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Better stands envisioned

Extension researchers are working out the particulars of a system that could help flue-cured tobacco farmers reduce spiral roots in the greenhouse and ultimately get a better stand in the field.

Spiral roots are one of the biggest causes of reduced stands in North Carolina, says David Smith, North Carolina State University Extension tobacco specialist.

Smith and his colleagues have found reduced spiral root numbers by covering the seed in the greenhouse trays. They've also found that certain varieties can be covered and still germinate, while others can't.

He is also using an experimental product from F.W. Rickard that shows promise in reducing spiral roots in greenhouse transplants.

Fifty-six percent of the acreage in North Carolina is planted to varieties that have high levels of spiral root. That 56 percent takes into account varieties such as NC-71, NC-72, NC-297 and Speight 168. Spiral roots cause tobacco farmers 7 percent to 10 percent stand loss each year. “That 10 percent is about $15 an acre, assuming straight production costs, but not taking into account the cost of replanting,” Smith says.

“If tobacco farmers can increase the number of usable plants, they can reduce the costs of plants and in turn the cost per acre,” Smith says. In trying to determine the cause of spiral roots, he has looked at a combination of environmental and varietal factors over the last three years.

Smith says keep the potting surface too wet and packing the trays too tightly can lead to spiral roots.

High temperatures also contribute to causing spiral roots. “Some varieties are more sensitive than others,” he says. “We don't know if it's a true genetic difference or not.”

He has found that covering the seed in the tray dramatically reduces the number of plants with spiral roots. That's the good news.

The bad news is, not all varieties will germinate when covered with potting soil. Early in the study, Smith found that NC-71, a popular variety, did well covered. NC-72, NC-297 and Speight 168 also did well covered. K-326, K-346, non-primed NC-71 and NC-72 didn't perform well covered.

“Covering has a lot of potential with varieties that have a history of spiral roots,” Smith says. “But you would have to use primed seed to get consistent stands.”

In the research, Smith took another route, using an experimental product from F. W. Rickard that shows promise for reducing spiral roots.

He used a very shallow, quarter-of-gram covering of this “kitty litter type product,” per cell. He put out the material using a plate-type seeder. “Most any variety will come up through that little of a covering,” Smith says. “We liked the way the product worked.”

In tests this fall, Smith found 19 percent spiral roots in varieties not covered and zero percent with seeds covered with the Rickard product.

“Covering the seeds is the only way we're going to eliminate spiral roots,” Smith says. “But we have to be careful, this is a complicated problem. We're not quite ready to recommend the practice for everybody right now.”

Instead, Smith advises producers to try covering their seeds on a couple rows of the greenhouse. He also advises using primed seeds when covering.

“I feel good about covering, but I'm not quite ready to make a recommendation,” Smith says. “I'm going to try the experimental product one more year. If it works on a fairly wide scale, we're going to recommend covering.”


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