Variegated cutworm infestations noted across state
Although it was rarely if ever mentioned in reports about pests infesting Wisconsin’s field and garden crops in previous years, the variegated cutworm has rapidly established a damaging presence through at least the northern three-fourths of the state this year.
This is according to the Department of Agriculture, Trade, and Consumer Protection’s Wisconsin’s Pest Bulletin (WBP) covering the second week of June.
Initial reports about the variegated cutworm suggested its larvae would be found mainly in the northern half of the state after egg masses laid on the sides of buildings hatched this spring.
Since then, however, reports of damage have come from as far south as Dane and Grant counties.
Among the particular infestations cited in the latest WPB were larvae more than one-inch long at populations of two to five per 100 corn plants in Marquette County, larvae on soybeans in Fond du Lac County, and larvae on alfalfa in Manitowoc, Waushara, and Waupaca counties.
Other counties that had variegated cutworm caterpillars feeding on alfalfa, potatoes, or soybeans included Adams and Rusk.
WPB entomologist Krista Hamilton advises an insecticide treatment if cutworm populations reach two per square foot in alfalfa. For soybeans, the economic threshold for damage is about 40 percent leaf defoliation, she adds.
With the onset of periods of hot and dry weather (before the rains last weekend), second and third crop alfalfa was becoming vulnerable to damage from population increases of the potato leafhopper, the WPB pointed out.
It listed upper tolerances of one leafhopper per net sweep for 8 to 11-inch alfalfa and two per sweep at 12 or more inches — numbers that were topped in some fields in Juneau, Richland, and Sauk counties during the second week of June.
A report from the University of Illinois Extension Service about the very early appearance of western corn rootworm beetles and the subsequent damage to corn roots is raising concerns.
That concern is due to the suspected but not yet confirmed failure of resistance to the pest by the Bt corn with the Cry3Bb1 protein, the WPB indicated. It advised Wisconsin corn growers to expect those beetles to appear here shortly and to monitor for failures of the Bt protein.
Among other corn pests, light to moderate infestations of European corn borers were found in six of the 38 fields checked during the WPB’s reporting week and stalk borer damage ranging up to 6 to 11 percent was found in the outside rows of fields in Grant, Sauk, Juneau, and Richland counties.
In addition, corn earworm moths were being caught in traps at Ripon, Prairie du Chien, and Janesville, and the western bean cutworm moth trapping season has begun with the first pheromone trap catch of two moths occurring at Ripon.
Small colonies of soybean aphids were located in fields surveyed in Columbia, Dane, La Crosse, Manitowoc, Marquette, and Sheboygan counties but not nearly at the numbers that would create concerns about damage.
However, defoliations by bean leaf beetles were calculated at 5, 15, 25, and 50 percent (40 percent is considered as the tolerance limit) in some fields although very few beetles were being found.
Soybean growers were also advised to undertake control measures if their fields have giant ragweeds or volunteer corn. Weed scientist Clarissa Hammond warned that failure to control those species will result in yield losses.
The emergence of the first Japanese beetles was anticipated by the end of June. The WPB warned that damage to fruits, perennials, field crops, and nursery stock was likely at least through July.
Hot and dry weather was setting the stage for onion thrips to cause damage on onions, cauliflower, and cabbage and possibly on snap beans, melons, cucumbers, and tomatoes, the WPB stated.
It indicated tolerance limits of 25 thrips per plant on onions and up to 45 on the other cultivars.
Damage from cabbage loopers was observed in southeast Wisconsin and Colorado potato beetles were well into their damaging larvae stage. The WPB also indicated that the tolerance for the striped cucumber beetle is 5 per 50 plants.
Apple orchard owners were informed that the large numbers were detected for the second flight of the codling moth
in eastern and southern areas. Oblique banded leaf roller populations were high while red-banded roller populations are low.
In addition, catches of spotted tentiform leaf miner moths in pheromone traps were high, and the first apple maggot fly of the season was caught on a yellow sticky trap at Mineral Point — three weeks earlier than in 2011.
Recommendations for spraying those orchard pests are to do so for the maggot flies when the catch is one per week on an unbaited sticky trap or five flies per week on a baited trap.
For the tentiform leaf miner, spraying is advised if the infestation is at least one per leaf.