Progressive Crop Consultant - September - October 2016

Progressive

Crop Consultant The Leading Magazine For Ag Professionals

September - October 2016 New Efforts on Fusarium Wilt of Lettuce Brings Disease Front and Center PCA Budgeting Nutrition for Stone Fruit Battle to Keep Crop Protection Tools Heats Up Leaffooted Bug

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In This Issue New Efforts on Fusarium Wilt of

6 Lettuce Brings Disease Front and Center

Contributing Writers & Industry Support Paul Brierley Executive Director, Yuma Center of Excellence for Desert Agriculture W. D. Gubler Department of Plant Pathology University of California, Davis Dr. Michael Matheron School of Plant Sciences, University of Arizona Cecilia Parsons Contributing Writer Stephanie Thara Communications Manager, Western Growers Kris Tollerup IPM Advisor, Fresno/Madera Counties, UC Statewide IPM Program and Cooperative Extension, Kearney Ag Research and Extension Center

UC Cooperative Extension Advisory Board Kevin Day

County Director and Pomology Advisor, Tulare/Kings County

David Doll

UC Farm Advisor, Merced County

Dr. Brent Holtz

County Director and Pomology Farm Advisor, San Joaquin County

“Esca” and Petri Disease of Grapevine

12 in California

20 PCA Budgeting Nutrition for Stone Fruit Battle to Keep Crop Protection Tools 22 Heats Up

Cancellation of Belt is Latest in Registration Kerfuffle

Bug 26 Leaffooted How Can Monitoring of Leaffooted Bug Be Improved?

Steven Koike

Plant Pathology Farm Advisor

Emily Symmes

IPM Advisor, Sacramento Valley

Kris Tollerup

IPM Advisor, Fresno/Madera Counties, UC Statewide IPM Program and Cooperative Extension, Kearney Ag Research and Extension Center

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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Photo Credit: Paul Brierley

Lettuce

Attendees of the November, 2015 International Symposium on Fusarium wilt of lettuce examine the commercial field trials of varieties and crop protection products for efficacy against the disease.

New Efforts on Fusarium Wilt of Lettuce Brings Disease Front and Center

Dr. Michael Matheron School of Plant Sciences, University of Arizona

S

hortly after hiring on as the inaugural executive director of the University of Arizona’s new Yuma Center of Excellence for Desert Agriculture, a public-private partnership devoted to applied agricultural research needed by the desert agriculture industry, Paul Brierley asked his stakeholders what they would like the Center to address first.

The answer was resounding: Help us mitigate plant diseases! And not just any plant disease – help us with the seemingly impossible-to-eradicate Fusarium wilt of lettuce. And thus began the Center’s odyssey against the insidious disease that is wiping out entire fields during warm-season production of iceberg lettuce – costing the industry millions of dollars.

First step: figure out what we already know. No need to re-invent the wheel.

For that, Brierley turned to Dr. Mike Matheron. Matheron is an extension plant pathologist and professor at the University of Arizona’s Yuma AgriculPage 6

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tural Center. When the disease first migrated to California and Arizona at the turn of the twenty-first century, Dr. Matheron and others from the University of Arizona and UC Davis undertook research to better understand the disease and how to fight it.

Characteristics of the plant pathogen Fusarium wilt of lettuce (Figure 1) is caused by the soil-borne fungus Fusarium oxysporum f. sp. lactucae. This particular form of Fusarium oxysporum is known to cause disease and visible symptoms only on lettuce. There are three reported races of Fusarium oxysporum f. sp. lactucae. All three races of the lettuce pathogen are present in Japan, whereas only race 1 is known to occur in the United States (Arizona and California), as well as in Argentina, Brazil, Iran, Italy, Portugal, and Taiwan.

The plant pathogenic forms of Fusarium oxysproum can also live on dead plant tissue when living host plants are not available, enabling the pathogens to survive in soil indefinitely. Forms of Fusarium oxysporum that are not plant pathogens also reside in soil, living only on dead plant tissue.

Disease development on lettuce Fusarium oxysporum f. sp. lactucae

September/October 2016

Photo Credit: Paul Brierley

Paul Brierley Executive Director, Yuma Center of Excellence for Desert Agriculture

Figure 1. Foliar symptoms of Fusarium wilt include yellowing and necrosis of leaves as well as stunting and wilting of plants. invades lettuce plants through small roots, then grows within the xylem tissue, which transports water and nutrients from roots to plant foliage. As the pathogen advances into the plant taproot and lower stem, the xylem tissue becomes plugged by the fungus and byproducts of its presence, resulting in restricted water uptake, stunting, wilting, and often plant death. Plants infected when older may survive but are usually stunted. Taproots of infected plants look normal externally; however, examination of internal tissue usually reveals the presence of a reddish-brown discolContinued on Page 8

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Photo Credit: Paul Brierley

Figure 2. Reddish-brown to black necrosis of internal taproot and crown tissue is a common symptom on lettuce infected with Fusarium oxysporum f. sp. lactucae.

Continued from Page 6 oration (Figure 2). Fusarium wilt was first found in the United States in 1990 within a lettuce field in Fresno County, California. In Arizona, the disease was first observed in 2001 in six Yuma County lettuce fields. The number of fields known to be infested with Fusarium oxysporum f. sp. lactucae in Yuma County had increased to 50 by 2010, with further increases thereafter.

