Invasions by unfamiliar insect species highlighted in state's latest Pest Bulletin

This year's weekly editions of the Wisconsin Department of Agriculture, Trade, and Consumer Protection's Pest Bulletin continue to mention insects which seldom gain attention of entomologists or other observers in the state.

Two more such insects were mentioned in the report covering the final week of May.

The Pest Bulletin reported that winter cutworm moths were being caught in black light traps in Dane, La Crosse, and Trempealeau counties.

The larvae of this insect, whose history of infestation in the state has been sporadic, can be a threat to ornamental plants and agricultural crops. Tracking of catches in traps will continue.

As if cherry growers aren't already facing enough problems with severe crop losses due to spring freezes, high numbers of cherry scallop shell moths were being caught in Wood County, according to a report by Extension Service entomologist Phil Pellitteri.

He notes that the larvae defoliate black and native cherry trees.

This insect is seldom found in Wisconsin but once it arrives, populations can remain for two to three years - until they are greatly reduced by a wasp, which is a parasite to the eggs, Pellitteri points out.

He says it is still uncertain on whether there will be a major larval outbreak in the central part of the state later this month as a result of the recent moth catches in Wood County.

The most fascinating and attention-getting appearance of a relatively unknown insect is the huge population of the variegated cutworm - the highest in at least 35 years, Pellitteri indicates.

Entomologists and other insect observers have identified it in most Wisconsin counties north of a line from Door to Eau Claire counties. Damage in gardens and farm fields by the larvae is possible by late June.

Emerald ash borer beetles were active in infested trees near West Bend by May - 12 to 14 days earlier than in 2011 and 2010, the Pest Bulletin stated.

To track the movement and infestation of this pest on ash trees, state agencies are placing 2,118 traps in 61 Wisconsin counties.

Owners of ash trees within 15 miles of a known infested area are being advised to check with an arborist about the possibility of treatments to protect those trees from the pest.

Although several types of treatment are available, the Pest Bulletin cautions that there is no guarantee on preventing or reversing an infestation by the pest, which was probably imported from China and was first detected in the Detroit area about a decade ago.



Familiar Pests Less Threatening

Among more familiar insects, the Pest Bulletin cited survey reports that indicated 2 to 10 percent defoliation in Monroe, La Crosse, Richland, and Vernon counties on leaves of the bean family plants that are vulnerable to the bean leaf beetle.

No soybean aphids were found anywhere in early surveys for the pest.

Whorl damage is expected soon in the most advanced corn fields from the larvae of the year's first generation of European corn borers.

The moth flights had already peaked in the southern part of the state before the end of May, meaning that leaf pinholes and shotholes should be evident within the coming days and weeks in much of the state.

Stalk borer migrations to corn from adjacent grassy areas are expected during the first part of June. The Pest Bulletin notes that damage to 10 percent of the plant is the economic threshold for crop losses.

Corn earworm moths were being captured at reporting period totals of 3 to 37 in traps at Janesville, Prairie du Chien, and Ripon.

The Pest Bulletin noted, however, that virtually no corn in the state is developed enough to be vulnerable to the earworm at the moment.

Field surveys on the true armyworm are finding damage to 1 to 12 percent of corn plants and scouting is suggested for several more weeks.

Colorado potato beetle eggs have been laid and eggs are hatching. The Pest Bulletin indicates that an insecticide treatment is justified if defoliation exceeds 20 to 30 percent on potato plants at heights of 6 to 8 inches.

Growers of pumpkins, squash, and other vine crops were advised to be on the alert for the squash vine borer, whose adult emergence period was expected to begin this week in the southern areas.

Control of eggs and very young larvae is necessary before the larvae bore into the vines, the Pest Bulletin explained.

Except for alfalfa weevil defoliation reaching 50 to 70 percent in a few growths of second crop in Richland and Green counties, there was nearly an all-clear on insects in alfalfa fields in late May.

Pea aphids fell victim to crop harvest and heavy rains in some areas, plant bug nymph numbers were low, and no economic loss populations of potato leafhoppers were noted.

In the weed control department, the Pest Bulletin called attention to wild parsnip (yellow flowers) growth along roadsides, suggested cutting, noted that removal is ideal, and warned anyone undertaking pulling of the parsnip to wear protective equipment because of the photo-toxic sap exuded by the weed.

Control of weeds in soybeans by 9 to 19 days after emergence was also recommended. The Pest Bulletin indicated that yield losses begin when competing weeds reach a height of 4 to 6 inches.