Topping & Sucker Control – Chemical Sucker Control
Chemical sucker sucker control programs are critical for removing and managing sucker growth following topping. The number of applications, approaches, and programs for acceptable chemical sucker control vary widely and there is not one recipe for always managing suckers. Moreover, crop management such as avoiding excessive nitrogen, having uniform plants, and managing root growth for upright plants indirectly affect and facilitate good sucker control. For specific programs and recommendations, refer to Flue-Cured Tobacco Guide Chapter 7. The following pages briefly discuss various chemicals used in sucker control in tobacco.
Contact alcohol chemicals desiccate (burn) tender sucker tissue. The degree of sucker kill with contact alcohols is directly related to the ratio of chemical to water. Therefore, it is extremely important to mix a specific amount of contact chemical with an exact amount of water. Most other chemicals used to control insects, weeds, and diseases do not share this requirement because growers need add only enough water to uniformly distribute the chemicals.
Flumetralin (Prime+, Flupro, and Drexalin Plus) is a contact-local systemic because it must touch the suckers to be effective, although it retards sucker growth by inhibiting cell division.
Flumetralin should be applied like a contact solution but not until the plants are in the elongated-button-to-early-flower stage. This is a few days before MH application is suggested. The objective is to apply flumetralin so that it touches the small suckers like contact solutions do because, unlike MH, flumetralin does not move to sucker buds through the leaves. Flumetralin must first wet the suckers like a fatty alcohol contact before it can stop cell division like a systemic. Therefore, flumetralin is referred to as a contact-local systemic. It has no true contact activity, and the controlled suckers do not turn brown or black but rather look yellow and deformed for several weeks after treatment. Thorough coverage is a key to maximizing the effectiveness of flumetralin.
Maleic hydrazide (MH) is the only true systemic because it is absorbed by leaves and translocated through the plant to small sucker buds.
Unlike fatty alcohol contacts and flumetralin, MH is absorbed by leaves and moved within the plant to small sucker buds. Good absorption and systemic movement depend on having good crop growing conditions. Therefore, MH should never be applied on drought-stressed crops or on those wilted by too much rain, high temperatures, or both. It is best to apply MH 1 to 3 days after a good rain or irrigation. When irrigation is not available, many growers use flumetralin or one extra contact application to control suckers until enough rain comes for good MH absorption. This should be viewed as “buying time” until rainfall occurs. If soil moisture is adequate but afternoon temperatures will be high enough to cause partial wilting, MH should be applied only during the morning, starting when the leaves are just slightly wet with dew. Afternoon spraying generally is not suggested except on cool, cloudy days when soil moisture is good. It is extremely difficult for growers with large acreages and only one sprayer to take advantage of the best weather conditions for MH application; some should consider buying another sprayer or using larger nozzles to allow faster application
The labeled rate of MH on flue-cured tobacco is 1 quart per 1,000 plants. Most tobacco in North Carolina is planted at approximately 6,000 plants per acre. The correct rate for 6,000 plants is 1.5 gallons per acre. (This rate is suitable for most formulations available in North Carolina, which contain 1.5 pounds of active ingredient per gallon of product; some products contain 2.25 pounds of active ingredient per gallon and should be applied at 1 gallon per acre for 6,000 plants per acre.) Only one application is permitted unless the first application is washed off by rain. Even then, research indicates that reapplication of the full MH rate is not needed unless a substantial rain occurs within 4 hours after the first application. Only a half-rate (0.75 gallon of MH per acre) is needed if rain occurs between 4 and 10 hours after the first application. No reapplication is needed if rain occurs more than 10 to 12 hours after the first application. Following these important guidelines will ensure good sucker control with only minimal increases in MH residues.