Alan Sundermeier, Extension Agriculture and Natural Resources Agent
Bruce Eisley, Integrated Pest Management Research Associate
To evaluate corn response to soil rootworm insecticides in a field following soybeans.
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A randomized, complete design used four replications of three treatments. The design was duplicated at two fields about one mile apart with the same cropping history. The treatments included a check with no insecticide, corn seed encapsulated with Force insecticide, and liquid Regent insecticide applied in furrow at planting. Individual plots were 15 feet wide and 300 feet long.
On July 20, 2000, corn roots were evaluated for rootworm damage. For each treatment, five root masses were dug, washed, and inspected for rootworm damage. The Iowa scale of 1 = no damage to 3 = economic impact to 5 = severe root pruning was used.
Corn stalk population counts were taken near harvest time. Results reported are the combination of both fields and represent eight replications of each treatment.
| Treatments | Root Damage Index |
Harvest Population (plants/A) |
Yield (bu/A) |
| No insecticide | 1.73 b | 28,000 b | 168.5 a |
| Force | 1.40 a | 26,500 a | 169.9 ab |
| Regent | 1.42 ab | 28,750 b | 174.2 b |
| LSD (0.05) | 0.28 | 998 | 4.8 |
| Means followed by the same letter are not significantly different. | |||
These fields were selected because of a history of rootworm damage on past corn crops. Economic thresholds for root damage were not reached in the control treatment. This may have been due to above-average rainfall during the growing season that possibly reduced rootworm larvae numbers.
The Regent insecticide treatment had significantly better corn yield compared to no insecticide. However, the application of Regent would not have increased net return based upon the yields compared to no insecticide.
For additional information, contact:
Alan Sundermeier
Ohio State University Extension, Henry County
104 E. Washington St., Suite 107
Napoleon, OH 43545
419-592-0806
sundermeier.5@osu.edu