Agrometeorologisch adviesbureau Erno Bouma Sumatralaan 28 7314 CL Apeldoorn The Netherlands E bouma.weer@planet.nl I www.boumaweeradvies.eu
w w w. r o o d b o n t . c o m
www.boumaweeradvies.eu
T
he weather has a greater influence on crop protection than many farmers think. It affects the development of diseases and pests, the application and effectiveness of products and the protection of plants and harvested crops. These relationships are explained clearly in the practical guide Weather & Crop Protection. What are the ideal weather conditions for spraying? Not a gale or downpour, but certainly not a dead calm either. What demands do crop protection agents impose in terms of temperature, humidity and other meteorological factors? Insects are more active in warm weather, for example, and may pose a problem. But, at the same time, insecticides are more effective in warm weather. Weather & Crop Protection has the answers to these and many other questions. After reading Weather & Crop Protection, anyone involved in outdoor cultivation will understand the influence of weather on diseases, pests and their control. He will be able to take preventive action or respond in good time to the first signs of disease in order to achieve the best possible results for his crop, his wallet and the environment.
Did you know? Reducing the quantity of spray mixture in a wet crop in order to limit droplet roll-off would seem to make sense. But it’s pointless. A crop can easily contain 7,000 liters of condensation per hectare. Reducing the spray mixture by 100 liters per hectare is a drop in the ocean.
Weather
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Erno Bouma is an expert in the field of agrometeorology. He works as a lecturer at the HAS University of applied sciences in ‘s Hertogenbosch where he teaches integrated crop protection and plant sciences. He is also the founder of the Erno Bouma Agrometerological consultancy firm. He was closely involved in the development of CERDIS, a decision support system for cereals, and in SprayWeatherWise, the system that explains all you need to know about the effectiveness of crop protection agents. He is co-author of the Agrarisch Weerboek (1998) and the Natuurkalendergids (2005) and has written many specialist articles on a wide range of crops. Furthermore he gives lectures and presentations on four continents. “The weather has fascinated me since childhood. I find it odd that many people know little about the relationship between the weather and all sorts of things that happen on the farm, even though the weather is so important in the development of pests and diseases and their control.” A much sought-after speaker and course leader in the Netherlands and abroad, Erno Bouma also hosts events such as information meetings for the grant of crop protection licenses.
‘You can’t change the weather, but you can change your response to it’
Weather Crop Protection
About the author
Main author: Erno Bouma Co-authors: Annemiek Schilder, Jeff Andresen, John Wise
Crop Protection ISBN 978-90-8740-185-6
9 789087 401856
North American edition
When do insecticides work best? In warm weather, when the insects are more active. They move about more, eat more and exchange more gas. As a result, insecticides work better and insects kick the bucket quicker.
Never spray insecticides in the middle of the day. They are very sensitive to light and degrade quickly in sunlight. At the end of a sunny day the temperature in the crop is still high enough to obtain a good effect, and the insolation level will be low after spraying. In short, spray at the end of a sunny day.
Colophon Publisher
Illustrations Studio Flip, www.flip.nl Studio Hiddink, Jolanda Hiddink
Roodbont Publishers BV
Design
Authors
Studio Flip, www.flip.nl Studio Hiddink, Jolanda Hiddink
Main author: Erno Bouma Co-authors: Annemiek Schilder, Jeff Andresen, John Wise
Editing Roodbont Publishers B.V.
Text editing
PO Box 4103 7200 BC Zutphen, the Netherlands T +31 (0)575 54 56 88 E info@roodbont.com I www.roodbont.com
co pr py ot rig ec h te t d
Erno Bouma, Ton van Schie
Agrolingua
Thanks to
Carel Bouma, Paul Goorden, Lenus Hamster, Hans van Leeuwen, Henk Scheele, Aaldrik Venhuizen, Kees Vogelaar and to Nick Bradshaw, Leslie Dowley, Mike Krahe, Brian Prince.
