This year’s early season rain has increased the risk of soybean disease in Iowa. We knew it was coming and now the wait is over.
For the past month, we have seen Septoria brown spot and bacterial blight. This past week, we identified sudden death syndrome (SDS), frogeye leaf spot and other diseases for the first time this year.
The 2015 season is primed for being another “SDS year” because of the weather conditions experienced to date. As we’ve learned from SDS outbreaks in years past, this disease likes it wet. The early wet weather helps increase the root rot phase of the disease.
SDS has been identified in different parts of the state, especially in Central and Southeast Iowa. SDS foliar symptoms appear as yellowing and death of tissue between leaf veins.
There are a few other diseases that may be confused with SDS, such as brown stem rot and stem canker. Look for lesions on the outside (stem canker) and browning in the pith (brown stem rot) to distinguish from SDS.
Frogeye leaf spot
We do not normally see frogeye leaf spot this early in Iowa, but it has already been identified in a Central Iowa field.
Frogeye leaf spot is fairly easy to distinguish from other leaf spot diseases of soybean. It has a dark purple ring at the margins of lesions with a light tan center. Lesions are usually found in the middle to upper canopy.
Phyllosticta leaf spot
Phyllosticta leaf spot is a minor disease and we’ve received one report in Iowa so far this year. Look for the dark spots within the lesion to help identify this disease.
(Source – http://www.iowafarmertoday.com/news/crop/soybean-diseases-starting-to-pop-up/article_42195512-4070-11e5-9b4e-b3a719ba470f.html)