Pesticide mixtures and adjuvant

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Pesticide mixtures and adjuvant

Combining two or more pesticides and applying them at the same time is convenient and cost effective. Most pesticide manufacturers sell some of their products as pre-mixes, but often you must combine two or more pesticides at the time of application. Combinations may, however, affect the toxicity and the physical and chemical properties of any of the components of  the  tank mix  increase residues, and  damage or  injure the target site, plant, or animal.

Adjuvants are products that have no pesticidal activity, but are also available to add to spray mixtures to increase mixing, ease application and help the pesticide work better. In this Section, pesticide applicators will learn how to safely mix different pesticides and use adjuvants.

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Learning objectives:

Describe how you would determine if two mixed pesticides might be incompatible. Describe what labels may tell you about pesticide adjuvant. Terms to Know:

•       Tank mix

•       Field incompatibility

•       Adjuvant

•       Surfactants

Pesticide Mixtures:

When  you  combine mixtures of  two or more pesticides and/or fertilizers at the time of application, you create a tank mix. A common tank mix involves combining fungicides with insecticides as a spray for tree fruit crops. Another involves combining two or more herbicides to increase the number of weed species controlled. Some people mix pesticides  with  micronutrients  or   fertilizers. 

This   practice saves money by reducing the time, labor, and fuel required for multiple applications. Tank mixes reduce equipment wear and decrease labor costs. They lessen the mechanical damage done to crops and soil by application equipment. If you mix danger- poison pesticides with warning or caution pesticides, treat the mixture as danger-poison pesticide. You must use the required safety equipment and follow all other label restrictions found on the component of the pesticide mixture that has the greatest toxicity—the label with the greatest restrictions.

Incompatibility:

Incompatibility is a condition that prevents pesticides from mixing together properly to form a uniform solution or suspension. The formation of flakes, crystals, oily clumps, or severe separation is unacceptable. Such incompatible mixtures clog application equipment and limit even distribution of the active ingredient in the spray tank. This prevents good pesticide coverage.

Some   adjuvant   manufacturers  have   named their  products  “extenders.”  Extenders  function  like  stickers by retaining pesticides longer on the target area, slowing evaporation, and inhibiting degradation by sunlight.

The cause of  incompatibility may be  the chemical nature of the materials you are mixing. Impurities in the spray tank or water also may affect compatibility. Even the order in which you mix pesticides in the spray tank is important. Sometimes the types of formulations being mixed influence compatibility. Pesticide formulations of the same type are rarely incompatible with one another because they usually contain many of the same inert ingredients and solvents. Always evaluate a tank mixture by performing the compatibility test described in.

Adjuvants:

Adjuvants are chemicals that do not possess pesticidal activity. Adjuvants are either pre-mixed in the pesticide formulation or added to the spray tank to improve mixing or application  or  to  enhance  pesticidal  performance.  They  are used  extensively in  products designed for  foliar applications. Adjuvants can be used to customize the formulation to specific needs and compensate for local conditions. The right adjuvant may reduce or even eliminate spray application problems, thereby improving overall pesticide efficacy. Before using any adjuvant, consult the pesticide label. Many registered pesticide products have very specific label recommendations on use with one or more adjuvants. Failure to follow these instructions is as much a violation of the product label as misuse of the pesticide.

If  you  have questions about the  specific properties of  an adjuvant, contact the manufacturer before attempting to use it. Companies that produce adjuvants can provide labels, technical data sheets, Materials Safety Data Sheets (MSDS), supplemental labeling, and promotional literature about their products.

Adjuvants are designed to perform specific functions, including wetting, spreading, sticking, reducing evaporation, reducing volatilization, buffering, emulsifying, dispersing, reducing spray drift, and reducing foaming. No single adjuvant can perform all these functions, but compatible adjuvants often can be combined to perform multiple functions simultaneously.

Types  of  adjuvants:

Much  of  the  confusion  surrounding adjuvants can be attributed to the lack of understanding of adjuvant terminology. For example, many people use the terms Adjuvant  and   surfactant  interchangeably.  These  terms   can refer to the same product because all surfactants are adjuvants. However, not all adjuvants are surfactants. Adjuvants include:

Stickers:

A sticker is an adjuvant that increases the adhesion of solid particles to target surfaces. These adjuvants can decrease the  amount  of  pesticide that  washes  off  during  irrigation or rain. Stickers also can reduce evaporation of the pesticide, and some slow down the degradation of pesticides by sunlight. Many adjuvants are formulated as spreader-stickers to make a general- purpose product.

Extenders:  

Some   adjuvant   manufacturers  have   named their  products  “extenders.”  Extenders  function  like  stickers by retaining pesticides longer on the target area, slowing evaporation, and inhibiting degradation by sunlight.

Plant penetrants:

These adjuvants have a molecular configuration  that  enhances  penetration  of  some  pesticides into plants. An adjuvant of this type may increase penetration of a pesticide on one species of plant, but not another. Enhanced penetration increases the activity of some pesticides.

