Iowa corn plants infected with Stewart’s Wilt

Connie Pettinger

Early predictions from ISU agricultural experts, who said this year’s corn growers would experience the worst outbreak of Stewart’s Wilt in history, appear to be accurate.

Paula Flynn, extension program specialist in the plant pathology department, said corn plants were infected earlier than normal this year by Stewart’s Wilt, and as a result, many young corn plants will die.

“Once a plant has been infected, there are no curative measures,” Flynn said.

“Because the infestation is affecting very young plants, it is likely to cause many of the plants to die.”

Stewart’s Wilt is caused by the Erwinia stewartti bacteria, which is transmitted to corn plants by the corn flea beetle, Flynn said.

The beetle chews on the plant, causing lesions in the leaves that ultimately dry the leaves, and the plant dies prematurely.

Flynn said the damage will be more severe this year than in the past because of the large population of corn flea beetles, the primary carriers of the disease.

Last year, there was also a larger-than-normal number of the beetles and because of the mild winter many of them survived, leading to enormous populations.

The early planting season will also affect the damage done by the corn flea beetle, Flynn said.

“Because of the early growing season, the beetles are attacking corn plants much earlier than normal,” she said.

Boyd Brodie, agronomy manager at the Heart of Iowa Cooperative in Roland, said this year’s dry conditions will compound the beetles’ effect.

“The beetles first feeding ended about two weeks ago,” Brodie said. “They laid their eggs, and the second generation will start feeding in early June.”

Brodie said he is unsure at this time how serious the situation will be for his customers but said it will affect the entire state.

“The wild card in all this is that they [flea beetles] carry the Stewart’s Wilt bacteria, and we just aren’t sure how hard it will affect the seed,” Brodie said.

Brodie said Heart of Iowa sprayed corn crops for the beetles early.

“We lowered the spraying thresholds due to the corn being stressed from dry conditions,” he said.

He said he expects seed corn to be affected more than commercial corn because some of the hybrid numbers have some resistance to Stewart’s Wilt.