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Sugarbeet Root Maggot: High Activity Expected Next Week! (06/02/16)

Sugarbeet root maggot (SBRM) fly activity is currently at low levels throughout most of the Red River Valley (RRV); however, several sites within the Valley will experience very high populations this year.

Sugarbeet Root Maggot:  High Activity Expected Next Week!

Sugarbeet root maggot (SBRM) fly activity is currently at low levels throuent.boetel.sticky trapghout most of the Red River Valley (RRV); however, several sites within the Valley will experience very high populations this year. Root maggot populations have steadily increased during each of the past five growing seasons. In 2011, an average of 42 flies per trap were captured on NDSU sticky stakes. In 2015, we captured 210 flies per trap, which was a 400% increase over that observed in 2011. This trend suggests that some fields could have severe SBRM fly infestations this year.

Peak fly forecast. According to the NDSU root maggot developmental model, peak SBRM fly activity typically coincides with the first rain-free, warm (about 80°F), low-wind (< 10 mph) day at the accumulation of 650 degree-day (DD) units. To monitor SBRM DD accumulations for your area, consult the Root Maggot model application on the North Dakota Agricultural Weather Network (NDAWN). The site also includes a “help sheet” with information on how to use the model, recommendations for when insecticide applications are justified, and tips on when to apply them. American Crystal Sugar Company, in cooperation with NDSU, has developed a mobile device app based on our SBRM developmental model. The app is free, and available for both Android- and iOS-based mobile devices.

This year’s DD accumulations suggest that fly activity will intensify very soon, and that activity peaks are expected during the early to middle part of next week. Latitude typically impacts the timing of peak fly activity, with infestations in southern latitudes peaking two to five days before those in northern areas. The current forecast for four representative RRV locations is presented in Table 1.


*Maximum likelihood for peak fly activity is based on extended weather forecasts for wind speed, air temperature, and precipitation.

Peak fly in current-year beets usually coincides with the first rain-free, calm/low-wind day to reach 80°F after 650 DD are accumulated.

IMPORTANT: The “Maximum Likelihood Peak Fly Date” is an additional feature of the SBRM forecast that is provided to give pest managers our best estimate for when peak fly may occur. It is important to realize the following about this estimate: 1) it is based on the 10-day extended weather forecast; 2) it includes considerations for impacts of expected wind speed, air temperature, and precipitation events on SBRM flight behavior; and 3) it has the same intrinsic limitations that any 10-day weather forecast can have.

Root maggot fly counts. NDSU, in cooperation with the American Crystal and MinnDak sugar cooperatives, is monitoring SBRM activity at 48 RRV sites in ND and MN this year. Traps are checked three days per week (MWF), and counts are posted online late-afternoon each count day. To view counts in your area, visit:

Postemergence SBRM Control. Growers in areas at high risk of having damaging SBRM infestations should plan on applying a postemergence insecticide for additive protection, especially if an insecticidal seed treatment or a low to moderate rate of a granular soil-applied insecticide was used at planting. Fields in which heavy rainfalls (> 3 inches) occurred within two to three days after at-plant insecticides were applied also may need additional postemergence protection.

Growers choosing to use a granular insecticide for postemergence SBRM control should apply it as soon as possible, because granules are most effective if applied between 4 and 14 days before peak fly activity. Postemergence liquid insecticides should be targeted at as close to peak fly activity as possible, but should provide good results if applied within 2-3 days before or after the peak. Treated fields should be monitored for potential fly resurgences, and may require retreatment if subsequent infestations reach or exceed 0.5 flies per plant.

IMPORTANT: If a chlorpyrifos-containing liquid spray (e.g., Lorsban 4E, Lorsban Advanced, or any generic chlorpyrifos product) is applied, 10 days must pass before another chlorpyrifos-containing liquid can be made to the same field. If retreatment is deemed necessary within 10 days of the initial chlorpyrifos application, an insecticide product containing a different active ingredient must be used. For more guidance on postemergence control strategies, consult the “Insect Control” section of this year’s Sugarbeet Production Guide. Always remember to READ, UNDERSTAND, and FOLLOW the label of your insecticide product – it’s the law.


Mark Boetel

Research & Extension Entomologist

Daryl Ritchison

Extension Meteorologist

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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