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Managing Common Root Diseases of Sugarbeet (5/18/17)

The most common root diseases of sugarbeet are Pythium, Rhizoctonia and Aphanomyces root rots.

Managing Common Root Diseases of Sugarbeet

The most common root diseases of sugarbeet are Pythium, Rhizoctonia and Aphanomyces root rots. In warm and wet conditions at planting or soon after planting, damping-off – which is more or less seedlings being infected at or just below the soil-line resulting in the seedlings toppling over and die – can be common. Except for a few days in late April, we have not had wet field conditions. As such, damping-off has not been an issue for our growers to date. As the plants get older, they can be affected by Rhizoctonia and Aphanomyces root rot. For diseases such as Rhizoctonia root rot, it will mean that a post application of fungicides such as Quadris, Priaxor and Proline will become more critical at the 4 to 8-leaf stage sugarbeet, especially if we do get wet and warm soils. Typically, we get best protection from Rhizoctonia root rot when the fungicide is applied just before a ¼ inch to ½ inch rainfall. It is always wise to use an integrated system of tolerant varieties, fungicidal seed treatments, and fungicide post application in a timely manner where it has been shown to be effective to manage diseases, especially.

Managing Aphanomyces

Tachigaren treated seeds will control Aphanomyces damping-off. In addition, the use of precipitated calcium carbonate, or waste lime from the sugar factories also help to control early season Aphanomyces damping-off and later season root rot.

Aphanomyces can be damaging when there is abundant free moisture and warm soils, especially to beets less than four weeks old. In fields with a history of Aphanomyces, growers should have a long-term plan that should include planting resistant varieties, using Tachigaren seed treatment, apply, and incorporate waste lime (5 to 8 tons/acre) at least in the fall prior to planting sugarbeet.

Impact of corn and soybean in the sugarbeet rotation on diseases

In many areas, corn and soybean are grown in rotation with sugarbeet. Rhizoctonia solani, the pathogen that causes Rhizoctonia damping-off and root rot also infects soybean and survives on corn root. As such, growers should try to avoid planting corn and soybean just prior to 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 better to plant sugarbeet following corn than beans to have fewer issues with Rhizoctonia. Use fungicide seed treatments that will help to reduce the population of the pathogen, plant early when the soils are cool and the pathogen is not at an infective stage, include a Rhizoctonia tolerant variety, improve drainage of fields, and use timely applications of effective fungicides.

Mohamed Khan

Extension Sugarbeet Specialist

NDSU & U of MN

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