ANR-984, Revised March 2001. Kathy Flanders, Extension Entomologist, Associate Professor, Entomology and Plant Pathology, and Paul Mask, Extension Agronomist, Professor, Agronomy and Soils, both at Auburn University; and G. David Buntin, Research Entomologist, Professor, Entomology, University of Georgia at Griffin

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Management of Cereal Leaf Beetles: Pests of Small Grains

The cereal leaf beetle, Oulema melanopus, was introduced from Europe into Michigan in the 1950s and is slowly spreading southward. It is now well distributed throughout the northern half of Alabama and Georgia and is partially established in the southern half of both states. In some years, as much as 50 percent of the winter wheat crop in northern Alabama and northwest Georgia has been sprayed with an insecticide to control cereal leaf beetle. The immature stage of cereal leaf beetle feeds on the leaves of wheat, oats, and certain other grasses.

Life Cycle

The cereal leaf beetle has one generation per year. Adult beetles spend the winter in the woods and field borders. During the first warm days of spring, the beetles disperse into small grain fields, mate, and begin to lay eggs. Eggs hatch in about 7 days, and larvae (immatures) begin to feed on the cereal leaves. Larvae are usually first found after flag leaf emergence but before the heads have emerged. The larvae feed for about 3 to 4 weeks, then leave the plant, and move down into the soil.

Cereal leaf beetles transform from the larval to the adult stage in earthen cells in the upper 2 inches of soil. This transformation (pupal) stage lasts about 10 days. The adults of the new generation come out in late May and early June, feed briefly, then move out of the fields, and remain inactive until the following spring. New generation adults may feed on corn leaves but seldom cause serious damage.

Description

Cereal leaf beetle adults are about 3/16 inch long and 1/16 inch wide (Figure 1). The adults have dark, metallic blue wing covers, orange legs, and an orange collar. The head and the rest of the body are black. Eggs are cylindrical with rounded edges (Figure 2). They are light orange when laid and darken gradually over time to almost black. Eggs are deposited singly or in rows of two to four on the topside of the leaves. Each female lays from 12 to 50 eggs.

Figure 1. Cereal leaf beetle adult		Figure 2. Cereal leaf beetle egg

Cereal leaf beetle larvae are pale yellow with a brown head and legs (Figure 3). In the field, they look mostly black because they smear excrement over their bodies. People walking through a field infested with cereal leaf beetle larvae may emerge with black stained pants legs because this black coating easily rubs off the larvae. The larvae are about 1/16 inch long just after hatching and 1/4 inch long when fully grown.

Figure 3. Cereal leaf beetle larvae

Damage

Cereal leaf beetle larvae feed on the leaves. Feeding activity results in long, windowlike slits in the leaf blade (Figure 4). When feeding is severe, the entire leaf becomes brown and ragged. Cereal leaf beetle larvae are especially damaging when they feed on the flag leaf and when large numbers of larvae are found before head emergence.

Figure 4. Damage to wheat leaf caused by cereal leaf beetle larvae

Scouting and Insecticide Recommendations

Begin checking for cereal leaf beetle adults, eggs, and larvae in early March in the vicinity of Talladega County, AL, mid-March in the Tennessee Valley region, and late March or early April in northern Georgia. Check fields weekly for about a month. Check the middle of the field as well as the edges. One way to check fields is to walk back and forth in the field in a zigzag pattern. Look for feeding damage, adult beetles, eggs, and larvae. Stop in five to ten areas in each field, and count eggs and larvae on the top two leaves of five stems.

If cereal leaf beetle larvae have begun to hatch and there is more than one cereal leaf beetle egg or larva per two stems, treat with one of the suggested insecticides. All suggested insecticides provide good control of cereal leaf beetle larvae. Because dying larvae are hard to distinguish from living ones, wait 2 to 3 days after treatment before checking to make sure the treatment was successful. Warrior T can be applied before any cereal leaf beetle eggs have hatched. In this case, treat using Warrior T if there is more than one cereal leaf beetle egg for every four stems.

Other Management Strategies

Beetles prefer thin stands so follow good agronomic practices that promote full stands and high-yielding wheat. Also avoid late planting because adult beetles typically prefer less mature plants to more mature plants.

Heavy rains can kill immature cereal leaf beetles. If heavy rains occur between the time a field is checked and insecticides are to be applied, wait for the foliage to dry and check the fields again.

Cereal leaf beetles are controlled by natural enemies in the northern United States. Since 1995, the USDA Animal Plant Health Inspection Service, the Alabama Cooperative Extension System, and the University of Georgia have been releasing stingless wasps that attack cereal leaf beetle eggs and larvae. In 1999, Tetrastichus julis, which attacks cereal leaf beetle larvae, was established in Crossville, AL (Figure 5). Eventually, this and other natural enemies will help keep cereal leaf beetle populations below economically damaging levels. Ladybird beetles are also important predators and can destroy many eggs and larvae.

Figure 5. Biological control agent attacking a cereal leaf beetle egg

Suggested Insecticides for Control of Cereal Leaf Beetle on Wheat

Insecticide	Rate	Comments
lambda cyhalothrin 0.02 to 0.025 lb. ai./A. WARRIOR T 1CS	2.6 to 3.2 fl. oz./A.	This is a restricted use pesticide. A 30-day interval is required before harvest for grain or grazing, and a 24-hour re-entry period is required for workers.
spinosad 0.03 to 0.09 lb. ai./A. TRACER	1 to 3 fl. oz./A.	The worker re-entry period is 4 hours. Do not apply within 21 days of grain harvest. There is no waiting interval for grazing.
carbaryl 1 lb. ai./A. SEVIN XLR SEVIN 50W SEVIN 80S	1 qt./A. 2 lb./A. 1.25 lb./A.	A 21-day interval is required before harvest for grain or grazing. The worker re-entry period is 12 hours.
methomyl 0.225 to 0.45 lb. ai./A. LANNATE 90 SP LANNATE 2.4 LV	1/4 to 1/2 lb./A. 3/4 to 1.5 pt./A.	This is a restricted use pesticide. A 10-day interval is required before grazing, a 7-day interval before harvest for grain, and a 48-hour re-entry period for workers.

Use pesticides only according to the directions on the label. Follow all directions, precautions, and restrictions that are listed. Do not use pesticides on plants that are not listed on the label.

The pesticide rates in this publication are recommended only if they are registered with the Environmental Protection Agency and the Alabama Department of Agriculture and Industries. If a registration is changed or canceled, the rate listed here is no longer recommended. Before you apply any pesticide, check with your county Extension agent for the latest information.

Trade names are used only to give specific information. The Alabama Cooperative Extension System does not endorse or guarantee any product and does not recommend one product instead of another that might be similar.