If Wisconsin's farmers didn't already have enough trouble with their alfalfa crop this spring, the latest update by the Wisconsin Pest Bulletin (WPB) doesn't offer any help.
In southwestern counties such as Green and Lafayette, between 279 and 650 alfalfa weevil larvae were being caught per 100 net sweeps in some fields, the WPB reported. Alfalfa plant defoliation between 60 and 100 percent was being calculated in those fields.
The WPB noted that most fields north of Dane County still had larvae catches of less than 20 per 100 sweeps and defoliation was below the 40 percent economic threshold at the end of the reporting period of May 23.
Alfalfa growers should apply an insecticide treatment at 40 percent defoliation if the field is not going to be harvested within the following 7-10 days, the WPB advised.
Some pea aphids and tarnished plant bugs are being found in the alfalfa field net sweeps but they are not a threat to the crop, the WPB indicated.
It added, however, that tarnished plant bugs present a threat to strawberries and growers should consider a treatment if catches exceed four per 20 net sweeps.
Low numbers of migrating potato leafhoppers were collected in 15 of the 35 alfalfa fields sampled during the reporting week. They were found as far north as Jackson County, confirming that a distinct arrival episode of the migrating pest has occurred, the WPB noted.
No major flights of true armyworm moths have been detected. The WPB pointed out, however, that eggs have been laid on grassy vegetation and that some localized outbreaks of larvae infestations are possible.
The spring flight of European corn borer moths was documented with the catch of 17 moths at a Prairie du Chien monitoring station on May 20.
Because of anticipated low populations, the WPB suggested that most concerns about corn borer infestations should be directed to conventional corn hybrids and non-Bt refuge acres.
Of greater concern with corn was the probable start of damage from black cutworm larvae by May 28 in southern Wisconsin, the WPB stated. This is not expected until the first week of June in central and northern areas but routine scouting of corn until its four-leaf stage is recommended.
Because of the major delay in the planting season for the crop, soybeans were not mentioned until the fourth issue of the weekly WPB. The first report indicated that bean leaf beetles were found on May 15 in early-planted soybeans in Richland County.
Colorado potato beetles had begun to lay eggs on potato plants in the Central Sands region. The WPB pointed out that egg laying usually continues for two-four weeks.
A variety of threats continue for fruit orchard owners as they hope for a return to a very productive season.
The WPB cited the first sustained captures of codling moths on May 19-21 at apple orchards in Racine, Kenosha, Grant, Green, and Fond du Lac counties. It urges daily monitoring in central and northern areas through at least next week.
Larvae of the oblique banded leafroller were found at Dodgeville. With the flight of the spotted tentiform leafminers having been completed, growers are advised to check under the tree leaves for miners with one per 10 leaves being the economic threshold for crop damage.
Imported cabbageworm larvae were being found in the southern half of Wisconsin by May 23. The economic threshold for damage is 20-30 percent infestation.