Black shank, caused by Phytophthora nicotianae, is the most damaging disease of burley tobacco in Kentucky. Along with sound cultural practices, soil and/or transplant water applications of fungicides are key management recommendations for growers. Until recently, the only fungicides labeled for use on tobacco for control of black shank were all in Fungicide Resistance Action Committee (FRAC) group 4. Although resistance to this group of fungicides has not yet been reported, there is potential for development of resistance with the repeated use of a single mode of action. In this study, a fungicide with a different mode of action is investigated.

The purpose of these studies was to evaluate the efficacy of oxathiapiprolin (OXTP) applied in transplant water and to soil after transplanting in two fields with histories of black shank. These studies compared management of black shank among OXTP, Ridomil Gold (RG), and Presidio treatments in addition to measures of plant safety.

OXTP demonstrated a level of suppression similar to RG (TPW or soil directed at transplanting, 1st cultivation, layby) when applied at 19.2 ounces/ac in TPW-only or at 19.2 ounces/ac in TPW treatment followed by applications of 9.6 ounces/ac and 3.8 ounces/ac at 1st cultivation and layby. Combinations of OXTP at 3.8 ounces/ac and RG at 8 ounces/ac in TPW and the same rates at layby were also effective and equivalent to RG. RG was effective as a single treatment in TPW in the Clark County study but not in Grant County due to a higher disease pressure where more applications for suppression would be necessary.

In conclusion, OXTP appeared to function as an alternative to RG and may be useful in a pest management program focused on alternating chemistries. (Reprinted with permission)