Across the corn belt depending on time of year | The 1970's study is valid today. It is all about insect biology.
If you protect the roots at the base of the plant, the rootworm away from the base of the plant have a food source, develop, prune roots and emerge in greater numbers than in fields where the roots are pruned at the base of the plants. Pruned roots die and the rootworms in the row starve to death.
These results were measured using emergence traps.
Insecticide at the base of the plant only kills rootworms at the base of the plant since insecticides applied in a 1" band does not move sideways, only down in a cone fashion. Most rootworm damage is root pruning away from the base of the plant causing water stress and reduced adsorption of those expensive fertilizer inputs.
Thus, the use of soil insecticide against rootworm only results in straight standing corn for harvest and does little to reduce rootworm more than 6" away from the plant base.
First year corn almost always out yields 2nd yr and continuous corn in the same field, particularly in dry years. Why? One of the major reasons is rootworm pruning roots outside of the "protected" area around the base of the plant when soil insecticides are used. When soil moisture is sufficient for quick root regeneration, the impact on yield is more muted. Corn for silage is extremely sensitive to rootworm feeding and yield losses because of the whole plant harvest. A 2-ton yield loss (which pays for the nematode application) equals a plant loss of less than 3 ozs per plant. Minor water stress reduces the plant size thus silage yields. When a corn plant is stressed, plant size is impacted as the plant channels all its energy toward grain production. Thus yield losses from rootworm to grain yields is more muted than silage yields.
Edited by Nematotode-guy 3/1/2026 09:35
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Biological Control of Rootworm - A link to a recent presentation
