Management of Axillary Shoot Growth and Maleic Hydrazide Residues with Diflufenzopyr in Flue-cured Tobacco

Abstract

Maleic hydrazide (MH) controls axillary shoot (sucker) growth in tobacco and is used on more than 90% of the acreage in North Carolina. Residues of MH are the highest of any pesticide used in flue-cured tobacco production in the United States. Many export customers have MH residue limits that are below the average crop residue level. Flue-cured tobacco produced in the United States has therefore been at a competitive disadvantage because competitors in the export market do not use MH.

Research was conducted at the Central Crop Research Station near Clayton, NC and the Border Belt Tobacco Research Station near Whiteville, NC in 2003 and 2004 to evaluate an experimental compound from BASF, diflufenzopyr, (2-(1-[([3,5-difluorophenylamino] carbonyl)-hydrazono]ethyl)-3-pyridinecarboxylic acid), for the control of sucker growth in flue-cured tobacco. Diflufenzopyr was evaluated alone and in tank mixtures with a registered rate of flumetralin, and registered and reduced rates of MH. Treatments were arranged in a factorial design with MH at four rates (0, 0.6, 1.3, and 2.5 kg ai ha-1), flumetralin at two rates (0 and 0.7 kg ai ha-1), and diflufenzopyr at two rates (0 and 0.017 kg ai ha-1). All treatments were applied approximately seven days after the second contact fatty alcohol application (equivalent to ten days after the removal of the terminal flower). Timing of diflufenzopyr application was based on extension recommendations for the proper timing for MH and flumetralin application.

Control of sucker growth with all treatments that included compounds currently registered for sucker control in tobacco in the United States (MH and flumetralin) was similar to previous research. Diflufenzopyr alone resulted in 64% sucker control, and control was similar to flumetralin alone and 0.6 and 1.3 kg of MH alone. Percent sucker control from diflufenzopyr alone however, was less than the standard treatment of a tank mixture of MH at 2.5 kg and flumetralin at 0.7 kg and was therefore below acceptable levels. Diflufenzopyr and MH at 1.3 kg (one-half the registered rate of MH) controlled sucker growth as well as any treatment in the experiment and was equivalent to the standard treatment. In addition, the three-way combination of diflufenzopyr, MH, and flumetralin allowed a further reduction in MH rate, down to 0.6 kg, without reducing sucker control compared to the standard treatment discussed above.

There were no yield differences at CCRS in either year. Yield at BBTRS in 2003 was improved with all chemical treatments and generally increased with increasing levels of sucker control. At BBTRS in 2004, however, seven of the eight treatments that included diflufenzopyr yielded less than chemical treatments that did not include diflufenzopyr. Chemical treatments did not consistently affect quality or average price, and differences in value per hectare were related to yield. Total alkaloids tended to be higher with treatments that resulted in high levels of sucker control. No treatment related differences in reducing sugars were observed.

Acceptable levels of sucker control can be achieved with the tank mixture of diflufenzopyr and the one-half the registered rate of MH (1.3 kg) or from diflufenzopyr, flumetralin and one-fourth the registered rate of MH (0.6 kg). Diflufenzopyr would therefore allow MH residues to be substantially reduced without reducing overall sucker control.