Monitor sugarbeets for seedling diseases

Common sugarbeet seedling diseases in Michigan include Pythium damping-off, Rhizoctonia damping-off and Aphanomyces.

Sugarbeet is susceptible to several seedling diseases, including seed decay, preemergence damping-off, postemergence damping off and infections of the hypocotyl of emerged plants. The severity of seedling disease is influenced by host susceptibility, inoculum level, favorable environmental factors and effectiveness of seed treatments. Environmental conditions this spring – excess moisture and warm conditions – have increased the incidence of seedling diseases. Sugarbeet producers will want to determine what seedling diseases they have in order to better identify appropriate seed treatments and varieties to utilize for the 2012 season.

Seedling disease types are often difficult to identify since all can cause seedling death. Laboratory analysis is the most accurate means of identifying particular diseases. However, by knowing environmental factors, seed treatments, genetic resistance and field history, we can often improve our odds of identifying which seedling disease may be causing problems. Agriculturists from Michigan Sugar Company should be utilized to assist in sorting things out.

Environmental conditions can favor one disease over the other. Pythium is favored by high moisture conditions, but because of different strains, it has a relatively wide temperature range. With this disease, seed rot and preemergence damping-off is more common than other seedling pathogens. Our standard sugarbeet seed treatments which include Apron and Thiram generally do an effective job of controlling this disease.

Rhizoctonia can cause some preemergence damping-off, but usually effects seedlings after emergence. A dark brown lesion begins just below the surface and extends up to the hypocotyl, with a sharp line between diseased and healthy tissue. When the hypocotyl is girdled, the seedling collapses and dies. This disease often occurs in fields with a history of Rhizoctonia root rot and warm wet field conditions. In-furrow Quadris applications and Strobilurin seed treatments are effective in controlling this disease.

Aphanomyces seedling disease, also known as “black root” is periodically a problem in Michigan. This disease requires warm and wet soils. Infections rarely occur when soil temperature is below 59 degrees. Early planted fields in cold soils rarely have a problem. Generally, seedling emergence is not affected, but one to three weeks after emergence a dark grey, water-soaked lesion develops on the hypocotyl and soon the entire hypocotyl appears dark brown to black and threadlike. Infected seedlings are stunted and have reduced vigor; they may fall over and die, but often they survive and show some recovery. Currently, Tachigaron seed treatments are effective in controlling this disease.

Seed treatments with protective fungicides are one of the least expensive and most efficient methods of controlling seedling diseases. Since many of our seed treatments are very selective in what they control, combinations of two or more seed treatments are required to control the spectrum of seedling diseases. If laboratory analysis is needed to determine seedling disease, contact your local agriculturist who can direct plant submissions to the Michigan State University Diagnostic lab.

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