By Mohamed Khan
Extension Sugarbeet Specialist
Although we have had a warm and relatively wet July and August, Cercospora leaf spot was not a major problem in most production areas early in the season up to mid-August. Since mid- to late-August, there were reports of some fields, especially in the southern Red River Valley and southern Minnesota, becoming infected. Warm and wet conditions in late August have also resulted in more leaf spots developing in fields in the northern Red River Valley. Fungicide treatments should continue until at least mid-September in fields with active leaf spot symptoms. Fungicides such as Headline, Proline, and Super Tin/Agri Tin with 7 day pre-harvest intervals can be used to help control the disease and fields sprayed (until around September 21 if conditions remain favorable for disease development) will still be ready for the full campaign which typically starts around October 1.
The forecast is for cool nights, which will not be favorable for new infection by Cercospora beticola. However, relatively warm days and the presence of moisture in the form of rain or dew will result in continued development of current infections. Late season leaf spot should be controlled or it will result in significant reduction in sugar concentration and increase processing costs to remove increased impurities. We need to keep the leaves of the sugarbeet crop as healthy as possible to maximize sunlight interception during September and increase sucrose concentration in the roots. Fungicides such as Proline and Headline with translaminar activities will help to control any current infections. Please follow pre-harvest restrictions for fungicide use in fields or areas of fields which will be harvested during pre-pile and in preparation for the full campaign. Consult your agriculturists for the best advice for controlling Cercospora leaf spot in your factory district and further information on pre-harvest interval.