Our Garden Manager, Steven Schwager, has been getting a lot of questions about certain red-colored potential pests. The weather conditions this spring have indeed been ideal for many insects.
Among the insect pests that seem especially abundant this year are the aphids. Although an individual aphid is very small, collectively, aphids can cause considerable damage. They are parasites that suck the sap from plants, causing wilt and weakening the plant so it becomes less resistant to other pests that can kill it.
You may see the tiny aphids, which can be green, white and of course, red, clustering on your plants. Another symptom of aphid infestation is a shiny coating on the leaves, caused by the sugary “honeydew” aphids excrete. Mold can grow on this layer of honeydew, blocking the light from the leaves and causing further damage to your plant.
Some aphid species will only attack certain types of plants. If you see red insects on your roses, chances are that you’ve got red aphids. Mix a couple of tablespoons of dish soap in a spray bottle filled with water and liberally spritz the affected plants. It’s best to do this in the cooler mornings so the plants don’t absorb the soap before it evaporates.
If you see a dusty coating on the underside of the leaves of an ailing plant, check closely. You may see webbing, or even the pests themselves moving around. These are likely red spider mites. They prefer warm and dry conditions, so it’s common to find these on houseplants in our climate. Your best approach to mites is simply to wash them off: use a strong jet of water to dislodge them, and add a little isopropyl alcohol (1 part to 1.5 parts water) if you get repeat infestations.
You could be forgiven for mistaking clover mites for spider mites: clover mites do look like tiny red spiders. They live in grass and aren’t harmful, although when the population gets so large that the mites start to migrate from the grass, it can be a nuisance.
Boxelder beetles are flourishing this year at MAGC and elsewhere in Marin. The juveniles are bright red and like to congregate on warm sunny surfaces. They mature into back and red beetles that aren’t known to cause damage to plants, but are known as “stink bugs” to many because they can release a bad odor if smashed. They may feed on apples or plums and cause fruit deformities; you can treat an infestation with a spray of equal parts water and vinegar.
If you have a maple tree, you may have noticed weird growths on the leaves. These are galls, also caused by mites, although these eriophyid mites are too small to see, but feed on developing leaves. Galls form when the plant’s own growth regulating hormones are affected by chemical produced by the mites, stimulating them to produce abnormal growths that enclose the mite and protect it from both predators and pesticides. You can read more about galls here.
Galls generally aren’t harmful, although they can mar your maple’s appearance. You can pick off any leaves that are especially affected.