Disease management considerations Disease resistant plants. The most effective management tool for Fusarium wilt of most hosts is to grow plants with genetic resistance to the pathogen. Unfortunately, 88 crisphead, 6 green leaf, 5 red leaf, and 4 butterhead varieties tested in Arizona in 2002 and 2003 were very susceptible to Fusarium wilt (Matheron et al. 2005). On the other hand, some of the 20 romaine varieties in the same trials, especially BOS 9021, King Louie, and Slugger, were quite resistant or tolerant to the disease. Two recent field trials conducted in 2015 again demonstrated that romaine cultivars (Valley Heart, King Henry, Rio Bravo, Green Thunder, and Vanguard PIC) were less affected by Fusarium wilt than crisphead cultivars (Midway, LT 4083, Raider, Prestige, Sunquest, Dover, and Crusader). However, Midway sustained significantly less disease than all other tested crisphead cultivars in one field trial.

Sanitation. The goal of implementing sanitation procedures is to minimize the movement of Fusarium oxysporum Page 8

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f. sp. lactucae from infested to noninfested fields. Any farming operation or activity that can move infested soil or plant material may spread the pathogen, such as seedbed preparation activities, cultivation, harvesting operations, use of contaminated irrigation pipe, workers’ footwear, tractors and other farm equipment. To be successful, these sanitation procedures must remain in effect even when the contaminated field is planted to crops other than lettuce. Effectively preventing the spread of Fusarium oxysporum f. sp. lactucae from infested to noninfested fields requires thoroughly removing contaminated soil from tractors, farm equipment, irrigation pipe, harvesting equipment, and footwear before leaving the infested field.

Crop rotation. Research has shown that the lettuce Fusarium pathogen can colonize roots of living tomato, cantaloupe, watermelon, cotton, broccoli, cauliflower, and spinach plants without causing disease symptoms (Hubbard and Gerik, 1993; Scott et al. 2013). Also, pathogenic Fusarium oxsporum can grow on organic matter such as crop residue. The importance of nonhost plants and organic matter in sustaining the population of Fusarium oxysporum f. sp. lactucae in soil is unknown; however, the value of crop rotation as an effective management tool for Fusarium wilt on lettuce is questionable.

Bare soil fallow. In an Arizona/California microplot study (Scott et al. 2012), when soil containing Fusarium oxysporum f. sp. lactucae was maintained free of plants and not irrigated, the pathogen population decreased over time, with an estimated half-life of 5.9 ± 0.7 months (time interval required for pathogen population to decline to 50 percent of the original level). Using this estimate, a one to two year bare soil fallow period may reduce the pathogen population by about 75 to 93 percent, respectively. These results should be considered preliminary findings until confirmed by further research.

Treatment of soil with fumigants and fungicides. In one Arizona field trial, a preplant application of metam sodium (Vapam) reduced disease incidence at crop maturity by 44% in a subsequent planting of a susceptible lettuce variety.

In another Arizona field trial, an at-seeding application of thiophanate-methyl (Topsin M), fludioxonil (Cannonball), or

September/October 2016

boscalid+pyraclostrobin (Pristine) had no suppressive effect on development of Fusarium wilt of crisphead lettuce.

Cultural practices. Soil temperature has a profound effect on development of Fusarium wilt of lettuce. In two Arizona field trials, the proportion of 11 different lettuce varieties that were diseased or dead was 83.2, 10.0, and 1.5 percent when seeded in September, October, and December, respectively (Matheron et al. 2005). When lettuce plantings were started in these respective months, the mean soil temperature at the 4-inch depth during crop growth was 78, 59, and 57°F. Planting late in the lettuce production season can dramatically reduce disease incidence and crop loss in infested fields.

Disease incidence on romaine lettuce generally was much lower than that on crisphead lettuce. In the same two field trials mentioned earlier, that were conducted in 2002 and 2003, the mean incidence of diseased or dead crisphead lettuce plants sown in September, October, and December was 94.0, 23.0, and 1.3 percent, respectively. On the other hand, the incidence of diseased or dead romaine plants for the same planting months was 34.0, 0.7, and 0.2 percent, respectively. Field trials conducted in 2002, 2003, and 2015 have demonstrated that romaine lettuce cultivars in general are significantly more tolerant to Fusarium wilt compared to crisphead lettuce.

Continued evaluation of crisphead cultivars currently available or in development will occur in 2016 and beyond.

Summer soil solarization. In four separate field trials in Arizona, summer solarization of soil (covering moist soil with clear plastic) for 30 days reduced the incidence of Fusarium wilt on a subsequent crisphead lettuce planting from 42 to 91 percent compared to nonsolarized plots (Matheron and Porchas, 2010).

This procedure can significantly reduce the population of Fusarium oxysporum f. sp. lactucae in soil and the resulting incidence of Fusarium wilt in a subsequent lettuce crop; however, care must be taken to avoid incorporating untreated soil from the furrow into the treated bed.

International Symposium on Fusarium Wilt of Lettuce In October of 2015, with funding received from the Arizona Department of Agriculture’s Specialty Crop Block Grant

Photo Credit: Paul Brierley

Program, the Yuma Center of Excellence for Desert Agriculture (YCEDA) teamed with Dr. Barry Pryor, Professor of Plant Pathology and Mycology at the University of Arizona College of Agriculture and Life Sciences, to host an international symposium on the disease. The symposium was not just a research symposium, but rather a meeting of the minds of industry and academia from around the world. Researchers shared their work, and the knowledge they had learned.

They came not just from California and Arizona, but also from Italy, Brazil, and Japan, where the disease seems to have originated in the 1950’s.

The grower/PCA community soaked up all the knowledge and ideas offered, but they also returned the favor to the researchers: they shared what they were experiencing in the field, what they had tried, what had worked, and what had not worked. This mixing of industry and academia was by design — it is exactly what the founding fathers had in mind when they created the privately-funded Center of Excellence.

With over 175 people in attendance in the middle of the Yuma, Arizona winter

Over 175 attendees participated in the Center’s International Symposium on Fusarium wilt of lettuce in November, 2015 in Yuma, Arizona. produce season, the symposium definitely accomplished one thing: raising the profile of the disease. It became clear that it isn’t just a desert problem, but is increasingly affecting production areas in central California also. Not to mention the challenges faced in other countries previously mentioned. And it is spreading.

