Tobacco wilt diseases

Dr. Emily Pfeufer of the University of Kentucky shows area farmers a tobacco plant afflicted with tomato spot wilt during the Tobacco Twilight Tobacco Tour this year at Murray State University's West Farm.

MURRAY — Heading into her presentation at this year’s Tobacco Twilight Tours on the West Farm at Murray State University, Emily Pfeufer was expecting to discuss the usuals. 

There obviously would be angular leaf spot, which has become a particular concern for farmers and it did, in fact, occupy a significant amount to time. Also on the list were such old “favorites” as frogeye, which leaves particularly nasty white spots with dark spots inside that not only are unattractive, but extremely damaging to a harvest. 

Target spot was also another unwelcome traditional rival of farmers that found its way into the lecture, with Pfeufer, an extension assistant professor from the University of Kentucky, presenting her program while standing in front of a pickup truck. She called it “tailgate diagnostics.”

However, there were a couple of other diseases to tobacco leaves that Pfeufer admitted she was not expecting to cover as the sun set that day. And both are as destructive as they sound – “wilt.” One of these is called fusarium wilt, while the other is known as tomato wilt.

“This plant came from the field you see behind us,” Pfeufer sad, pointing to the large trial field behind her guests, who were seated on hay bales on a large trailer pulled by a tractor. She then asked if anyone knew what disease was harming the large tobacco stalk she was holding in her hands.

Several guesses were made, but no one answered correctly.

“Fusarium is a fungus associated with the soil, while tomato spotted wilt is caused by a virus. This was the only plant that looked like this, so that tells you this is tomato spotted wilt (identified by unique blotched lesions),” she said. “With this being the only plant affected, that’s more consistent with a viral disease, and typically these types of diseases are of low incidence.

“If this had been fusarium wilt (identified by a vertical yellowing on one side of the dark green leaves), we’d see long stretches with plants like that. Another giveaway is that the sync tissue looks like it got hit by herbicide, which is more typical of viruses. You also could cut into the stem with a knife and look for vascular discoloration. You’d be looking for reddish-brown discoloration in the stem.”

The bad news, Pfeufer said, is that viral diseases are almost impossible to combat. Once they are present, damage is certain.

“There’s nothing you can do, so if it really bothers you, go ahead and pull the plant out to save the rest of them. Also, if you could see the symptoms while they’re still in the greenhouse, then don’t put them out. They’re not going to get better and they’re definitely not gong to produce for you. You basically will have to get new plants,” she said. 

Pfeufer also said that tomato wilt is carried by thrips, tiny insects that can be very prevalent inside greenhouses. They do their damage by moving from plant to plant. 

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