Contact sensors produce electrical pulses based on the conditions of the surface with which they are in contact. For example, a flowmeter within a pipe through which water passes spins a turbine and creates an electric signal denote speed of the turbine. A thermocoupler has dimetal plates or rods which when temperature changes creates an electrical signal which denotes temperature. (Most thermometers work on the basis of the changing volume of a substance such as mercury to indicate temperature.

The two different metals, expand and contract at different rates resulting in

March/April 2018

change in electrical signal). A transducer can identify pressure on a tube-like device which is converted to an electrical signal.

These electrical signals can be fed to a datalogger or computer to record the signals, but are very meaningless to a human…unless they are converted to units which are more meaningful.

Converting an electrical value to a gallons per minute, pounds per square inch, or degrees Fahrenheit includes a process of calibration. Calibration of sensors is very important and a valuable skill, which may need to be done by the manufacturer before delivery of a device, or something that needs to be done in the field during installation by a technician, with regular checks and adjustments.

However if the sensor is communicating directly with a control device, it doesn’t need to be converted to gallons, pounds, or speed. The control Continued on Page 12

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Continued from Page 10 device just needs an electrical signal.

Now before this sounds too easy, it is pretty rare that a sensor and a control device “speak the same language”, meaning the electrical signal coming from the sensor is different than what the control device needs. Standard electrical protocols are being worked on, but it is still a problem facing precision ag which prevents different manufactured systems from “talking”.

“Open source” equipment means the manufacturer has made public their design or code allowing other manufacturers to interact or talk with their equipment.

As examples of contact sensors, controllers, and automation, some

spinning creates an electrical signal that is really the speed of rotation.

A calibration that requires an actual measurement of water that passes through a specific pipe diameter for a specified period of time, is then associated with the rate of rotation. Once calibrated, a gauge or digital readout shows the gallons per minute.

Tensiometer Another contact sensor used at the Farm of the Future is a tensiometer soil moisture probe. This probe has a porous tip, that when buried in the soil allows contact with moisture in the soil. Because the probe is sealed, excess moisture or lack of moisture changes the amount of pressure within the probe.

This change is measured by a pressure transducer, which produces an electrical signal based on the level of pressure.

Again this electrical signal needs to be

Receiving node; receives digital signal that is used to move the solenoid valves and adjust flow based on the sensors in the system.

Flowmeter; The flowrate and total flow can be read on analog display under lid or the cable shown is transmitting the digital data to a transmitter.

Actuators The other half of automation in agricultural field activities is the control side. This relies a variety of devices, some of which have been around many years, but are now being used for these unique automation applications. Before providing some examples, it is necessary to cover some specific components.

Actuators are devices that convert energy or power to some type of movement. Depending on the type of actuator, the source of energy could be electrical, hydraulic, or pneumatic and the movement could be linear or circular. A simple everyday example is your remote key car lock; when you press the unlock button the electrical signal cause the door lock to spring up.

One type of an actuator is a servo,

Tensiometer; These are being used in class to demonstrate the operation and use of tensiometers for detecting soil moisture. They use pressure to sense the amount of water in the soil.

Photos are courtesy of Terry Brase.

systems that we use on the West Hills College Farm of the Future pistachio orchard are described. Most of these systems are used based on their educational value to students in learning new technology.

calibrated so that a specific electrical signal is associated to a pressure reading and then to a percent of moisture present in the soil.

Flowmeter

One more example of a contact sensor is a sap flow sensor. It relies on measuring thermal dissipation within the tree’s xylem to determine the flow of sap and thus the uptake of water. This requires measuring a precise change in temperature. A thermocoupler probe is inserted in the tree and produces an electrical signal based on the bimetal rods. As in the previous examples, this electrical signal needs to be calibrated to a temperature which is then used to estimate water uptake.

One simple example of a contact sensor used in agriculture is a flowmeter.

Flowmeters are common in irrigation systems and liquid sprayer systems to determine the amount of water or product flowing through the lines or pipes. A turbine flowmeter is a common type, which relies on a paddle or fanlike unit within the pipe or line that spins as water passes it. The more water that passes by, the faster it spins. The 12

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Sap Flow Sensor

March/April 2018

which uses an electrical feedback signal to create linear or circular motion. The difference from other actuators is that servos use feedback. A feedback signal is based on the current position of the controlled device, which is then used by the servo to move the device to maintain a desired position. A simple example of this is a water level sensor and a pump controller. As long as the water level is maintained, the servo operates the pump at a constant rate; if the water level drops, the feedback to the pump is to speed to maintain the desired water level.

Solenoid Valves Solenoid valves are a type of actuator, which uses an electrical signal to control

a valve. Solenoid valves are usually used to adjust the amount of fluid moving through the system. Liquid variable rate systems use solenoids to adjust the flow rate going to a spray boom or water through an irrigation system.

Microcontrollers are the electronic part of the control system that is the bridge between the sensors and the controllers. As a previous paragraph discussed, sensors do not necessarily “talk” with actuators, servos or solenoids. Microcontroller boards provide that communication link and common protocal. Most of the systems used on the Farm of the Future rely on manufactured, ready-to-use systems. However, for educational activities Arduino and Raspberry Pi microcontrollers are used in class to demonstrate the setup of sensors and controllers.

