Mild winter may mean bigger sweet corn threat from Stewart's wilt

04/04/2012 03:50:00 PM
Vicky Boyd

corn flea beetleCourtesy University of Illinois at Urbana-Champaign; bugwood.orgThe corn flea beetle harbors the Stewart's wilt bacterium in its gut and transmits it to sweet corn plants during feeding.Mild winter temperatures in many northern sweet corn production areas may equate to a greater threat from Stewart's wilt this season, Extension specialists warn.

Bob Mulrooney, University of Delaware Extension plant pathologist, predicts a severe threat from Stewart's wilt.

Based on average monthly temperatures, he says the state's three counties haven't had such a mild December, January and February since the winter of 2001-02.

A similar warning was made by Ron Goldy, Michigan State University Extension vegetable educator, in a recent e-newsletter to growers.

Stewart's wilt is caused by a bacterium that overwinters in the gut of corn flea beetles, and the beetle transmits it during feeding.

In severe cases, the bacteria can kill the corn plant.

The threat from the disease is directly related to beetle survival.

Beetle survival is calculated based on average December, January and February temperatures.

In years when the temperatures average less than 27 degrees Fahrenheit, Stewart's wilt is typically not a problem.

When winter temperatures average more than 33 degrees, Stewart's wilt can be severe.

In Michigan's lower peninsula, temperatures point to slight to possibly severe Stewart's wilt symptoms this year.

Several sweet corn cultivars are available with genetic tolerance to the bacterium.

In addition, consider having seed treated with the proper insecticide, Goldy says.

This will protect the early, most susceptible growth stages.

The alternative is to use untreated seed and wait to see how beetle populations develop.

Treat when beetle numbers reach five per 20 plants from five locations in the field.

Because this option requires scouting fields several times per week, many growers opt for treated seed.

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