From the Field-Agronomy Notes: Vol. 2, Num. 11
A large portion of the current tobacco crop is quickly approaching first contact application. Some of the crop that was transplanted early has already received a second and third application at the time of this email. As we transition to this portion of the growing season, we’ve received a few comments and questions regarding sucker control in pesticide residue free (PRC and ELI) and organic tobacco production systems. For the purpose of this note, all three of these systems can be lumped together because systemic suckercides (such as butralin, flumetralin, and MH) are prohibited in their production. Below are a few considerations that producers should keep in mind.
1.) Be extremely proactive when making the first contact application. The conventional rule of thumb is that the first application should begin at the 50% button stage. It can be suggested that producers consider starting this application before 50% button is reached, possibly at the 40% button stage. Beginning slightly earlier should allow for sufficient control of suckers growing in some of the larger, more advanced plants. It is possible that chemical topping might occur in smaller plants; however, it should not be enough to result in yield or quality losses at the end of the season. In addition, it can be argued that the small leaves most affected by early contact application are likely to be removed at topping anyway.
2.) Producers should recognize that hand suckering will likely be necessary. Contact materials approved for use in residue free and organic programs will provide excellent sucker control, but they do have their limitations much like conventional contact products. Any sucker in excess of 1.0 to 1.5 inches in length is going to be difficult to control. For this reason, it is advisable to hand sucker a field if the first contact application is delayed beyond the 50% button stage (scouting fields will aide in this decision), or if more than 5 days has passed between contact applications. Simply stated, hand suckering will help ensure that acceptable sucker control is achieved by final harvest. As growers approach the third or fourth contact application, it is possible that the window between applications might expand by one or two days. Should a grower consider lengthening the number of days between applications, proper scouting of fields should occur to ensure that sucker growth allows for this.
3.) Producers should spray early (bullet point one) and spray often. We typically suggest a 5-7 spray rotation for contact followed by contact or contact followed by flumetralin and/or MH in conventional programs. It’s likely that this window should be no greater than 5 days to ensure that sucker growth between applications does not surpass the 1.0 to 1.5 inch maximum. Additionally, there is no “one size fits all” program that will provide insight as to how many times contact should be applied. Some producers have been successful with four or five contact applications, while others have needed more. The major issue associated with over-application of contact is leaf drop (where leaves simply fall off the plant due to weakened leaf axils). Leaf drop is promoted by a number of factors, such as environmental conditions, nitrogen application, and disease. Generally speaking, the deeper the contact burn into the leaf axil, the weaker the leaf axil will be. The weakening of the leaf axil is promoted when leaves are heavy (primarily from excessive nitrogen) and/or when a disease such as Erwinia is present in the leaf axil. The presence of Erwinia will be promoted by wet weather, much like we have been experiencing. The bottomline regarding how many times contact can be applied is that producers will have to treat each field on a case-by-case basis and practice what they feel comfortable with.
4.) Application rates of contact type materials in these production systems should follow the current recommendations for conventional systems (4% concentration followed by subsequent applications of a 5% concentration). In most areas of the state tobacco is tender due to sufficient or excessive moisture and moderate temperatures; therefore, beginning with a 4% solution concentration (2 gallons of contact + 48 gallons of water) will help to reduce the potential for leaf injury while still ensuring sufficient sucker burn. Subsequent topping and additional leaf expansion will allow plants to better withstand the 5% applications that follow. Producers should feel comfortable with this program, as it mirrors standard recommendations that have been in place for decades. Lastly, producers should monitor environmental conditions and stop applying contact when temperatures reach and surpass 90 degrees. Again, this is standard protocol as material activity tends to increase as temperature increases.
As always, if you have any questions, please do not hesitate to contact your local Extension Agent!