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Corn
Volume 61 Number 18 Date 09/01/2016


CORN ROOTWORM - Review of annual beetle survey data shows that populations decreased from 2015 levels across southern, central and east-central Wisconsin, while beetle counts in the west-central and northern counties were markedly higher. Averages declined in five of the nine crop districts and increased in four. The largest decreases were found in the south-central and southeast districts where averages fell sharply from 0.8 to 0.4 beetles per plant and from 0.7 to 0.2 beetles per plant, respectively. Beetle counts were also lower in the southwest, central and east-central areas. By contrast, the survey found significantly higher averages in west-central and northern Wisconsin, particularly in the northeast where the district count more than tripled from 0.2 to 0.7 beetles per plant. The 2016 state average of 0.5 beetles per plant compares to 0.6 per plant in 2015.

Results of the survey suggest a greater threat of larval rootworm damage to non-Bt continuous corn in the northern and west-central counties next season, while beetle pressure may be lower across the southern, central and east-central areas.

WESTERN BEAN CUTWORM - Larval populations returned to moderate levels in 2016 after a three-year low. Surveys in August found larvae in about 15% of the 229 cornfields sampled, with moderate to heavy infestations in Chippewa, Dunn, Eau Claire, Green Lake, Juneau and Marquette counties. Larvae are in the late instars and should enter the pre-pupal overwintering stage by early September.

EUROPEAN CORN BORER - The 75th annual fall corn borer survey is now underway. Second-generation larvae have been detected at low levels in 15 of the 73 fields (21%) examined as of August 31. Counts in the infested fields were low overall, although two sites in the Holmen and Centerville areas of La Crosse and Trempealeau counties had exceptionally high averages of 1.8-1.9 larvae per plant and 2-3 borers per ear. The increase in conventional corn acreage due to lower commodity prices could provide more ECB habitat and favor larval populations this fall. Evaluating non-traited and traited corn for ECB larvae and damage is recommended before harvest.

-- Krista Hamilton, DATCP Entomologist