Commercial Field Trials It had been 12 years since researchers had tested the effectiveness of lettuce varieties and chemical and biological controls in Arizona commercial field trials. The problem with that time lapse was made glaringly clear at the symposium: growers complained that Continued on Page 10

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the research data on resistant varieties had all been gleaned from old varieties that were no longer in use. What they needed, they said, was annual field trials testing current varieties and crop protection products in commercial fields infested with Fusarium wilt. And trials of varieties under development would be a bonus — speeding up the introduction of these hoped-for silver bullets.

Fortuitously, the Center had teamed up with Dr. Matheron and Dr. Pryor to conduct just such a field trial, and the trials were on display for the symposium audience to observe. The results of these trials were made available at www.

DesertAgSolutions.org to everyone, just in time to help with planting decisions for the 2016 fall produce season.

Following the seminar, the Center worked collaboratively with researchers at UC Davis and the University of Arizona to apply for grant funding to conduct annual variety and crop protection field trials in California and Arizona, as well as developing a tool to rapidly measure the extent of disease pressure to be expected on a field-by-field basis and devising tools for early detection of the disease in the lettuce plants. To date, we have received funding for Arizona field trials and early/remote detection of the disease. New field trials are underway as of September, 2016.

Brainstorming to Move Forward Another feature of the international symposium was a brainstorming session that brought together experts in the areas of Cultural Practices, Breeding and Resistance, Product Development, Containment and Regulation, and Resources and Funding. This resulted in five pages of suggested steps forward, which are available at www.DesertAgSolutions. org. The ideas range from creation of an international consortium focusing on soilborne diseases of leafy greens to development of Best Management Practices for seed and soil health, speeding up development of resistant varieties, and developing multi-disciplinary disease management approaches.

This group of experts will come together again to take concrete steps to implement the ideas generated during brainstorming. Priority will be given to those ideas ranked highest in a follow-up Page 10

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Photo Credit: Paul Brierley

Continued from Page 9

Experts in the areas of Cultural Practices, Breeding and Resistance, Product Development, Containment and Regulation, and Resources and Funding came together to brainstorm possible paths forward in the fight against Fusarium wilt of lettuce. survey of the symposium participants.

Big Data Analytics to Focus on Fusarium Wilt Another promising project that the Center is moving forward on is applying Big Data Analytics to USDA research and growers’ historical data to determine the triggers of disease outbreaks. Then, with real-time sensor data and climatological predictions, growers and PCA’s will be armed with additional decision tools to make choices that mitigate disease incidence and severity. Field work starts this fall, and you can rest assured that Fusarium wilt will be the first target in their crosshairs.

Final comments There is no single magic bullet that will eliminate Fusarium wilt as a disease of concern for lettuce growers in California and Arizona. However, implementing an Integrated Disease Management (IDM) program using proven strategies outlined above can provide a meaningful level of disease control. Possible future development of resistant crisphead varieties and validation of other potential disease management tools through additional research may provide new IDM strategies in the future. It is the goal of the Yuma Center of Excellence for Desert Agriculture that, thanks to the power of industry and academia working together, Fusarium wilt becomes just another nuisance rather than the severe threat that it is today.

September/October 2016

PCC

References Hubbard, J. C., and Gerik, J. S. 1993. A new wilt disease of lettuce incited by Fusarium oxysporum f. sp. lactucum forma specialis nov. Plant Dis. 77:750-754.

Matheron, M.E., McCreight, J. D., Tickes, B. R., and Porchas, M. 2005. Effect of planting date, cultivar, and stage of plant development on incidence of Fusarium wilt of lettuce in desert production fields. Plant Dis. 89:565-570.

Matheron, M. E., and Porchas, M. 2010. Evaluation of soil solarization and flooding as management tools for Fusarium wilt of lettuce. Plant Dis. 94:1323-1328.

Scott, J. C., Gordon, T. R., Kirkpatrick, S. C., Koike, S. T., Matheron, M. E., Ochoa, O. E., Truco, M. J., and Michelmore, R. W. 2012.

Crop rotation and genetic resistance reduce risk of damage from Fusarium wilt in lettuce. California Agriculture 66:20-24.

Scott, J. C., McRoberts, D. N., and Gordon, T. R. 2013. Colonization of lettuce cultivars and rotation crops by Fusarium oxysporum f. sp. lactucae, the cause of Fusarium wilt of lettuce. Plant Pathology 63:548-553.

Grapes

“Esca” and Petri Disease of Grapevine in California Photo Credit: W. D. Gubler

W. D. Gubler Department of Plant Pathology University of California, Davis

R

ecent research has led to assigning the foliar symptoms of Esca or Black Measles to vascular pathogens, therefore different from the wood decay agents originally described as the esca causal agents. This complex of diseases is also known in USA as black measles since the most frequent and relevant symptoms appear on the berry in the form of small gray-purple spots on berry surfaces. The fungi mentioned are typically vascular pathogens that can give different symptoms and syndromes at different developmental stages in vine life. These syndromes were given different names: black wood streaking of rootstock, Petri disease, and leaf stripe disease (also known as “young esca”).

Petri disease, initially called by many names such as young vine decline or black goo, occurs in many of the world’s production areas. It is a form of decline, usually associated with vines younger than 7 years old showing fungal infection of grapevine rootstock. It has become a common disease mostly in California’s north coast production area, but it has also been reported in many other grape growing areas – Europe, Australia, New Zealand, and South Africa. The increased prevalence of the disease in CA coincided with massive replanting of grapevines in Napa, Sonoma, and Mendocino counties as a result of phylloxera (Daktulosphaira vitifoliae [Fitch]) infestation. The commonly planted rootstock AXR1 was replaced with rootstocks that were resistant to phylloxera. However, the new rootstocks were more susceptible to the fungal pathogens that cause the disease. Leaf symptoms, previously not common on grapevines unless the vine was older than 10 years of age, are

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September/October 2016

now seen commonly even on vines one to six years old.

