ISSUE 6 June 6, 2002
CRISIS EXEMPTION: MUSTANG INSECTICIDE FOR FLEA BEETLE IN MUSTARD SEED
The ND Department of Agriculture issued a Section 18 Crisis Exemption for the use of Mustang Insecticide (zeta-cypermethrin) for the control of flea beetles in Yellow and Brown mustards grown for seed. The delayed emergence and large populations of flea beetles migrating into the young fields was overwhelming some of the natural tolerance of these plants, prompting the need for control. Use the 25% leaf area damage recommendation for canola as a treatment guideline in making decisions.
The exemption took effect May 31 and expires June 14. The exemption allows an application rate of 2.9 to 4.5 fluid ounces of product per acre with a maximum season rate use of 8.6 ounces. Applicators must follow all instructions, precautions and warnings on the product label and have a copy of the exemption use directions in their possession during application.
A copy of the label is available in *PDF format at the NDSU Pesticide Training and Certification website:
We appreciate the quick response form ND Dept of Ag, EPA, and FMC.
ALFALFA INSECTS TO SCOUT FOR -WEEVILS AND LEAFMINERS
In the past two seasons, there have been problems with alfalfa weevil in the south central counties of ND. Alfalfa is finally getting some good growth after the warm weather. Its time to scout for this insect to avoid losses from their feeding.
Begin scouting for alfalfa weevil larvae. Monitor tip injury to assess infestation levels and damage. This method is relatively simple and provides adequate estimates for the pre-harvest damage potential from alfalfa weevil when planning management decisions.
Select 50-100 alfalfa stems, (10 to 20 randomly selected stems from each of 5 locations) and examine for signs of feeding damage in the leafbuds and growing tip leaves. Divide the number of stems with recent tip injury by the total stems collected, convert to a percent, and compare with the threshold.
Many of the problems with weevils have come after the first cutting. It is important, when cutting alfalfa that has weevil larvae feeding, to assess the need for post-harvest weevil management. Monitor regrowth for potential stubble infestations, particularly beneath windrows. After the hay has been picked up, sample the stubble and early regrowth in 20 one square foot samples, 4 chosen randomly from 5 locations. When regrowth after harvest is sufficiently tall, go back to monitoring tip injury.
Insecticides labeled for alfalfa weevil include Baythroid, carbaryl (Sevin), Furadan, Imidan, Lorsban, malathion, methyl parathion (including Penncap M), Mustang, permethrin (Ambush and Pounce), and Warrior.
Alfalfa Weevil thresholds
Before 1st Cutting
35% (weak stand) plants with feeding damage
40% (vigorous stand) plants with feeding damage and/or 2 live larvae/stem
After 1st Cutting in stubble
8 or more larvae/ft2, (6/ft2 on sandy soil);
Finally, watch for the Alfalfa blotch leafminer in the central areas of ND. Infested fields take on a whitish cast due to extensive infestations of this fly pest. The same field appearance can be confused with alfalfa weevil feeding, however, leafminer damaged leaves are not ragged or skeletonized.
The first signs of an infestation are "pinholes" in the leaves, caused by the adult fly, and a comma shaped mine formed by the larva tunneling through the leaf. The pinholes are easily visible if you hold the leaf up against the sunlight.
Insecticides have not provided consistent or significant control. The best recommendation would be to cut a little early to avoid leaf loss from rapid drying due to the larval mines. Early harvest in either the first or second cut should reduce the future generations in the season.
SOYBEAN APHID UPDATE
Buckthorn plants, the overwintering host of the aphid, have been sampled during the past month, looking for hatched aphid nymphs. So far, no soybean aphids have been found on any buckthorn in the survey. Unfortunately, this wasn’t entirely unexpected. Surveys last year in Illinois, Michigan, Wisconsin, and Minnesota failed to find aphids on buckthorn, either. The soybean aphid still showed up in soybean fields in great enough numbers to justify control.
A shift in surveying emphasis is about to change. As the soybean plants emerge, field surveys to detect the presence of the aphid are beginning.
Though treatment decisions won’t be made until late vegetative to early flowering growth stages, growers and consultants are encouraged to look at plants for those first aphids expected to colonize a field. Check field margins at first. Winged aphids should land on plants on the field edge, give birth to one or more live nymphs, then move to another plant to repeat the process.
SUGARBEET ROOT MAGGOT: PEAK FLY ACTIVITY FORECAST
Continued cool weather has resulted in delayed development of overwintered sugarbeet root maggot populations. The first detection of root maggot flies in the Red River Valley this year was recorded in a current-year sugarbeet field near St. Thomas, ND on May 28. As would be expected, degree-day accumulations in the area remain substantially behind normal. Our monitoring sites are averaging about ten days worth of heat unit accumulation behind last year’s values, which were also slightly behind normal. This abnormality makes forecasting difficult.
Based on current DD accumulations and the extended weather forecast, peak emergence from previous-year fields is anticipated to occur within 5 and 14 days and peak fly activity in current-year beets is projected to occur on a warm (80 degrees Fahrenheit or above) day between June 16 and 23. Peaks are expected to occur slightly earlier in the southern 1/3 of the valley due to moderately higher recorded DD accumulations; however, root maggot populations are not expected to be at threatening levels in that area. Watch for an updated forecast in next week’s issue of Crop & Pest Report.
POSTEMERGENCE OPTIONS FOR SUGARBEET ROOT MAGGOT MANAGEMENT
Cool weather has delayed sugarbeet seedling development and several thousand acres have been replanted recently due to a variety of environmental factors. The resultant small beet plants will be extremely vulnerable to attack by sugarbeet root maggot larvae. Therefore, growers in areas of anticipated high maggot populations are advised to consider applying a postemergence liquid or granular insecticide, especially if seedling development is significantly behind normal.
Typically, granular treatments perform better if applied slightly before anticipated peak fly activity and liquid products provide the best activity if applied within three days (either before or after) peak. Soil moisture and the severity of fly population levels should be considered in choosing whether to use a liquid or a granular formulation.
Postemergence granular insecticides are most effective under moist soil conditions or if applied within a few days prior to a rainy period. Granules are also advised in fields that have been re-seeded without a second planting-time insecticide. Liquid insecticides will perform better than granules if soil conditions are dry. In addition to fly control, a liquid formulation of an organophosphate such as Lorsban 4E may provide fly control as well as residual larval control, especially if rainfall is received within 1 or 2 days of application to adequately incorporate it into the soil. A liquid product may also be a better choice if an unusually high flare-up of fly activity occurs. Research suggests that adult fly control can also be achieved with Asana; however, it and other pyrethroid products are not particularly active against larvae when applied postemergence. Also, although the label for Mustang 1.5EW offers fly "control", its performance in NDSU field trials is not sufficient to warrant my recommendation for that use at this time. Refer to the "Insect Control" section of the 2002 Sugarbeet Production Guide or the "Sugarbeet Insects" section of the 2002 Field Crop Insect Management Recommendations for more detail and specific product recommendations. The respective web locations for online versions of these publications are:
Research & Extension Entomologist