Disease clinic update

Field crop samples have been common over the past two weeks, indicating a variety of problems but no major disease outbreaks.

Anthracnose infection of hail-damaged corn plants can lead to plant death.

Corn. Seedling samples have generally been diagnosed with seedling disease caused by Fusarium species. Seminal roots and mesocotyl tissue on these plants have brown to reddish-brown decay. In some cases, the infection was compounded by problems with planting depth or possible herbicide injury. So far, we have not seen samples with early-season anthracnose lesions, but it's likely this will show up in fields where there has been a lot of rain. Recent hail injury to corn in some parts of the state might lead to some disease problems. Hail-injured corn often is infected by Colletotrichum graminicola (anthracnose), Ustilago maydis (smut), or Sclerophthora macrospora (crazy top). Early-season infection by any of these three fungi can lead to plant death or failure to form an ear.

Soybeans. Seedling samples with damping-off symptoms have started to appear. It is a little too soon to say how widespread this disease will be in 1998, but some reports indicate that damping-off is a considerable problem in certain areas, especially in southern Iowa.

Alfalfa. Several samples from second- or third-year stands with areas of poor first growth and pale color have been received. Some of these are from poorly drained areas and Aphanomyces is a likely culprit. Because it takes more than a week to confirm Aphanomyces diagnoses, we are not yet certain about these samples. Most of these samples also have prominent leaf diseases, primarily spring black stem and Leptosphaerulina leaf spot.

Wheat. Several samples have had foliar disease problems, including powdery mildew, Septoria leaf blotch, and tan spot. Wheat in southern Iowa appears to be having a rough year for foliar diseases. If wet conditions occurred during flowering, expect to see a considerable amount of scab as well.

Oats. Crown rust seems to be making an early appearance this year. The disease was observed in Iowa and even in Minnesota in mid-May. These infections were probably started from local buckthorn sources.

This article originally appeared on page 103 of the IC-480(13) -- June 8, 1998 issue.

Updated 06/07/1998 - 1:00pm