The disease is linked to water stress or other stress factors that limit root growth thus interfering with water uptake. Vine stress triggers the pathogen to become capable of rapid movement through the vessels causing further plugging of the vascular system. In addition, the pathogen releases metabolites that are shuttled to the foliage and fruit causing leaf and fruit symptoms.

Although widespread in occurrence, vines showing decline due to Petri disease usually constitute a minor portion (one-five percent) of a newly planted vineyard. Esca or Black Measles can be found in California on wine, table, or raisin grapes in areas with high spring rainfall and high summer temperatures.

The disease affects crop quality and quantity, and also the productive life of the vineyard. Losses are normally underestimated since the disease occurrence fluctuates considerably; a vineyard may show variable disease incidence from season to season, as individual vines, though still infected, may show symptoms one year but not the next. In California table-grape growers, especially those with older Thompson Seedless vineyards in the San Joaquin Valley of California, suffer the most serious losses. Affected table-grape clusters are unsaleable because of their disagreeable appearance and flavor; also, they are more susceptible to bunch rot. On table grape an acrid taste can occur. Affected and symptomatic wine grapes give lower quality wine, with a lower sugar content and a higher acidity (Calzarano et al., 2009).

The cause of Esca is not fully understood, although the appearance of foliar symptoms is invariably correlated with Continued on Page 16

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Continued from Page 12 an internal vascular streaking often beginning at pruning wounds of any size. These internal symptoms have been reproduced in many laboratories by inoculation with Phaeomoniella chlamydospora (Pch) and Phaeoacremonium aleophilum (Pal). On the other hand two research groups have on one occasion in Italy and several occasions in California, reproduced foliar and fruit symptoms by inoculating those pathogens into healthy Thompson Seedless vines.

Pathogens The primary pathogen consistently associated with vines showing symptoms of Petri disease in California has been Pa. chlamydospora whereas the pathogen more closely associated with black measles of older vines in California vineyards is Pm. eophilum though both pathogens occur together in many wood samples of cordons and spurs.

Both pathogens are vascular disease agents. Although several other Phaeoacremonium spp. have isolated on grapevine (25 species up to now) and some Page 16

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are pathogenic to grapevine, within the genus Pm. aleophilum is the most prevalent species on this host in California and worldwide.

Phaeomoniella chlamydospora produces tiny, pycnida on exposed vascular tissue on cordons and spurs of grapevines that serve as sources of inoculum in infected vineyards. Togninia minima, recently confirmed as the sexual stage of Pm. aleophilum, spreads via ascospores produced by perithecia on infected vines. Though Pm. aleophilum occurs in different host species such as stone fruits, olive trees, and kiwifruit vines, no perithecia have been found on those crops. Perithecia of Togninia minima were discovered on grapevine exhibiting leaf stripe and black measles symptoms in vineyards located throughout California.

Both Pa. chlamydospora and Pm. aleophilum produce conidia. Routine isolations carried out in California from symptomatic samples yielded cultures of one or both organisms. When isolations were made from declining younger vines (<seven-eight years old), pathogens were primarily associated with the

September/October 2016

rootstock. Pruning wounds have been shown to be good sites of entry into the spur positions and the cordon. In a California study, shoots from spur positions inoculated in February showed severe stunting of shoots (approximately 50 percent) in early summer and both leaf and fruit symptoms developed by August. The pathogens were able to colonize the vascular tissue and move into the cordon tissue in only seven months.

In older vines, and in younger vines symptoms of esca are usually associated with infection of pruning wounds.

Symptoms The first sign of infection is described as brown-black wood streaking. Longitudinal sections show dark streaks, single or in bundles appearing in cross section as spots or group of black vessels along the wood rings. A black, gum like exudate appears after a few minutes after cutting through affected vessels. The streaking often starts at the graft junction in young vines or at the pruning wound surface on vines. These internal symptoms of fungal infection may be related to decline symptoms (see

Petri disease) once cuttings are planted in the field.

Symptoms also include reduced trunk diameter, shortened internodes, stunted shoot growth, shoot dieback and chlorotic and/or necrotic leaves.

The most prominent internal symptom is the presence of brown to black spots or streaks in the xylem vessels of the woody cylinder when viewed in cross-section.

The most visible symptoms of Esca in California are leaf spots to interveinal yellowing and berry spotting, particularly noticeable on white grape varieties.

The skin is peppered with small, tan to purplish spots. These spots may appear at any time between fruit set and ripening though are more common on just nearly full sized berries and affect either entire clusters or parts of them. In severely affected vines or vines showing early symptom expression, berries often crack and dry on the vine.

Shoot tip dieback, tendril dieback and leaf collapse may occur in the spring. Leaf symptoms usually develop, in table grape or wine grape, on canes with fruit symptoms, but also can develop on shoots with normal fruit. Typically, affected leaves display small, chlorotic, interveinal areas that enlarge and dry out; and in dark-colored varieties, red margins surround the dead interveinal areas. The succession of chlorotic/pigmented and necrotic interveinal tissues gives the so called “tiger stripe” pattern. Severely affected leaves drop and the cane may die back from the tips. Fruit and foliage symptoms may appear at any time during the growing season, but the most of diseased plants show external symptoms during July and August (June and July in other areas of grapevine cultivation).

Entire vines or only portions of a vine may be affected; occasionally, the symptoms appear so quickly and dramatically that the entire vine dies (apoplexy). The latter symptom is most commonly seen in full summer in higher temperature production areas. Apoplexy is more common in the Mediterranean areas of Europe and it is debated to be the effect of a multiplicity of causes.

