48th TWC, Tob. Work. Conf., 2018, abstr. 73

Assessment of a stalk applied MH spray system installed on a mechanical harvester

North Carolina State University, Raleigh NC USA

Current maleic hydrazide (MH) applications on flue-cured tobacco require spraying over the top of the plant to insure proper coverage and effectiveness, but depending on a number of factors the cured leaf residues can be elevated and negatively affect the U.S. cured-leaf global marketability. Some studies have indicated that MH applied directly to the tobacco stalk may be effective if the spray can be targeted properly. On-farm performance information was collected using a precision spray system implemented on an existing two-row mechanical harvester. A nozzle assembly and triggering mechanism were mounted to the defoliator unit of each row to intermittently spray a three to 4-inch vertical band of MH solution near the stalk base immediately after removal of the lower-stalk leaves during first harvest. An electromechanical limit switch with a rod actuator was used to contact the stalk and energize the spray system nozzle solenoid. MH was stalk applied at 5%, 10%, 15%, and 20% concentrations and leaf samples were collected for residues. The maximum green leaf residue measured across all stalk applied solutions was 66 ppm and 50 ppm for the 24 hour and 7 day sampling interval, respectively. The average cured leaf residue across all stalk applications was 34 ppm and the maximum cured leaf residue measured was 73 ppm. Although no differences in sucker growth were measured across all stalk applied concentrations, the green leaf residue samples indicate the rapid movement of MH throughout the plant at the rates applied to the lower portion of the stalk. After modifications, the stalk applied delivery system functioned consistently during multiple acres of operation. More work is still required to optimize the solution concentration and volume delivered per plant to maximize sucker growth control. (Reprinted with permission)