As the corn that Wisconsin farmers were able to plant in May begins to emerge, black cutworm larvae are ready to start feeding on it and cut the seedlings, the early June issue of the weekly Wisconsin Pest Bulletin (WPB) reminded growers.
Surveys during the reporting period in Columbia, Green Lake, Marquette, Waupaca, and Waushara counties found damage from the pest in some fields, topped by a 23-percent infestation in one Marquette County field.
The WPB advised growers and crop consultants to watch for signs of feeding until corn reaches the V-4 stage and noted that damage to three percent of the young plants is the threshold for economic losses.
A corn pest that attacks much later in the season is the Western bean cutworm, for which pheromone traps for catching moths will be set out during the next two weeks.
Anyone still wishing to take part in the trapping network should send an e-mail to email@example.com immediately.
Although populations of the insect have been greatly reduced, the remaining European corn borer moths have begun their egg laying, the WPB pointed out.
It observed that crops such as potatoes, snap beans, peppers, and lima beans are likely to be more vulnerable to the corn borer this year because very little corn in the state has reached the minimum 18-inch height, which the moths prefer for laying eggs.
Corn in the state is also not anywhere near the stage for damage from earworms, but the moths that lay the eggs arrived on southerly winds in late May and early June, the WPB reported.
Sixty-nine moths were caught in traps in southern Wisconsin from May 30-June 5.
The WPB suggested that the migrating first generation corn earworm moths are likely to lay eggs on other host plants instead.
It added that the cool and wet conditions that prevailed into the early part of June have not been favorable for the development of corn rootworm larvae.
Given the continued documentation of moth flights, some concern remains for localized outbreaks of true armyworm larvae on small grains and corn, the WPB indicated.
It noted that the edges of fields and crops adjacent to grassy weeds are the most vulnerable.
On June 4, the first soybean aphids of the season were detected on plants at the West Madison Agricultural Research Station.
The WPB commented that the population was surprisingly high for so early in the season - aphids on 13 of the 100 plants that were checked with a high of 17 on one plant. It suggested that the insect probably overwintered on buckthorn plants in the area.
Populations of alfalfa weevils were still high but harvest time had arrived in the areas where the damage from infestations was the highest, the WPB stated.
It cited defoliation rates of 40-80 percent in a few fields in northeast Jefferson and southeast Dodge counties.
Potato leafhoppers, pea aphids, and plant bugs were also being caught in the net sweeps in alfalfa fields but not in numbers causing any immediate concern.
A few grass sawflies were also showing up in the nets but they are not a threat to alfalfa, the WPB pointed out.
Regarding other crop pests, the WPB noted that egg laying by Colorado potato beetles is well underway, and carrying of the pathogen by only 10 percent of striped cucumber beetles can cause bacterial wilt in vined plants.
In addition, flies of the onion maggot were active in northern Wisconsin, and imported cabbageworm larvae have appeared.