Fungus on Underside of Basil
Purchased 5 Basil plants from a gardening spot. Almost immediately began getting yellow leaves at the bottom. (The spot is perfect - Have been using it for years.) When I harvested some today, noticed the underside of the yellowish/green leaves have a sandy, dark collection on them. It can't completely be washed away. Not sure what it is but will not eat it. Do you have any idea what to spray it with or how to treat it?
Certified GKH Gardening Expert
It may be aphids or a similar pest. You can treat the plants with a pesticide. As they are food plants, I like neem oil as it is organic, safe for people and beneficial bugs and effective on pests. This article may also be helpful: https://www.gardeningknowhow.com/plant-problems/pests/homemade-aphid-control-a-natural-way-to-kill-aphids.htm