MH has saved many hours of labor since its introduction in the early 1950s. It is widely used for sucker control because it usually is effective, relatively inexpensive, and easy to apply. But high residues can reduce demand by domestic as well as export customers. No suitable alternative to MH has been developed, and sucker control programs without this product have not given consistently good results.
Periodic droughts and the adoption of improved varieties and cultural practices that emphasize yield extend the harvest season and therefore the period needed for good sucker control. Unfortunately, longer harvest seasons, coupled with greater use of mechanical harvesters, have sometimes led to excessive use of MH initially or in additional late-season applications. Consequently, MH residues on and in cured tobacco are often higher than acceptable to buyers.
Several members of the European Community, the major importers of United States leaf tobacco, have adopted an 80-parts-per-million (ppm) MH tolerance on tobacco products. This tolerance may be established by other European countries in the near future. The major competitor for American-style flue-cured tobacco, Brazil, does not use MH and could capture a more significant share of the export market if MH residues do not drop to and remain near the 80-ppm level.
Although an official MH tolerance has not been established in the United States, domestic cigarette manufacturers and all members of the industry are very concerned about poor public perception of any pesticide residues that could reduce tobacco use both here and abroad. Although domestic cigarette consumption is not increasing, the United States is a leading cigarette exporter. Our continued success will depend partially on the domestic manufacturers’ ability to provide cigarettes that meet current or potential pesticide tolerances in other countries.
MH is very water-soluble, and residues vary substantially among years and regions. Residues are generally lower when both rainfall and yields are relatively high. Also, don’t forget that the Farm Services Agency certification you sign annually states that all pesticides you used for flue-cured tobacco production were applied according to label directions. In addition to possible loss of domestic and export markets, continued overuse of MH could result in greater use restrictions.
It is important that the entire tobacco industry, including producers and farm supply dealers, understand the significance of the pesticide residue issue to our industry, particularly to our export market. Also, it would be wise to assume that all pesticides that leave residues on tobacco (not just MHS) will very likely undergo even greater scrutiny and regulation soon.
MH is absorbed more effectively by younger, upper leaves than by older, lower leaves. Therefore, MH should be applied to the upper third of the plant using the three-nozzles-per-row arrangement. Some growers use drop nozzles with high pressure, as they do when spraying for aphids or flea beetles. This will not substantially improve sucker control but will increase MH residues because more of the spray is deposited on the undersides of leaves, where rainfall is less apt to wash it off. Therefore, the use of drop nozzles for MH application is strongly discouraged. MH residues are often higher on lower leaves than on upper leaves because the lower leaves are harvested sooner after MH application. The MH label states that you should wait at least 7 days between MH application and harvest, with the anticipation that rainfall during this period will wash off some residues. If tobacco is ready for MH application and harvest, make every attempt to harvest first, then apply MH. It will most likely be at least 7 days before the crop will be ready for another harvest. This will assure MH-free first primings and minimal residues on the second primings.