Herbicide carryover in fall-seeded crops a concern
Fields in southeast Barton County southeast of Lockwood were scouted on Aug. 8 by Wyatt Miller, an agronomy assistant with University of Missouri Extension in Barton County.
"A few corn fields in the area have been harvested with several reporting low test weights. Aflatoxin concentrations have been acceptable, but continue to be a concern in later planted corn," said Miller.
Soybeans scouted this week were between R3 and R5, beginning seed stage according to Miller. He reported finding several larvae, the majority of which were soybean podworm, also known as corn earworm.
Soybean podworms have four pairs of abdominal prolegs in the center of the body and typically have dark horizontal stripes and black spots with protruding hairs. Treatment is justified when larvae exceed one per linear foot of row and 5 percent or more of pods are damaged. Yield potential should be considered prior to treatment.
Some potash deficiency was seen resulting in leaf yellowing and stunting, which is typically worse in dry years. Those considering using soybeans as a forage, should check pesticide labels for harvest restrictions and can expect yields of 2 to 4 tons per acre with removal rates of approximately 10 pounds phosphate, 25 pounds potash, and 45 pounds of nitrogen per ton.
"Because of the drought there is an increase chance of herbicide carryover to fall-seeded crops. Those who plan to plant winter wheat or fall-seeded forage grasses should consider factors that influence the likelihood of herbicide carryover. These include type of herbicide applied, rate of herbicide applied, time herbicide was applied, and most importantly amount of rainfall received since herbicide application," said Miller.
A soil bioassay should be conducted on fields with high concern or uncertainty.