Internal symptoms of Esca include the same brown to black spots or streaks in the xylem vessels in the main trunk Continued on Page 18

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September/October 2016

Your Edge – And Ours – Is Knowledge.

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Continued from Page 17

Photo Credit: W. D. Gubler

or starting from wounds, often oozing out a typical black sticky gum when cut, described in brown-wood streaking and in Petri disease, and caused by Pa. chlamydospora, and to lesser extent Pm. aleophilum. These two pathogens cause a brown-red necrosis that develops mainly along the central part of the trunk. Sectorial light-brown necrosis can be also found, caused by the agents of other wood diseases such as Botryosphaeriaceae species, Phomopsis or Eutypa species that can also easily colonize grapevine wounds.

The peculiar discontinuity from year to year of the foliar symptoms of GLSD has not yet been explained, although in California there appears to be a close correlation between symptom expression and current year infection. Symptomatic vines can appear fully healthy the following year, and then show symptoms again after one or more years in an unpredictable way. Foliar symptoms are reported to be linked to toxic metabolite production by Pa. chlamydospora and Pm. aleophilum. The involvement of toxic metabolites in foliar symptom development possibly forms part of a complex interaction, not yet clarified, between the pathogens, the host physiology, the host response to the pathogen and environmental factors.

Wood decay was the first internal symptom to be described as the typical Esca symptom. However, although this thinking stood for nearly 65 years, no one was able to reproduce typical foliar or fruit symptoms when inoculating with basidiomycete fungi that caused the white heart rot in vines. Recent research tends to consider white rot in wood as wood damage which does not affect vine performance, although extensive decay occurring in older vines appears to be associated with apoplectic symptoms. However, apoplexy has not been reproduced by inoculation with any pathogen.

Management of the Disease At present control of the different syndromes here examined needs a wide spectrum approach. As a general approach to all the syndromes including a vascular infection the first step in disease control is prevention of infection in the nurseries and protection of prunPage 18

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September/October 2016

ing wounds from the day first wounds are made. Reduction of infections in pre-planting propagation material (brown wood streaking) involves a careful set up of the best nursery practices prior to and during the grafting process.

Though this is true, no laboratory has been able to show complete eradication of pathogens from nursery stock.

For Petri disease it is also essential to reduce inoculum in new vineyards (using plant material with no or reduced infection), planting in areas where standing vines are not present (not practical), and avoiding stress in the vines.

Reduction of infections can be obtained by reducing surface inoculum obtained with winter treatments, while new infections can potentially be reduced by protecting pruning wounds by wound sealants containing fungicides or biological control agents specifically selected to this use, selecting pruning systems that reduce the size of pruning wounds or, following results obtained in California, adopting double pruning or late pruning programs.

As for winter treatments, some work with liquid lime sulfur has shown promise in controlling Esca by killing the spores prior to their release thus protecting new pruning wounds. However, in order for this product to work, the spray needs to be in high volume to thoroughly wet the cordons and spurs.

This can only be done by directing two nozzles to either side of the vine so that the full volume is forcibly blasted into exfoliating bark and down into the rotted tissues. Pruning grapevines before spraying is recommended to improve coverage and to reduce the amount of chemical needed.

As stated above, inoculum dispersal of grapevine wood pathogens is strongly influenced by rainfall and temperature.

In areas where spore release is concentrated in winter and early spring, the practice of double pruning or late pruning has the potential to reduce new infections for wood diseases. Infections that may occur on canes following the first pruning are pruned out of the vine during the delayed dormant pruning, before the infection reaches the lower bud positions. Prune spur positions to five-seven buds in early winter using a tractor mounted rotary saw. This leaves the entire vineyard with spur positions that, even when infected with

winter rains, do not allow the pathogen progress due to the slow progress of the pathogens during winter months.

The final cut should be made in late February or early March after most spores have been released and pruning wounds are much less susceptible. The final cut should be followed up with an efficient fungicide application. This can be applied with a tractor using directed nozzles.

When the disease is already present in the vineyard, trunk renewal or retraining cordons at first symptom appearance gives a good immediate, but often temporary reduction in symptomatic vines. It has never been shown that pathogens can spread from vine to vine by pruning implements. Therefore it is not recommended that pruning of healthy vs diseased vines be done separately. Diseased wood should always be removed from the vineyard and burned if possible. Sanitation will help reduce inoculum pressure within the vineyard.

PCC

References

A. Eskalen, A. J. Feliciano, and W. D. Gubler. 2007. Susceptibility of grapevine pruning wounds and symptom development in response to infection by Phaeoacremonium aleophilum and Phaeomoniella chlamydospora.

Plant Disease 91: 1100-1104.

Rooney-Latham, S., A. Eskalen, and W. D. Gubler. 2005.

Occurrence of Togninia minima perithecia in esca-affected vineyards in California. Plant Disease 89: 867- 871.

Feliciano A.J., A. Eskalen and W.D. Gubler, 2004. Differential susceptibility of three grapevine cultivars to Phaeoacremonium aleophilum and Phaeomoniella chlamydospora on grape berries in California. Phytopathol. Mediterr. 43, 66-69.

Weber, E.A., F.P. Trouillas, and W. D. Gubler 2007. Double Pruning of Grapevines: A Cultural Practice to Reduce Infections by Eutypa lata. Am. J. Enol. Vitic.

58: 61-66.

Rooney-Latham, S., A. Eskalen, and W. D. Gubler. 2005.

Teleomorph formation of Phaeoacremonium aleophilium, cause of esca and grapevine decline in California. Plant Disease 89: 177-184.

