Wheat and tobacco injury resulting from flumetralin usage in Tennessee burley tobacco production

A three year study was conducted from 1985 to 1988 at two locations in Tennessee to evaluate injury to a wheat (Triticum aestivum L.) cover crop following burley tobacco (Nicotiana tabacum L. 'Clay 501') that had been treated with 0, 29, or 86 mg/plant flumetralin for sucker control. Tobacco plots received either no herbicide or a preplant incorporated application of pendimethalin at 1.7 kg ai/ha. Tobacco plots were sub-divided for 8 and 15 cm tillage depths following tobacco harvest and wheat was sown. Wheat population counts were made at Feekes 2-3 stage. Soil samples were taken with a soil probe to a depth of 8 cm when the wheat counts were made. Soil concentrations of flumetralin and pendimethalin were determined by gas liquid chromatography. Wheat biomass was harvested from each plot the following spring. Measurements on tobacco were made in each plot to evaluate flumetralin carryover injury into succeeding tobacco. Flumetralin provided >75% sucker control with either the 29 or 86 mg/plant treatment. Flumetralin residues of 0.23 ppmw were detected in plots that received 29 mg flumetralin per tobacco plant. Flumetralin residues of 0.83 ppmw were detected where tobacco received 86 mg/plant. Pendimethalin residues averaged 0.25 ppmw. Wheat injury from the low rate of flumetralin averaged 14% where pendimethalin was not used. Wheat injury increased to 48% where pendimethalin was applied. Wheat injury from the high rate of flumetralin averaged 58% where pendimethalin was not used and increased to over 75% where pendimethalin was used. Injury from pendimethalin carryover alone was ≤17%. Interaction between flumetralin and pendimethalin on wheat injury was determined to be synergistic. The 15 cm tillage depth was found to be ineffective in reducing residues or carryover injury from flumetralin and/or pendimethalin. Carryover injury to succeeding tobacco where 29 mg/plant flumetralin had been used the previous year was <8%. Where 86 mg/plant flumetralin had been used the previous year injury to succeeding tobacco averaged 18%. Pendunethalin had no effect on carryover injury to tobacco. A statewide survey revealed that approximately 18% (i.e. 1,182 ha) of the hectares treated with flumetralin experienced carryover problems. At one location, incidence of false broomerape increased concomitantly with sucker control. There was no false broomerape detected at the other location.