Chapter 24

Greenhouse Pesticides

Pre-Mix versus Tank-Mix Pesticides

Sometimes, product manufacturers combine pesticides with other pesticides or fertilizers for sale as pre-mixes (commercial blend of two active ingredients). However, when pre-mixes are not available (or are not offered in the desired combination), growers often opt to tank mix products—combining two or more crop-production products (pesticides and/or fertilizers). Sometimes, tank mixing is mandated by the product label.

Pre-mixed Pesticides

A pre-mix is a commercial product containing two or more active ingredients. Use of pre-mix pesticides can be driven by a variety of goals, including resistance management, ease of use, cost effectiveness and breadth of activity. Premixes have both positive and negative aspects. Some of the positive aspects include: 1) diagnosis is less critical; 2) mixed infections are covered; 3) plant safety is known; 4) resistance management; 5) improved efficacy; 6) fewer products on the shelf; and 7) can be more cost effective.

Tank-mixed Pesticides

Tank mixing involves combining two or more crop-production products (pesticides and/or fertilizers) into a single spray solution. Tank mixing has both positive and negative aspects. Tank mixing is less time consuming, costly and labor intensive to mix two or more pesticides and make one application as opposed to applying each pesticide separately. Another benefit of pesticide mixtures is the potential for improved pest suppression. For instance, mixing two pesticides may result in greater kill than applying either pesticide separately, which is referred to as synergism or potentiation. Synergism is when the combined toxicity of two compounds is greater than the sum of the toxicities of each individual compound.

Compatibility of Pesticides

Compatibility is the ability of two or more chemicals to be combined without danger. Compatibility can be influenced by the pH—the acidity or alkalinity—of a solution. A neutral solution has a pH of 7. Various pesticides are unstable in alkaline solutions (pH greater than 7), but quite stable in solutions that are slightly acidic (pH of approximately 6).

Physical Compatibility Test

Before you mix pesticides or pesticide-fertilizer combinations in your spray tank, conduct a jar compatibility test. This test shows whether the components are physically compatible and whether you need to add a compatibility agent. This test cannot detect chemical incompatibility. To conduct a jar test, you need to add proportionate amounts (convert gallons or pounds to milliliters, ounces, or teaspoons) of all the products you intend to mix in your spray tank to a clear quart jar.

Federal Law

Federal law allows applicators to combine pesticides unless the labeling of one or more components of the intended tank mix specifically prohibits it.

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