Palmer amaranth has caused corn, soybean and cotton farmers a world of trouble.

Now, tobacco farmers may be in danger of a big loss due to the weed.

That's because their No. 1 customer, the People’s Republic of China, says it has found seeds of Palmer amaranth and other weeds it doesn’t like in tobacco leaf they have bought here. They don't want any more.

"The Chinese do not tolerate invasive weed seeds," said Peter Thornton, assistant director for international marketing with the North Carolina Department of Agriculture.

“We need to provide a solution to this problem.  China is the largest potential growth market we have.”

The objectionable infestations— which also included crabgrass and foxtail — were discovered by the Chinese national quarantine agency. 

This appears to be a bigger problem in mechanized flue-cured harvest than any form of hand harvest.

“We think the problem occurs mainly where you are trying to mechanically harvest in the presence of big weeds,” said Matthew Vann, North Carolina Extension tobacco specialist.

That's why one of the Extension recommendations is that you keep the field border clean and mowed so you don't take any weed seed in with you, he said.

Entire weed pulled in

“When you turn a mechanical harvester around at the end of the row, whole weeds can get pulled into the harvester,” Vann said. “We don't want to get this contamination outside the actual planting.”

The most important step in controlling pigweed in tobacco, said Vann is don't plant in weedy soil in the first place. “Field choice can really help in solving this problem.”

Ironically, tobacco farmers have a few advantages compared to other crops in controlling pigweed:

• Cultivation: “We still cultivate tobacco after transplanting ,” Vann said. “That is unlike most other row crops and gives additional chances to control pigweed.”

• The opportunity to hand pull: “Most tobacco farmers use hand crews to top and sucker, and these workers can pull up larger weeds while they are out there,” he said. “There is a lot to be said about getting the seed out of the ground altogether. That certainly reduces the seed bank for future crops.”

But it takes roughly one person to hand weed one acre. ”As you get over a certain acreage, this becomes hard to do,” Vann said.

• Effective available herbicides: Vann says three herbicides will probably play the most important roles in the current situation — Spartan, Prowl and Aim.

Spartan will probably give better control of pigweed than the other two. It does extremely well on pigweed, and about half the crop now is getting an application of Spartan.

Aim has an unusual fit in tobacco. “You apply it just after first harvest, and it works well,” he said. “But the pigweeds need to be two to three inches tall for good results. If they are bigger, there may be some initial control but there will be a rebound later.”

• Deep tillage with a moldboard plow. This is something of a new concept, but Vann says that in field testing, it has been shown that deep tillage can substantially improve your pigweed control. “It gave a reduction of about 50 percent in pigweed,” said Vann. “If we included application of Spartan, the reduction was 80 percent.”

Expensive practice

Unfortunately, this is an expensive practice. It costs about $33 an acre compared to shallow tillage, said Vann. “But you get good control, and because you are burying seed, you are reducing the seed bank in following years.”

Palmer amaranth is prolific in terms of seed production. A single plant can produce 500,000 seed. The seeds are very small, round, and black in color, and they attach to the leaf.

“Once the seed is in the tobacco, it is extremely difficult to remove,” said Tommy Bunn, president of United States Tobacco Cooperative (USTC), the flue-cured cooperative in Raleigh, N.C.

Weed seed contamination has been largely a problem of flue-cured tobacco so far, said Bunn. “Since burley is harvested by the stick in the field, it is less likely to have this happen.”

But Daniel Green, the chief executive officer of Burley Stabilization Corporation of Springfield, Tenn., said his cooperative would keep a close eye on the issue. “We take it very seriously,” he said. “We want to be part of the solution if we need to.”

The consequences of not solving this problem are frightening, but Bunn is very optimistic.

“There is no doubt in my mind our growers will do whatever they need to to overcome this problem. We just need to present them with the answers.”

Vann is also optimistic. He expects Extension crop scientists will have an updated control program to recommend to growers at winter meetings. “This situation should be manageable,” he said. “We have the tools to develop a program to deal with this problem.”

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