Crop pest control complicated by water-logged fields
Although the timetable for reacting to some crop pests was at hand by the first week of May, farmers who had crops threatened by such pests could do little about it because of the virtual elimination of field travel in many parts of the state.
This was due to heavy rainfalls in the immediate wake of the issuance of the Wisconsin Department of Agriculture, Trade, and Consumer Protection's first Pest Bulletin update for May.
The southern two tiers of counties in the state had fields coping with alfalfa weevils, anticipated damage on young corn from black cutworm larvae, and potential true armyworm outbreaks.
Rapid growth of weeds such as garlic mustard, giant ragweed, and leafy spurge (a noxious weed in Wisconsin) also merited control but the options were minimized due to the rains.
Leaf defoliation by alfalfa weevil larvae hit 40 to 90 percent in a few fields in Lafayette, Grant, and Rock counties as sweep net catches reached a high of 87 larvae per 50 sweeps.
Taking the first cutting of alfalfa, which is rapidly approaching in those counties, is considered the most effective and lowest cost way to control the weevil.
North of the southern three tiers of counties, however, the net sweep totals remained below 10 after 50 sweeps.
Pea aphid populations exploded with counts of up to 99 in southwest counties and 221 in west central counties per 50 sweeps while in the east central area the top count was 22. Alfalfa plant bugs were being found in the southern half of Wisconsin with counts of up to 17 on 50 sweeps.
Potato leafhopper migrations appeared to be limited to the southern two tiers of counties with populations being found in all of the fields that were checked in Grant, Lafayette, Rock, and Jefferson counties.
Of the 67 alfalfa fields checked, including many north of the Wisconsin River and in east central counties, 11 had leafhoppers with counts of up to 16 per 50 sweeps.
An acceleration of migrating black cutworm moth flights was documented with the catch of 369 moths during the reporting week for a year's total of 1,406 at 31 sites.
The Pest Bulletin recommends scouting of corn fields by 10 to 14 days after emergence until the V-5 growth stage and calculated a May 15 start date for likely damage - a threat amplified by the recent rains because the insect thrives in poorly drained, low lying, weedy, and minimum tillage fields which are adjacent to natural vegetation.
What the Pest Bulletin described as "another significant flight" of true armyworm moths was recorded at Janesville with the catch of 76 moths from April 26 to May 1. This represents a possible threat to small grains and corn in the upcoming month.
Among vegetable crop pests, the Pest Bulletin again referred to the imported cabbageworm, whose larvae can be controlled with Bt insecticide once the degree day temperature accumulation reaches 300 (base of 50).
Moths of the variegated cutworm, whose brown larvae feed on potatoes and tomatoes during the night, were caught at Mazomanie and Janesville in late April.
For fruit trees, the week's list of concerns from moth flights to larvae feeding included the plum curculio, oblique banded leafroller, codling moth, redband leafroller, spotted tentiform leafminer, and plant bugs.
Landowners with garlic mustard infestations were asked to pull, cut, spray, or burn those plants with the additional request that any already having pods not be composted. Leafy spurge, which has already begun to flower, can quickly degrade pastures and is difficult to control, requiring several herbicide treatments, the Pest Bulletin noted.
The Pest Bulletin also gives weekly updates for forestry and nursery concerns along with degree day accumulations for dozens of locations in the state. The entire report and archives are available at http://datcpservices.wisconsin.gov/pb/pests.jsp.