Crop & Pest Report


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Sugarbeet Root Maggot Alert: Fly Activity Peaks Expected Next Week (06/11/20)

The recent periods of hot weather have accelerated the accumulation of sugarbeet root maggot (SBRM) growing degree day (DD) units, and fly activity has increased significantly in the past couple of days throughout much of the Red River Valley (RRV).

The recent periods of hot weather have accelerated the accumulation of sugarbeet root maggot (SBRM) growing degree day (DD) units, and fly activity has increased significantly in the past couple of days throughout much of the Red River Valley (RRV). In a collaborative effort between NDSU and American Crystal Sugar Company, 149 Red River Valley (RRV) field sites are being monitored every Monday, Wednesday, and Friday by using sticky-stake traps (Figure 1).



Current SBRM outbreak areas include the following (in descending order of cumulative fly counts): Thompson, St. Thomas, Bathgate, Warren, East Grand Forks, Buxton, Crookston, Reynolds, Crystal, Auburn, Fisher, Hoople, Cavalier, Ada, Grafton, Argyle, Voss, and Grand Forks. Over 600 flies per site (2-trap total) have been recorded near St. Thomas and Thompson thus far, and at least 100 flies per site have been captured on stakes in the other above-mentioned locations. This is very concerning, as peak fly activity is not expected for another 3 to 6 days in most of the problem areas. Therefore, it is highly likely that many more flies will be emerging and colonizing beet fields in the coming week to 10 days.

Visit here to monitor SBRM fly counts in your area and throughout the RRV. NOTE: this monitoring project provides a general idea of where potential root maggot fly hot spots are developing throughout the growing season; however, it is 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 2.


As presented in Table 1, SBRM fly activity will be peaking in the southern Red River Valley late this week. Peaks in the central Valley (Ada/Hillsboro areas) are expected to occur around Saturday, June 13. In the more northerly parts of the Valley, activity peaks are expected on June 16 in the Grand Forks/Crookston areas, and on June 17 in the vicinity of Grafton, St. Thomas, Cavalier, and Bathgate.


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 for late-planted fields, because those plants are atypically small and more 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 who have already applied a postemergence liquid insecticide and expect to make a second application should rotate with a different mode of action (e.g., if chlorpyrifos was used for the first treatment, rotate to a pyrethroid such as Asana XL or Mustang Maxx for the second treatment.

There is also still time to apply a granular insecticide, as they should be applied at a minimum of 5 days before peak fly. They also work well in moist soils, which are now quite common throughout much of the SBRM problem area.

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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