Eskalen, S. Rooney-Latham, and W. D. Gubler. 2005. Occurrence of Togninia fraxinopennsylvania on esca-diseased grapevines (Vitis vinifera) and declining ash trees (Fraxinus latifolia) in California. Plant Disease 89:528.

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Stone Fruit

PCA Budgeting Nutrition for Stone Fruit Cecilia Parsons Contributing Writer

M

aintaining a balance in nutrients and well-timed applications are tools to ensure stone fruit quality and tree health. A sound nutrient management program for stone fruit aims to deliver the right amounts of macro and micronutrients at the right time of the year.

Both deficiencies and excesses of nutrients should be avoided not only for economic reasons, but also for the long-term sustainability of tree health.

Balance is important because when one element is deficient, plant processes are impacted and uptake or use of other elements may be inhibited. An excess of one element may have toxic effects on the tree.

The 13 essential nutrients needed for normal growth and peak production are the macro nutrients nitrogen, phosphorus, potassium, calcium, magnesium and sulfur. The micro nutrients are chlorine, iron, manganese, zinc, boron, copper and molybdenum.

Visual signs of nutrient deficiency alert growers to a potential problem, but when determining a nutrient budget, University of California (UC) researchers and advisors recommend a nutrient analysis of tissue samples. Taken at the right time to determine nutrient levels, samples of leaves, roots and shoots will show where macro and micro nutrients fall in the range of acceptable levels.

Leaves, dormant shoots and flowers have all been sampled to determine nutritional status. Visual inspections of flower density, fruit set, early shoot growth, fruit size at thinning and final fruit size and quality are other indicators of nutritional status.

Richard Kajihara, PCA for Family Tree Farms of Reedley, said the nutrition program for their stone fruit might be different from year to year, depending on the testing results and visual observations. At Family Tree Farms, Kajihara said leaf and soil samples are taken twice a year— early spring and in late July.

Spring samples indicate nitrogen levels Page 20

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and how much will be needed by the trees. The post harvest samples show how much fertilizer was used and how much will be needed to replace— a figure he said is also based on crop yields.

“All nutrition levels need to be watched, especially the macro nutrients.

Nitrogen for growth, phosphorus for root development and disease management and potassium for enhancing sugar in fruit, color and disease resistance,” he said.

The practice of applying a set amount of nitrogen each year is outdated, Kajihara said, because over applications can lead to leaching of water-soluble nutrients beyond the root zone.

Sources of nitrogen other than fertilizer should be noted in a nutrient budget. Soil humus, crop residues, irrigation water and residual nitrate in the soil should be considered as part of the total nitrogen application.

University of California (UC) farm advisor Kevin Day, who is based in Tulare County, said nitrogen is the primary macronutrient for stone fruit growers budget in their fertilizer program and zinc is the most important micronutrient.

“You want the grower to apply enough nitrogen to ensure a tree canopy that does the job of carrying and ripening a crop, but not to excess where the canopy shades out and has to be pruned back,” he said. Most growers understand that over application of nitrogen won’t increase fruit size, Day added.

Kajihara said nitrogen applications are best done in the late summer to fall at the time of root flush because the trees are able to take up nutrition during that time. A second root flush, in later winter when buds open, is a second window for nitrogen applications. These applications can be 50 percent each for the total annual nitrogen budget or, Kajihara said, 65 percent in fall and 35 percent in late winter. The percentage decision can depend on when fruit is harvested.

Applying a higher percentage in the winter/early spring budget may cause fruit softness, he warned.

Once leaf analysis results are received,

September/October 2016

Kajihara said he references the data with the leaf nutrient requirements for stone fruit to determine the rate necessary. Typically, the bulk of soil nutrient applications are made in the fall. Early spring applications may be an option if minor adjustments are necessary to meet the nutrient requirement for the season.

This is a particular concern for late season fruit crops.

Micronutrients command the same budget consideration. One of the most common micro nutrient deficiencies in stone fruit is zinc. Day said symptoms of zinc deficiency include black flowers at bloom, small leaves and leaves with wavy margins. These symptoms early in the growing season should be corrected with foliar applications of zinc sulfate.

Day said when a deficiency is observed, growers should not wait to make a corrective application.

Foliar applications of micronutrients are best done, Kajihara said, when there is rapid leaf expansion— or if a deficiency is found in the second sample. Growers may chose to do another application prior to dormancy.

He said looking at thresholds for nutrients and comparing them with leaf and soil analysis is a reliable way to ensure both macro and micro nutrients are in balance. Where leaf analysis shows nitrogen deficiency, researchers recommend split applications.

As an example, Kajihara said if an analysis shows a lack of zinc and potassium, zinc would be applied as a foliar treatment since that is the most efficient way to add minute amounts of zinc for rapid uptake. The foliar application would hold true for most micronutrients. Since potassium is a macronutrient it would be side dressed at the bottom of a furrow.

Among the other macronutrients important in stone fruit, phosphorus deficiency is not common as this element is recycled by the tree. Annual requirements range from 5-10 pounds per acres. Calcium deficiency has never been an issue in California, although it is found in other states. Magnesium deficiency is also rare. It is associated

Photo Credit: Cecilia Parsons

Bins of yellow peaches moving from the orchard to cold storage.

Leaves from the peach trees are sampled after late July harvest to determine nutrient levels. Nutrients will be applied at the optimum time to correct any deficiencies.

September/October 2016

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Photo Credit: Cecilia Parsons

with high potassium levels in the soil. It does not affect yield. Sulfur deficiency in stone fruit is rare due to this element’s abundance and availability in the soil and atmosphere.

Among other micro nutrients, iron deficiency is common despite its abundance in the soil. Most iron exists as insoluble mineral and is unavailable to plants. Iron is absorbed only by root tips as iron chelates. Day noted that insufficient iron causes tree leaves to fade to pale yellow with interveinal chlorosis.

