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Corn
Volume 61 Number 17 Date 08/25/2016 CORN ROOTWORM - Below are two maps summarizing the findings of the 2016 corn rootworm beetle survey, completed earlier this week. Surveys found a marked increase in beetle counts in the west-central, northwest, north-central and northeast areas as compared to 2015, while populations in the southern, central and east-central districts were well below last season's averages. The state average of 0.5 beetle per plant is a decrease from the 2015 average of 0.6 per plant. 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 2017. Beetle populations exceeding this threshold were recorded in 51 (22%) of the 229 fields surveyed from August 1-24, represented by orange circles on the second map. EUROPEAN CORN BORER - Surveys show that larvae range in development from second- to fifth-instar in the central, west-central and northwest districts, as far north as Dunn County. Larval infestations affecting 2-52% of corn plants were found in 12% of fields checked. Nearly all of the older, fourth and fifth-instar larvae present by late August will enter diapause and will not pupate until next spring. CORN EARWORM - The primary migration accelerated this week. Locally heavy flights of 259-1,095 moths per trap were reported from the Arlington, Mayville and Ripon monitoring locations. A cumulative total of 3,507 moths have been captured in 17 pheromone traps since the late-season flight began in full from August 11-17. Sweet corn growers should continue to follow CEW migration reports and maintain treatments as long as moth activity persists and green silks are available for oviposition. Counts for the week ending August 24 were: Arlington 890, Beaver Dam 32, Hancock 0, Janesville22, Marshfield 0, Mayville 259, Pardeeville 89, Prairie du Chien 0 and Ripon 1,095. -- Krista Hamilton, DATCP Entomologist 
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