By: Kirk Williams, Lecturer-Texas Tech University
Pesticide applications in the vineyard whether using an organic product or a synthetic product, are often needed to maintain a weed free vineyard with a healthy canopy, to prevent the loss of fruit and preserve fruit quality. We want to ensure that when we make a pesticide application in the vineyard that we get the most efficacy out of that product that we apply. There are many factors that contribute to a successful and effective vineyard spray application. One factor is good coverage of the target, which, for foliar applications to grapevines, includes the fruit and canopy. The primary factors affecting coverage are the application rate, pressure, droplet size, and penetration into the grapevine canopy which is usually assisted with air produced by the sprayer.
The use of adjuvants in the spray tank can help assist in making a good application perform its best. Adjuvants are not going to fix poor coverage, poor timing of applications or bad weather conditions at the time of the application. Adjuvants are materials added to a spray tank to aid or modify the action of a pesticide or the physical properties of the mixture.
There is a wide selection of adjuvants that perform distinct functions so understanding how each adjuvant type works is important in choosing the right one. We will be looking at different adjuvants that can help in making an application perform its best. Most adjuvants are used at low rates and their rates are expressed on a volume per volume basis (e.g. 2 pts per 100 gallons).
We will only be looking at the main adjuvants that are used in grape production. There are many different brand names with most large agricultural retailers having their own brands. Due to this we will be talking in general, not about specific branded products. Adjuvants selection should be based on several factors including what is specified on the pesticide label, your specific water quality and cost.
Buffers/Water Conditioners
In certain water situations such as high pH or the presence of large amounts of hard water cations such as calcium or magnesium you might need to consider adding a buffer or a water conditioning agent to the spray tank. Buffers or water-conditioning agents are compounds that reduce the damage caused by alkaline hydrolysis and adjust the pH of the spray solution to maintain it within a pH range of 4 to 6. Alkaline hydrolysis is a degradation process in which the alkaline water breaks and reduces the effectiveness of the pesticide’s active ingredient. Certain insecticides such as the pyrethroids and carbaryl are susceptible to alkaline hydrolysis. Certain weak acid herbicides such as glyphosate and glufosinate perform better in an acidic spray solution than an alkaline solution. Buffers or water conditioners are normally added to the spray tank prior to adding the pesticide.
Special Purpose Adjuvants
There are several adjuvants which may be used in certain situations which may not always be needed for all vineyard applications. Many of these are also components in blended purpose adjuvants.
Many vineyards spray applications tank mix several products and sometimes include foliar fertilizers. Some combinations can be physically or chemically incompatible, which may cause clumps to form or products to separate in the spray tank. Compatibility agents prevent mixing and settling out problems that can occur in these situations.
•Antifoam agents suppress surface foam in the spray tank and minimize air entrapment which can cause pump and spray problems.
•Drift control agents modify spray characteristics by minimizing small spray droplet formation. Small spray droplets are more prone to drift so by reducing the number of small spray droplets off site droplet movement should be reduced.
•Sticking agents, commonly called stickers, assist the spray deposit to adhere or stick to the target such as clusters or leaves. The sticking agents usually come combined with other adjuvants such as surfactants to allow for easier mixing. Sticking agents are helpful when periods of rain are expected after an application. A good example of the need for a sticking agent is the use of contact fungicides in the spring where rainfall is likely.
Surfactants
One of the most used adjuvants in vineyard spray applications are surfactants. The primary purpose of a surfactant, also known as a surface-active agent, is to reduce the surface tension of the spray solution to allow closer contact between the spray droplet and the plant surface. Water droplets are held at contact angles ranging from 60° to 140° with a significant variation between species. Water droplets with high contact angles on grape leaves are shown on the left side shown above. Water droplets with surfactant added are shown on the right side shown above. The water droplets have completely spread out with the addition of the surfactant. Complete coverage of the target is important for most pesticides and the addition of the surfactant demonstrates how they can improve coverage.
Non-ionic and organosilicone are the most used types of surfactants. Organosilicone surfactants are noted for their increased spreading ability versus traditional surfactants and the low surface tensions of their spray solutions. Organosilicone surfactants have lower use rates but may be more expensive than non-Ionic surfactants. Non-ionic surfactants have a higher use rate but may be less expensive.
Blended Purpose Adjuvants
Blended purpose adjuvants contain various combinations such as a surfactant plus a water conditioner plus a drift inhibitor plus an anti-foaming agent. Because of the multiple adjuvants included they serve primary and secondary purposes.
If you don’t need all the components included in the blended purpose adjuvant, then you might be better off from a cost standpoint to just use those adjuvants that you need. Blended purpose adjuvants are becoming more common because multiple ingredients are included in one product.
Choosing the proper adjuvant for a vineyard spray application can be confusing but knowing the major types and functions of adjuvants should make selection easier. Read pesticide labels to see what adjuvants if any are recommended for use. Once you know which adjuvant you need, select a product that you can source and read the adjuvant label as well.
Sources:
Curran, W. S., and D. D. Lingenfelter. (2009). Adjuvants for Enhancing Herbicide Performance. Penn State Extension.
Hazen, J. L. (2000). Adjuvants: Terminology, Classification, and Chemistry. Weed Technology, 14(4), 773–784.
Kirk Williams is a lecturer in Viticulture at Texas Tech University and teaches the Texas Tech Viticulture Certificate program. He is also a commercial grape grower on the Texas High Plains. He can be contacted at kirk.w.williams@ttu.edu
