Managing Early Season Fungal and Fungal-like Diseases of Sugarbeet
The most common early season diseases are damping-off which may be caused by Pythium, Rhizoctonia and Aphanomyces. Commercial sugarbeet seeds are treated with Apron fungicide which typically controls Pythium damping-off. Rhizoctonia damping-off may be caused in wet and dry conditions but Aphanomyces damping-off occurs only in wet conditions. Since most of our fields were relatively dry in April and early May, Aphanomyces damping-off was not expected to be a major issue. There have been no reports of Rhizoctonia damping-off, to date.
How do you control Aphanomyces?
The fungus, Aphanomyces cochlioides, can cause early season damping-off and late season root rot. In fields with a history of this pathogen, growers should use varieties that are resistant to Aphanomyces for the chronic or root rot stage of the disease and the fungicide Tachigaren as a seed treatment to control the acute damping-off stage of the disease. The use of precipitated calcium carbonate (waste lime) at 5 to 10 tons per acre incorporated into the soil in the fall preceding the sugarbeet crop, and then for up to 10 years, helps to significantly reduce damage caused by Aphanomyces.
Rhizoctonia is common in soybean and corn grown in rotation with sugarbeet. How should Rhizoctonia be managed?
There is no simple solution since soybeans and corn are typically grown in the sugarbeet rotation and are likely to be more profitable than growing wheat in most years. My recommendation is to try to avoid corn and beans as the crop preceding sugarbeet. If possible, plant a wheat or barley crop just before sugarbeet. If a grower must have corn and bean in the rotation, it may be wiser to follow corn than beans so as to have less issues with Rhizoctonia. When possible, planting early into cool soils will help to get the plants off to good growth early and hopefully become tolerant by the time the pathogen becomes infective. Use fungicide seed treatments which will help to reduce the population of the pathogen, include a Rhizoctonia tolerant variety, improve drainage of fields, and use timely applications of effective fungicides to control root rot caused by the same pathogen.
What type of fungicides should growers be using?
Seed treatments of Apron provides good protection against Pythium; Tachigaren proves good protection against Aphanomyces; Kabina and Rizolex provide good control against Rhizoctonia damping-off.
Growers have the option of using a seed treatment such as Kabina (penthiopyrad), Rizolex (tolclofos methyl) + Kabina, or Vibrance (sedaxane) which are labeled for providing seed and seedling protection from Rhizoctonia damping-off. Growers can then apply an effective fungicide such as Quadris (9.2 fl oz/ac), Priaxor (6 to 8 fl oz/ac) or Proline (5.7 fl oz/ac with an NIS at 0.125%v/v) in a 7-inch band application directed at the soil around roots when plants are the 4 to 6-leaf stages to protect against Rhizoctonia root rot.
In fields planted without a seed treatment, effective fungicides may be used in-furrow to provide disease control, or fungicides may be applied when the average daily bare soil temperature at the 4-inch soil depth is about 60 to 62 F and just prior to a ¼ or ½ inch rainfall.
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