ISSUE 5 June 1, 2000
HIGH RISK PLANTING DATES FOR WHEAT AND WHEAT MIDGE, 2000
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 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 majority of the state is in the 0 - 200 midge per square meter. This places risk of midge problems in a low category. However, if what was planted in high risk window, it will be heading when midge are active. Scouting for midge should still be done to identify the few fields where treatable numbers are likely to occur. Needless to say, the wheat in Divide and Burke counties where populations are large should most definitely be scouted and treated if needed.
For more information on wheat midge, visit the web site for updates and degree day information to determine when emergence begins in your area.
CEREAL APHIDS BEING REPORTED AROUND THE STATE
As mentioned in the May 18 pest report, cereal aphids were bound to show up soon. This past week, several reports of aphids in small grain fields have come to our attention. The aphids have been reported in fields from counties in the southern half of the state, as well as the North Central Researcha nd Extension Center in Minot. At the Carrington REC, English grain, Greenbug, and Corn leaf aphid were all found in low numbers in winter wheat plots. The English grain aphid was the most frequently found aphid. The populations have been small and well below the treatment guidelines. Temperatures in the 70's favor population increases. Cool, wet weather in eastern ND over the Memorial Day weekend should slow population increases. Scouting small grains for aphids should get underway.
CUTWORMS . . . WATCH FOR INCREASED ACTIVITY
We have reached the time of the season when the next wave of cutworm activity gets underway. The cutworms that will make their presence known in the next ten days are the species that overwinter as eggs and have been hatching over the past two weeks. The most familiar cutworm will be the Redbacked cutworm. Only a few reports of current problems but expect them to increase. Some control has begun in sugarbeets and sunflower in the southern end of the Red River Valley and southeastern ND. Jan Knodel, NDSU Plant Protection Specialist, reports that some cutworm feeding in canola. was reported from the Dickinson area.
MONITOR ALFALFA FOR LEAFHOPPERS, WEEVILS AND LEAFMINERS
Minnesota is reporting the arrival of Potato leafhopper, at least in the southern part of the state. As we prepare for first cutting, sample fields prior to cutting so you are aware of populations that are present. See last weeks newsletter for treatment recommendations.
Alfalfa weevil are feeding at this time. Last season we had infestations reported from ND counties bordering South Dakota. During the 90's, most reports of feeding damage have come from counties along the Missouri River.
Monitor tip injury to assess pre-harvest damage. This method is relatively simple and provides adequate estimates for the pre-harvest damage potential of alfalfa weevil for making 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.
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.
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); or larvae are suppressing regrowth
Finally, watch for the recently established Alfalfa blotch leafminer in eastern ND. Last year, infested fields took 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 larval damage will be white. The pinholes are easily visible if you hold the leaf up against the sunlight.
Currently, 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. Long term control of this insect should be achievable through natural enemies. In the eastern US where this insect arrived in 1968, the release of a parasite from Europe has reduced populations to insignificant levels. Hopefully we could have the same success.