Bermad valve with regulating solenoid valve; This is one of the four valves that control water flow to the four blocks of the West Hills Pistachio orchard.

speed and pressure, a regular sprayer will apply a specific amount of product.

If the speed is changed then the amount of product changes. However if the sprayer includes a closed loop system, then sensors are measuring flowrate and speed and a solenoid is controlling the rate of product. If travel speed is increased the microcontroller sends a signal to the solenoid to increase flow rate and maintain the same rate of product.

An upcoming project for West Hills Ag students will be to build a sprayer.

Welding students will be fabricating the frame; Industrial Maintenance students will be constructing the sprayer, and the Precision Ag students will install the technology. We will be using Ag Leader flowmeters, Raven solenoids, and an AgLeader 1200 as the display controller.

The value of this project is not only will

rate and pressure is maintained within the irrigation lines. Reservoir level sensors and flowmeters will control well pumps to make sure that the water going into the reservoir matches the flow out and the level is maintained.

Sensors aren’t just for data collection; they are for automation control on Smart Farms too.

One more note on comparison between remote sensors and contact sensors. It is possible to get similar information using either type of sensor, but it is the proper calibration or ground truthing that determines much of the accuracy. For example the sap flow sensor can measure the uptake of water by the plant. Remote sensing uses a thermal sensor to determine the temperature of a leaf and with other information determine an approximate

Control solenoid; another example of solenoid valves that control the flow of liquid through a variable rate sprayer system.

Pressure gauge; Shown is an analog dial gauge, but the digital data is also transmitted to the internet.

Photos are courtesy of Terry Brase.

Together these hardware components are used to create a closed loop system which is a key part of precision agriculture. A closed loop includes a sensor, a servo or solenoid, and a microcontroller. The sensor is able to measure some condition; this information is fed through the microcontroller to the solenoid; the solenoid adjusts the flow to correct the condition. The sensor (or in the case of many systems, more than one sensor) continues to measure and the solenoid continues to adjust based on that information in a continuous loop.

Variable Rate Sprayer A practical example of this is a variable rate sprayer. At a given travel

the Farm of the Future have a variable rate sprayer, but the experience the students will gain in building a variable rate system from scratch.

Wireless Sensor/Control Irrigation System Another example of animation on the Farm of the Future is the wireless sensor/ control irrigation system. Flow meters and pressure sensors on the downstream side of pumps will be used to control solenoids that are on pressure regulating valves to four separate blocks on the pistachio orchard. This also allows us to set a unique irrigation schedule for each block of pistachios. The flow meters and pressure sensors also allow automation of the booster pumps to make sure flow

uptake of water. The contact sensor is a more direct measure of the condition.

A remote hyperspectral sensor is being looked at to identify specific causes of a plant’s stress such as aphids, something that would be difficult for a contact sensor to do. Each type of sensor have their advantages and are playing increasing valuable roles in collecting field data, but both need to be properly calibrated and referenced.

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

March/April 2018

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13

Plant Resistance Breaking Tomato Spotted Wilt Virus:

What It Is, What Is Known And What We Can Do

By Thomas Turini | University of California Cooperative Extension Vegetable Crops Advisor

The character of the discolorations and distortions of mature fruit caused by TSWV.

T

omato spotted wilt virus (TSWV) is a persistent challenge faced by tomato producers. It is transmitted by thrips and has many weed and crop hosts. This virus has caused economic losses in several crops that include processing and fresh market tomatoes.

An integrated pest management (IPM) program used to manage this disease included sanitation, site selection, thrips control and plant resistance. However, in 2016, a strain of the virus capable of infecting resistant varieties was documented in Fresno County. There have been few other reports of this occurring and none in the Continental United States. In this article, some background and details regarding the appearance of the resistance-breaking strain will be provided. In addition, the implications of this strain on disease management will be discussed.

Background Symptoms of Tomato spotted wilt virus are familiar to most who work in large scale tomato production.

The rings and distortions of the fruit are the most striking feature of this disease. The symptoms on the leaves are characterized by a bronzing or yellowing with necrotic spots.

Photos are courtesy of Tom Turini.

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March/April 2018

Western flower thrips transmits TSWV in Central California. Only thrips that feed on TSWV-infected plants as nymphs can transmit the virus as an adult. Thrips retain the virus for life, and viral transmission is optimum after several minutes of feeding.

The host range of TSWV includes many crops and weeds. Crops such as lettuce, common bean, celery, pepper and potato are hosts. In addition, it has been documented in weeds such as sowthistle, prickly lettuce, mallow, mustards, wild radish, London rocket, shepherd’s purse, pineapple weed and even field bindweed can support the virus.

Tomato spotted wilt virus levels in the environment vary over time. In the winter, in the absence of crop hosts in the Central Valley, the virus is detected in a relatively low number winter weeds. There is also some experimental evidence that it may persist in thrips pupating through the winter. In most situations, the levels in early season, tomatoes is low, but the thrips and the virus amplify through spring and summer in areas in which tomatoes are concentrated. Risk of experiencing loss due to TSWV is much higher in lateseason tomatoes than in early season tomatoes.

Management The most effective TSWV management approach is an integrated management program consisting of sanitation, site selection, timing, thrips management and resistant varieties.