Compatibility agents:

Pesticides are commonly combined with liquid fertilizers or other pesticides. Certain combinations can be physically or chemically incompatible, which causes clumps and uneven distribution in the tank. Occasionally the incompatible mixture plugs the pump and distribution lines resulting in expensive cleanup and repairs. A compatibility agent may eliminate these problems. Read product label directions carefully before adding a compatibility agent to a spray mix. You may wish to do a compatibility test in a quart jar to determine the stability of the mixture. After adding the desired pesticides and the compatibility adjuvant to the jar, shake the mixture and then check for clumping, separation, thickening, and heat release. Any one of these signs indicates an incompatibility problem.

Buffers or pH modifiers:

Most pesticide solutions or suspensions are stable between pH5.5 and pH7.0 (slightly acidic to neutral). Above pH7.0 (alkaline or basic), the pesticide may be subject to degradation. Once a pesticide solution becomes alkaline, the risk exists that the pesticide degrades. Buffers and acidifiers are adjuvants that acidify and stabilize the water in the spray tank. Buffers must be added to the tank mix water first. The water must be neutralized or slightly acidified prior to adding pesticides and adjuvants.

Drift Control additives:

Drift is a function of droplet size. Small, fine drops with diameters of 100 microns or less tend to drift away from targeted areas. Drift control additives, also known as deposition aids, improve on-target placement of the pesticide spray by increasing the average droplet size. Drift reduction can be very important near sensitive sites and may well be worth the small reduction in efficacy that may result from the change in droplet size.

Defoaming agents:

Some pesticide formulations create foam or a frothy “head” in spray tanks. This is often the result of both the type of surfactant used in the formulation and the type of spray tank agitation system. The foam usually can be reduced or eliminated by adding a small amount of a defoaming agent.

Thickeners:

As the name suggests, thickeners increase the viscosity (thickness) of spray mixtures. These adjuvants are used to control drift or slow evaporation after the spray has been deposited on the target area. Slowing evaporation is important when using systemic pesticides, because they can penetrate the plant cuticle only as long as they remain in solution.

How  to  choose  the  right  adjuvant:  Many  factors  must be  considered when choosing an  adjuvant for  use  in  a  pest- management  program.  Following  are  some  guidelines:  Use only adjuvants manufactured and marketed for agricultural or horticultural uses. Do not use industrial products or household detergents with pesticides, because they may interfere with pesticide performance.

Remember, there are no miracle adjuvants. It is generally wise to be skeptical of such claims as “keeps spray equipment clean” or “causes better root penetration” unless the manufacturer has supporting evidence to back up such claims.

Make sure the adjuvant has been thoroughly tested and proven effective for your intended use. Test questionable products on a limited area before proceeding with full-scale use. Certain pesticides and application procedures require certain types of adjuvants. Determine the correct type and use only an adjuvant of that type. For example, do not substitute an anionic surfactant when a nonionic surfactant is recommended.

A particular pesticide label may require one or more adjuvants for a certain use, yet prohibit any adjuvant for another use. Read the pesticide label carefully. Using an adjuvant is not always necessary. It is just as important to know when not to use an adjuvant as it is to know when to use one to achieve the best results. Spray adjuvants can contribute substantially to safe and effective pest control. Many spray adjuvants are available, each formulated to solve problems associated with a particular type of application. Check pesticide and adjuvant labels to make sure adjuvants are suitable for the site you plan to spray, the target pest, your equipment, and, of course, the pesticide you plan to use.

Remember, many pesticide products already contain an adjuvant. If a pesticide is already formulated properly for your crop, using an additional wetting agent, for example, may not give better spreading or coverage; instead, it could increase runoff, reduce deposition, and even severely damage the target plants.

Surfactants:

Surfactants, also called wetting agents and spreaders, physically alter the surface tension of a spray droplet. For a pesticide to perform its function properly, a spray droplet must be able to wet the foliage and spread out evenly over a leaf. Surfactants enlarge the area of pesticide coverage, thereby increasing the pest’s exposure to the chemical. Surfactants are particularly important when applying a  pesticide to  waxy or hairy leaves.

Without  proper  wetting  and   spreading,  spray  droplets often run off or fail to cover leaf surfaces adequately. Too much surfactant, however, can cause excessive runoff and reduce pesticide efficacy. Surfactants are classified by the way they ionize or split apart into electrically charged atoms or molecules called ions. A surfactant with a negative charge is anionic. One with a positive charge is cationic, and one with no electrical charge is nonionic. Pesticidal activity in the presence of a nonionic surfactant can be quite different from activity in the presence of a cationic or anionic surfactant. Selecting the wrong surfactant can reduce the efficacy of a pesticide product and injure the target plant.

Anionic surfactants are most effective when used with contact  pesticides (pesticides that  control  the  pest  by  direct contact rather than being absorbed systemically). Cationic surfactants should never be used as stand-alone surfactants because they usually are phytotoxic.

Nonionic surfactants, often used with systemic pesticides, help pesticide sprays penetrate plant cuticles. Nonionic surfactants are compatible with most pesticides, and most EPA- registered pesticides that require a surfactant recommend a nonionic type.

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