Horticulture oil for hemlocks harmful

Asked June 4, 2020, 11:54 AM EDT

My neighbor sprayed the hemlock between our properties, on my side as well, and I have a vegetable garden a few feet back from the spray area. The worker attempted to spray only on either side of the garden. As the trees sit back, but you could see some drift. Would this be harmful to a vegetable garden if some drifted onto it near it? Cheryl K.


1 Response

Hello Cheryl,

Horticultural oil is commonly used as a low-impact pesticide for many garden plants, including vegetables. If properly diluted (if needed, as some formulations are ready-top-spray) and not sprayed during temperatures above 85 degrees F, it should not harm any plants the spray drifted on to. There are a few decorative plants known to have chemical sensitivities (some ferns and begonias, for instance), but we are not aware of such problems with common vegetable crops. You can look for signs of phytotoxicity (chemical burn, in essence), though the leaf spots and discoloration this causes can be very similar to pest or disease symptoms and difficult to differentiate. https://extension.umd.edu/hgic/topics/phytotoxicity Phytotoxicity can appear fairly soon after exposure, so if no worrisome symptoms appear in a few days, there was likely no harm done. If there is, the plants should outgrow the exposure and heavily damaged leaves can be individually clipped off. As with any pesticide use, produce should be washed before consuming.