The verified return of Monarch butterflies to Columbia, Grant, Green, and Monroe counties during the early days of June was heralded in the latest edition of the Wisconsin Pest Bulletin (WPB) that is issued weekly by the Department of Agriculture, Trade, and Consumer Protection (DATCP). A report by a gardener indicated the presence of a Monarch butterfly in northeast Fond du Lac County on June 6.
DATCP entomologist and WPB coordinator Krista Hamilton observed that the return of Monarchs to Wisconsin and other northern locations was in doubt because the number of the butterflies returning to their winter hibernating mountainside forest in Mexico was the lowest total ever documented. The entire hibernating population during the past winter occupied only 1.6 acres of forest — a 44 percent decrease from the previous winter, she noted.
Hamilton pointed out that farmers in Wisconsin and elsewhere can contribute to population recovery of the Monarchs and other pollinating insects by limiting or eliminating the application of herbicides on the milkweed growing on their property and by supporting the restoration of milkweed plants. Conservation of milkweeds on agricultural property is more important than ever because of the perils to Monarchs during their migration and the risk that they might disappear entirely, she commented.
In the weekly update on insects that are not so welcome, the WPB noted that the window of vulnerability of young corn plants to cutting by black cutworm larvae is likely to extend to late June this year. It urged crop consultants and corn growers to inspect their fields until the plants reach their five-leaf stage and advised an insecticide treatment if there is damage to least 3 percent of the corn plants.
Flights of European corn borer moths were expected to peak this week in the southern part of the state, in central and southeast Wisconsin by June 21, and in the north during the latter days of the month. The WPB pointed out that eggs can be laid on potatoes, peppers, snap beans, and lima beans if the moths do not find corn that is at least 18 inches tall.
The WPB predicted that stalk borer larvae were likely to be moving into corn from grassy areas by next week. The tracking of true armyworm moths has detected very few flights so far, it added.
With the delays in cutting alfalfa because of heavy rains and water-logged fields in many areas, the odds for severe damage from the third and fourth instar stage alfalfa weevils have increased greatly, the WPB warned. If at all possible, the first crop should be cut as soon as possible in order to avoid the need for applying an insecticide, it suggested.
Pea aphids have been moving alfalfa fields to stands of peas or other vegetables, according to the weekly survey of 40 fields. Potato leafhopper populations were reported to be very low so far this year.
Of more concern, though for strawberries, apples, and other fruits, is the recent increase of plant bugs in alfalfa stands, the WPB indicated.
During visits in La Crosse, Trempealeau, and Monroe, WPB representatives found no evidence of soybean aphid colonization but bean leaf beetles were found on 2-5 percent of the plants.
Numerous pests are in various stages of activity in apple and other fruit orchards. These include plu curculio beetles in southern and central areas, the first of the year's two flights by the oblique banded leafroller, severe damage by an unknown leafroller in a north central apple orchard, and a soon expected flight by spotted tentiform leafminer moths.
Codling moth emergence accelerated in late May and early June. The WPB suggested that the biofix was set at most locations, thereby indicating the ideal time for treatment.
Among vegetable crop pests, the WPB mentioned the start of egg laying by Colorado potato beetles, the detection of first generation of onion maggot flies near Appleton, Eau Claire, Fond du Lac, and Hancock, the likely appearance soon by the striped cucumber beetle for which the tolerance is 4-5 per 50 plants, and the surprise discovery of red turnip beetles in Waushara County.