Contact, systemic and translaminar: How insecticides move in plants

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Understanding how an insecticide moves, or doesn’t move, in a plant is critical to insecticide/miticide selection and proper application. Contact materials cover only the plant’s surface and insects or mites must directly contact the active ingredient for control. Good coverage is important – any surface not covered isn’t toxic, including new shoots and the newest leaves in the growing tip.

Systemic materials, on the other hand, move within the plant; applied to the media they will move throughout the entire plant, including new shoots. However, systemics take time to move up to the new shoots and control doesn’t happen until the toxic material is present where the insects or mites are feeding. The woodier the plant, the more slowly systemics move. In very woody stock plants, the material may not move into the shoots at all. One solution is to spray systemic materials on the tops of plants (Marathon II). Remember that insecticides tend to move upward in the plant, not downward; there will be little control of insects or mites below where the application was made.

Another problem with systemics is that the amount of toxic material present in the new shoots is very small. Aphids may concentrate enough toxic material in the sap they feed on to be killed, but chewing insects may not get enough to be controlled. Translaminar materials don’t have surface residues but move into the leaf where a reservoir of active ingredient remains for a period of time providing longer control. Don’t confuse translaminar with systemic – translaminar materials move only short distances not through the entire plant. Thorough coverage is still very important.

Most insecticides today are contact materials, some are systemic and a few (imidacloprid and similar materials) are all three. Check the label for more information. Thanks to Dr. Ray Cloyd, Kansas State University, for information for this article. Any errors are mine.

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