Sanitation in terms of quickly tilling susceptible crops after harvest and controlling weeds can greatly reduce risk. Eliminating winter weeds in fallow fields and orchards can be critical. Do not wait until the tomatoes are planted to treat weedy areas with herbicide or to disc. This would cause movement of any of the insects that were in those areas and could make the conditions in those tomatoes worse. In the Central San Joaquin Valley, seven to 15 percent of the sowthistle thistle and prickly lettuce were documented as TSWVpositive in late winter in two fields. In the northern San Joaquin Valley, the virus was frequently detected in rough seeded buttercup in walnut orchards.

While these are specific examples, there are many hosts of the virus and many potential issues.

Avoid planting tomatoes in situations with high risk of TSWV damage. If there are weedy areas beyond your control near a potential site being considered for tomatoes, reconsider if possible. If you must plant tomatoes, plant those higher risk fields first to avoid the increased risk of damage associated late season plantings.

Eliminate potential sources of the virus from in and outside the field during the tomato season. This may include removal of infected tomato plants at early stages of disease development. While this roughing technique may help, it has limitations.

If there are high densities of TSWVinfected thrips from outside of the field, this approach will not be effective. Also, you will need crews that have capacity to recognize the symptoms.

Use of insecticides to reduce thrips population densities can be a component of a control program. Foliar applications have most consistently shown promise in reduction of thrips population densities and TSWV incidence. The

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most efficacious materials have been Radiant, dimethoate and Lannate.

Insecticide applications will not keep disease incidence within commercially acceptable levels under very high pressure.

A single gene resistance (SW5) has been incorporated into many commercial processing and fresh market tomato varieties which has been widely used over the past five to seven years.

There is incomplete gene expression, so it is possible to see three percent TSWV expression even in a resistant variety. Also, under very heavy virus pressure, there may be abnormal disease expression of brown concentric rings on the fruit in the absence of symptoms on the leaves.

Resistance Breaking Strain In 2016, reports of high levels of TSWV on resistant varieties were received. In spring, very high incidence of typical TSWV symptoms were present on a TSWV-resistant fresh

Continued on Page 16

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15

Continued from Page 15 market variety in Fresno County. In some portions of the field, over 50 percent of the plants were affected. In Dr. Gilbertson’s laboratory at UC Davis, results of molecular tests demonstrated the presence of SW5 gene in the affected variety and that there was an alteration in the viral protein sequence. The virus had a protein that was different than what had been present in this area previously and showed an change in a sequence of amino acids similar to what was reported in a resistance-breaking strain in Europe. More than 20 miles from the original area, two additional sites with the same resistance-breaking strain were confirmed later in 2016.

Distribution of the new strain increased in 2017. In January and February of 2017, the resistancebreaking strain was detected in weeds (sowthistle) in two of the three areas

surveyed. In processing tomatoes, the resistance-breaking strain caused substantial levels of disease in several resistant varieties outside of the areas reported in 2016. By the end of September there were very high disease levels in resistant fresh market varieties that resulted in abandonment of the field. In addition, the resistance-breaking strain was reported in Merced and Contra Costa Counties by the end of the 2017 season.

There is evidence that the resistancebreaking strain is likely to persist in our environment. Not only has it been detected in sowthistle, but this strain was causing disease in the susceptible tomato varieties, in lettuce, celery and in peppers. This is evidence that it can cause disease in the absence of the resistance gene, and that there may not be a fitness compromise that sometimes prevents long term survival.

Bronzing of the leaves is a characteristic symptom of Tomato spotted wilt virus.

TSWV infected plant with distorted fruit on a shoot with wilted leaves.

Photos are courtesy of Tom Turini.

Circular yellow/ orange patterns on fruit are typical Tomato spotted wilt virus symptoms.

16

Progressive Crop Consultant

In the areas of Fresno County where the resistance-breaking strain is detected, both the wild type TSWV strain as well as the resistance-breaking strain were present in the susceptible varieties and other hosts. Where the resistance-breaking strain is involved, the SW5 gene will not provide any level of protection: differences observed in TSWV expression among varieties are due to differences in background genetics. However, because the presence of this strain is very new, there is not information regarding relative levels of susceptibility among resistant varieties.

Furthermore, the dynamics between the

March/April 2018

resistance-breaking and wild-type strains are not well understood at this point.

It may be that the resistant varieties have lower levels of disease because of the inability of the wild-type strain to cause disease, but this is not taking into consideration the contribution of background genetics to virus expression.

Currently, there is no alternative to SW5 in commercial varieties. There are other approaches to resistance being tested under greenhouse conditions with plans to evaluate these lines under field conditions in 2018. In addition, relative severity of TSWV in commercial varieties are being compared in collaboration with commercial seed companies in 2018.

Management in the Presence of the Resistance-Breaking Strain Many fresh market and processing tomato varieties have SW5 resistance and it is reasonable to continue to use these varieties. The resistance-breaking strain has not been reported in most of the tomato production areas at this time. However, it is not advisable to use the SW5 varieties as the only means of management of this disease even if you are in an area without reports of the new strain. As suggested above an integrated approach is the most reasonable means of reducing risk. In particular, manage potential sources of the virus, avoid extremely high thrips population densities and recognize high risk situations.

Much of the research on which this article is based was and is currently being supported by the California Tomato Research Institute.

Acknowledgements to Robert Gilbertson, Ozgur Batuman, Monica Macedo, Michelle LeStrange, Brenna Aegerter and Scott Stoddard for major laboratory and field research contributions.

