MURRAY — A trial conducted by the University of Kentucky to determine the best ways to handle a problematic tobacco disease showed that the disease was much worse in one part of western Kentucky than another.
During a presentation in last week’s annual Tobacco Twilight Tours in Murray, University of Kentucky Extension Assistant Professor Dr. Emily Pfeufer told about 40 area farmers and other observers that testing at UK’s facility in Princeton resulted in a much more widespread presence of the disease angular leaf spot (ALS) than what was observed in trials at another field at the West Farm on the campus of Murray State University.
“In fact, the disease is three times as bad in Princeton as it is here,” Pfeufer said during the beginning of her presentation, immediately giving a reason she thought this was the case. “The Princeton crop was a week ahead of the one here. So we actually sprayed the bacteria on the crops and it was the same strain and same concentration.
“The reason (for the more prevalent ALS cases in Princeton) is that, when we inoculated this crop on July 3, it was right after a heavy rain and we hardly got any rain since then. It’s been real dry (in Murray) and I think that has made the difference completely between the two crops.”
The more wet conditions east of Murray allowed for a more opportunistic breeding ground for the ALS bacteria, she said.
The main weapon in the fight against ALS is streptomycin, but Pfeufer said this allows for marginal control at best. However, she also said it is important for farmers to know, for sure, that they are targeting ALS when spraying their plants.
That is because ALS has a similar to appearance to another disease, frogeye.
“It is critical to be able to tell the difference between the two because the management is really different,” she said. “With ALS, we’re spraying streptomycin to try and manage it. With frogeye, the main management is through Quadris or oxystrobin. So you might think you have ALS and you’re throwing all of this streptomycin at it, but if it, in fact, is frogeye, it can get worse and worse and strep won’t do a thing against it.”
Near the end of Pfeufer’s presentation, she was asked if she had heard about farmers near Hopkinsville utilizing what was dubbed “the biggest concoction ever seen” to combat ALS and reportedly results were positive. Pfeufer quickly came to the conclusion that the concoction, which she dubbed as the “Thanksgiving dinner” was something called PAA, which she said is similar to hydrogen peroxide.
“And we’re using PAA,” she said of activity in Princeton. “The active in PAA would kill pre-living ALS bacteria. Those bacteria are inside the leaf so spraying would sterilize the outside and wouldn’t allow it to get into the leaf. Still, I’d want to see data on this.”
Pfeufer also said that a fairly new substance is joining the anti-ALS fray, copper.
“We are looking for alternatives to streptomycin for ALS management out there and, with copper, it is not necessarily brand new,” she said. “I know a couple of organic producers that have used Nordox and they have had pretty decent crops that are just managed with Nordox, which is one of the copper options.”
However, she said copper must be treated carefully.
“Some of these copper products do leave a pretty thick residue, so a buyer could have concerns with that if they see it that residue,” she said of how copper treatments tend to leave a reddish color on the leaf. “You’d want to put them on the plant at the front end of the season. You want to get as good of control as you can early on to get a nice residue layer to protect the plants from initial ALS infections. When you get to the point that it’s thigh-high tobacco, you’re hopefully not having to spray as often.
“Now, to my knowledge, nobody is checking for copper residues right now, but I wouldn’t spray it any closer to harvest than two weeks and even after topping, that may be too close. It’s kind of your own lookout, your own decision to make.”