Volume 65 Number 17 Date 08/27/2020
NOTE TO READERS: This is the last scheduled weekly issue of the Wisconsin Pest Bulletin for 2020. Our end-of-season summary Bulletin will be published on November 12, 2020.
CORN ROOTWORM - Beetle counts in southern and western Wisconsin increased substantially from the historic low levels of 2017-2019.This month's corn rootworm survey found higher populations in seven of the nine crop districts compared to last year, and a state average count of 0.6 beetle per plant, which represents a two-fold increase from the low average of 0.3 per plant in 2019. Approximately 27% of the corn sites sampled in August had above-threshold beetle pressure (>0.75 per plant). Corn producers and crop advisors are reminded that beetle populations must be evaluated by early September to inform next year's rootworm management decisions and planting rotation.
FALL PESTS - Nuisance insects such as boxelder bugs, brown marmorated stink bugs, and multicolored Asian lady beetles will begin aggregating on warm southern and western exposures of buildings next month, in advance of their indoor invasion. Although exterior insecticide treatments may temporarily deter these insects from entering homes, non-chemical exclusion measures such as sealing cracks around windows, doors, siding and other openings are preferred. Fall nuisance insects do not reproduce inside the home or cause structural damage. Insecticides should only be considered for severe infestations, and any treatments must be applied by a licensed pest control technician.
CORN EARWORM - Locally heavy flights were reported from the Arlington (184 moths), Beaver Dam (153 moths), Mayville (115), and Ripon (81 moths) monitoring locations, while eight other sites from Grant to Marathon counties collected no more than 40 moths per trap in the past week. A cumulative total of 1,650 moths have been captured in 18 pheromone traps as of August 26. Egg laying is likely to intensify with this late-season migration and the risk of damage to sweet corn will persist into September.
BROWN MARMORATED STINK BUG - This invasive pest has been collected on orchard survey traps in Chippewa, Dane, Fond du Lac, Racine, and Walworth counties in July and August. Similar to the multicolored Asian lady beetle and boxelder bug, BMSB aggregates on the exteriors of buildings in autumn and overwinters in homes and other structures. Densities in southern and eastern Wisconsin are high enough that BMSB swarming is expected this fall.
WESTERN BEAN CUTWORM - The annual trapping program from June-August captured a cumulative total of 3,783 moths in 58 traps, or 65 per trap. This is the second highest average in 16 years of surveys, following the record of 79 moths per trap set in 2010. This season's relatively large flight has produced damaging larval populations scattered through the central and west-central areas of the state this month.
LATE BLIGHT - A second report of late blight was confirmed by the UW on August 20, on tomato in Pierce County. The season's first case was diagnosed in an Adams County potato field on August 10. Potato and tomato growers in counties surrounding the recent late blight detections are advised to continue routine scouting through harvest for disease symptoms, including leaf, stem, and fruit lesions that have a water-soaked appearance. Removal and destruction of infected plants is required if lesions are noticed. Composting will not kill the pathogen and is not recommended.
-- Krista Hamilton, DATCP Entomologist