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

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17

O

M O N I T

RING

A ND TRE ATMENT OF NO W IN WA LNUTS: Photo courtesy of USDA/ARS.

RESEARCH UPDATE

By Chuck Burks | USDA, Agricultural Research Service, San Joaquin Valley

Agricultural Sciences Center

By Emily Symmes | University of California Cooperative Extension Integrated Pest

Management Advisor, Sacramento Valley

By Jhalendra Rijal | University of California Cooperative Extension Integrated Pest

18

Management Advisor, northern San Joaquin Valley

Progressive Crop Consultant

March/April 2018

T

he navel orangeworm (NOW) has been an increasing problems in walnut in recent years.

While NOW is usually not the most important insect pest in walnuts the way it is in other tree nuts like almonds and pistachios, a recent survey by the entomology group of the Production Research Advisory Committee of the Walnut Research Board indicated that NOW and walnut husk fly (WHF) were the top research needs. The California Walnut Board’s current research project, examines monitoring and treatment of NOW around husksplit, the period of greatest walnut vulnerability to NOW damage.

Biology Effective monitoring and treatment for NOW is tied to its biology, which is quite different from other important walnut pests like the walnut husk fly (WHF) and codling moth (CM). Compared to these others, NOW is more of a generalist and has a greater dispersal capacity.

since the number of acres of almonds, walnuts, and pistachios in California has

males and females driven by different objectives. NOW does not feed during its short adult lifetime; males exist solely to fertilize females, and females exist solely to lay eggs which will became damaging larvae. Males seek a pheromone plume whereas females seek a particularly susceptible nut. This can be thought of as seeking a smoke signal compared to seeking a pin in a hay stack.

Thus biological theory suggests that males and females are using their considerable dispersive capacity in very different ways; males searching broadly and females searching on a more localized scale.

Another analogy is that a car going up the highway between cities (i.e., males following a pheromone plume) and a single air blast sprayer treating every row of a quarter-mile square block each travel approximately 60 miles (i.e., females search for a suitable oviposition site).

increased by 50 percent from 2006 to 2015. This means that these NOW hosts are in closer proximity than before.

A study recently published by Jay Rosenheim (UC Davis), Brad Higbee (Trece LLC) and co-workers in the Journal of Economic Entomology provides practical evidence that this

As a generalist, NOW has a broader host range than other walnut pests, but fewer specializations to overcome the defenses of specific hosts. NOW infestation is therefore more dependent on injury from another source (for example, CM feeding, blight, or sunburn), or on natural husksplit near harvest.

The strong dispersal capacity of NOW is illustrated by laboratory flight mill studies that showed that the strongest fliers consistently flew over 20 miles a night, and the median flight distance for NOW in a single night is three to four miles.

These laboratory studies are consistent with a study indicating increased damage over distances of three miles from areas of higher NOW abundance.

This strong dispersal capacity has recently become even more relevant,

While both NOW males and females can fly far, how quickly they do so might differ. This is in part because

March/April 2018

Continued on Page 20

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19

Continued from Page 19

Percent of total moths with identifiable host

might be the case. Their study found a stronger correlation between traps for gravid females and subsequent damage compared to pheromone traps (for males only) and subsequent damage. While this study is complicated by mating disruption in the study area, which reduces the utility of the pheromone traps, other unpublished work suggests that the relationship between NOW pheromone traps and subsequent damage is “noisy” (low correlation), and the large area over which males are sampled may be why.

Males from pheromone traps

the period of husksplit until harvest.

The 2017 trial involved application of selected insecticides to individual walnuts in the field, followed by artificial infestation with paper containing 50 NOW eggs two to four days after these applications to individual walnuts in the tree with a hand sprayer. Nuts were removed from the field a week after insecticide treatment and incubated in the laboratory for an additional 20 days to allow any surviving navel orangeworm to mature and therefore to simplify evaluation. There were significantly fewer infested nuts among those treated with Brigade® and Intrepid Edge® compared to Lorbsan® and

Females from ovibait traps

100 80 60 40

Larval host Almond Walnut

20 0

Almond Walnut

Almond Walnut

Crop where adults were trapped Crop where adults were trapped

Monitoring In the California Walnut Boardfunded NOW study, we compared pheromone traps for males and pistachio meal traps for females in adjacent almond and walnut orchards. These locations offered a practical way to ask whether males and females dispersed across orchard boundaries and were detected at equal rates. A total of nine such almond-walnut locations were monitored in 2017; three each in the areas of Chico (Sacramento Valley), Modesto (northern San Joaquin Valley), and Parlier (southern San Joaquin Valley).

This comparison is aided by the fact that fats from almonds and walnuts have distinctly different biochemical signatures. Since NOW feeds in tree nuts as a larva but not as an adult, the fats extracted from adults are a reflection of the host in which it developed as a larva.

20

The trapping data alone provided weak statistical support for the idea that the relationship between the capture of NOW males and females in adjacent walnut and almond orchards differed.

There was a significant correlation later in the year between the number of males trapped in walnuts and in adjacent almonds. In other words, peaks and valleys of male trap catches later in the season followed similar trends in the neighboring orchards. This was not the case for females trapped in adjacent orchards at any point during the season.

This finding was consistent with the idea that males moved back and forth between the adjacent orchards more than females.

