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Sugarbeet Root Maggot: Peak Fly is Here! (06/09/16)

Sugarbeet root maggot (SBRM) fly activity has increased significantly in the past couple of days, and by the time this report is published, activity levels will have peaked in the southern and central Red River Valley (RRV).

Sugarbeet Root Maggot: Peak Fly is Here!

Sugarbeet root maggot (SBRM) fly activity has increased significantly in the past couple of days, and by the time this report is published, activity levels will have peaked in the southern and central Red River Valley (RRV). The northern RRV is expected to be at about peak Thursday, June 9; however, due to the cooler weather pattern that occurred earlier in the week, extremely high activity is expected into the weekend. 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.

boetel.1.table

Root maggot fly counts. Current hotspots include Ada, Auburn, Merrifield, and St. Thomas. Moderately high activity has also been observed in the Cavalier, Minto, and Thompson, ND. Other areas could also develop relatively high infestations as well. As such, growers in SBRM risk areas should be ready to apply additive postemergence insecticide applications if fly activity in their areas increases 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.

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

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