Ag Answers:Check Crops for Flood Damage, Disease

Corn and soybean growers in Ohio and Indiana should check for plant damage if heavy rains saturated their fields earlier this month, says Ohio State plant pathologist Pat Lipps.

Flooding in both states has killed some corn or caused yield- reducing damage, Lipps says. Surplus soil moisture in soybean fields has promoted Phytophthora damping off and Rhizoctonia stem rot, which could lead to serious development problems, he says.

Corn damage depends on how long plants were under water, Lipps says. Plants under water for less than two days are generally in good shape, while fields flooded for two to four days have varying injury. Plants definitely died if flooding lasted more than four days.

Lipps recommends that farmers check corn by cutting open plants to look at the growing point. The plant will survive if the growing point is firm and cream-colored, even if the upper leaves show some soft rot, he says.

Soft, brown growing points indicate plants will die soon. Stunting and delayed development will occur in plants with soft rot in the top leaves that prevents new leaves from emerging in the whorl.

"It's hard to say what effect this will have on yield, but damaged plants will not yield as well as those that were not flooded," Lipps says.

As for soybeans, damping off and stem rots have not generally required replanting, except in fields with extensive damage, Lipps says. However, further damage still can occur if heavy rains lie ahead.

"Damage to roots and stems now may show up as more problems later if drier weather causes drought stress and plant wilting," Lipps says.

Plants damaged by Phytophthora damping off will have shriveled-up seedling roots. The most seriously-damaged roots will turn brown and die.

Rhizoctonia rarely attacks the developing root, but it does cause the stem to rot at the soil line. Symptoms are reddish-brown cankers near the soil line.

"This is a year when the use of seed treatments has really paid off," Lipps says.