One of the less rewarding tasks of pest management is gleaning information from pesticide labels. Because of the complexity of labels, many people rely on guides produced by universities or distributors to identify solutions for pest problems. While these guides are convenient, they are not intended to replace the label in terms of making management decisions. The importance of this was made clear in a recent herbicide problem.
The situation. A grower had a stand failure with RR corn and didn’t want to use tillage to eliminate the existing stand. A provider used a popular weed management guide to determine that clethodim was labeled for killing a failed stand of corn prior to replanting. The guide listed a 6 day interval before replanting. He then went to the 'Weeds Controlled' table on the clethodim label to determine the recommended rate for volunteer corn.
The problem. While clethodim is registered for this purpose, the use rate for burndown of a failed corn stand is 3 oz/A rather than the 6 to 8 oz recommended for volunteer corn in the rate table. The reason for the low rate is to prevent clethodim residues from damaging the replanted corn. At a 3 oz rate with a 6 day interval, the clethodim degrades to non-toxic concentrations. Over 200 acres of replanted corn was killed due to application of an inappropriate rate (8 oz).
The lesson. Guides provide a quick way of determining labeled products for ‘atypical’ situations. However, these guides cannot provide all of the detailed information included on the label. The guide used in this situation did not provide information on the reduced clethodim rate for controlling corn in a replant situation, only specifying the 6 day replant interval. As they say, always read the label before going to the field.