Preharvest Interval PHI, Vol. 10, No. 09
Preharvest Interval
PHI
Before 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 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 are rarely the same for all crops. It depends on what crop is being sprayed. For example, Hi-Yield Indoor/Outdoor Broad Use Insecticide (permethrin) has a 0-day PHI on tomatoes, 1-day PHI on lettuce, a 3-day PHI on peppers, a 7-day PHI on potatoes, and a 14-day PHI on blueberries. The following table gives PHIs for six insecticides that are commonly used in home vegetable gardens.
Pre-harvest Intervals (in days) for Some Common Home Garden Insecticides
| Crop |
Active Ingredient | |||||
| Pyrethrin* |
Spinosad |
Malathion |
Bifenthrin |
Permethrin |
Zeta-cypermethrin | |
| Tomatoes | 0 | 1 | 1 | 1 | 0 ** | 1 |
| Peppers | 0 | 1 | 3 | 7 | 3 | 1 |
| Squash | 0 | 3 | 1 | 3 | 1 | 1 |
| Okra | 0 | 1 | 1 | 7 | (not labeled) | 1 |
| Turnips | 0 | 3 | 7 | 21 | 1 | 1 |
considerably lower than other products in table.
** “up to day of harvest”
Based on information in this table, zeta-cypermethrin is a good choice for a home garden insecticide because it controls most major garden insects, and it has a 1-day PHI on most garden vegetables. The photo shows a portion of the label for a product that contains zeta-cypermethrin, 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 be able to pick all three crops at the same time a day or two later. However, there are some pests, such as aphids, spider mites and whiteflies, that zeta-cypermethrin will not control. Also, there are some crops, such as onions and sweet corn, for which the PHI for zeta-cypermethrin is longer than 1 day. Check that label before you spray!
Note that if the label does not list the crop you plan to spray and give a PHI for that crop, then the product is not labeled for application on that crop. Check 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 recommendations tables. The labels for each of these products indicate the crops on which they can be used and the PHIs for those crops. Check that label before you spray!
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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