Progressive Crop Consultant

The fat analysis provided strong reinforcement of this evidence. Males that had developed in almonds were the majority of NOW captured in pheromone traps in both almonds and walnuts. In contrast, the majority of females captured in almonds developed in almonds, but the majority of females captured in walnuts develop in walnuts.

These observations are very much consistent with the hypothesis that traps for females have a smaller trapping radius and/or are more directly relevant to potential damage in the block being monitored.

Treatment While Walnut Board NOW research in the recent past has examined the premise that a stringent program of in-season insecticide treatments (CM timing) could reduce NOW damage, the most obvious critical period determining NOW damage to walnuts is from near

March/April 2018

the water control. Infestation in nuts treated with Perm-Up® and Delegate® was intermediate, and not significantly different from either the nuts treated with water and the Lorbsan® treatments, or those treated with Brigade® and Intrepid Edge®.

At the same time that the treated walnuts were taken to the laboratory, untreated Chandler and Serr walnuts were taken to the laboratory, frozen until December 19, and then artificially infested and incubated until evaluation.

Groups of 20 walnuts of the same variety were placed in round gallon plastic containers with a paper-covered wire mesh over the top. Papers with 40 NOW eggs were randomly assigned to the containers, and infestation was evaluated 26 days later. Given that Chandler is generally considered less susceptible than Serr to NOW in the field, we hypothesized that Chandler would have lower infestation than Serr. In fact, 17

percent of the Chandler were infested, but only two percent of the Serr. This difference was statistically significant.

Summary A laboratory comparison of 100 nuts each collected from a single orchard each does not broadly prove that Chandler is more susceptible to NOW than Serr. It does, however, call into question any presumption that, post-husksplit, Chandler is less susceptible to NOW compared to Serr. A plausible alternative explanation to field observations of greater damage in Serr is that NOW abundance and fertility is already diminished by the time Chandler

ovipositional medium compared to males in pheromone traps, these captures seem to be biologically and practically meaningful. Future research of NOW monitoring in almonds should examine use of NOW pheromone traps season-long to provide sensitive and cost-effective monitoring of seasonlong flight dynamics, in combination with trapping for gravid females with ovipositional bait in the late season only to provide more informative trap-based risk assessment.

PISTACHIOS

ALMONDS

WALNUTS

Mention of trade names or commercial products in this publication is solely for the purpose of providing specific

Water

A

Lorsban

A

Perm-Up

AB

Delegate

AB

Brigade

NOW L2 High Lure

B

Intrepid Edge

B 0

20

40 60 80 Percent nuts infested

is harvested (often in October), whereas Serr often goes from husksplit to harvest from late August to mid-September; i.e., during the period of greatest NOW abundance of the year.

100

information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer.

More generally, the difference in Comments about this article? We want origin between males and females to hear from you. Feel free to email us at trapped in adjacent walnut and almond article@jcsmarketinginc.com orchards are consistent with the hypothesis that females are often more local to an area Power any 3-phase pump with solar in which they are captured compared On grid, off grid & hybrid systems to males. Historically, egg traps (which use Reduce your demand charges a bait like that used in with Solar + Storage the female traps here) have been frustrating because of variability and poor detection.

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March/April 2018

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21

Best Practices for California Rice Weed Management

By Whitney Brim-DeForest | UCCE Rice Advisor Photo courtesy of Kathy Coatney.

F

or California rice growers, weed management is an increasingly complex and expensive endeavor.

Herbicide resistance has been identified in many of our major species, and several are resistant to multiple modes of action. We have new modes of action, as well as new herbicides in the research pipeline, but many of the new herbicides are granular herbicides, with small windows of efficacy and application timing. Further complicating our management are new weed species, including weedy red rice (Oryza sativa L.) and two in the watergrass complex (Echinochloa spp.). Weedy rice cannot currently be managed with herbicides, and the two new watergrass species appear to be more tolerant of California rice herbicides than barnyardgrass and late and early watergrass.

Photo courtesy of Kathy Coatney.

22

Progressive Crop Consultant

March/April 2018

All of these factors lend themselves to a discussion about integrated weed management, which requires the use of many different tools to control weeds.

Weeds—what are they?

Sometimes, how we define a weed can be ambiguous. The same plant found in one location may be considered a crop, and when found in another place, a weed. So what makes a plant “weedy”?

One of the best definitions is that it is a plant growing in a location where it is unwanted. In agriculture, a weed species usually causes an economic loss, either through yield reduction in the field, or damage to or devaluation of the harvested crop. In rice, weedy (red) rice is a good example of a plant

which may or may not be considered a weed, depending on the context. Weedy rice is the same species as cultivated rice (both are Oryza sativa L.), so it is edible, and causes no harm to humans or the environment. The reason that it is considered a weed is due to the large yield loss it causes, as well as the reduction in quality of the harvested crop, when contaminated. The lack of a clear definition of weedy rice and no set of identifying characteristics is what allowed it to spread over more than 10,000 acres in California, largely unchecked.

In order to have good weed management practices, carefully defining and identifying weeds is a critical first step. Without proper identification,

weeds will be left to propagate and further infest fields. As a crop advisor or pest control advisor, being able to quickly identify weed species in the field is key to being able to plan a weed management program.

