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Corn
Volume 60 Number 19 Date 08/27/2015 CORN ROOTWORM - Below are two maps summarizing the early findings of the 2015 corn rootworm beetle survey, completed in four of the state's nine crop reporting districts. Surveys thus far have found a marked increase in beetle counts in the south-central and north-central areas as compared to 2014, while populations in the southwest and northeast districts are comparable to last season's averages. The preliminary state average of 0.6 beetle per plant is an increase from the 2014 average of 0.4 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 2016. Beetle populations exceeding this threshold have to date been recorded in 34 of the 140 (24%) fields surveyed as of August 26. EUROPEAN CORN BORER - The second flight of moths continued at very low levels this week. Surveys show that larvae range in development from second- to fifth-instar in the central, west-central and northwest districts, as far north as Chippewa County. Larval infestations affecting 2-24% of corn plants were found in 10% of fields checked from August 20-26. Nearly all of the older, fourth and fifth-instar larvae present by late August will enter diapause and will not pupate until next spring. -- Krista Hamilton, DATCP Entomologist CORN WILT DISEASES - Corn leaf samples from seed corn production fields were tested at the Plant Industry Laboratory for the bacterial diseases Goss's wilt and Stewart's wilt. Goss's wilt was confirmed in 15 of 39 samples from Adams, Dane, Eau Claire and Rock counties, for a 38% positive rate. This represents a marked increase from 2014 when only 9% of samples tested positive. Results for Stewart's wilt were negative for the fifth consecutive year. Northern corn leaf blight and common rust were the most prevalent diseases observed in the fields inspected this season. -- Anette Phibbs, DATCP Plant Pathologist 
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