Formulations
Pesticide products are formulated as either liquids or solids. The appropriate formulation to choose may be dependent upon several factors, including the equipment available, the cost of the product, the pest(s) to be controlled, and both user and environmental safety. The formulation of a product is often indicated by a suffix to the trade name:
- Emulsifiable concentrates (EC) are less troublesome to spray equipment than wettable powders (WP). The water-based flowable concentrates and wettable powders are less likely to cause plant injury than oil-based concentrates of similar materials
- Wettable powders/suspendable powders (WP) are less likely than ECs to cause injury to sensitive plants or to cause trouble when mixed with fungicides or other pesticides.
- Dry flowables (DF) are similar to wettable powders in their formulation but are pelletized to minimize dust.
- Flowables (F) are liquid formulations with similar properties to latex paint. Clean equipment immediately after use.
When tank-mixing pesticides, mix in the proper order. The order is: Wettable Powders (WP), Water Dispersible Granules (WDG), Flowables (F) (DF) (SC), Water-dispersible liquids (AS), Emulsifiable Concentrates (EC), and Solutions (S). Always follow the pesticide label when using adjuvants such as spreader stickers, surfactants, etc.
Adjuvants
Adjuvants are non-pesticide chemicals that are added to pesticides or to pesticide spray mixtures to improve their chemical or physical characteristics. The most common types of adjuvants are nonionic surfactants, crop oil concentrates, spreader/stickers, drift control agents, buffering agents, compatibility agents and foam-reducing agents. Adjuvants can reduce or eliminate many spray application problems by performing specific functions. These functions include spreading, wetting, sticking, reducing drift, buffering, improving compatibility, reducing foaming, and improving the effectiveness of certain pesticides. Non-ionic surfactants are usually best for improving mixing of pesticides, for enhancing coverage of leaf surfaces, and for improving retention of the pesticide on the crop or weed. Although several adjuvants perform more than one function, no one adjuvant can perform all of these functions.
The most important source of information you have to determine whether or not to use an adjuvant is the pesticide label. Some prohibit the use of adjuvants due to the potential for severe crop injury or loss. Surfactants can increase the potential for crop injury by enhancing penetration of pesticides into the foliage or by causing burning on their own. High temperature and humidity enhance this potential injury. Avoid spraying in the mornings or middle of days when you can add the temperature (ºF) and % humidity together and get 150 or more.
It is best to avoid silicone-based surfactants, ionic surfactants, or others that you are not familiar with unless you have a specific purpose for using them. If a label does not list a certain tank mix that you want to use AND, at the same time, does not preclude it, you may make the tank mix. Remember, however, that you should try it on a small scale first to make sure that there will be no problems.
Some labels provide no mention of adjuvants; in this case, consult the manufacturer or pesticide dealer.
Know Your Water
The pH of the water in your tank mix can sometimes affect the efficacy of pesticides. Insecticides, in particular, tend to break down (hydrolize) rapidly in alkaline water. Water pH can vary, depending on the source, from 5.0-9.5. Neutral water has a pH of 7.0, while alkaline water is higher than 7.0. If your water pH is much higher than 8.0, you may want to consider using an acidifying agent such as vinegar to lower the pH in the tank. Many of the pH-sensitive pesticides have acidifying agents in the formulation that moderate the effect of alkaline water. However, growers who suspect a pH problem should have their water tested. This can be done on the farm with pH test kits. Also, organic matter can tie up certain pesticides or clog nozzles, so be sure to use water that is free of organic debris.
Selection of Sprayer Tips
The selection of proper sprayer tips for use with various pesticides is very important. Nozzle tips must be selected according to the spray coverage, droplet size, and application volume desired. Flat fan spray tips are designed for preemergence and postemergence application of herbicides. These nozzles produce a tapered-edge spray pattern that overlaps for uniform coverage when properly mounted on a boom. Standard flat fan spray tips are designed to operate at low pressures (30-60 psi) to produce small- to medium-sized droplets that do not have excessive drift. Flood-type nozzle tips are generally used for complete fertilizer, liquid N, etc., and sometimes for spraying herbicides onto the soil surface prior to incorporation.
Full and hollow cone nozzles deliver circular spray patterns and are used for application of insecticides or fungicides to crops where thorough coverage of the leaf surfaces is extremely important and where spray drift will not result in crop injury of nearby plants. They are used when higher water volumes and spray pressures are recommended. With cone nozzles, the disk size and the number of holes in the whirl plate affect the output rate. Various combinations of disks and whirl plates can be used to achieve the desired spray coverage.