Date: 3/30/99

Time: 2:40

Type: Symposium

Number: 152

Challenges of northern and western corn rootworm areawide management in South Dakota

*L.D. Chandler, D. Hartman and W. Riedell, USDA-ARS, Brookings, SD 57006
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In support of the nationwide Corn Rootworm Areawide Management Program a 16 mile2 site in eastern Brookings County, South Dakota was organized into an areawide management unit in 1997. Northern (Diabrotica barberi Smith and Lawrence) (NCR) and western (D. virgifera virgifera LeConte) (WCR) corn rootworms equally infest corn within the area. High percentages of extended diapause NCR individuals exist and create interesting challenges for corn/soybean rotations and the areawide management concept. Rootworm egg samples taken after the1997 season showed that NCR egg numbers were higher than WCR egg numbers in all but one corn field. NCR egg numbers exceeded a 10/liter of soil threshold in 9 fields treated in 1997 with the insecticide-bait, SLAM. Sixty-nine corn fields (49 first year, 16 continuous, and 4 mixed fields) were monitored within the management area in 1998. Root damage ratings were taken from 23 of these fields. Three first year corn fields had increased root damage attributed to NCR. Continuous corn generally had smaller root systems and higher feeding damage caused by NCR and WCR larvae. SLAM was applied to 25 corn fields (7 continuous, 16 first year, and 2 mixed fields) within the area during 1998. Applications were triggered when beetle counts on yellow sticky traps exceeded treatment thresholds, and significantly reduced corn rootworm adult numbers. However, as indicated by egg populations and root damage ratings following the 1997 season, SLAM may not be as effective against NCR as with WCR. Continued evaluation of SLAM and the areawide management concept will be conducted in 1999.

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