ISSUE 5 JUNE 3, 1999SUGARBEET ROOT MAGGOT EMERGENCE UNDERWAY
Hopefully beet growers have sticky stakes out to monitor adult densities around fields in areas where the SBRM has been a problem. The fly catches should be used in combination with degree-day (DD) accumulations for post treatment decisions.
Using ambient (air) DD accumulations
Calculating ambient DDs uses 47.5EF as the base temperature. With this procedure, the first 80E day following accumulation of 600 DD usually coincides with peak activity in new beet fields. Currently we have reached the mid-500's in the southern end of the valley, and low-500's in the northern half of the valley. Significant fly activity was observed in the Glyndon area over the Memorial Day weekend.
Post liquid treatment for SBRM control need to be applied 3 days before peak fly activity, which would be around 520 to 550 DD and when the daily temperature gets up to 80E. High winds and low temperatures can keep SBRM from moving from the old beet fields to the new beet fields. It is very important that 520 to 550 DD have accumulated and the weather has warmed up to 80E for post liquid applications.
Post treatments of granular insecticides may be a very good option for controlling the SBRM since we have adequate to more than adequate soil moisture at the present time. Granular insecticides can be applied up to ten days ahead of peak fly activity.HIGH RISK PLANTING DATES FOR WHEAT AND WHEAT MIDGE
We have reached the point where 600 degree days (40 F) have been accumulated around the state. The first date corresponds with the accumulation of 200 DD; the second is when 600 DD were reached. Now is a good time to review planting dates for individual fields, and begin to prioritize scouting efforts for adult midge based on those planting dates and expected head emergence.
The overwintering midge population determined from the fall collected soil samples reveal slightly higher larval numbers for the 1999 season. The wheat midge soil survey was conducted again this year with financial support from the North Dakota Wheat Commission. Under the direction of the Department of Entomology at NDSU, soil samples collected by local extension agents last fall were processed. The computer generated map below summarizes the distribution of wheat midge.
The latest wheat midge surveys reveal that a general increase in North Dakota's overwintering population occurred throughout the northern and central counties. But dramatic population increases occurred in Divide and Burke counties, where wheat midge had not caused significant problems during the past three years.
The population increases in an area from Pierce to Dickey counties in the central part of the state are particularly alarming, from the standpoint that past economic infestations were more localized. These increases emphasize the need for all wheat growers to plan for potential wheat midge problems this coming season. In particular, wheat producers in the northwest corner of the state and in western Benson and central Stutsman counties must plan for control in 1999.
GRASSHOPPER HATCH IN EAST ND AND MN
The warm weather brought on several reports of grasshopper activity in the Red River Valley Region. Some spray activity is underway in situations where large numbers of young hoppers are hatching within field boundaries, usually on fields where late season crops were grown last year.
No serious cutworm activity has been reported around the region . . . yet. Watch emerging crops closely the next two weeks. Last year, the cold snap at the end of May delayed activity, but when it warmed up significant widespread feeding was reported. Our young crops will be very vulnerable to cutworms at this time.
GRASSHOPPERS IN SUGARBEET
Grasshoppers pass the winter (overwinter) in the egg stage. Eggs are deposited about ½ to 2 inches below the soil surface in pod-like masses about 1 inch long. Each egg pod consists of 20 to 120 elongated eggs cemented together, and a single female may deposit about 8 to 25 egg pods. Egg pods are primarily deposited in uncultivated ground such as pastures, field margins, and roadside ditches. Most eggs hatch in May and June, and small grasshoppers start feeding on weeds and other vegetation. Late infestations may develop when grasshopper adults migrate from harvested small grain fields. Grasshopper feeding on sugarbeet begins early season around the field margins and continues into the fields. Early feeding results in shot-holes in the leaves of sugarbeet seedlings. Heavy infestations may result in leaf and petiole loss which may make replanting necessary.
Cultural practices, such as plowing, disking, and harrowing, can destroy grasshopper eggs in the soil and thus reduce grasshopper populations.
The grasshopper also have many natural enemies that assist in regulating their populations. The larvae of a tachinid fly, a bee fly, and a sarcophagid fly are parasites. Some ground beetles feed on grasshopper nymphs and eggs. Other predators include a robber fly and birds. Disease organisms, such as the fungal pathogen, Entomophthora grylli, also contribute to reducing grasshopper populations. However, natural enemies may not prevent grasshopper from causing economic damage to the sugarbeet crop.
Consequently, insecticides labeled for grasshopper control in sugarbeet, such as Asana XL, Lorsban 4E, and Diazonon AG 500, are recommended for controlling grasshopper whenever 20 or more adults per square yard are found in field margins or 8 to 14 adults per square yard are present in the crop.
Extension Sugarbeet Specialist