Photography Erno Bouma
Additional photography:
Annemiek Schilder: 25, 26 tl, 33, 34, 38, 45 br, 50 tl, 53, 58 bl, 59 bl, 63 bc, 65, 71, 94, BASF: 22 br, 70, BayerCropScience: 18 tl, 18 cl, 18 bl, 46, 64 tl, 64 cl, 64 bl, Bernard Zandstra: 43 tr, Dacom Plant-Service BV: 49, 98 bl, Frigjalk, Dreamstime.com: 83, Global Climate Change, impacts in the United States: 85 b, 86 tl, Hans Mulder: 96 t, Hugo.arg.: 91 tr, Internet: 84, 97 bc, 97 tc, 98 br, 99, Itor, Dreamstime.com: 93, Jeff Andresen: 58 br, 60 tr, 61, 62 tc, 62 cl, 62 bc, 63 tc, 75 tr, 97 r, 101 t, 101 b, 102, 105 l, 106, 107, Jerry Gillet: 10 tl, John Wise: 22 tl, 89, Karl Foord extension educator horticulture: 13, Luc Viatour: 91 cr, Marijke van Oostende: 6, 35, 72, 108, Mark Longstroth: 12 bottom serie, 14, 15 br, Natalia Bratslavsky, Dreamstime.com: 82, NFO: 12 tl, 99 b, Olaf Leillinger: 91 br, Opticrop BV: 98 t, PPO-AGV: 9 bl, 36, 52 br, PPO-BB: 27 tr, Sebastian Stabinger: 95 tr, 95 br, The Cuticles of Plants (1970): 44 tl. t = top, b = bottom, r = right, l = left, c = centre
Cover photography John Deere (tractor), www.flip.nl (cloudy sky) Insets: Marijke van Oostende, NFO
Š Roodbont Publishers B.V., Erno Bouma, 2015
Agrometeorologisch adviesbureau Erno Bouma Sumatralaan 28 7314 CL Apeldoorn, the Netherlands E bouma.weer@planet.nl I www.boumaweeradvies.eu
No part of this book may be reproduced and/or published by printing, photocopying or any other method, without prior permission in writing from the publisher. The publisher and editors have compiled this publication with great care and to the best of their knowledge. The publisher and editors cannot be held liable for any damage, whatever its nature, resulting from treatments and/or decisions based on the information in this book. The crop protection products mentioned in Weather & Crop Protection relate to the legislation applicable in Ireland/the UK. When using crop protection products, always comply with the legislation of the country in question. The publisher has made efforts to trace the owners of the visual material. Where a source is uncredited, the owners can contact the publisher. ISBN 978-90-8740-185-6
Introduction Clear descriptions of what happens at plant and leaf level during the uptake and transport of crop protection agents show how best to go about the task of crop protection. Combined with many practical examples, these descriptions give you a better understanding of the relationship between weather and crop protection.
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Why can’t you spray insecticides and fungicides together effectively? Why shouldn’t you tackle volunteer potatoes during a dry, sunny spell? Is it better not to spray at all when there is no wind? Answers to all of these questions can be found in Weather & Crop Protection, an handbook for field and specialty crop growers, top and soft fruit growers, extension agents, consultants, and livestock producers who grow forage crops. Bookshelves are already overflowing with volumes about the weather, diseases, pests and crop protection, but approaching pests and diseases from an agrometeorological perspective is something entirely new. Pests and diseases, crop protection and weather are so closely interconnected that it is surprising that nothing like this has been published up until now.
The central focus of this practical guide is the influence of weather on the efficacy of crop protection products. It gives an insight into the role of temperature, humidity, precipitation and wind on pests and diseases and the effect of these weather parameters on the uptake, adhesion and efficacy of crop protection products.
Weather & Crop Protection is filled with photos, text boxes, figures and graphs which make the information highly accessible. This unique and practical guide is bad news for insects, fungi and other pests, but good news for the farmer!
Contents 1 Sun, a source of heat
6
The difference between mortality and survival 26 Or is mild, wet winter more fatal? 27 A lot of insects after a harsh winter? 27
2 Moisture, something in the air
28
How does water occur in the air? 28 Water vapor in the air 29 Dew point temperature, in general 29 A closer look at the dew point temperature 30 Measuring humidity 31 Condensation 32 Drought symptoms 32 Transpiration 33 Wind chill 34 Transpiration equals cooling 35 What happens to evaporated moisture? 36 Dew 37 Fungal infections 37 39 Germination of fungi Where does dew come from? 40 Water and air 41 Uptake of soil herbicides 42 Leaf cuticle: a barrier to absorption? 42 Selectivity 43 43 Old or young leaves Dynamics of the wax layer 44 How are products absorbed? 45 Water-based formulations 46 Oil-based formulations 46 The right time to apply 47 Adjuvants 48 Ideal formulation 48 Release of fungal spores 49 Leaf wetness and fungal infection 50
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Solar energy 6 Global radiation 7 Everything radiates heat 8 Night frost 8 Cloud cover: a warm blanket? 9 Frost damage 10 Ice to prevent freezing 12 Frost prevention with irrigation 12 in blueberries, beware! Limits to protection with sprinklers 13 Only use sprinklers around bloom time 14 Microclimate: Weather observations don’t tell the whole story 16 Weather forecast temperatures not very useful for agriculture 16 Differences in development 17 due to temperature Warming the soil 17 18 Effect of temperature on pesticides Formulations 18 Rate of uptake 19 Weakest link dictates rate of uptake 19 Persistence and temperature 20 21 Insecticides in warm weather Persistence of cereal fungicides 21 Insects prefer warmth 22 Thermal time 22 Powdery mildew no lover of heat 23 Heat soaks into the soil 24 Risk of bruising 24 Mulch strawberries with straw 25 Risk of disease 25 Soil freezes 26 Snow cover 26
Powdery mildews love dry weather When is the best time to apply contact fungicides? Systemic fungicides Transport of products in the plant Downy and powdery mildew Evaporation of spraying liquid Drying equals cooling
51 52 53 53 54 55
56
4 Wind, both friend and foe Wind equals transport Measuring wind Wind speed indicator Velocity of wind Wind force Variable flow Boundary layer turbulence Obstacle flow No wind? Don’t spray! Right droplet size Weight and speed of droplets Contact herbicides Pesticide coverage Droplet size of contact fungicides Droplet size of soil-acting herbicides Droplet size of systemic fungicides Droplet size of insecticides Changing wind speed
72 72 73 73 74 74 75 75 76 77 78 78 78 79 79 79 80 80 81
Higher carbon dioxide concentrations 89 92 Decreasing effect Herbicides 93 Foliar herbicides (including growth regulators) 93 Fungal diseases 94 Bacteria 95 Nematodes 95 Several harvests a year 95
6 Resources and information 96
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3 Precipitation, a gift from the gods
50
Where does rain come from? 56 Every raindrop starts as a snowflake 56 The other opportunity, repeated collisions 57 The force of raindrops 58 Hailstones: like a yo-yo 59 Precipitation patterns in 60 the Midwestern USA Large differences from year to year 61 Precipitation forecast 62 Usefulness of weather radar 62 Sprinkle irrigation and crop protection 63 Not too cold 63 64 Precipitation after spraying 64 Liquid formulations Timing of application 65 Rainfastness of insecticides 65 The wash-off potential 67 Drying time of 2-6 hours 67 67 Judge not only the residue wash-off Herbicides 68 Drying time of a crop protection product 69 Role of additives 69 Fungicides 70 Rain after spraying 70 Systemic fungicides 71
5 Climate change and plant protection
82
Change in temperature 82 Increase in temperature 83 Breaking dormancy 83 Precipitation 84 Seasonal snowfall 84 Causes of climate change 84 Future climate projections 85 Scenarios for Midwest USA 85 Seasonal changes in annual mean precipitation 86 Expected occurrence 87 Historical trends in agreement with future projections 87 Potential impacts 87 Green fruit stage of tart cherries 88 Soil moisture and soil 88
Decision support systems 96 The Enviro-weather system 97 Don’t rely on them blindly 98 Potato late blight 98 Network for Environment and Weather applications (NEWA) 99 Scab and fireblight in apples and pears 99 SprayWeatherWise 100 101 Online info Do-it-yourself weather monitoring 101 Temperature 102 Humidity and leaf wetness 102 Leaf sensor options 102 Placement of automatic leaf wetness sensors 103 Precipitation 104 Wind direction and speed 104 Measuring air pressure 104 Deployment 106 Upkeep and maintenance 107
7 Practical applications
108
The practical approach 108 Fungicide 109 Insecticide 113 Index
115
1 Sun,
a source of heat
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Sunlight is the source of almost all the energy that drives the earth’s climatic system. It also provides plants with the energy they need for photosynthesis and the creation of plant dry matter. Solar radiation affects crop development, the flowering process, and the shape, color and stem elongation of plants, while temperature has a direct or indirect influence on the application and effect of crop protection products. Unfortunately, the sun is also a source of life for weeds, pathogens, fungi and insects.
