The Q&A Archives: Pesticides In Hot Weather

Question: I would like to spray either Sevin or BT or other insecticides on my plants but the labels say not to spray if the temperature is over 85 degrees within 24 hours of spraying. It has been over 100 for days now and has not gone much below 80 degrees at night. The Japanese beetles are eating my roses. Can I spray or will the spray burn the plants because of the heat?

Answer: Your concerns about using insecticides in ways not listed on the labels should be commended! Applying sprays when weather is hot can definitely lead to leaf burn, especially on tender-leaved plants such as roses. Bt is an excellent treatment for caterpillars and worms (it's a stomach poison), but it's not effective against adult beetles. Japanese beetle populations can be very destructive. Try applying milky spore disease to the soil to eliminate the grubs. You can also cultivate the soil frequently to expose the grubs to natural predators. The adults can be handpicked and destroyed, and you can purchase pheromone traps to trap the beetles.

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