Integrated Weed Management In weed science, we talk a lot about integrated weed management, or using a variety of tools to manage weeds, not relying solely on herbicides. We do this for a number of reasons, but one of the primary reasons is to decrease the chances of certain species evolving herbicide resistance. Herbicides are expensive and time-consuming to develop, and the rate at which new

Continued on Page 24 March/April 2018

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23

Photo courtesy of Kathy Coatney.

Continued from Page 23 herbicides are being discovered and developed has decreased significantly over time. Utilizing more than just herbicides as part of a weed management program extends the life of herbicides, ensuring they can be useful for controlling weeds for more than just a few years.

Integrated weed management can take on a variety of forms: 1) cultural methods such as irrigation, tillage, or crop rotation; 2) mechanical methods such as tillage or a barrier (plastic sheeting, for example); 3) sanitary control methods such as cleaning equipment, using certified seed; 4) biological control (using a living organism such as a predator or parasite); and of course, 5) herbicides. In rice, the use of biological controls is currently not available for weeds.

Cultural and Mechanical Management Rice, as we all know, is a unique crop.

One of the aspects of rice agriculture that makes it unique is the management 24

Progressive Crop Consultant

of water. Irrigation practices can be manipulated to suppress certain weed species, or to encourage others to germinate, where they can then be controlled with an herbicide or through tillage (Table 1, on page25). A combination of irrigation, tillage and herbicides can be utilized to manage some weed species:

•

Deep-flooding: A deep flood of 10 to 12 inches at the beginning of the season can be used to suppress watergrass species (late and early).

This may encourage the growth of some aquatic species (broadleaves and ricefield bulrush).

•

Dry-Down: At about five weeks after planting, the field can be drained, to control some aquatic species such as ricefield bulrush and broadleaves including ducksalad.

The dry-down should last for about 8 to 10 days. However, this may encourage the germination of other weed species including

March/April 2018

barnyardgrass and smallflower umbrella sedge.

•

Stale Seedbed: Before planting rice, the field is flushed or flooded to promote weed germination. If the field is a conventional field, a non-selective herbicide such as glyphosate can be used to control emerged weeds. At approximately one to two weeks, most of the watergrass species will have emerged. It may take longer for the emergence of other weed species.

Instead of an herbicide, shallow tillage can also be used to control emerged weeds. However, this may

Photo courtesy of Kathy Coatney.

Table 1. California rice species adapted to dry and wet-seeded systems

DRY

WET

BOTH

Sprangletop

Ricefield bulrush

Smallflower umbrella sedge

Barnyardgrass

Redstem

Late watergrass

Ducksalad

Early watergrass

Monochoria Arrowhead Note: Sprangletop and barnyardgrass may come up under a flood, but populations are much higher under a dry-seeded system. Likewise, smallflower umbrella sedge populations may be higher under a dry seeded system.

require an extended period of time, as the field must be dry enough for equipment to move across it.

•

Crop Rotation or Fallow: Crop rotation or a managed fallow can also be utilized to reduce the amount of rice-specific weeds in the weed seedbank. Crop rotation allows for rotation of herbicide

modes of action, and since most rotational crops are not flooded, crop rotation can have a similar effect to dry-seeding, shifting the weed species found in the field. A managed fallow, utilizing multiple stale seedbeds through the course of a season, can be used in a field that has weeds that are difficult to manage with rice herbicides. Like

crop rotation, a managed fallow allows for the use of MOAs not found in rice. For some multipleresistant weed species, including late watergrass, there are no registered rice herbicides remaining, making the species difficult to manage. A managed fallow can be a means to

Continued on Page 26

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25

Continued from Page 25 Table 2. The major weed species in California rice, the number of registered herbicides available that control those species, the number of modes of action the registered herbicides cover, and how many of those modes of action have recorded resistance, including multiple resistance.

SPECIES

REGISTERED HERBICIDES

MODES OF ACTION

Early watergrass

8

6

4 MOA’s (multiple-resistance)

Late watergrass

8

6

4 MOA’s (multiple-resistance)

Barnyardgrass

8

6

2 MOA’s (multiple-resistance)

Sprangletop

4

3

2 MOA’s ( no multiple-resistance)

Smallflower umbrella sedge

9

4

2 MOA’s (multiple-resistance)

Ricefield bulrush

9

5

2 MOA’s (multiple-resistance)

quickly reduce the weed seedbank in a short amount of time (over one season).

of weedy rice has been through contaminated seed and sharing of equipment. Thankfully, we have a vigorous Seed Certification program, Sanitary Control and a new Quality Assurance program, both administered by the California It is now known that one of the Crop Improvement Association (CCIA). most important vectors for the spread In particular, the use of certified seed can prevent the spread of weedy (red) rice and wingleaf primrose willow. The amount of seeds tolerated in certified seed for wingleaf primrose willow and weedy (red) rice is zero.

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Progressive Crop Consultant

March/April 2018

HERBICIDE RESISTANCE RECORDED

Herbicide Resistance Herbicide resistance is a growing problem in California rice. Due to a small total number of herbicide modes of action (MOAs) available, and little crop rotation, it is difficult to plan a program that effectively rotates MOAs. This is especially true of the herbicides used as clean-up sprays late in the season. Lack of rotation late in the season has led to the evolution of multiple-resistance in several of our most troublesome weed species (Table 2, on top of page 26). For several of the species, there are only one or two remaining MOAs for which there is no resistance.

