Sucker Control And Harvest Timing For 2010 Tobacco Crop

PRINCETON, KY.
   The 2010 tobacco field season in western Kentucky and Tennessee started out much like 2009, with wet conditions through May and the first half of June. By mid-June however, conditions turned dry with some extreme heat from mid-June through early August with very sporadic rainfall. Ideally, we would like to see dryer conditions in the first month of the season, with just enough moisture for the crop to survive and force it to expand root growth, and then get good moisture around topping time. The reversal of these conditions in 2010 has resulted in unevenness of many dark and burley crops which make topping and sucker control more difficult and time consuming. For burley tobacco, we would like to make one topping and one chemical sucker control treatment if possible. For dark tobacco, we would like to make no more than two toppings and two chemical sucker control treatments.
    For uneven crops like we have frequently seen in 2010, burley tobacco will require two toppings and some dark tobacco will require three. Contact fatty alcohol products such as Off Shoot-T, Royal Tac M, Fair 85, and Sucker Plucker become valued tools with uneven crops because they give us control of suckers that are present at the time of treatment without adversely affecting smaller plants that are not yet ready to top. Fatty alcohols can buy us some time to allow smaller plants to flower before being exposed to more systemic sucker control chemicals. The drawback of fatty alcohols are that they provide only short-term control for 5 to 7 days and spray application is much more difficult than MH applications since the material must come in contact with every sucker at every leaf axil on the plant. Straight plants with no crooked stalks, consistent row spacing, and use of course nozzles applying at least 50 gallons per acre are required for consistent sucker control with contact fatty alcohols. Recommended rates of application for fatty alcohols are a 3 percent to 4 percent solution for burley (1.5 to 2 gallons fatty alcohol per 50 gallons of spray solution) and 4 percent to 5 percent solution for dark tobacco (2 to 2.5 gallons fatty alcohol per 50 gallons of spray solution).
    Once all plants have been topped, standard sucker control programs with MH and/or local systemics such as Butralin, Prime+, or Flupro can be applied. With spray applications, remember that these also require the use of coarse nozzles and spray volumes of at least 50 gallons per acre. If Butralin, Prime+, or Flupro are used alone without MH, remember that these also require precise application to contact each leaf axil on the plant and so the same requirements for straight tobacco and consistent row spacing apply as in fatty alcohol application. MH applications are more flexible since MH is a true systemic, and contact with every leaf axil is not required for MH. MH must be mechanically applied as a spray. Dropline or manual stalk rundown applications with MH are not effective as MH has to be absorbed by the leaves. Good soil moisture is required for effective sucker control from MH, as MH does not move through the plant as well to control sucker growth during excessively dry conditions. Remember that all suckers that are 1 inch long or more much be removed by hand before making any chemical sucker control application.
   Remember that tobacco buying companies are becoming increasingly concerned about the presence of MH residues in tobacco. The standard threshold level of no more than 80 ppm MH residue in cured burley leaf may soon be reduced to a new standard of no more than 40 to 50 ppm. This reduced residue limit could require those using MH to reduce application rates or even consider growing at least a portion of their crop without MH. In many cases, high MH residue in burley leaf can be attributed to the wrong choice of nozzles used for application. Flat fan or hollow cone nozzles used for MH applications can result in reduced sucker control and increased MH residues. Dry conditions between MH application and harvest can also increase MH residue, but probably the most common reason for high residue is when MH is reapplied when it is thought that a rainfall washed off the initial application. The rule of thumb on MH reapplication has been to reapply the full rate if significant (0.1 inches or more) occurs within 3 hours of application. If significant rainfall occurs between 3 and 6 hours of application, a reapplication can be made at one-half of the full rate. If rainfall does not occur within 6 hours, no reapplication is needed. With the increased scrutiny over MH residues and the possibility of lower residue limits being used, growers should now strongly consider reapplying no more than one-half of the full rate even if rainfall occurs within 3 hours and not reapplying if rainfall occurs between 3 and 6 hours.
   Optimum harvest timing for burley tobacco is 3 to 4 weeks after the final topping for early maturing varieties such as KY 14xL8, and 4 to 5 weeks after final topping for later maturing varieties such as NC 7, TN 90, KT 204, KT 206, KT 209, and KT 210. Remember that burley treated with Butralin should not be harvested for 30 days following application. Optimum harvest timing for dark air-cured tobacco is 5 to 6 weeks after final topping, and 6 to 8 weeks after final topping for dark fire-cured tobacco with the exception of earlier maturing varieties such as TN D950 and PD 7305. Δ
DR. ANDY BAILEY: Extension Tobacco Specialist, University of Kentucky