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Corn
Volume 63 Number 16 Date 08/23/2018 CORN ROOTWORM - Surveys in the last two weeks have found generally low or moderate beetle populations, with district averages in the southern, central and northwest areas nearly equivalent to last season's counts. The preliminary state average of 0.3 beetle per plant is only slightly higher than the 0.2 survey average in in 2017. An average of 0.75 or more adult corn rootworms per plant in continuous corn indicates control in the form of crop rotation, using a Bt-rootworm hybrid, or applying a soil insecticide at planting should be considered to prevent root damage in 2019. Beetle populations exceeding this threshold have been recorded in only 16 (9%) of the 174 fields surveyed from August 7-22, represented by yellow circles on the map below. The annual survey will be finalized early next week. CORN EARWORM - The primary migration accelerated this week. Large flights of 101-348 moths per trap were reported from the Beaver Dam, Mayville, and Ripon monitoring locations. A total of 1,086 moths were captured in 15 pheromone traps this week, for a cumulative total of 1,936 moths to date. The Janesville black light trap also collected 65 moths. Sweet corn growers should continue to follow corn earworm migration reports and maintain treatments as long as moth activity persists and green silks are available for oviposition. Counts for the week ending August 23 were: Arlington 36, Beaver Dam 348, Coon Valley 14, Cottage Grove 44, Hancock 15, Janesville 23, Madison north 64, Marshfield 1, Mayville 273, Ripon 101, Sun Prairie 108, Watertown 58, and Wausau 2. JAPANESE BEETLE - Adults are still numerous on corn silks in later-planted fields. A heavy infestation was encountered this week in the Ettrick area of Trempealeau County. As many as 16 beetles per ear were feeding on the silks of edge row plants, though most ears were infested with 3-5 beetles. The infestations extended 10 rows into the field. Beetle emergence has peaked and much of the threat to the state's corn and soybean crops has passed, but scouting should continue in fields where pollination is incomplete and silk feeding remains a concern. Japanese beetle activity is expected to diminish by early September. WESTERN BEAN CUTWORM - Moth flights have ended at all pheromone trap monitoring locations. As of August 23, the state total is only 625 moths in 55 traps (11 per trap average), a marked decrease from the 1,856 moths in 70 traps (27 per trap average) collected last year and the second-lowest state cumulative count since western bean cutworm trapping surveys began in 2005 (after 2014). The highest individual count for the season was 78 moths near Durand in Pepin County. -- Krista Hamilton, DATCP Entomologist 
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