Fusarium head blight of wheat and barley
A 2005 epidemic of Fusarium head blight (FHB, scab) is making itself known in the Valley. Bleached spikelets are more the norm rather the exception across wheat fields this year (Figure 1). Disease pressure is high enough that even the most resistant spring wheat varieties are likely to have yield losses. Worse yet, losses (yield as well as quality) are expected to be huge this year for those producers who planted scab susceptible varieties.

The scab epidemic is widespread. Few locations in Minnesota have escaped the disease and our neighbors to the west, South Dakota and North Dakota, are also affected. Constant rain, clouds, and saturated soil prior to plant heading worked to promote Fusarium spore production. Unfortunately, that might be only part of the story. According to Kevin Thorsness, Bayer CropScience, another contributing factor may have been the amount of corn residue remaining in fields from last year’s prevented harvests. Corn is an excellent over-wintering host for the fungus.

Rusts of wheat
Leaf rust is well established on susceptible varieties . Tender flag leaves in some fields functioned only a short time before being injured by leaf rust. Stripe rust, on the other hand, has not been a production issue this year.

Bacterial stripe of wheat and barley
This disease continues to be a production issue, especially on Granite spring wheat. See last week’s edition of Cropping Issues for more details (http://nwroc.umn.edu/Cropping_Issues/2005/issue9/07_19_05.htm).

Bacterial blight of soybean
Like other bacterial diseases, bacterial blight is promoted by cool, wet weather. Bacterial blight is widespread, but incidence and severities remain low. The warm temperatures that we’ve been experiencing recently, should keep this disease in check. Bacterial blight looks a lot like brown spot and soybean rust, with one exception. Its lesions fall out, giving leaves a tattered appearance (Figure 2). Crop rotation is recommended to reduce the residue-borne inoculum. Fungicides do not have any activity when applied on bacteria, so they aren’t recommended.

Brown spot of soybean
Often found in the lower plant canopy on the unifoliate leaves, brown spot is considered an early season disease in Minnesota. Caused by Septoria glycines, it produces small chocolate brown spots on leaves which look like early soybean rust symptoms (Figure 3). If brown spot becomes severe, defoliation can occur. The pathogen over-winters on infected crop residue, so crop rotation is usually the only management practice needed to control the disease. The disease is rarely, if ever, a production issue in the Valley, so fungicide application is not recommended.

Root rots of soybean
Some fields have had substantial pre- and post-emergence damping off (seedling death either before or after emergence). Cool, saturated soils promoted plant infections early in the growing season. One or several pathogens may be responsible. Fungi and fungi-like organisms commonly isolated from diseased roots in the Red River Valley known to cause damping off and root rots are from genuses such as Rhizoctonia, Phytophthora, Pythium, and Fusarium. Dr. Carl Bradley, Extension Plant Pathologist at North Dakota State University, has done some work with fungicide seed treatments. His research results can be found at: