“My plants are covered with black bugs.” “My tree’s leaves are all curled up.” “There’s sticky goo under my trees.” These are a few of the comments I’m receiving. A reader named Patricia wrote “Is there a reason this year has been particularly bad regarding aphid infestations? We’ve often had trouble with them infesting our two small nectarine trees. We try to get to them early and stay on top of them, but this year those small green aphids just would not stop. I’ve resorted to just spraying the trees with water every other day to keep the aphids at bay. But, the odd thing is that just about the same time as I discovered them on the nectarine trees, I found tiny (almost microscopic) black aphids on some of our Rose of Sharon bushes. They’re smaller than the green ones I’m used to battling every year. They looked like black mold on the leaves, but under my magnifying glass, I could see that they were some sort of bug. And a few days later, I noticed some really big red aphids on the new growth of our rose bushes.”
Aphids, green or black, do seem bad this year. Patricia hadn’t seen black aphids before. I too hadn’t seen these quantities of small black aphids, yet this year almost all the plants at the community garden are covered with black aphids. Parks staff have brought in samples of tree leaves covered with black aphids.
Patricia has been diligently spraying them off, but daily spraying isn’t always possible and it doesn’t work when the aphids hide inside curled leaves. The good news is that on most of the samples I have seen, ladybird beetles (ladybugs), lacewing larvae, syrphid flies, wasps and other beneficial predators and parasites are also present feeding on the aphids. They are probably doing your control job for you, so you don’t want to spray chemicals that can kill them.
What are the alternative management strategies? If the population is localized in just a few curled leaves or shoots, prune these out and dispose of them. Control the ants that herd the aphids. Fertilize with slow release products since high nitrogen fertilizers encourage aphids. Insecticidal soap, neem oil or horticulture oils are additional alternatives when temperature are below 90 degrees. Dormant oil sprays in late winter to early spring can smother overwintering eggs.
For more information, see http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7404.html.