Volume 65 Number 14 Date 08/06/2020
CORN ROOTWORM - Beetle counts are mostly low or moderate for early August. Surveys in 61 grain corn fields in the southern, west-central and northwest areas found no detectable beetle population at 29 (46%) of sites. Twenty-one fields (34%) contained low adult rootworm populations ranging from 0.1-0.7 beetles per plant, while 12 (20%) of the sites had above-threshold averages of 0.75 or more beetles per plant. An exceptional field in Marathon County had an extremely high average of 5.6 beetles per plant. The official 2020 corn rootworm survey is now underway and will continue during the next two weeks.
LILY LEAF BEETLE - Vilas County has been added to the list of Wisconsin counties with confirmed populations of the invasive lily leaf beetle. According to an inspector's report, the beetles were observed on Asiatic lilies near Eagle River on July 30. Lily leaf beetle was also recently detected in Brown, Calumet, Clark, Milwaukee, Outagamie, Vernon, Waukesha, and Waupaca counties, for a total of nine new county records this season. The addition of Vilas County brings the total number of infested Wisconsin counties to 21.
SOYBEAN APHID - Densities remain generally low. Although a few soybean fields have developed populations of 50-150 aphids per plant since late July, most fields have average counts below 20 per plant. Final aphid treatments, if required, must be applied before the R5.5 (mid-seed) growth stage to provide any economic benefit.
WESTERN BEAN CUTWORM - Trap counts have begun to decline at southern and central monitoring locations, signaling the end of the moth flight period. A total of 776 moths were captured July 30-August 5, compared to 1,589 the week before. The cumulative state count is now 3,455 moths in 58 traps, or an average of 60 per trap. Results of the 2020 trapping survey are summarized in the map in the CORN section.
EUROPEAN CORN BORER - Summer moth emergence has peaked across the southern half of the state. Larval development is variable at this time, with 1st to 4th-instar caterpillars observed in the past week. Controls directed against second-generation larvae must be applied during the period after egg hatch and before the caterpillars bore into corn stalks and ears, prior to the accumulation of 2,100 degree days (modified base 50°F). The treatment window for second-generation larvae will close by August 20 in southern Wisconsin.
CORN EARWORM - A significant flight of 78 moths was registered at Arlington in Columbia County, while 12 other monitoring sites captured fewer than 10 moths for the week ending August 6. Pheromone traps have captured a cumulative total of 618 moths since migrants began arriving in July. Although the corn earworm flights recorded over the last four weeks have not been especially large (with the exception of the Arlington flights), fresh-market sweet corn growers should continue to monitor silking sweet corn fields and follow CEW flight reports through early September.
-- Krista Hamilton, DATCP Entomologist