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Corn
Volume 56 Number 20 Date 11/17/2011 CORN ROOTWORM - Results from the August beetle survey showed a marked population increase in the southern and central districts. The state average beetle count of 0.7 per plant represents a more than two-fold increase over the historic low average of 0.3 per plant documented last year. The largest increase occurred in the south-central district where the average escalated sharply from 0.3 to 1.4 beetles per plant. Population increases were also noted in the southwest, southeast, west-central, central, east-central and northeast districts. By contrast, beetle counts in the northwest and northeast areas were extremely low at 0.1 per plant. The survey findings suggest that southern and central Wisconsin corn producers will need to consider crop rotation or another form of rootworm management next year. BLACK CUTWORM - Migrants were detected in the state by April 6 and an initial cutting date of May 30 was anticipated based on an April 11 biofix. The spring trapping survey registered 2,090 moths in 30 traps from April 1-June 1, with a peak occurring from May 5-9. Subsequent waves of migrants arrived from May 12-16 and May 21-23. As previously mentioned, localized infestations developed in corn by early June as a result of the large migration and various environmental factors. Summarized below are the spring 2011 moth counts. EUROPEAN CORN BORER - Larval populations remained historically low in 2011. The seventieth annual fall abundance survey in September revealed a state average of 0.09 borer per plant, the fourth lowest since record-keeping began in 1942. Minor population reductions from 2010 were charted in the southwest, central and northeast agricultural districts and increases occurred in the south-central, southeast, west-central, east-central, north-central and northwest areas. Larval densities in the south-central district increased to 0.20 per plant, or 20 larvae per 100 plants. On the basis of the fall survey results, a continued low population trend is expected for 2012. CORN EAR DROP - Low to moderate rates of ear drop were documented in scattered corn fields this fall. The statewide average incidence was less than 4% and severity was 10%, but individual fields had severity levels as high as 28%. European corn borer shank tunneling appears to have been the leading cause, although drought stress in August accounted for much of the ear drop observed in south-central Wisconsin corn fields. WESTERN BEAN CUTWORM - The seventh annual trapping survey registered a 55% reduction in moth counts in the state. The 2011 cumulative capture was 4,895 moths, compared to 10,807 moths in 2010. Larval infestations were observed or reported in Adams, Chippewa, Clark, Door, Dunn, Eau Claire, Green Lake, Jackson, Marquette, Waupaca and Waushara counties in August and September, but damage to corn was far less common this season. --Krista Hamilton, DATCP Entomologist CORN WILT DISEASES - The Plant Industry Laboratory tested 58 corn leaf samples from 271 seed plot acres for bacterial diseases of export significance. Goss's wilt infected 20 samples (34%) from fields in Columbia, Dane, Eau Claire, La Crosse and Rock counties. Results for Stewart's wilt were negative. Goss's wilt, a disease historically limited to the Great Plains, continues to spread across the Midwest. This is the second consecutive year that Goss's wilt was prevalent in Wisconsin seed corn fields. --Anette Phibbs, DATCP Plant Industry Laboratory 
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