Solar energy
The sun emits energy in the form of electromagnetic radiation. Some of the radiation that reaches the earth (a little less than one-third) is reflected back, but most is absorbed by the earth or the atmosphere. Part of the radiant energy spectrum is observable as visible light, but there are also invisible regions, e.g., ultraviolet (UV) and near-infrared. Some of the radiation emitted by the sun goes unnoticed, such as short-wave gamma radiation or X-rays. Fortunately for us, much of it is blocked
6 | Weather & Crop Protection
by the ozone and other gases in the atmosphere and never reaches the earth’s surface. This type of radiation becomes noticeable only if there is a sudden, enormous burst of it from the sun’s surface. While such bursts can severely disrupt radio, television, and cellular telephone communications, they are of no relevance to plants. Crops thrive best on UV-A, blue, red and far-red bands of radiation, from which they derive their growing power. Solar radiation is pure energy.
Global radiation North America occurs across the southwestern USA, where an arid climate with relatively few clouds and low humidity make a major difference.
1 yd
Low sun 1y
Incoming solar energy is distributed over a horizontal surface. When the sun is lower in the sky, as in winter, the energy is distributed over a larger surface area, which means much less energy per unit area, and overall less energy to heat the surface.
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d
The radiation falling on a horizontal surface is known as global radiation, which is usually expressed in terms of energy per unit area (e.g., Joules of energy per square meter per day). On a clear, dry summer’s day, the maximum global radiation in Michigan, for instance, is between 2,800,000 and 3,100,000 Joules per m2 over the course of a day. On a cloudy day in late December, radiation levels sometimes drop below 100,000 Joules per m2, which is less than 5% of the level on a sunny summer day! The amount of radiation can be relatively high in the summer. Levels may actually be lower in southern states such as Louisiana than in northern states, despite the sun’s higher elevation angle. This is because summer days are markedly longer at northern latitudes than at southern ones, and because clouds and atmospheric aerosols such as haze or dust can significantly reduce the amount of solar radiation that makes it to the earth’s surface. Even within a state, differences occur: for instance, in mid-summer, day length in northern Michigan is about 50 minutes longer than in southern Michigan, whereas the opposite is true in mid-winter. Overall, the highest average daily total radiation during the summer in
What does the plant see? A plant ‘sees’ or senses more of the solar radiation spectrum than a human being. Even colors outside the visible spectrum are useful to plants. Blue light (400-500 nanometer (nm) wavelength) and red light (600-700 nm wavelength) have an effect on the plant’s photosynthesis. Radiation in these and nearby wavelengths from 400-700 nm is known as photosynthetically active radiation, or PAR. Blue light influences crop development and red stimulates the flowering process. UV radiation (300-400 nm) affects the shape and color of the plant, while far infrared radiation (700-800 nm) influences stem elongation and flowering.
100
280
315
visible
infrared
UVA
UVC
forms include ultraviolet and near-infrared light. Both visible and non-visible radiation contain usable energy. Chlorophyll in plant leaves absorbs mainly blue, violet, and red light.
UVB
ultraviolet
Observable radiation is visible light. Invisible
400
700
wavelength (nm)
Sun | 7
Everything radiates heat radiation (W/m2)
700 600 500 400 300 200 100
net radiation
0 -100 0
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Every object with a temperature above absolute zero (-460°F/-273°C) emits radiant energy. The energy emitted increases rapidly as the temperature rises. In agriculture and horticulture, it is important to know how much energy different types of radiation supply or remove from the soil and crops. The result of this give and take process is the net radiation. If a crop gains more radiation (= energy) than it loses, the net radiation is positive and it will become warmer.
global radiation
800
Night frost
E ven if the air temperature is not
freezing at a height of 5 ft (1.5 m) above the ground, the crop is at risk of freezing.
8 | Weather & Crop Protection
Imagine the crop temperature is precisely 32°F (0°C) on a clear, dry, still night. At 32°F, the radiation emitted by the plants upwards is 316 W/m2. Due to radiant energy heading downward from the atmosphere itself, the leaves and plants receive 240 W/m2, resulting in a net radiation amount of -76 W/m2. In this case, the crop loses more energy than it absorbs with time and cools down. As a result, the air just above the leaves and crop also cools down, and air temperature above the crop increases with height above the crop. If this situation persists long enough (e.g. for several hours), the crop temperature will fall below freezing, resulting in the formation of frost.
4
8
12
16
20
24
time (hours)
Progression of incoming global radiation and
net radiation on a surface over the course of a summer’s day. Global radiation is zero during the night due to the absence of solar radiation. As a result, the net radiation at night is negative, only becoming positive once the global radiation exceeds a certain threshold. It becomes negative again a few hours before the sun goes down.
