Rainfastness of Pesticides

It’s important to avoid fertilizer or pesticide application when a heavy rain is expected.  As you know, this may result in runoff of these chemicals- can end up polluting our water, reducing the effectiveness of the product, and wasting customers’ money.  In South Florida, rain can be frequent and unpredictable, so its a good idea to be in tune with the weather and the products you are applying.

Some pesticides can withstand rain better than others, and foliar-applied products are extremely variable.  A rainfast pesticide is one that has dried and/or been absorbed by a plant’s tissues.  Labelling for rainfastness is variable.  Some product labels contain significant detail, while others don’t address rainfastness.

Keep the following in mind:

  1. Some products provide a specific time frame needed to achieve rainfastness, while others don’t.  ALWAYS check the weather and the label.
  2. Some products will prohibit application when rain is forecast.
  3. Adjuvants, such as surfactants and product thickeners, can be used to improve a product’s rainfastness.
  4. Rainfastness is variable based on insecticide class, amount of rainfall, and plant part (fruit or leaves).  For example, with up to 1/2″ of rain, Neonicotinoids are highly rainfast, while Pyrethroids are only moderately rainfast.  (see the full publication, linked below, for a detailed chart)
  5. The label is the law!  No exceptions!

This post was adapted from a new EDIS publication, Rainfastness of Pesticides, by Bonnie Wells and Fred Fischel.  You can read more here.

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