CORN ROOTWORM - Beetles continue to emerge across the state. Surveys in the south-central and southwest areas found average counts of 0-1.5 per plant in Jackson, La Crosse and Monroe counties. Corn with fresh silks should be inspected at this time to determine if pollination is being impaired. A threshold of five or more beetles per plant has been established for fields where the silks have been clipped to less than ½ inch and pollination is incomplete. Peak beetle emergence remains approximately two weeks away.
WESTERN BEAN CUTWORM - The annual flight has produced low numbers of moths at most black light and pheromone trap locations, with the exception of 112 moths at Sparta in Monroe County. According to the degree day model for this insect, 50-75% of the adult population has emerged in the south-central, southwestern and west-central counties, 25% has emerged in the southeast and east-central counties, and emergence is just beginning in the northern areas. The DATCP network of 100 pheromone traps registered 173 moths from July 24-30, compared to 93 moths during the previous week. The state cumulative count thus far is only 320 moths. The map below summarizes the preliminary results of the western bean cutworm trapping survey as of July 30.
CORN LEAF APHID - Light infestations of 10-30 aphids per plant were noted in Jackson and Monroe counties on July 29. Pressure of 50 or more aphids per plant on 50% of the plants can interfere with pollination and may require treatment.
EUROPEAN CORN BORER - Surveys this week found no significant larval infestations. Fifth-instar larvae, pupae and new moths were the predominant developmental stages in the south-central, southwest and west-central areas. The treatment window for the second generation has opened near Beloit, Madison, La Crosse and other locations where 1,550 degree days (modified base 50°F) have accumulated, and will stay open until 2,100 degree days are surpassed.
Krista Hamilton, DATCP Entomologist
CORN EARWORM - Moth counts remained low during the week of July 24-30, with pheromone traps in Green Lake, Janesville, Mazomanie, Oak Grove, and Ripon registering minor flights of 1-19 moths. A pheromone trap capture of 10 moths in two consecutive nights indicates the need for protective treatment of sweet corn fields with green silks. Counts this week were as follows: Coon Valley 0, Cottage Grove 1, East Troy 0, Green Lake 10, Janesville 1, Madison 0, Marshfield 0, Mazomanie 1, Oak Grove 19, Ripon 8, Sun Prairie 0, and Watertown 0.
Tracy Schilder, DATCP Plant Pest & Disease Specialist
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