No. 9/May 22, 1998
Soil Insecticide Use and Replant Decisions: What Do the Labels Say?
During the past week, many questions have surfaced regarding whether or not a soil insecticide could be used again in a replanted field. In essence, is it legal to apply a soil insecticide to a field that already has received one application at planting? The product labels for the various products offer the following guidance:
- Aztec 2.1G--A maximum of 7.3 pounds of Aztec 2.1G may be applied per acre per crop season.
- Counter CR--Do not exceed 6.5 pounds of Counter CR per acre. If application is made at planting, do not make postemergence or cultivation-time treatments of Counter CR.
- Force--Use Force 1.5/3G only once per crop.
- Fortress 2.5/5G--Do not make more than one application per year.
- Lorsban 15G--For soil insect control, do not exceed the equivalent of 16 ounces of Lorsban 15G per 1,000 feet of row or 13.5 pounds of Lorsban 15G per acre per crop season.
- Thimet 15/20G--One additional application may be made at cultivation. Do not make any applications of Thimet after cultivation treatment.
These label statements do not offer growers much flexibility with regard to the use of a soil insecticide a second time during a replanting operation. Given the low water solubility of soil insecticides, movement of a product away from a row is most likely not a problem, even after heavy rains. Because soil insecticides adsorb to soil particles, severe erosion on sloping ground can move a portion of soil insecticides off the target site. If erosion has not occurred, a high percentage of the soil insecticide should remain in place.
Soil insecticides applied in-furrow are even less prone to movement after heavy rains. Soil insecticides are not prone to leaching. Most vertical movement of soil insecticides is limited to 4 or 5 inches downward in the soil profile. If a grower is able to match up rows during the replanting operation, the soil insecticide used during the original planting operation should be able to provide the necessary root protection. With the normal rootworm egg hatch expected (late May), soil insecticide persistence should not be the issue that it was in 1997.
What if a grower can't match up the rows because the field has "been worked?" The use of a soil insecticide a second time (two planting-time applications) would constitute a label violation for most products. The use of Lorsban 15G a second time appears to be an option, particularly if a reduced application rate was used during the original planting operation. Some folks have asked, "Is it OK just to use a different soil insecticide while replanting?" In my opinion, this approach violates the spirit of the label for the various products. The main goal behind each label's planting-time use restrictions is to limit the overall amount of insecticide applied per acre in a growing season. Simply switching to another product to skirt the real intent of the label has potential environmental consequences. Mike Gray, (email@example.com), Extension Entomology, (217)333-6652