June 5, 2003

 

Peak Activity Time for Sugarbeet Root Maggot

Based on current degree-day accumulations and the extended weather forecast, peak sugarbeet root maggot fly activity is underway in area beet fields and should peak by June 15, according to a North Dakota State University entomologist.

Although degree-day accumulations had been slightly ahead of schedule in mid- to late-May, recent rains and cool weather slowed the development of overwintered sugarbeet root maggot populations. "Peaks are expected to occur slightly earlier in the southern third of the Red River Valley due to moderately higher degree-day accumulations," according to Mark Boetel. "However, root maggot populations are not expected to be at threatening levels in that area."

Most growers in the Valley were able to plant their beets somewhat earlier this year. The earlier planting will help plants withstand low-level sugarbeet root maggot feeding injury. Fields in low-risk areas should be adequately protected if a planting-time soil insecticide was used at a standard application rate.

"Growers in areas of anticipated high maggot populations should consider applying a postemergence liquid or granular insecticide, especially if seedling development is significantly behind normal," Boetel says. "Granular treatments usually perform better if applied slightly before anticipated peak fly activity while liquid insecticide is best if applied within three days before or after the peak."

Soil moisture and the severity of the fly population should be considered when choosing a liquid or granular.

A postemergence granular insecticide is most effective under moist soil conditions or if applied within a few days before a rainy period. Granules are also advised for use in fields that have been reseeded without a second planting-time insecticide.

Insecticides in liquid form will perform better than granules if soil conditions are dry. A liquid formulation of an organophosphate such as Lorsban 4E may provide fly control as well as residual larval control. That is especially true if it rains within one or two days of application, Boetel notes.

"Liquid insecticides may perform better if an unusually high flare-up of fly activity occurs," Boetel says. "Adult fly control can also be achieved with Asana however it and other pyrethroid products are not particularly active against larvae when applied postemergence."

More information is available in the 2003 Sugarbeet Production Guide and the 2003 Field Crop Insect Management Recommendations. The two publications are available on the Web at:

http://www.sbreb.org/Production/production.htm  and at http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143wl.htm

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Source: Mark Boetel, (701) 231-7901, mboetel@ndsuext.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu