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Mexican/Texas weed spreading

In late September, Chad Norton received a call from a farmer near Grady, Ark. “He wanted me to stop at his shop to look at a weed pulled out of his rice field,” says the Lincoln County Extension agent.

“I called Ken Smith (Arkansas Extension weed researcher) and described the plant, and we figured it was Texas weed. When I got back to the office, I looked it up in the weed guide and, sure enough, that's what it was.

“There's a big area, maybe half an acre to three-quarters of an acre, infested on this farm. It was the worst infestation I've seen. Thinking back, it had to have been there last year, but nobody noticed it. One thing's for sure: there's a bunch of it now.”

Such calls, says Smith, are coming with more frequency.

Texas weed (also called Mexican weed) isn't a brand-new problem in the southern United States. But it's relatively new for Arkansas.

“Most of us haven't seen it, but it's becoming increasingly common to get calls from Extension agents and farmers wondering what they've found,” says Smith. “It's been in Texas and Louisiana for some time now. But in Arkansas' southeast counties we're seeing a marked increase in it.”

Smith says the belief is the weed is spreading through rice seed.

“We're somehow getting contaminated rice seed,” says the researcher. “We have pretty good seed laws, and they work. When you're talking about one or two tiny weed seeds that get through, it's almost impossible to insure totally clean seed. No matter what you do, a certain percentage of weed seed will get through. We've just got to deal with it.”

Unfortunately, that's hard to do. The weed isn't as prolific as pigweed, but it's very difficult to control. And it doesn't respond well to conventional herbicides.

“To control it, you've got to catch it when it's very small,” says Smith. “If you spray it at a very early growth stage — perhaps with Blazer or Reflex — it can be dealt with pretty well.

“However, if it gets up to 4 inches tall or taller, nothing will kill it. Then, producers are forced to just look at it from the combine. That's the bad thing about it. It's a big, bushy, woody plant that competes with the crop. I'm not sure how much yield is lost due to Mexican weed, but we lose a lot due to harvest inefficiency. With big plants, it's hard to send a combine through.”

Mexican weed is impressive when seen the first time. It can be 5 feet tall, branched out and aggressive looking.

“Someone told me the weed looks like a pigweed crossed with teaweed (prickly sida),” says Smith. “The leaf is serrated and has seedpods that look similar to teaweed. Its size and branching characteristics look like pigweed. It also has a semi-woody hardened stem, so unlike pigweed there is no soft, herbaceous stem.”

Normally, the weed spreads steadily. In some areas of Ashley and Chicot counties (in southeast Arkansas), the weed now infests entire fields.

“We're finding it in rice and soybean fields. I don't know if it's coming in through rice seed, and we're getting it in soybean fields due to rice/soybean rotations. I'm not seeing much in cotton fields — maybe one or two plants. On more upland, sandier soils where most of our cotton is grown, it doesn't seem to do well.”

Recently, Smith got a call from a rice farmer out of Missouri wanting advice about a strange weed he'd found. He described the plant, and Smith concluded he had Mexican weed.

“Again, the suspicion is it came in through his rice seed. I haven't heard anything else from up there, though.”

Smith says if you see the weed, and there are only a few plants, you need to go out and hand-pull it or “do whatever is necessary to get it out of the field. Once the field is full of Mexican weed you'll be fighting it until a control is found.”


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