Root rot killing corn

Fields in southeast Iowa have been hit hard by root rot in the past month, which will force some farmers to replant their corn. Iowa State University Crop Specialist Jim Fawcett said the problem stems from the hard rain that fell on the area in early May.

Fawcett said that farmers who planted corn between April 23 and April 27 are taking the brunt of the root rot. He said a disease known as Pythium is killing the newly emerged seedlings. The plants are not able to grow properly and are easily pulled from the ground because the disease attacks their roots. Pythium took advantage of the cool and wet conditions following the hard rain in early May to devastate farm fields in the state.

The extent of the damage is not yet known because some corn plants are still dying, Fawcett said. He has heard that about one-eighth of the corn in Henry County and as much as one-quarter of the corn in Lee County will have to be replanted. He did not have an estimate of the scale of replanting in Washington County but said that the root rot seemed more dispersed in Washington County.

Another problem, with similar symptoms, is floppy corn syndrome. Floppy corn syndrome causes the plant to fall over when it is about a foot tall because its roots have not developed. Fawcett said this is often the result of erosion, which causes the roots to grow into the air and thus dry out easily. This is especially problematic when cracks form along the corn rows, exposing all the roots in the row to the air.

The rain in early May also eroded the soil, which left the roots more vulnerable because they were closer to the surface. Fawcett recommends planting corn seeds 2 inches deep to lessen the effects of erosion should it occur.

?Farmers do no-till to prevent erosion, but we?ve seen erosion even in fields that were no-tilled,? Fawcett said.

The only good news about the root rot coming this time of year is that there is enough time for farmers to replant and get good yields. Fawcett said seeds vary in their maturation lengths, typically between 95 and 110 days. He said farmers who replant will probably want seeds that mature in 95 days or fewer at this point in the year.

Fawcett said that farmers might have already prepped their fields to grow only corn.

?If herbicides are already down, you?re basically stuck planting corn,? he said. ?If you haven?t put herbicides down, you have the option of planting soybeans, too. You might think about that if you have to replant in June.?

Fawcett said farmers who replant will probably have to till their current crop under. He said it was commonplace in the past to simply spray the field with chemicals to kill the original crop, but he said that wouldn?t work now because the corn is resistant to Round-up.

Some agronomists are worried that the Pythium killing corn plans may be a new race of the disease.

?It?s showing up in ways that were not expected,? Fawcett said. ?We normally find it on cool, wet soils, but now we have found it on upland soils that are not as wet.?