From Watts to Joules
The intensity of global radiation (the solar radiation falling on a given area of a horizontal surface per unit of time) is expressed in W/m2. Adding up the global radiation over a period of time represents the incoming energy in that period per unit of surface area (power x time = energy). An entire day’s worth of energy is the total radiation, expressed in J/m2.
Cloud cover: a warm blanket?
The underside of the cloud layer has a rela+340 W/m2 40°F (5°C)
40°F (5°C) +24 W/m2
tively high temperature of around 40°F (5°C). The crop radiates –316 W/m2 at 32°F (0°C) and receives +340 W/m2 (because the clouds have a temperature of 40°F (5°C)). The net radiation goes from strongly negative to +24 W/m2 and results in a net warming of the crop.
-316 W/m2
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As noted above, under relatively clear, calm nighttime conditions, plant and soil surfaces cool down more quickly than the air above them, and temperatures are lowest at ground level. However, if clouds move in, the cooling stops and may actually reverse. Clouds consist of water droplets or ice crystals and actually reemit radiant energy back toward the surface. The clouds also act as an insulator and slow down the rate of energy radiating upwards. With a full cloud cover, nighttime net radiation values are typically near zero or even slightly positive.
H ere you see two images of a black currant field. The right image is an infrared image of the same area as the image on the left. In the infrared image, one can easily see the colder and warmer areas in the field. The plant canopy is relatively warm at 30 to 31°F (-1.0°C to -0.5°C) but in the grass alleyway, the temperature is quite low: 21°F (-6.0°C).
In spring, the sun warms the soil (particularly
dark soils). Mechanical weed control can increase the risk of freeze injury to crops during periods of frequent night frosts. This operation introduces additional air into the soil, which acts as an insulator and reduces the thermal conductivity between the topsoil and subsoil. If you need to disturb the soils (e.g. by hoeing), do it in the morning. This will allow the soil to settle over the course of the day and its conductivity to recover to some extent.
Sun | 9
Frost damage Damage from freezing temperatures depends on the developmental stage of the fruit crop. The tables on page 11 allow you to quickly assess the risk for your tree fruit crops.
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During winter, fruit trees can withstand very low temperatures. As fruit trees develop in the spring and buds start to swell, they lose the ability to withstand low temperatures. Swollen fruit buds can often withstand temperatures in the teens without any damage. As the buds open, temperatures in the low 20s 째F can cause
harm. Young, actively growing tissues will be killed at even higher temperatures. Early in their development, there is often a wide range between temperatures that cause little damage and those that cause severe damage. As bloom nears, temperatures in the upper 20s 째F can cause considerable harm to an early blooming species or variety and leave other fruit crops unaffected or with only slight damage. Near bloom, the range between slight and severe damage is very small. The stage of bud development determines how susceptible any given fruit crop is when freezes occur.
T he flower buds at the tip of this
blueberry twig are brown and frost damaged, whereas the leaf buds below are still alive and green.
Freeze damage to blueberry flower buds. On the left: no damage. In the middle: one flower killed. On the right: all flowers killed.
10 | Weather & Crop Protection
Critical spring temperatures (in Fahrenheit) for tree fruit bud developmental stages Pome Fruit Silver Tip
Green Tip
0.5 inch Green
Tight Cluster
First Pink
Full Pink
First Bloom
Full Bloom
Post Bloom
Old temp 10% kill 90% kill
16 15 2
16 18 10
22 23 15
27 27 21
27 28 24
28 28 25
28 28 25
29 28 25
29 28 25
Pears
Bud Swell
Bud Burst
Tight Cluster
First White
Full White
First Bloom
Full Bloom
Post Bloom
Old temp 10% kill 90% kill
18 15 0
23 20 6
24 24 15
28 25 19
29 26 22
29 27 23
29 28 24
30 28 24
Apricots
Bud Swell
Bud Burst
Red Tip
First White
First Bloom
Full Bloom
In the shuck
Green Fruit
Old temp 10% kill 90% kill
15 -
23 20 0
22 9
25 24 14
25 19
28 27 22
27 24
31 28 25
Peaches
Bud Swell
Calyx Green
Calyx Red
First Pink
First Bloom
Full Bloom
Post Bloom
Old temp 10% kill 90% kill
23 18 1
21 5
23 9
25 25 15
26 21
27 27 24
30 28 25
European Plums
Bud Swell
Side White
Green Tip
Tight Cluster
First White
First Bloom
Full Bloom
Post Bloom
Old temp 10% kill 90% kill
14 0
17 3
20 7
24 16
23 26 22
27 27 23
27 28 23
30 28 23
Sweet Cherries
Bud Swell
Side Green
Green Tip
Tight Cluster
Open Cluster
First White
First Bloom
Full Bloom
Post Bloom
Old temp 10% kill 90% kill
23 17 5
23 22 9
25 25 14
28 26 17
28 27 21
29 27 24
29 28 25
29 28 25
30 28 25
Tart Cherries
Bud Swell
Side Green
Green Tip
Tight Cluster
Open Cluster
First White
First Bloom
Full Bloom
Old temp 10% kill 90% kill
15 0
24 10
26 22
26 24
28 24
28 24
28 24
28 24
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Apples
Stone Fruit
U nfortunately, spring freezes are
a common threat. Fruit growers need to constantly assess the stage of development of their crops and their susceptibility to freeze injury.
