Preharvest Interval, Vol. 5, No. 14

When using any pesticide on any edible crop, one of the most important things you need to know is the pre-harvest interval or PHI.  How long do you have to wait after you spray the crop before you can harvest the crop?  If the product is labeled for use on an edible crop, this information is stated on the product label.  For some products on some crops the wait is very short— “spray up to and including day of harvest.”  For other products on other crops the wait can be as much as 21 days, or even longer. 
 
The PHIs for a given product will not be the same for all vegetables.  It depends on what vegetable is being sprayed.  For example, Ortho Bug B Gon Insect Killer for Lawns and Gardens (bifenthrin) has a 1 day PHI on tomatoes, a 3 day PHI on squash, a 7 day PHI on peppers and eggplants, a 14 day PHI on pears, and a 21 day PHI on pecans.  The following table gives PHIs for six insecticides that are commonly used in home vegetable gardens.

          * Pyrethrin is an organic insecticide with short residual activity.
            Overall efficacy is considerably lower than other products in table.

 Based on information in this table, zetamethrin is a good choice for a home garden insecticide because it has a 1 day PHI on most garden vegetables. The photo shows a portion of the label for a product that contains zetamethrin, showing the pre-harvest interval for fruiting vegetables, such as tomatoes, peppers and eggplant.  Bifenthrin may be a bit more effective on some pests, but it has a 7 day PHI on peppers and a 3 day PHI on squash.  If you have leaffooted bugs feeding on the tomatoes and the peppers, and squash bugs on the zucchini, it is helpful to know you can spray them all at the same time and still be able to harvest on the same day.  However, there are some pests, such as aphids, spider mites and whiteflies, that zetamethrin will not control.  Also, there are some crops, such as onions and sweet corn, for which the PHI for zetamethrin is longer than 1 day.
 
Note that if the label does not list the crop you plan to spray, then the product is not labeled for application on that crop. Read that label before you spray! 
 
For more information on insecticides for use in home vegetable gardens see Extension Publication 2347, Insect Pests of the Home Vegetable Garden.  Pages 15 and 16 of this publication give examples of brand name products that contain the active ingredients listed in the table.

Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service. The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.
 
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