Sustaining maleic hydrazide: an alternative application technique for reduced residues in flue-cured tobacco
Cured leaf residues of the plant growth regulator maleic hydrazide (MH) remain as a serious concern to the allied tobacco industry in the United States. Current MH application programs rely on foliar, over-the-top delivery systems that saturate the plant with the spray solution. We tested an alternative delivery system in three different growing environments that applied an MH solution to the base of tobacco plants after first harvest. Treatments comprising the alternative delivery system contained three MH concentrations (40 %, 50 %, and 60 % MH v/v), each applied at four different output volumes: 5 mL, 10 mL, 15 mL, and 20 mL plant-1. A treatment containing topped, but not de-suckered plants was included as a negative control. A conventional, over-the-top MH application (3 % v/v at 31.5 mL plant-1) was included as the current grower standard. After the final leaf harvest, sucker growth, yield, visual quality, economic value, and MH residues in three stalk positions were quantified. Relative to the over-the-top application, the alternative stalk applied treatments had similar sucker control, yield, quality, and value. However, MH residues in each alternative treatment were significantly lower in the cutter stalk position. In the leaf and tip position, the 40 % and 50 % MH concentrations applied at 5 mL to 10 mL plant-1 most consistently resulted in lower MH residues than the conventional standard. When the conventional standard was excluded from the data analysis, we observed a yield decline in the tip leaf stalk position in treatments containing the 40 % and 60 % MH treatments. In addition, it was noted that MH residues were typically lowest in treatments containing the 40 % or 50 % v/v concentrations that were applied at 5 mL or 10 mL plant-1. Our results suggest that stalk applications of MH at a 50 % v/v concentration applied at 5 mL to 10 mL-1 may prove to be a useful residue reduction strategy that does not compromise end of season sucker control or yield.