Severe deficiency will cause terminal shoot die back or even limb death.

Where iron deficiency has been an extensive problem in stone fruit orchards, Day said, it can be a soil chemistry issue where the soil pH is out of whack or too much lime has been applied. Correcting the imbalance in the soil chemistry will fix the problem, but Day noted that as the stone fruit industry has condensed, most orchards on soils with this issue have been removed.

Manganese in a plant helps with photosynthesis and nitrogen and carbohydrate metabolisms. If a deficiency is determined, a foliar spray of manganese sulfate is effective. Boron and copper deficiencies are rare in California stone fruit. Boron deficiency can be corrected with a soil application, but this element can also be toxic at slightly higher levels than normal. Correction of copper deficiency can be made with a soil or foliar application of .25 to 2 pounds per tree of copper sulfate.

Chlorine is another element where excess can cause major problems. Peach, plum and nectarines are sensitive to excess of chloride salts. The trees only need a few parts per million so deficiencies are rare.

Molybdenum deficiency has not been found in the field, but it is essential to nitrogen metabolism.

Day said irrigation management might have an effect on nutrient applications. While some nutrients will remain in the soil profile, those that are water soluble may be leached out of the root PCC zone.

Battle to Keep Crop Protection Tools Heats Up Cancellation of Belt is Latest in Registration Kerfuffle Stephanie Thara Communications Manager, Western Growers

W

ithout crop protectants, up to 40 percent of the world’s food production would be lost to pests and diseases. So why are crop protection tools constantly in jeopardy of being taken away?

In the past several years, regulations around the use of pesticides, herbicides and insecticides have significantly increased. Just this August, the Environmental Appeals Board (EAB) of the U.S. Environmental Protection Agency (EPA) released their final decision and order regarding EPA’s request for Bayer to cancel all uses of flubendiamide, or Belt, in the United States. The EAB essentially upheld the decision of the EPA Administrative Law Judge supporting the cancellation of Belt without a hearing to challenge EPA’s decision.

Belt was previously approved for use in 49 states and on more than 200 crops, including lettuce, strawberries, stone fruit, melons, tomatoes and bell peppers, to name just a few. Nut crops— such as almonds, walnuts and pista-

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chios—were also a specific area where Belt was heavily relied upon because of its strong pest performance. For instance, Belt has been extremely effective in controlling pests like the navel orangeworm and the peach twig borer which plague pistachio production in California. Not being able to use Belt would force tree nut growers to resort to older, less effective, but more potentially disruptive chemicals to manage these same pests.

Despite the fact that the cancelation would be a significant loss for growers, the EPA still flexed its regulatory muscle and took actions to ban all flubendiamide products produced by Bayer CropScience, LP and Nichino America, Inc. As noted in the case, the EPA stated that the insecticide posed a risk to aquatic invertebrates. However, Bayer believed that the EPA’s methodology to evaluate the risk of crop protections tools was significantly flawed. Belt has an outstanding safety profile and is not an issue to human health, pollinators or beneficial insects. The disagreement is exclusively related to aquatic invertebrates in the sediment of rivers and

September/October 2016

ponds whose occurrence is predominantly concentrated in the Southeast of the United States.

On a more positive note for Belt, the EAB made a change in EPA’s cancellation order regarding the distribution of existing stocks of the canceled flubendiamide products. Though the EAB upheld EPA’s decision prohibiting further distribution of Belt, it did not support EPA’s restriction as it applies to products in the hands of dealers and distributors.

The EAB decided that products held by dealers and distributors can be further sold and distributed. Growers can continue using existing product.

There is no doubt that the battle to keep these critical crop protection tools is heating up. Western Growers—a trade association representing local and regional family farmers growing fresh produce in Arizona, California and Colorado—has a long history of advocating for the registration and safe use of pesticides that are important in the production of healthy crops. Crop protection is at the forefront of Western Growers’ core policy concerns, and the Association is continually educating decision makers on the unique challenges

Photo Credit: Stephanie Thara

that face the agricultural industry. With plants competing with 30,000 species of weeds, 3,000 species of nematodes and 10,000 species of plant-eating insects, crop protection products are crucial for an abundant and reliable food supply.

Considering that California already has the most restrictive crop protection regulations in the country, Western Growers’ priority is to advocate that any future restrictions need to be based on scientific evidence.

All pesticides that are registered in California must also first be registered with the EPA. EPA requires all pesticides to undergo up to 120 health, safety and environmental tests before a product is registered for sale and use.

Furthermore, the use and development of these products are regulated by the EPA primarily under two federal laws: the Federal Insecticide, Fungicide and Rodenticide Act and the Federal Food, Drug and Cosmetic Act. This pesticide registration process takes an average of nine years and costs pesticide manufacturers $150-$250 million for each crop protection product. In fact, only one Continued on Page 24 September/October 2016

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Continued from Page 23 in 139,000 chemicals make it from the laboratory to the farmers’ fields.

Once federally registered, pesticides must be cleared through the California Department of Pesticide Regulation’s (DPR) stringent approval process before use in California. To start, DPR requires that each product registration must be accompanied by the following: • • • • • •

Cover letter detailing in-depth data and reasoning for submission.

California Application for Pesticide Registration with information about active and inert ingredients.

Proposed marketing/production/ container labels with copies of different sizes and various languages.

Scientific data (e.g., residue data, exposure information) to support registration.

U.S. EPA stamped-accepted label and accompanying letter of acceptance.

Up to $6,350 in application fees.

After all the information is received

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and indexed by DPR, only then does the actual pesticide registration process begin. This includes a submission evaluation process to ensure that no additional data is needed, a formal scientific evaluation where the request is routed to a number of different departments for even more assessment, and a 30-day period for public comment prior to approval or denial.

Compared to EPA, DPR’s process for pesticide registration requires far more data and steps. For example, EPA does not generally require product performance data to be submitted to support registration of non-public health products. DPR requires data to be submitted for each and every product. DPR may also require supplemental data to support the registration or amendment of a pesticide product (e.g., hazards to bees, indoor exposure).

Thousands of pages of test data are rigorously reviewed and scrutinized by scientific and administrative branches of the EPA and DPR before crop protection products gain approval. Because the process to deem a pesticide safe for use is extremely extensive, any type of addi-

September/October 2016

tional restrictions should be scientifically justified. There needs to be hard data to support new rules requiring growers to limit their use of certain application methods.

Anti-pesticide groups that push for more regulation in our state fail to understand (or, more likely, don’t care about) the multi-level process that governs the manufacture, sale, distribution and use of pesticide products. They also ignore the fact that the decision to develop pesticides is carefully based on current and potential crop threats and the increasing consumer demand for fresh, safe food.

The world population has doubled in the past 40 years and the land devoted to crop production has remained nearly constant. The crop protection toolbox has enabled growers to produce higher yields on the same amount of land. With so many people to feed, farmers will need to continue relying on crop protection tools and technologies to sustain a reliable global food production.

PCC

September/October 2016

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Leaffooted Bug

How Can Monitoring of Leaffooted Bug Be Improved?

W

e currently have tools for monitoring leaffooted bug (Zalom et al. 2014), Leptoglossus zonatus (Dallas) on almond (Fig. 1) but need to develop better sampling methods for monitoring leaffooted bug (LFB) when they first move into almond during March. The University of California Pest Management Guidelines recommends monitoring for LFB in almond during March and April by examining aborted nuts for gummosis, or oozing on the nut surface (Fig. 2) (Zalom et al. 2014). An important note is that if gummosis is found, it should be distinguished from a physiological disorder by cutting a cross section through the nut and looking for a puncture wound.

Although the Guidelines provide an effective tool for detecting damage from LFB feeding, the drawback is that considerable economic damage can occur before the presence of LFB is detected. Additional sampling methods that can be used in April and May include using a beat tray for mid-canopy sampling or a long pole to knock upper-canopy branches to startle adults, causing them to fly. Beat trays provide a useful tool for detecting nymphs but if nymphs are found it indicates that adults have been present long enough to lay eggs and for the eggs to hatch. In other words, feeding damage has likely already occurred.

The first way that we are working to improve LFB monitoring is by developing the ability to forecast LFB pressure based upon winter temperatures. We conducted research funded by the Almond Board of California (ABC) in 2014 and 2015 showing that cold winter temperatures potentially have a considerable negative impact on overwintering populations of L. zonatus.

In laboratory experiments we found that temperatures below approximately 27°F for an exposure period of six hours substantially decreased survival. Our data agree with that of Daane et al. (2007) who monitored field populations of LFB on citrus and made a similar conclusion. In their results, Page 26

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although they did not determine the exposure period at 27°F to cause mortality.

By having a better understanding of how environmental factors, such as temperature affect LFB populations could help almond producers, as well as producers of other susceptible crops, plan monitoring schedules and management tactics for spring.

The second approach that we are taking to improve LFB monitoring is to gain a better understanding of their early-season and within-season movement. We currently have ongoing research projects funded by the ABC and the California Pistachio Research Board (CPRB) focusing on this.

Conventional knowledge is that in California, LFB begins forming aggregations in the fall (Fig. 3) on citrus, Cyprus, olive, palm, pomegranate, and in protected areas such as pump houses (Daane et al. 2008), and that dispersal, or movement from aggregations typically occurs from early to late spring.

In the winter of 2015 we surveyed several host crop orchard sites but found aggregations only on pomegranate. In early 2016, we surveyed citrus, olive, and pomegranate orchards in Tulare County and located relatively small aggregations (averaging about 33 individuals) again, only on pomegranate.

We observed that those LFB aggregations in Tulare County dispersed very quickly during early spring, likely due to warm temperatures that occurred during the weeks of Feb 14, Feb 21, and Feb 28. The warm temperatures, rather than another environmental cue such as day length, likely acted as the primary cue for adults to leave aggregations and begin searching for food.

A third approach that we are taking is to improve detection of LFB when they first begin moving into almond very early in the season. Through research funded by the ABC and the CPRB, we are working to develop an egg trap baited with a lure based on host-plant material such as whole almond, whole-ground almond (WGA), whole-ground pistachio (WGP), or peanuts.

The idea is the lure and trap could be placed at the edge of almond orchards and when gravid females move from overwintering aggregations, they would detect the lure i.e. food source and lay eggs on the trap. We placed host-plant baited traps constructed

September/October 2016

from modified navel orangeworm traps in almond, pistachio, and pomegranate. Initial results suggest that adults are attracted to WGA and WGP. However, adults were observed on traps only in pomegranate with an existing LFB population.

In summary, we are improving our understanding of how temperature can affect populations of LFB and how this is essential for effective management. Our observations indicate that LFB has a propensity for overwintering on pomegranate and that temperature likely provides a primary cue for initiating dispersion. Almond producers near plantings of pomegranate need to be especially diligent in monitoring orchard edges nearest the pomegranate. And moreover, when warm temperatures occur in late winter or early spring, monitoring should begin. Although more work is needed to develop a lure/egg trap monitoring system, we have encouraging results and plan on continuing our research to develop such a PCC system.

Photo Credit: Kris Tollerup

Kris Tollerup IPM Advisor, Fresno/Madera Counties, UC Statewide IPM Program and Cooperative Extension, Kearney Ag Research and Extension Center

Figure 1. An adult leaffooted bug almond.

Figure 2. Leaffooted bug feeding damage.

Figure 3. Overwintering aggregation of leaffooted bug on pomegranate.

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