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ISSUE 6  June 8, 2000

 

SUGARBEET ROOT MAGGOT FLIES ACTIVE

    Sugarbeet root maggot development is well under way and fly activity has increased significantly in the Red River Valley. Fly counts on NDSU sticky stakes indicate that the highest fly activity is in the northern end of the valley between Minto and St. Thomas, ND, whereas, activity is very light in the central and southern areas between Climax and Hillsboro, ND, and Foxhome, MN. Although the largest counts are being recorded in old beet ground, fly numbers are also increasing in
current-year beet fields.

    Based on temperature accumulation data (compiled by Dr. Robert Carlson, NDSU Entomologist) and anticipated weather patterns for the next few days, the degree-day model suggests that peak fly activity in current-year beet fields should occur between June 9-12 for the region.

    Producers needing to apply postemergence insecticides are advised to begin treating as soon as practical if using granular formulations. Those applying liquid insecticides should treat around 2-3 days ahead of anticipated peak activity for their locale to get optimal insecticidal acitivity.

Mark Boetel
Sugarbeet Entomologist

 

BUG BRIEFS . . .

    No single, widespread insect concern this week for the state. However, there are situations where fields are having problems with many of the insects that have been mentioned in previous weeks newsletters.

    Cereal Aphids are still only being detected at low levels. Some observations from South Dakota have indicated increased numbers of aphids are being found in their wheat fields. At the deadline for this weeks newsletter, the weather outlook is favorable for aphid populations to increase. Temperatures in the 70 to 80 F range are good for aphids. On the plus side for grain growers is that the English grain aphid is still the most common aphid for the region in our wheat. It has been my experience that this aphid stays low in numbers until the heading stage. At that point, the population increases rapidly.
Continue to watch for aphids in the fields and hope the numbers stay low for a while.

    Cutworm activity is spotty, but definitely out there in the fields. People who are reporting problems have indicated cutworms are in the to 1 inch size range. No control difficulties are being reported. Crops affected have included sugarbeets, sunflower, corn, and a few beans. The feeding has been above ground, though due to the size of some of the cutworms much of the feeding has been on leaves.

    There was one call this week from the Dickinson area about caterpillars in barley. The caller thought they were cutworms. However, it sounds like a situation that might be more like Armyworm. The worms were only inch long and the caller could not recall if there were any distinct stripes. We haven’t had many armyworm problems in the region in recent years. When they have been found, barley has tended to be one of the first cereal crops affected. Again, I can not say for sure but it might
be good to watch for armyworm activity.

    A few reports have made it into the office on Alfalfa weevil infestations. Be sure to check your alfalfa prior to your first cutting. If the pale green larvae are feeding in terminals prior to cutting and no treatment is made, watch the regrowth under the swath to check survival and density of larvae. If there are 6 to 8 larvae per square foot, feeding by larvae will delay regrowth in those areas. Treatment of the swath area where larvae have been concentrated is usually all that is required in these circumstances.

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    Flea beetles in canola continue to bother young fields in north central and northeastern ND production areas. In many areas, the recent rains and cool to moderate temperatures gave canola a boost to outgrow most flea beetle problems. In cases where emergence was delayed or plants are drought stressed, the young plants should be watched closely. The warm temperatures forecast for June 7 - 10 should get remaining beetlesout and moving around. Typically, flea beetle activity continues on through mid-June, then declines.

 

RUSSIAN WHEAT APHID . . .  NEARBY IN MONTANA

    Russian wheat aphid were detected in winter and spring wheat fields during a visit to the Miles City and Forsyth, Montana area May 31 to June 1. I was a little surprised at the level of the infestations for late May. Montana State University entomologists have indicated that winter survival of RWA occurred in the state, likely due to the milder winter.

    Why do I bring this up? We have not detected RWA in North Dakota since 1992 and 1993. Back then, detections of RWA were in the southwestern counties of Golden Valley and Slope. They were found during August in maturing wheat and posed no yield threat. In 1992, Montana growers treated an estimated 250.000 acres for RWA, the most since detection of RWA in Montana. With the early detection and close proximity to western ND (Miles City is only about 90 miles west of the ND state line) it would not be a surprise if RWA were detected in western ND counties this year. IPM survey scouts are being asked to watch for them along with surveying for Cereal leaf beetle.

    If detections of RWA occur, infestation level and growth stage of the wheat are important. Typically, aphids will have there greatest impact on grain yileds when infestations exceed thresholds prior to heading. RWA is no different for the northern spring wheat regions. To realize the greatest benefit from an insecticide program, controlling the aphid prior to heading will produce the best results.

Currently, the treatment decision for RWA in  pre- headed wheat is determined using the following formula:

Threshold   =

(Control costs / acre) x 200

(% infested tillers)

[expected yield/a]x[bu/a selling price]

    If field scouting determines that the percent infested tillers is greater than the calculated threshold then a treatment should be considered.

For headed wheat, the fomula is changed slightly, increasing the constant from 200 to 500:

Threshold =

(Control costs / acre) x 500

(% infested tillers)

[expected yield/a]x[bu/a selling price]

    Not familiar with RWA damage in wheat? RWA Damage: Leaves infested by RWA have long white, purple or yellowish streaks. Under some conditions, infested wheat tillers have a purplish color. Heavily infested plants are stunted and some may appear prostrate or flattened.

    After flowering, some heads are twisted or distorted and have a bleached appearance. Heads often have a "fish hook" shape caused by awns trapped by tightly curled flag leaves. At this time most RWA are found feeding on the stem within the flag leaf sheath or on developing kernels. There may be poorly formed or blank grains and the entire head sometimes is killed.

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Phillip Glogoza
Extension Entomologist
pglogoza@ndsuext.nodak.edu


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