Corn Flea Beetle

A. Genetzky, E. C. Burkness and W. D. Hutchison
Department of Entomology, University of Minnesota

Introduction

Biology and Life Cycle

Damage

Management Options

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Photo Courtesty of Marlin Rice, Iowa State University

Introduction

The corn flea beetle, Chaetochema pulicaria, is a small, black beetle that is a frequent pest of corn. As the adult corn flea beetle feeds upon the corn plants, it is capable of spreading a bacterial wilt called Stewart's wilt, which can cause serious damage. In addition to the damage caused by the wilt, heavy infestations can cause detrimental amounts of feeding damage on plant foliage.

Identification

The adult corn flea beetle is a small, round beetle measuring 1.6 mm in size. It is usually a shinny black, grayish black, or brown color. A distinguishing feature of this beetle is its enlarged hind legs that are used to produce powerful jumps if disturbed. The larva of the corn flea beetle has a white body with a brown head and is about 4.5 mm in length.

Biology and Life cycle

Only the adults will over winter in soil or bushes near fields, fencerows, roadsides, or wooded areas. The digestive track of these adults harbors Stewart's wilt throughout the winter as well. When the spring temperatures reach around 65°F and the vegetation begins to emerge, the corn flea beetle will start to emerge from its winter shelter. The beetles tend to be more active on warm, windless days and will hide in the soil cracks during bad weather.

After mating, the corn flea beetle adults will lay their eggs on leaves or next to the roots of the plant. Once the larvae hatch from their eggs, they will feed on the plant's roots for a period of two weeks. After two weeks the larvae pupate and emerge as adults.

Damage

Most of the damage by the corn flea beetle is caused during the adult stage and can reduce yields by causing the plant to wilt, to become stunted, or to die. Damage is more severe after mild winters because of the increased survival of the beetle over the winter months. An easy way to monitor the possible level of infestation is presented in the table below.

An infestation during the previous year increases the possibility of infestations the following year.

Usually, most of the damage is done during the first two or three weeks after the corn begins to emerge; therefore, plants are more affected by feeding damage if they are planted early in cooler weather. This is due to the fact that lower temperatures will slow the plant's growth allowing for prolonged feeding by the beetle. A high flea beetle population can cause serious damage alone without the presence of the bacterial wilt associated with them. The wilt spread by the corn flea beetle is most often what calls for serious concern.

The wilt is called Stewart's bacterial wilt and is caused by the bacterium Pantoea Stewartii. An indicator for the disease is dark feeding scars that eventually turn to a straw-like color when bacteria begin to grow. This damage can be misidentified and attributed to drought, nutritional problems, or insect injury. The symptoms include long, wavy streaks that are green or yellowish along the plant's veins, and it is possible for the whole plant to appear scorched.

Thresholds

The corn flea beetle is usually seen in the months of April and May. It is important (if there is a risk for an infestation; use table to determine risk) to check young plants several times a week for the presence of corn flea beetles. To monitor, check 20 plants in five different locations around the field. Count the number of beetles and find the average number per plant. Generally, if there are more than five beetles per plant before the V4 growth stage, then treatment is recommended, especially if the plants are experiencing environmental stress. For seed production crops, it may be beneficial to apply treatment at first detection of beetles.

An alternative way to monitor the presence of the corn flea beetle is to use yellow sticky cards. Use 6 in. by 8 in. cards placed two feet above the ground on posts. Threshold is reached if there is an average of 8.5 beetles per card per week.

Management

The most effective prevention is to keep fields and surrounding areas weed free. This is important because both larvae and adults can feed on weeds. Also, it is helpful to have a late planting date so plants can grow quickly-shortening the time they are susceptible to heavy feeding damage. If an infestation is apparent, frequent cultivation will help by driving the beetles away. Finally, effective prevention is also accomplished by choosing varieties of corn that are resistant to Stewart's wilt disease such as: 'Apache', 'Comet', 'Comanche', 'Gold Cup', 'Incredible', 'Sweet Sue', 'Seneca', 'Sentry', 'Miracle', and 'How Sweet It Is'.

If a heavy infestation is evident, a vertical sheet covered with tangle foot can be hung between the rows just above ground level. The sheet is capable of trapping large quantities of the pest.

Insecticides may also be needed. To ensure proper use of insecticides, refer to the most recent edition of the Midwest Vegetable Production Guide (BU-7094-S). It may be necessary to spray more than once since new infestations may occur in a field throughout the growing season.

Selected References

Cornell University. 2003. Vegetable Disease ID and Management http://vegetablemdonline.ppath.cornell.edu/

Esker, P. & F.W Nutter Jr. 2000. Severe risk for stewart's disease. http://www.ipm.iastate.edu/ipm/icm/2000/5-1-2000/sevstew.html

Illinois fruit and vegetable news vol. 6 #3. 2000. Flea beetles and stewart's wilt in sweet corn. http://www.aces.uiuc.edu/~ipm/news/frveg0003.html

Metcalf, R.L. & R.A. Metcalf. 1993. Destructive and Useful Insects; Their Habits and Control. 5th Edition. Insects Injurious to Vegetables Gardens and Truck Crops. McGraw-Hill, Inc. New York.

Midwest Vegetable Production Guide for Commercial Growers. University of Minnesota Extension Service BU-7094-S; http://www.entm.purdue.edu/entomology/ext/targets/ID/index2001.htm
To order: http://www.extension.umn.edu/abstracts/nonweb/abstract.html?item=07094

Munkvold, G. & M. Rice. 1999. Stewart's disease in 1999. http://www.ipm.iastate.edu/ipm/icm/1999/4-5-1999/stewart1999.html

O'Day, M., A. Becker, A. Keaster, L. Kabrick, and K. Steffey. 1998. Corn insect pests. MU Extension, University of Missouri-Columbia. Updated versions posted at: http://muextension.Missouri.edu/xplor/manuals/m00166.htm

Rice, M. 2000. Flea beetles in field corn. http://www.ipm.iastate.edu/ipm/icm/2000/5-1-2000/Fleabeetle2000.html

Welty, C. Corn flea beetle on sweet corn. http://www.ag.ohio-state.edu/%7Eohioline/cv-fact/1000.html

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