Corn rootworms usually are managed by rotating corn with another crop or by using a granular soil insecticide at planting. When using an insecticide, you also should consider performance, safety, environmental impact, control of other pests, and cost.
Liquid formulations of soil insecticides, such as Dyfonate 4EC, Furadan 4F, and Lorsban 4E, are labeled for use against corn rootworms, but have not been commonly used. Furadan 4F, (carbofuran), is being marketed widely as a post-plant broadcast application to replace at-planting granular insecticides. This article answers many questions that have been raised about this post-plant approach to corn rootworm management.
What data were evaluated?
University data were gathered from entomologists at 10 land-grant universities in the Corn Belt (Illinois, Indiana, Iowa, Kansas, Kentucky, Minnesota, Missouri, Nebraska, South Dakota, and Wisconsin). Because Furadan 4F application is a relatively new approach to rootworm management, only three years of data are available. In my summary, I included test results when:
(1) Furadan was applied between May 15 and June 15,
(2) it was sprayed at the rate of one quart per acre, and
(3) root injury was greater than 3.0 on roots from the untreated plots.
How were the university data evaluated?
Consistency of performance indicates the percentage of time the insecticide did a good job of protecting corn roots. In my evaluation, consistency was indicated by the percentage of tests in which the untreated roots averaged moderate to heavy root injury (>3.0) and the treated roots had moderate to minimal root injury (3.0 or less). If the insecticide-treated roots from a particular states test had a rating higher than 3.0, then the insecticide was categorized as not providing good root protection. Counter 15G at planting (or Counter CR in some 1993 tests) was used as a standard to compare with Furadan 4F performance.
How well did Furadan 4F protect corn roots from rootworm injury?
Table 1 shows that there is a wide range of performance in Furadan 4F. During the drier springs of 1991 and 1992, the broadcast application was not highly consistent in providing root protection. The banded application during these two years also was not quite comparable to Counter 15G at planting. The data from 1993 present a completely different picture. The performance of the broadcast application was greatly improved and the banded treatment was similar to Counter 15G at planting.
The data suggest that Furadan 4F works better during a wet spring. Furadan 4F is highly-water soluble and, when it is sprayed on the soil surface, rainfall can move the insecticide to the root zone for better protection. During a dry spring, Furadan 4F has not been consistent in providing good root protection. The best approach is to look at all the data together, from both the dry and wet years, and critically review the performance. This information is summarized on the bottom line of the table.
Are there any special directions for using Furadan 4F?
There are several noteworthy considerations on the Furadan 4F label that arent on granular insecticide labels. The application period is narrowly defined and should be timed closely to 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 if Furadan 4F is cultivated into the soil, especially if it hasnt rained and if it was applied before June 5th. If the insecticide is tank mixed with a herbicide, consult the herbicide label for cultivation restrictions. Do not apply Furadan 4F where the water table is close to the surface, or in permeable soils.