East central and central crops bearing the brunt of variegated cutworms
Field reports from more than a dozen Wisconsin counties indicate that crop damage from variegated cutworm larvae is extreme in some cases, according to the Department of Agriculture, Trade, and Consumer Protection's Wisconsin Pest Bulletin (WPB) for the third week of June.
In western Fond du Lac County, a soybean field near Ripon had what an observer described as "uncountable numbers" of larvae.
A four-acre soybean field near Loganville in Sauk County was "chewed down to the the stems." A picture submitted by an agricultural products company representative depicted a soybean field which resembled crop disappearance normally associated with flooding.
Nine of 42 alfalfa fields surveyed in the state's east central, central and northwest districts had variegated cutworm larvae infestations high enough to constitute economic damage to the crop, the WPB reported. These were in Fond du Lac, Winnebago, Green Lake, Manitowoc, Marathon, Barron, Clark and Grant counties.
Other counties in which infestations were noted during the reporting week were Adams, Columbia, Marquette, Sauk, Waupaca and Waushara.
Yellow-striped armyworm caterpillars were found in localized populations in Dane, Dunn, Eau Claire, Grant, Lafayette, Rock, Sauk, Vernon and Waushara counties during the latest two reporting weeks.
The WPB pointed out that a combination of the armyworm and variegated cutworm larvae could push infestation rates over the economic threshold for losses.
Potato leafhopper populations of 2-3.5 per net sweep - above economic threshold for crop losses - were tabulated in Chippewa, Polk, Waupaca and Waushara counties.
The WPB also reminded apple growers to check for leafhopper infestations on their non-bearing and one- and two-year-old trees, for which the tolerance is no more than one insect per leaf.
Western corn rootworms were reported to be hatching in Vernon County.
The WPB expects fairly high emergence of the beetles in many areas during the next two to three weeks.
Flights of the western bean cutworm moths began during the reporting week with catches of up to 17 moths in traps in Adams, Brown, Columbia, Jackson, Juneau, Rock, Waushara and Wood counties.
Crop scouts were advised to check for eggs and larvae on the flag leaf of corn plants.
No European corn borer larvae were found in 74 percent of the corn fields surveyed in Chippewa, Dunn, Eau Claire, Pepin, Pierce, Polk, and St. Croix counties. Fields with a population had infestation rates of one to 14 percent as the development of the insect is two to three weeks ahead of normal, the WPB observed.
The zebra caterpillar, which is a pest that seldom appears in Wisconsin, nonetheless was found this month in corn near Coleman in Marinette County. The WPB notes that the caterpillar, which has long black-and-yellow stripes, is also a potential threat to vegetables, other broadleaf plants, flowers and ornamentals.
Jagged leaves are a sign of its presence.
Japanese beetles have emerged in Rock, Racine and Dane counties, the WPB stated. It warned that property owners as far northwest as Barron County and as far northeast as Oconto County can expect damage to fruit trees, perennials, field crops and nursery stock for as much as two months.
Soil-applied insecticide treatments should already have been completed in areas where there are known to be Japanese beetle populations, the WPB advised. It noted that three to four weeks are needed for the active ingredient to be translocated before the beetles start feeding.
Apple orchard owners were advised that maggot flies were caught in traps at Mequon and Rosendale and that up to 500 spotted tentiform leafminer moths were caught in eight of 28 traps. Economic threshold tolerances are one per leaf for the leafminer and 7.5 per leaf for the European red mite.
Among vegetable pests, the WPB noted that squash vine borer larvae have hatched and that striped cucumber beetles and flea beetles are active.
Tomato growers were advised to check for hornworms and to physically remove them.
After an initial observation by an arborist, the presence of emerald ash borers has been verified in the village of Mukwonago in Waukesha County. This increases the list to 11 counties in Wisconsin which have an infestation of the pest that is a serious threat to native ash tree species.