Grower 101: Pesticide Application and Equipment
Selecting the correct product for the job is very important to the success of a pest management program, but equally important is the equipment and application technique used to apply the pesticide. To help select the right application and equipment, we turned to Dick Lindquist, a senior technical manager of Olympic Horticultural Products, Wooster, Ohio. The following information is confined to products applied to aboveground plant parts.
Selecting the correct product for the job is very important to the success of a pest management program, but equally important is the equipment and application technique used to apply the pesticide. To help select the right application and equipment, we turned to Dick Lindquist, a senior technical manager of Olympic Horticultural Products, Wooster, Ohio. The following information is confined to products applied to aboveground plant parts.
Application
According to Kurt Becker of Dramm Corp., many pesticides can be applied using different application equipment.
High-volume hydraulic sprayers. There are numerous kinds, with differences in efficiency, depending on the type of spray nozzle and the person doing the spraying. High-volume sprayers have high flow rates, produce (mostly) large spray drops and are wet sprayers, applying 200-plus gal. per acre, and can be used to make localized or spot applications.
Targeted low-volume sprayers. These have lower flow rates, produce smaller spray drops and apply less spray volume, 5-45 gal. per acre. They can be used to make localized applications within a greenhouse. Examples include electrostatic sprayers, coldfoggers and rotary atomizers.
Ultra low-volume sprayers. These use very little water, or carrier in the case of thermal foggers, produce very small spray drops, and cannot be used for localized applications. The air movement system in the greenhouse can be used to help distribute the pesticide. Examples include total release aerosols, smoke generators, thermal pulse-jet foggers, mechanical aerosol generators and autofoggers.
Distribution
According to Lindquist, one must obtain thorough coverage to get good pest control. The amount of pesticide deposited on a plant may or may not be related to successful control. It is the distribution of the pesticide that is more important. Where are the pests located?
Before selecting an application method it is important to find out how the product works. Does the pesticide just sit where it was applied, or does it redistribute? Does it have vapor activity? What about translaminar (locally systemic) movement following application? Does the product have to be eaten to be effective, or will direct contact with the spray or pest movement over treated surfaces do the trick? When in doubt, Lindquist said, ask your local extension specialist, pest management consultant or the technical service folks at the company marketing the product.
Application Equipment
All three application methods were tested by The Ohio State University while Lindquist was working there and resulted in pretty good control, but the wetter sprays (high-volume, 200-plus gal. per acre and targeted low-volume, 45 gal. per acre) left fewer live mites five days after application than did the ultra-low-volume thermal fog application (see Figure 1, below). Movement of the Avid from the upper leaf surface to the underside, following application, may be related to the amount of liquid used to apply it, said Lindquist. The thermal fogger uses only a few liters of solution in an application, so this dry spray may not have produced enough liquid. Another reason for the differences might be that the high-volume spray and Coldfogger (Dramm Corp.) applications deposited more pesticide on leaf undersides. Clearly, though, the thermal fog application did provide some control.
Figure 2, below, compares application methods using Azatin for silverleaf whitefly control on poinsettias. “We used an electrostatic sprayer from ESS, Watkinsville, Ga., as the targeted low-volume applicator as well as an autofogger for a second ultra-low-volume sprayer,” Lindquist explained. “In this case, the high-volume sprays were much better than any of the low-volume sprays. All three of the low-volume applications were ‘dry’ sprays, with the ESS used at 5 gal. per acre, and the other two sprays at even lower volumes.”
Azatin also moves within the leaf after application, but according to Lindquist, either the amount of liquid deposited on the leaf was too little with the low-volume sprays, or Azatin does not move well within poinsettia leaves. The high-volume spray probably covered both upper and lower leaf surfaces with enough spray volume to produce movement within the leaf and/or contact the immature whiteflies.
Spray Volume
Looking at the results in Figures 3 and 4, above, Lindquist explained that two things stand out: The whitefly population was very high, and spray volume did make a difference in control. The higher spray volume from both sprayers resulted in fewer whiteflies. The ESS sprayer is supposed to be used at about 5 gal. per acre and the coldfogger at 30-45 gal. per acre, so in this case, one sprayer will be better than the other.
However, Lindquist said that, as seen in Figure 4, Marathon II was applied to chrysanthemum for melon aphid control using the same two sprayers at the same spray volumes as in Figure 3. The suggested spray volumes applied with each sprayer provided excellent control. However, the lower spray volume from the Coldfogger — equal to the high volume of the ESS — did not control the aphids. “Marathon acts primarily by ingestion and somewhat by contact. It is locally systemic or translaminar. It is possible that the lower volume from the Coldfogger did not get enough pesticide deposited where the aphids were feeding,” he explained.
According to Lindquist, we can conclude that 1) There are interactions among pest, pesticide, application equipment and method and plant species. 2) Deposition and distribution of the pesticide following application are very important. 3) Getting more pesticide on the plant will not necessarily result in better control. 4) Total spray volume may or may not be important.
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