Northern Plains Integrated Pest Management GuideIPM

Authors: Buyung Hadi, Robert Wright, Loren Giesler, Jim Stack, Jennifer Chaky, Jeff Whitworth, Holly Davis, and J.P. Michaud.

Identification

The adults of corn flea beetle (Chaetocnema pulicaria Melsheimer) are small (0.05- 0.1 inch or 1.3-2.5 mm long) oval-shaped, metallic black-blue in color. The beetle has enlarged hind legs that are adapted for jumping. When disturbed, the beetle jumps vigorously like a flea, hence the common name corn 'flea' beetle.

The eggs of corn flea beetle are white and pointed at one end. The larvae are white and slender grubs, between 0.12 and 0.33 inch (3.2 - 8.5 mm) long when fully grown. Both the eggs and the larvae are found under the soil surface. The eggs are typically scattered in the soil on the base of the host plant while the larvae can be found feeding on underground plant parts.

An adult corn flea beetle on corn leaf

Life Cycle and Seasonal History

Feeding injuries of corn flea beetle typically results in scraped leaf surfaces; economic damage due direct feeding is scarce. Higher levels of injury are expected in seasons with cool springs and preceded by mild winters. In this scenario, high populations of overwintering beetles survive and injury is favored by the cool spring which increases the length of time beetles have to feed on corn in susceptible growth stages.

Higher economic damage is caused by the spread of bacterial disease (Stewart's wilt) transmitted by corn flea beetle. While certain susceptible inbreds of field corn are susceptible to Stewart's wilt, this disease is more common on sweet corn. Although direct loss of Stewart's wilt on hybrid field corn is relatively low, plants with Stewart's wilt are predisposed to stalk rot. Stewart's wilt disease is caused by the bacterium Pantoea stewartii, formerly known as Erwinia stewartii. The pathogen survives the winter in the gut of overwintering corn flea beetles. Thus the amount of inoculum introduced to the field in a given year is dependent on beetle survival . The bacterium enters host plants through feeding wounds caused by corn flea beetles. If susceptible seedlings are infected, long water-soaked chlorotic streaks appear on the seedlings; which may later wilt and die. If infection occurs after tasseling, long water-soaked chlorotic streaks appear on the leaves and the leaves may later turn necrotic. Wilting and death of plants infected after tasseling is not common.

Scraped leaf surface, a symptom of corn flea beetle feeding injury

Long chlorotic streak symptomatic of Stewart's wilt disease

Management Approaches

Scouting and Threshold

Scouting for corn flea beetle should be conducted early in the season. Treatment is warranted if 50% of the corn plants are infested with five or more corn flea beetles. Sometimes satisfactory results can be obtained by spot or border treatment.

Cultural Methods

Excessive nitrogen and phosphorus in corn increases the severity of Stewart's wilt. Balanced fertility management can help mitigate disease severity.

Host Plant Resistance

Many field corn hybrids contain resistance toward Stewart's Wilt and should be used as the primary management tool against this disease.

Chemical Control

Seed treatment using imidacloprid has been shown to decrease Stewart's wilt incidence in susceptible varieties of sweet corn. If resistant varieties are used, seed treatment does have an effect on disease severity.