Monday, September 19, 2011

Chinese Rose Beetle

It is common to find leaves riddled with holes in an appearance of lace. In addition to feeding by slugs, snail and caterpillars, the Chinese rose beetle (Adoretus sinicus) is the likely culprit.

These beetles especially like beans, cabbage, roses, as well as over 250 commonly grown plants.  The immature stage, called grubs, looks like white worms and lives in loose soil and leaf litter.  The grubs do not feed on leaves but may feed on the roots of some plants.  The adult is nocturnal in habit, remaining under leaf litter during the day and emerging to feed at dusk.  If you are in the garden at this time, and a few hours later, you will be able to see the beetles feeding on the leaves. 

Controlling the beetles is difficult. Sevin is one insecticide that will control Chinese rose beetle but frequent rains lessen its effectiveness.  Neem products can also be used to deter feeding.  A systemic insecticide, with the active ingredient  imidacloprid, works well.  Check labels for registration on food crops.

Beetles are attracted to weak light. Some gardeners have constructed traps utilizing solar powered patio lighting to attract the beetle.  The light is placed over a container of soapy water into which the beetles will fall.  On the other hand, beetles are deterred by bright light. Placing a flood light over the plant will keep beetles away. Lights only need to be on for about 3-4 hours after sunset.

Placing a shade cloth barrier around newly planted trees or areas of the vegetable garden will exclude the beetles from those plants. Newly transplanted trees are more susceptible than older established trees.

Perhaps the surest way of controlling this pest is to go out into the garden after sunset, when the beetles are feeding, and collect them by hand and dispose of them.

Ask the Garden Guy, Science Based Answers to Garden Questions, is an excellent resource book for gardeners. Some popular topics include Slugs and Snails, Organic Pesticides, Reasons, Why Vegetable Seeds Do Not Germinate, What’s So Hot about Manure? Mushrooms in the Lawn.  Purchase by clicking on the image of the book above.