Under hot conditions the metabolism of (some) target insects is significantly faster. Control of the pest is more complete when the metabolism of the pest is slower which is generally associated with cooler or moderate temperatures. It is also known that control of some insect species with pyrethroid insecticides decreases as temperature rises. Some pests are also more available in cooler or moderate temperatures.
Flea beetles. Flea beetle insecticides are not recommended for use on hot days. Decis and RipCord specify that they should not be applied when temperatures are above 25°C. For Matador/Silencer, the recommendation is to apply early morning or in the evening, past the heat of the day.
Cutworms. When using chlorpyrifos for cutworms, avoid application under hot temperatures. The crop protection guides, which are based on label information, say best results will be obtained for cutworms when application is made in evening (after 7 p.m.) or morning (before 8 a.m.). DO NOT apply to plants under extreme drought stress or crop injury may occur.
When using permethrin for cutworms, the guides say: For cutworm control, application should be made under warm, moist conditions in the evening or at night.