48th TWC, Tob. Work. Conf., 2018, abstr. 51

Mangagement of Target Spot in broadleaf cigar wrapper tobacco

LaMONDIA J.
Connecticut Agricultural Experiment Station, Windsor CT USA

Target spot of tobacco, caused by Rhizoctonia solani (Thanatephorus cucumeris) (AG-3) has occurred in the cigar wrapper production area of Connecticut and Massachusetts annually since 2010. Cigar wrapper leaves must be blemish free and require excellent disease control. The only fungicide active ingredient currently registered for control of this disease is azoxystrobin. While azoxystrobin can be applied to foliage of shade-grown tobacco without phytotoxicity, application to foliage of field-grown broadleaf tobacco can, and often does, result in white fleck symptoms that make the leaf unmarketable. We conducted replicated experiments in 2016 and 2017 both to determine fungicide efficacy and to minimize foliar phytotoxicity symptoms. Azoxystrobin fungicide (8 oz per acre per application) was applied to B1 broadleaf wrapper tobacco in field plots as a single foliar band application 6-inches wide over the top of transplants in 25 gpa seven days after transplanting, or as a combination treatment consisting of a drench in 1 oz water per plant (50 gpa) at transplanting followed by a 6-inch-wide layby application to both sides of the plant in 50 gpa two to three weeks after transplanting at the last cultivation. Controls consisted of plots that did not receive any fungicide. Fleck symptoms occurred on leaves that were contacted by fungicide sprays, but these were not leaves that were harvested as wrapper at the end of the experiment. Azoxystrobin application reduced both the number of diseased leaves and the number of target spot lesions compared to the untreated controls. While the numbers of diseased leaves and numbers of lesions per plant were numerically lower for drench and layby treatments with two 8 oz per acre applications, there were no significant differences between the drench/layby treatment and a single application of 8 oz per acre over the row 7 days after transplanting in either year. (Reprinted with permission)