SPOKANE, Wash. – Eastern Washington grain growers should be on the lookout for cereal leaf beetles, which have caused significant damage at a number of locations in the region the past few years.
Both the adult and the larval stages of the beetle feed on most cereal and grass, according to Diana Roberts, WSU Spokane County Extension educator.
“The adult cereal leaf beetle is about a quarter of inch long with a blue-black, shiny, rectangular abdomen,” Roberts said. “The legs and the region above the abdomen must be red-orange; if not, it is a different, beneficial species.”
She said that adult beetles are now laying eggs in many areas, while in warmer regions the eggs are hatching into larvae that will begin chewing on leaves of oats, wheat and barley crops. “The uppermost leaves of heavily infested cereal crops, where larvae have eaten away the upper chlorophyll layer will have white tips, giving them a frosted appearance.”
While this sight may alarm growers, Roberts does not recommend applying insecticide as a first option. “Unless there are no spring cereals in the area, most winter wheat crops should not need spraying because the beetle tends to move on to younger, lusher grains once winter wheat leaves become a little tough. At this point in the season, the spring crops are more vulnerable, and you should monitor them carefully.”
WSU Extension is coordinating a biological control project intended to keep cereal leaf beetle populations below the economic threshold. “We are using two species of wasps, which are tiny and harmless to people, pets, livestock or other plants and animals,” Roberts said. “They lay their eggs in the larvae or eggs of cereal leaf beetle and prevent further development of the pest.”
She said that larval parasitoids are becoming increasingly effective and have spread 50 miles or more beyond where they were released. “In 2006, cereal leaf beetle larvae in many fields showed a 50 percent parasitism rate and there was a sub-economic infestation of the beetle,” she said. “In these situations I am optimistic that farmers should never need to spray to control the pest. In fact, using insecticides is often detrimental in the long term as the chemicals destroy the biocontrols and other predators, such as ladybird beetles, which may cause a worse infestation in subsequent years.”
Farmers can determine if the cereal leaf beetles in their fields are parasitized before they spray by contacting Roberts at WSU Spokane County Extension (509) 477-2167 or robertsd@wsu.edu. “We will arrange for someone to come and collect a sample,” she said “or farmers can collect a sample of 30 to 40 larvae by clipping off the leaves they are on. Bigger is better because bigger larvae are easier to dissect.
“Put the larvae and leaves in a 2 pound yogurt or margarine container; poke some small holes in the lid and keep them in the refrigerator until we can arrange collection. We are eager to learn how well the wasps are dispersing, so we want to receive beetle samples from across eastern Washington, and we want to work with farmers to help them make spray decisions.
Roberts cautions against spraying at the first sight of cereal leaf beetle because unhatched eggs may be left in the field and necessitate another application. “The eggs are individual, tiny (1 mm) orange-brown specks on the upper surface of the leaf at the midrib about 1 inch from the plant stem,” Roberts said. “Insecticides are more effective when larvae are about one-eighth inch long. The larvae are dark, slimy, stubby caterpillars.”
Before spraying, she recommends that farmers scout across their entire field to make certain that spraying is warranted. “Eradicating the insect is unlikely because the adult is very mobile,” she said. “There are plenty more where the first ones originated. The cereal leaf beetle has an extremely wide host range and can survive on most species in the grass family, including corn, CRP , timothy hay, wild oats and cheat grass.
Farmers can determine when it makes sense to spray by counting eggs and larvae. “Prior to the boot stage, the economic threshold requires three eggs or larvae per plant,” Roberts said. “Past the boot stage one larva per flag leaf can cause a yield loss of five- to six bushels per acre. Use this figure with your estimated crop income and the cost of applying insecticides to pencil out the economics for your fields.”
“In areas where biocontrols are multiplying, we recommend that farmers leave buffer strips in their fields so that the beneficial insects can survive and multiply.”
For pictures, information on labeled insecticides, and reports on biocontrol of cereal leaf beetle, visit www.spokane-county.wsu.edu.
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