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Sugarbeet Root Maggot: Peak Fly is Here! (06/07/18)

Sugarbeet root maggot (SBRM) flight activity began substantially earlier than average this year; however, recent cool and wet weather has resulted in a few day of relatively low activity throughout much of the Valley.

Sugarbeet Root Maggot: Peak Fly is Here!

Sugarbeet root maggot (SBRM) flight activity began substantially earlier than average this year; however, recent cool and wet weather has resulted in a few day of relatively low activity throughout much of the Valley. The very unusual spring weather (persistent cold in April, followed by periods of extremely warm temperatures in May) that has occurred thus far makes 2018 a nearly unprecedented year with regard to predicting peak fly activity.

Peak 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. The current forecast for four representative RRV locations is presented in Table 1.

According to SBRM degree-day (DD) accumulations, fly activity levels in the central and far southern reaches of the insect’s range within the Red River Valley (RRV) should have already peaked. Tuesday’s stormy weather and the subsequent windy conditions on Wednesday suggest that, both the Grand Forks/Thompson/Reynolds areas, as well as the Grafton, St. Thomas, and Cavalier areas, will probably peak Thursday, June 7; however, activity will probably not abruptly cease in these areas, due to anticipated windy conditions on Friday. 

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Root maggot fly counts. The highest numbers of SBRM flies captured on sticky stake traps has occurred in rural East Grand Forks (Sullivan TWP), Grand Forks (Grand Forks TWP), St. Thomas (S. St. Thomas TWP), and Thompson (Brenna TWP). Moderately high activity has also been observed near Auburn, Bathgate, and Crookston. Growers in areas of high activity should be ready to apply additive postemergence insecticide applications if fly activity in their areas increases (or resurges) to at least 45 flies per sticky stake or 0.5 flies per plant within a field. Fly counts from the NDSU trapping network can be viewed online. NOTE: fly counts for each field are cumulative totals from 2 stakes.

Postemergence SBRM Control. Growers in high-risk areas for 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 insecticide was used at planting. Fields in which heavy rainfalls (> 3 inches) occurred within two to three days after at-plant or postemergence insecticides were applied also may need additional postemergence protection.

The best control option this time is a sprayable liquid insecticide application, which can either be applied by ground-based equipment or aircraft. Postemergence liquid insecticides perform best if applied close to (within 2-3 days of peak fly; either on, before or after peak). Treated fields should be monitored closely after a postemergence application to determine if fly activity resurges. Some fields could 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 liquid can be made to the same field. If retreatment is necessary within 10 days of the initial chlorpyrifos application, an insecticide containing a different active ingredient must be used. For more information, 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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