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Sugarbeet Root Maggot Alert: Fly Activity Peaks Coming in Next 2 to 5 Days (06/13/19)

Sugarbeet root maggot (SBRM) fly activity has increased significantly at several grower fields throughout much of the Red River Valley (RRV) in recent days.

Sugarbeet root maggot (SBRM) fly activity has increased significantly at several grower fields throughout much of the Red River Valley (RRV) in recent days. NDSU is partnering with the American Crystal Sugar Company this year to monitor fly activity in a total of 111 RRV sugarbeet fields throughout the growing area. 

Earlier this week, the most severe outbreaks were occurring near the following communities:  Auburn, Bathgate, Crystal, Glasston, Grand Forks, Merrifield, St. Thomas, Thompson, and Walhalla, ND, as well as Argyle, Crookston, East Grand Forks, Eldred, and Stephen, MN. Fly counts from both NDSU and ACSC monitoring routes, are posted every Monday, Wednesday, and Friday evening at: 

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. Sugarbeet growers, crop consultants, county Extension personnel, and other crop production advisors are encouraged to do their own monitoring in fields for which they may have concerns.

A map of the accumulated root maggot DD units for all locations within the RRV is presented in Figure 1. 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 about 650 degree-day (DD) units.


Although high fly activity has already developed at several locations, major increases are expected in the central and northern RRV between Thursday, June 13 and Wednesday, June 19. An updated forecast for periods of high SBRM fly activity and expected peaks at four representative RRV locations, based on current DD accumulations and the extended weather forecast, is presented in Table 1. 


The similarity among peak fly date predictions for the three more northerly locations listed in Table 1 is based on two factors.  First, and most obvious, is that DD accumulations are quite similar among those latitudes.  A second consideration is the extended weather forecast which suggests an unsettled weather pattern that includes wind, up to 50% chances of rain, and less-than-optimal temperatures on some days where peaks would otherwise occur. 

CONTROL:  The expectation for unsettled weather on or close to the predicted peak fly activity dates listed in Table 1 makes it difficult to predict a precise date for peak activity at this time.  However, current recommendations for postemergence insecticide applications should provide adequate flexibility for growers in affected areas to achieve successful root maggot management with postemergence insecticide applications. 

Growers in hotspots or high-risk areas for SBRM infestation should plan to apply a postemergence insecticide, especially if an insecticidal seed treatment or a low to moderate rate of a soil insecticide was used at planting.  This is particularly the case for late-planted or replanted fields because plants in those fields will be atypically small and vulnerable to attack by root maggot larvae.

Growers choosing to use a granular postemergence insecticide should have already applied it by now; however, adequate control may still be achievable by applying granules immediately, or at least 3 days before peak fly if the application is made shortly before an expected rain.  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 week to 10 days for potential fly activity resurgences.  Growers in the southern RRV who need to apply a postemergence liquid spray should do so as soon as possible.  Those in the central and northern RRV should plan to spray fields between Friday (June 14) and Sunday (June 16).  For more information, monitor local agricultural media sources (radio, The Crop & Pest Report, and the “Fly Counts” web page) 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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