Summary Weed management in rice is increasingly complicated. In order to best manage weeds for the longterm, it is important to consider more than just herbicides, especially since herbicide resistance appears to be an increasing problem. When scouting fields, be on the lookout for unusual and new weed species as well as weeds that are uncontrolled by herbicides that normally should control them. Report any suspected unusual weeds or possible herbicide resistance to your local University of California Cooperative Extension Advisors. Happy planning!

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

March/April 2018

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27

The Latest on Bot Control in Walnuts

by Julie R. Johnson | contributing writer

E

very walnut grower, pest control advisor (PCA) and certified crop advisor (CCA) wants to know and understand the latest in controlling Botryosphaeria (Bot) to reduce the damage this fungal disease can cause, both in the orchard and the pocketbook.

That is exactly what Themis Michailides, University of California, Davis plant pathologist in the Kearney Agricultural Research and Extension Center at Parlier, offered in his presentation, The Latest in Spray Applications for Controlling Botryosphaeria, during the Walnut Trade Show at the Yuba-Sutter Fairgrounds in January.

28

Progressive Crop Consultant

Along with Bot, Michailides also discussed Phomopsis, and the blight and canker produced by both.

Citing a study he led in Northern California, Michailides shared the results of his research which is a methodology to determine spray timing that reduces the frequency of fungicide sprays.

Bot and Phomopsis are widely distributed in walnuts orchards in counties where walnuts are grown.

In a collection of walnut cultivar/

March/April 2018

selections studies at UC Davis, the majority of them were infected with Bot, Phomopsis or both after inoculation. The collection was from a range of walnut varieties, including Howard, Chandler, Payne, Chico, Idaho, Solano and more.

Bot Symptoms and Spread There are 10 species of Bot and at least two species of Phomopsis, with both pathogen groups producing abundant water-splashed pyenidiospores and wind-borne asceospores.

Michailides said this means Bot can spread by spores

dripping and splashing or by blowing around in the orchard. Both spores types need water to trigger the infection.

Bot infection requires susceptible tissue, presence of infection Bot spores, and the right environmental conditions—at least a quarter inch of rain (or irrigation water directly on susceptible tissue) and temperatures at or above 50 degrees F. Michailides talked about Bot symptoms of pycnidia, pseudothecia, cankers, fruit and spur blight, as well as Phomopsis canker and blight.

Bot reduces yields by killing small fruit wood and their buds (next year’s crop) and large branches and directly infecting the nut. It is most obviously seen in walnut orchards as blighted shoots (dead branches with the leaves still stuck on), blighted twigs (dead, darkened and shriveled), and fruit with the entire hull blackened but still on the trees. Spores can infect intact fruit and all kinds of wounds throughout the season and post-harvest. Michailides explained 60 to 75 percent more shoots were infected on walnut trees when walnut scale was present.

Disease Management Michailides said the best disease management intergrades cultural and chemical control practices, as well as control of walnut scale to avoid stressing the trees.

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As he discussed disease management, Michailides said cultural practices and other factors affecting Bot canker and blight include irrigation, pruning/ hedging, insects, and walnut blight and/ or other diseases.

He explained the importance of setting the right trajectory angle for sprinkler irrigation and avoidance of wetting the tree canopy.

When sprinkler trajectory was placed at 12 degree angle, studies found there were 20 percent infected clusters in the trees compared to 90 percent infection when sprinkler trajectory was set at 23 degree angle, Michailides said.

In addition, irrigation duration in hours had an impact on infection and

Continued on Page 30

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• What it does: The DA kairomone enhances the effect of the Codling Moth pheromone on male mating disruption. And, initiates female mating disruption through behavior changes in the female resulting in oviposition disruption, less mating, higher virginity and lower damage.

• How to use it: Fast hanging design, clips easily and securely onto branches, and eliminates lateral branch scarring.

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March/April 2018

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29

Continued from Page 29 spread of Bot. Irrigation hours from 18 hours upwards towards 72 hours showed an increase of infection from about 8 percent at 18 hours to 55 percent at 72 hour durations.

Selective hand pruning of dead wood and cankers was another avenue of

Orchards with moderate infection, 20 to 50 percent infection, Michailides advised pruning or hedging these orchards first and then move into more infected orchards. Prunings need to be removed out of these orchards, with “some” spraying.

Lightly infected orchards, one to 20 percent, need to be pruned or hedged first and then moving on to more

“There is no resistance in these fungi,” he added.

Michailides presented a simple chart, Leaf Wetness Model (LWM) he created through research that graphs low, medium and high risks for Bot infection in walnuts, and pistachios, based on the duration of leaf wetness in hours, and the average temperature during the wetness period (see chart #1).

All photos courtesy of Themis Michailides.

disease management. Reduce inoculum by pruning out dead branches, branch stubs, and blighted shoots in the summer or fall when not raining, and disinfect pruning equipment.

“By just doing selective pruning, we improve the disease control by 80 percent,” Michailides said.

infected orchards. Prunings need to be removed out of the orchard and one mid June/July spray.

In young orchards, five to seven years-old, with no Bot, prunings can be chipped and left in the orchards, and no Bot fungicide spraying is needed.

Chemical Control

Prunings from orchards that have heavy infection, need to be chipped and may be left in the orchard, with a yearly, full spray fungicide program.

Michailides said growers need to be sure and apply effective fungicides.

