Smartweed, always a concern for Arkansas rice farmers, has emerged as a serious problem this year, according to weed experts with the University of Arkansas Cooperative Extension Service.
Judging from the many calls they're receiving and the complaints they're hearing at meetings with farmers, the problem is widespread.
“We've had scattered fields with smartweed every year, but it seems worse this year. Everyone seems to have a smartweed problem this year,” says Ken Smith, Extension weed scientist.
Smith believes a mild winter and rainy spring have contributed to the problem. The winter never killed the weeds, he said, and the rain has insured their growth. Early burndown herbicides failed to kill the smartweeds present before planting. These weeds are much harder to control in the crop.
Smith said farmers complain they spray smartweeds with herbicides, but they keep coming back. “What we're probably dealing with here is that the plant is regenerating itself from a rhizome, or well-developed underground stem,” Smith said.
The scientist said a smartweed plant can grow almost 3 feet tall and nearly as wide, making it a serious threat.
“Farmers can't afford to ignore it. It can compete with a rice plant for light and nutrients, and push the rice plant out of the way, causing it to lodge and making it impossible to harvest. Smartweeds suck up expensive fertilizer that should be going to rice plants.”
Bob Scott, another Arkansas Extension weed scientist, said the emergence of smartweed this year could also be tied to a change in herbicide programs used by rice farmers.
Scott said farmers traditionally used propanil to control grasses after those grasses emerged. Propanil also helped control broadleaf weeds, including smartweed. Smith added that propanil mixed with Storm, another herbicide, was the standard for controlling smartweed and grass.
Smith said, “Aim herbicide is also effective on young smartweeds that have not developed a rhizome system. However, neither of these programs is effective for long-term control of older smartweeds.”
Now farmers rely on Command, a pre-emerge herbicide that's more economical than propanil, according to Scott. It's effective on grasses, but it has no control over broadleaf weeds. This may have led to a shift in weeds in many fields, especially no-till rice fields, he said.
“Smartweed and other broadleaf weeds such as ground cherry, pigweed and morningglory, have become more prevalent. But smartweed has really emerged as a problem, because we don't have a good herbicide program to control it.”
Scott said products such as Duet, Storm and Aim and various combinations of those products have done a “fairly good job” of burning down smartweed before farmers flood their rice. However, the weeds often recover and grow back.
Newpath herbicide, when used with Clearfield rice, has shown promise. “At times it has shown good control on smartweeds, but control has been inconsistent. Clearfield growers have tank-mixed Aim or Duet with Newpath or made separate applications of Storm to improve smartweed control.”
Scott said farmers need rain to activate herbicides, but heavy rains can break down herbicides, leading to a loss in their effectiveness.
Lamar James is an Extension communications specialist with the University of Arkansas.