LSU AgCenter weed scientist Jim Griffin, right, talks to farmers about soybean harvest aids Tuesday (Sept. 6) at a harvest-aid clinic on the farm of Buster Hardee. (Photo by Bruce Schultz. Click on photo for downloadable image.)

News Release Distributed 09/08/11

GUEYDAN, La. – Timing of harvest aid application to a maturing soybean crop is critical, according to an LSU AgCenter expert.

Apply too soon, and yields can be reduced, said LSU AgCenter weed scientist Jim Griffin. Too late, and the potential benefit of earlier harvest won’t be realized, he said, speaking Tuesday (Sept. 6) at a harvest-aid clinic on the farm of Buster Hardee.

Several indicators are being used to advise farmers when to spray, Griffin said.

For example, one recommendation calls for spraying when half of the leaves have dropped, but that is not a reliable sign. “Some varieties will retain leaves longer than others,” Griffin said.

Griffin conducted a study to determine the best way to tell if a crop is ready for a harvest aid, and he determined the best way is by closely examining beans inside the pod.

A field is not ready to be sprayed until the beans have separated from the white membranes that line seed pods in the top four nodes of plants where seed will be the most immature. The separation of the beans from the membrane will create a space between the bean and the inner pod wall, and the beans should easily pop out of the pod, he said.

Once this occurs, the beans have reached maximum dry weight – or physiological maturity – and leaf removal will not negatively affect yield, he said. The longer harvest-aid application is delayed, the later the crop will be ready to harvest.

An application made too early is more detrimental to determinate varieties in maturity groups 5 and 6 than to indeterminate varieties in maturity group 4.

The highest labeled rate of Gramoxone Inteon is 16 ounces per acre, and it is critical that either a nonionic surfactant or crop oil concentrate be added, Griffin said.

Sodium chlorate can also be used as a harvest aid, but it can be inconsistent, he said. Good coverage of the soybean foliage is critical with both sodium chlorate and Gramoxone Inteon/paraquat products.

He recommended that spray volume be at least 15 gallons per acre with ground rigs and 5 gallons per acre for aerial application.

Roughly 95 percent of north Louisiana soybean fields are sprayed with a harvest aid, said LSU AgCenter soybean specialist Ron Levy. If an extended period of rain follows an application, bean quality could deteriorate, he added.