By Darrell Blackwelder
For the Salisbury Post
August is here and it has brought what we’ve all come to expect with heat and humidity.
It’s the month when insects and diseases are starting to become a serious problem in both vegetable gardens and landscapes. Below are a few inquiries I received over the past few days that you may also be pondering.
Q: I have used Malathion on the bagworms in my Leyland cypress and they don’t seem to be dying. What can I use to control them?
A: Bagworms are more difficult to control as they mature, especially in late summer. Talstar or Mavrik are recommended insecticides; however, these insects are impossible to kill once the larva pupates in the cocoon. Read and follow the label carefully before application.
Q: I have swarms of whiteflies on my tomato plants. They seem impossible to control. What is the best solution for these insects?
A: Whiteflies are a serious problem this summer in both vegetable gardens and landscapes. They reproduce so quickly, it’s almost impossible to get a complete kill. Insecticidal soaps available at local garden centers will knock them back, but will not completely control them. If you’re at the end of production season, its best to live with them. Make sure you remove all debris so they will not overwinter.
Q: My squash and dogwoods have what looks like a white powdery dust on the leaves. Anything I can do to control this?
A: Powdery mildew is the culprit. It is a fungal disease that can be a real problem on cucurbit vegetables and ornamentals such as dogwood, crape myrtle and roses. Fungicidal sprays for ornamentals at this stage of growth may not be of benefit or practical, especially in larger trees. However, fungicides are available to control the pest. Be sure to read the label. Most fungicides for ornamentals are not registered for use on vegetables.
Q: My tomatoes are turning pale yellow and the leaves are dropping off (sample brought to the office). What seems to be the problem?
A: Close inspection of the leaves reveals you have spider mites. Spider mites are very small arachnids, not insects that emerge in hot weather we’ve experienced. Rinsing the underneath with a hard spray of water will actually wash many of them off. Summer oils will also kill them, but they cannot be applied in hot weather. Again, if you’re at the end of the season, it may be best to live with what you have.
Darrell Blackwelder is an agricultural agent in charge of horticulture with the North Carolina Cooperative Extension Service in Rowan County.