The most common methods of managing corn rootworms are to rotate crops or use a granular soil insecticide at planting. When using an insecticide, items such as performance, safety, environmental impact, and cost should be considered.
Although they are not commonly used, liquid insecticides (Furadan 4F, Dyfonate 4EC, and Lorsban 4E) are labeled for use against corn rootworm larvae. This article, however, will focus on Furadan 4F (carbofuran) because it is being marketed as a post-plant broadcast application to replace granular insecticides and questions have been raised about this approach to rootworm management.
Is Furadan 4F, applied as a broadcast application after planting, as effective as the best planting-time granules? To answer this question, university research data from 10 midwestern states (Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Missouri, Nebraska, South Dakota, and Wisconsin) compared the performance of Furadan 4F (broadcast or banded) after planting and Counter 15G (banded or in furrow) at planting. The measure of performance in all the tests was the amount of root protection that the insecticide provided compared with an untreated check.
The results showed that Furadan 4F broadcast after planting provided good root protection in 44 percent of the tests (8 of 18); Furadan 4F banded after planting, 90 percent (18 of 20 tests); and Counter 15G at planting, 100 percent (41 of 41 tests). These data suggest that a broadcast application of Furadan 4F does not provide root protection equal to these other two application methods.
An obvious question is, why did the post-plant broadcast application of Furadan 4F perform worse than the banded application? I think it is a matter of product concentration. In a broadcast application, the insecticide may be spread too thin to provide protection in the root zone where it is most needed and should be applied. I am not confident that the broadcast application is a superior method of controlling larvae and protecting roots.
Are there any special directions for use?
Several noteworthy considerations are on the Furadan 4F label that aren't on granular insecticide labels. First, the application period is narrowly defined and "should be timed to closely coincide with corn rootworm hatch, usually May 15 through June 15." Also, cultivation of the insecticide into the soil is recommended "unless rainfall is imminent." Root protection should be improved with cultivation into the soil, especially if no rainfall has occurred and application was made prior to June 5. If applied tank mixed with a herbicide, consult the herbicide label for cultivation restrictions.
What about safety?
Furadan 4F is much more toxic orally than dermally. Dermal toxicity is similar to many granular insecticides. Standard protective clothing should be worn when handling any insecticide and that includes wearing a respirator when spraying Furadan 4F; or riding in a tractor or sprayer that has an environmental cab.
What about environmental impact?
Users are advised not to apply carbofuran where the water table (groundwater) is close to the surface and where soils are permeable, i.e., well-drained soils such as loamy sands.