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Sugarbeet Root Maggot: Flies could come Early this Year (05/26/16)

Recent periods of relatively warm temperatures in the Red River Valley (RRV) have likely accelerated development of overwintered sugarbeet root maggot (SBRM) larvae.

Sugarbeet Root Maggot: Flies could come Early this Year

Recent periods of relatively warm temperatures in the Red River Valley (RRV) have likely accelerated development of overwintered sugarbeet root maggot (SBRM) larvae. As such, SBRM fly activity is expected to begin and to peak slightly earlier than average. As such, it will soon be time to monitor fields for fly activity and to begin considering whether additive insecticide protection will be needed. Fly activity will increase considerably in the next two weeks. Actual peaks in fly activity in current-year sugarbeet fields are expected to occur between June 1 and 10, depending on latitude within the RRV.

Potential hotspots. Based on this year’s SBRM forecast, areas of greatest concern include fields near the following Red River Valley (RRV) communities: Auburn, Cavalier, Crystal, Grafton, Grand Forks, Nash, Oakwood, Reynolds, St. Thomas, and Thompson, ND, as well as Ada, Borup, Euclid, and Fisher, MN. An early, preliminary prediction for anticipated peak fly dates in the southern, central, and northern Red River Valley is presented in Table 1. Please watch for updated, more precise forecasts in future editions of CPR, because it is still too early to accurately predict actual peak fly dates at this time.


Weather determines peak fly. The actual occurrence of peak activity is highly weather-dependent. Calm to low-wind (12 mph or less) conditions are most conducive to fly activity, and 

flies will remain relatively inactive during cool, rainy, or windy weather. Peak fly activity in current-year beet fields typically occurs on the first warm (80°F or above), low-wind day following the accumulation of about 650 Degree-Day (DD) units. Temperature unit accumulations in all areas of the RRV are running near “normal” in relation to the 15-year average of SBRM DD accumulations for this time of year (Fig. 1).ent.boetel.2

To monitor degree-day accumulations for fields in your area, consult the Root Maggot application on NDAWN at: 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. 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 on both Android- and iOS-based devices.

NDSU, in cooperation with the American Crystal and MinnDak sugar cooperatives, is monitoring SBRM activity at 48 sites throughout the RRV in both ND and MN this year. Traps were initially deployed at all sites earlier this week. They will be checked three days per week (MWF), and the counts will be posted late-afternoon each count day at:

Control.  Growers in areas at high risk for damaging SBRM infestations should plan on applying a postemergence insecticide, 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) after at-plant insecticides were applied also may need additional postemergence protection.

Postemergence granules typically perform very well under moist soil conditions. Growers choosing to use a granular insecticide for postemergence SBRM control will likely achieve good control if the granules are applied between 1 and 2 weeks before peak fly activity; however, they also can be beneficial if applied within 4 to 5 days before peak fly.  As such, postemergence granules should be applied at this time or within the next 5-8 days to achieve good control.  Efficacy of granular applications can be enhanced by lightly incorporating them into soil and if light to moderate rainfall occurs after the application. 

In 2014, EPA approved supplemental labeling for Counter 20G that reduces the sugarbeet pre-harvest interval (PHI) to 90 days. This label change makes Counter 20G a more viable option for use as a postemergence SBRM control. NDSU research indicates that this product works very well as a postemergence control tool; however, as noted above, one application may be made per year. This makes Counter use as a postemergence material most applicable when either Lorsban 15G or an insecticidal seed treatment was used for planting-time protection.

Postemergence liquid insecticides work well under either moist or dry soil conditions. Applications should be targeted as close to peak fly activity as possible, but should provide good results if applied within 2-3 days before or after peak. Sprayed fields should be monitored for potential resurgences of flies, 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) is applied, 10 days must pass before another chlorpyrifos-containing liquid can be made to the same field.

Replanted Beets.  Frost, wind injury, and crusting occurred in some RRV fields in the past few weeks. Early estimates, courtesy of Tyler Grove, American Crystal General Agronomist, suggest that approximately 20,000 acres may have needed replanting. Such fields, if located in potential root maggot risk areas, may also require additional insecticide protection, either in the form of an at-plant insecticide or a postemergence application. NDSU research has shown that significant yield and revenue benefits can be achieved by applying additive insecticide protection in such fields. IMPORTANT: Counter 20G can only be applied to a field once per growing season. Therefore, if Counter was applied during the initial planting, it cannot be used in replanting the same field.

For more information on sugarbeet insect management, 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

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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