May 10, 2001

Reducing Insecticide Application Rates To Control Sugarbeet Root Maggot

Difficult economic times in the sugarbeet industry have some growers considering cutting back on such things as insect control by lowering applications rates according to Mark Boetel, North Dakota State University Extension and research entomologist. "Before they reduce application rates, growers need to consider the anticipated insect pressure in their area," says Boetel. "If growers are looking at moderate to high insect pressure, then they shouldn’t be going down to lower rates. They’ll end up having to more than compensate for that with a post-emergence application which could end up costing growers more in the long run."

Boetel says growers also need to calibrate accurately if they’re going to go to lower application rates. "Calibration is equally important even if growers are considering standard rates," notes Boetel. "One shouldn’t rely on last year’s applicator settings because output rates can change over time with normal wear and tear of the equipment. Without calibrating and knowing the amount that they’re applying, they may not put enough on the field and may not get the insecticide performance needed."

"Growers also need to use wind shields to make sure that even after they’ve calibrated the correct amount is actually reaching the target zone where it’s needed to control insects," says Boetel.

Planting has been delayed for many growers because of the cool wet weather this spring. In a cooperative effort, Boetel and retired NDSU entomologist Dr. Robert Carlson have been monitoring soil and air temperatures and the accumulation of heating units. "Right now we’re very far behind what we were last year but last year was unusual in that we were ahead of normal," says Boetel. " The cool rains and air temperatures are actually cooling the soils. It is very early to tell but it looks like peak maggot fly activity will likely occur toward the end of the first week of June."

Boetel says growers need to consider the likelihood or relative risks of other secondary pests like springtails and wireworms when deciding on application rates. Moist soil is a prime condition for the buildup of some of these pests, especially Springtails. These are tiny soil insects that can cause major loses in sugarbeet plant stands in the absence of a soil insecticide.. They are especially a problem in high organic matter and heavy-textured soils. Fields that have a history of problems with Springtail are most likely to be problem fields this year.

Growers need to monitor for fly pressure throughout the growing season and be poised to put on post-emergence applications. "We’ll be monitoring populations as well throughout the season," says Boetel. "We’ll be providing updates through the various media sources to advise growers as to when we expect peak activity to occur and when those post-emergence rescue applications will need to be made.

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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

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