C ommon tree fruit bud developmental stages and the critical temperatures that will cause cold injury to the flower buds. The old standard temperature (Old temp) represents the lowest temperature that can be endured for 30 minutes without damage. In addition, the chart shows the temperatures at which 10% and 90% of normal fruit buds will be killed (chart compiled by Mark Longstroth, MSU Extension).
Sun | 11
Agrometeorologisch adviesbureau Erno Bouma Sumatralaan 28 7314 CL Apeldoorn The Netherlands E bouma.weer@planet.nl I www.boumaweeradvies.eu
T
he weather has a greater influence on crop protection than many farmers think. It affects the development of diseases and pests, the application and effectiveness of products and the protection of plants and harvested crops. These relationships are explained clearly in the practical guide Weather & Crop Protection.
co pr py ot rig ec h te t d
Erno Bouma is an expert in the field of agrometeorology. He works as a lecturer at the HAS University of applied sciences in ‘s Hertogenbosch where he teaches integrated crop protection and plant sciences. He is also the founder of the Erno Bouma Agrometerological consultancy firm. He was closely involved in the development of CERDIS, a decision support system for cereals, and in SprayWeatherWise, the system that explains all you need to know about the effectiveness of crop protection agents. He is co-author of the Agrarisch Weerboek (1998) and the Natuurkalendergids (2005) and has written many specialist articles on a wide range of crops. Furthermore he gives lectures and presentations on four continents. “The weather has fascinated me since childhood. I find it odd that many people know little about the relationship between the weather and all sorts of things that happen on the farm, even though the weather is so important in the development of pests and diseases and their control.” A much sought-after speaker and course leader in the Netherlands and abroad, Erno Bouma also hosts events such as information meetings for the grant of crop protection licenses.
‘You can’t change the weather, but you can change your response to it’
Weather Crop Protection
About the author
w w w. r o o d b o n t . c o m
www.boumaweeradvies.eu
What are the ideal weather conditions for spraying? Not a gale or downpour, but certainly not a dead calm either. What demands do crop protection agents impose in terms of temperature, humidity and other meteorological factors? Insects are more active in warm weather, for example, and may pose a problem. But, at the same time, insecticides are more effective in warm weather. Weather & Crop Protection has the answers to these and many other questions. After reading Weather & Crop Protection, anyone involved in outdoor cultivation will understand the influence of weather on diseases, pests and their control. He will be able to take preventive action or respond in good time to the first signs of disease in order to achieve the best possible results for his crop, his wallet and the environment.
Did you know? Reducing the quantity of spray mixture in a wet crop in order to limit droplet roll-off would seem to make sense. But it’s pointless. A crop can easily contain 7,000 liters of condensation per hectare. Reducing the spray mixture by 100 liters per hectare is a drop in the ocean.
Weather Main author: Erno Bouma Co-authors: Annemiek Schilder, Jeff Andresen, John Wise
Crop Protection ISBN 978-90-8740-185-6
9 789087 401856
North American edition
When do insecticides work best? In warm weather, when the insects are more active. They move about more, eat more and exchange more gas. As a result, insecticides work better and insects kick the bucket quicker.
Never spray insecticides in the middle of the day. They are very sensitive to light and degrade quickly in sunlight. At the end of a sunny day the temperature in the crop is still high enough to obtain a good effect, and the insolation level will be low after spraying. In short, spray at the end of a sunny day.