Based on rainfall amount and temperature, use the LWM graph during a rain event to pinpoint the Bot risk zone and determine whether a spray is needed, Michailides said. A spray is applied when points fall in medium and high risk. If a point falls on the line separating low and medium risk, a spray is also applied.

Leaf wetness period in hours starts as soon as a rain begins, to the end of the rain, plus half an hour to one hour when

Continued on Page 32 30

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Drive Yields with Nutrition, Right Nutrient, Right Timing, Right Form, Right Mix Yield: ‘Chandler’ Walnuts

Replicated Trials - Two Bees Ag Research and Consulting, Escalon, CA LB Nutmeat/Acre

9000

8316

6750

6682 5445

5164

4500

6509

4000

2250 1634

1164

0

2015

lbs/acre

n UTC

Agro-K’s “Science Driven Nutrition” approach to foliar feeding walnuts delivers the right nutrients at the right time and in the right form. Walnuts, due to their sheer size, large root system and significant foliage have heavy nutrient demands to achieve maximum yield and quality. Zinc, manganese and other micronutrient requirements are larger than for other tree crops and are also more difficult to supplement because walnut leaves are thick, leathery and harder to penetrate effectively.

Agro-K’s science-based approach to soil and foliar nutrition delivers high yields and quality nuts while improving long-term tree health and productivity.

Maximizing early season growth processes and tree function requires a variety of micronutrients – zinc to maximize leaf development/size, vascular function and root growth; manganese for proper root development, root health and nitrogen utilization; magnesium and iron to maximize chlorophyll formation and efficacy. Agro-K’s Zinc Plus +4 D.L. provides all these nutrients in the proper balance.

Applying Zinc Plus +4 D.L. with Agro-K’s high orthophosphate/low potassium AgroBest 9-24-3 helps meet early season nutrient demands when soils are still cool and roots function is constrained.

Agro-K’s proprietary Dextro-Lac formulation is soft on foliage but designed to penetrate thick tissue rapidly and completely. Because the Dextro-Lac process is not a chelation process, but sugar based, once absorbed by the tree the nutrients are immediately available. Unlike chelated products, no energy requirement is needed to break the chelation bonds for the tree to access the nutrients. Zinc

1064

2016 n Agro-K Program

2017

n Increase Yield with Agro-K Program

Plus +4 D.L. is also specifically designed to be compatible with early season copper sprays.

As bloom, nut set and cell division occur demand for calcium peaks; in addition micronutrient demand is still occurring as new leaf and terminal growth continues. Applying VigorSeaCal in combination with AgroBest 9-24-3 followed by Zinc Plus +4 D.L. during rapid leaf growth help growers meet a walnut tree’s complex and significant nutrient demand at this critical physiological stage. Satisfying peak nutrient demand will result in improved nut set and cell division that sets the stage for large, dense nuts with maximum weight at harvest. Vigor-SeaCal combines calcium in a carbohydrate formulation with Agro-K’s powerful seaweed extract to enhance nut cell division. Applying an energy-stimulating high phosphate NPK like AgroBest 9-24-3 enhances seaweed efficacy helping drive more nut cell division for larger, denser nuts. AgroBest 9-24-3 is specifically designed with minimal potassium content for early season foliar applications. Foliar spray mixes with even moderate amounts of potassium applied during cell division will antagonize calcium uptake and negatively impacting leaf cell wall integrity and nut quality. The AgroBest 9-24-3 ratio provides more units of ortho-phosphate, for better foliar uptake, per dollar than most other NPK blends without antagonizing calcium incorporation into cell wall structures.

AGRO-K CORpORAtiOn 8030 Main Street, NE • Minneapolis, MN 55432

800-328-2418 • www.agro-k.com

Science Driven Nutrition

™

© 2018 Agro-K Corporation

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All photos courtesy of Themis Michailides.

Continued from Page 30 it is overcast after the end of the rain.

If rain is off-and-on but with less than half hour of clear skies or less than one hour of cloudy skies between showers, that also counts towards the leaf wetness period. Michailides said for more precision, use a leaf wetness sensor.

Temperature of the model is averaged over the wetness period. The higher the temperature the quicker Bot can appear and the higher the risk in a shorter period of time.

Using this model, growers, PCAs and CCAs can reduce their spray applications compared to the standard calendar or practiced number applications.

In his take-home advice, Michailides said it is best to spray fungicides from bloom through July/early August to reduce Bot and Phomopsis (see http:// www.ipm.ucdavis.edu).

Also, spraying before or after an infection event (rain) is very effective, and to always watch for rain events.

The best-timing for a spray application seems to be around second half of June to first half of July, and a post-harvest spray can also reduce disease, but it may not be sufficient.

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

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March/April 2018

All photos courtesy of Themis Michailides.

Notes: Based on rainfall amount and temperature, use this LWM graph during a rain event to pinpoint the BOT risk zone and determine whether a spray is needed. A spray is applied when points fall in medium and high risk. If a point falls on the line separating low and meidum risk, a spray is also applied. *Leaf wetness period in hours starts as soon as a rain begins to the end of the rain +1/2 hour or +1 hour when it is overcast after the end of the rain. If rain is off-and-on but with less than 1/2 hour of clear skies or less than 1 hour of cloudy skies between showers, that also counts towards the leaf wetness period. For more precision, use a leaf wetness sensor.

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The psyllid damages citrus directly by feeding on new leaf growth (flush).

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Progressive Crop Consultant

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