As the summer progresses insect pest damage often becomes more apparent. I was recently called out to a home in the Greenlake area of Seattle to look at a vine maple that was having a pest problem. The tree actually had two different pests feeding on it’s leaves. Leafhoppers and spider mites. Click on the images for a larger view.
Leafhoppers feed by sucking the plant juices from the top layer of leaves. This often shows up as a stippling or lighter areas on the upper leaf surface. A couple of low impact ways to control the population are:
-Encourage natural enemies such as parasitic wasps.
-Hosing the plant with water will work to some extent, but only on the wingless nymphs.
Some plants that will encourage parasitic wasps are members of the aster and mint families. One resource I found says that digger wasps, especially mud dauber wasp, feed their larvae leafhoppers as well as many other pest insects. Some of these beneficial wasp species prefer specific flowers, e.g., umbels (a flower shape), sumac, elderberry, milkweed, and Ceanothus species, as the adult wasp’s food is primarily nectar and pollen. In general a variety of wildflowers will help build a diverse population of predator species which can help control the leafhopper population.
There are many species of spider mites. Here are a few general control recommendations from WSU.
-High levels of nitrogen in the foliage encourage spider mite reproduction. Switch to a slow-release or low-nitrogen fertilizer when practical.
-Hose mites from plants with a strong stream of water.
-Predatory mites and insects such as ladybird beetles and green lacewings aid in control of mite populations. Avoid use of broad-spectrum insecticides which kill beneficial insects and bees.
-Provide proper culture. Healthy plants are more tolerant of damage, while drought-stressed plants are more susceptible.
An alternative food source for the predatory mites is grass pollen. So perhaps some ornamental grasses somewhere in your landscape would be a good edition.