Late last week, Phytophthora nicotianae (Black shank) was observed in an Horry County tobacco field. Although black shank is a fairly common tobacco disease in our area, it is uncommon to see the symptoms this early in the growing season. This one (20-acre) field with less than 1% infection is nothing to get overly excited about, but I think it is a good time to talk about what we can do to manage the problem.
It’s obviously too late to talk about variety selection and crop rotation, which are the backbone of a successful black shank control strategy. But we all know that even when we do use varieties with resistance to certain diseases and have a good rotation that it’s definitely not bulletproof when the conditions are just right.
Wounded roots are not a requirement of black shank infection. High soil moisture favors root colonization by the black shank fungus, although effects of early season infections become most apparent when soil moisture becomes limited. These conditions have been pretty close to what some areas of the county have experienced.
So, what can we do about it?
In addition to the ability to use Ridomil Gold in the transplant water, growers have the option of using Ridomil Gold at 1st cultivation and layby if disease pressure is high. In the case of pre-plant + layby the product application rate is 1pt/A +1 pt/A. In the case of pre-plant + 1st cultivation + layby, the product application rate is the 1pt/A + 1pt/A + 1 pt/A (not to exceed 3 pts/A per season). Incorporate after application.
Presidio fungicide can also be used to control black shank with one 4 fl oz/A (0.125 lb ai/A) application made at either first cultivation or layby. Direct sprayer nozzles to cover soil beneath lower leaves, and incorporate immediately with cultivators.
This year, Orondis Gold 200 has been labeled for the management of black shank on tobacco. Orondis Gold contains Oxathiapiprolin, which offers a new mode of action for managing oomycete diseases like black shank. No more than two sequential applications of Orondis Gold may be made, so if producers intend to make three applications, the third must be a fungicide with a different mode of action. However, Dr. Paul Peterson, tobacco plant pathologist at the Pee Dee REC, recommends that for resistant management purposes, only one application of Orondis Gold be made per season. The product rate per application is 4.8-19.2 fl oz/A (not to exceed 38.6 fl. Oz/A per season). Incorporate after application.
More information can be found on pages 278-279 of Clemson’s Pest Management Handbook.
This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. Brand names of pesticides are given as a convenience and are neither an endorsement nor guarantee of the product nor a suggestion that similar products are not effective. Use pesticides only according to the directions on the label. Follow all directions, precautions and restrictions that are listed.