Crop & Pest Report


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Sugarbeet Root Maggot Alert: High Fly Activity Expected During Next Five Days (06/08/17)

Recent periods of hot weather have accelerated the accumulation of root maggot growing degree day (DD) units.

Sugarbeet Root Maggot Alert: High Fly Activity Expected During Next Five Days

Recent periods of hot weather have accelerated the accumulation of root maggot growing degree day (DD) units. As such, emergence is well on its way, and fly activity has increased significantly in the past couple of days throughout much of the Red River Valley (RRV). NDSU is monitoring SBRM fly activity this year at 36 Red River Valley (RRV) sites in cooperation with American Crystal Sugar Company and the MinnDak Farmers Cooperative. Current outbreak areas include the following: Merrifield, St. Thomas, Thompson, East Grand Forks, and Grand Forks. To monitor where this year’s hotspots are, visit: NOTE: this monitoring project is aimed at providing a general idea of where potential root maggot fly hot spots are developing throughout the growing season; however, they are not a substitute for monitoring specific activity in individual fields.

Peak fly activity typically coincides with the first rain-free, warm (about 80°F), low-wind (< 10 mph) day on or after the accumulation of 650 degree-day (DD) units. Accumulated DD units for all locations within the RRV is presented in Figure 1.


Sugarbeet root maggot fly activity likely peaked in the southern Red River Valley earlier this week. Peaks in the central Valley are expected to occur on Thursday, June 8. Peaks will probably occur on Sunday, June 11 in the northern one-third of the production area. However, it should be noted that extremely high activity is expected throughout the weekend and into the first few days of next week.

Based on current DD accumulations, combined with the extended weather forecast, an updated forecast for periods of high SBRM fly activity and expected peaks at four representative RRV locations is presented in Table 1.


CONTROL: Growers in hotspots or high-risk areas for SBRM infestation should plan on applying a postemergence insecticide, especially if an insecticidal seed treatment or a low to moderate rate of an at-plant soil insecticide was applied. This is especially the case this year, because many fields in root maggot high-risk areas were planted late and plants in those fields are atypically small and vulnerable to attack by root maggot larvae.

Postemergence liquid insecticides work best if applied close to (i.e., 2-3 days before, during, or within 2 days after) peak fly activity. As such, growers expecting to use a liquid spray should monitor fields closely during the next two weeks for fly infestation buildups. Growers in the central RRV who need to apply a postemergence liquid spray should do so as soon as possible. Those in the northern RRV should plan to spray fields between Saturday (June 10) and Monday (June 12) if possible. Monitor local agricultural media sources (radio, Crop & Pest report, and the “Fly Counts” web page (address listed above) for further updates on root maggot control and other insect pest management topics.

Remember to always READ, UNDERSTAND, and FOLLOW all label directions and precautions. It is illegal to use a pesticide in a manner inconsistent with its label. For more guidance on postemergence control strategies, consult the “Insect Control” section of this year’s Sugarbeet Production Guide.

Mark Boetel

Research & Extension Entomologist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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