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Possibility of resistant sicklepod concern for peanut farmers

Staff writer |
The possibility of sicklepod weed becoming resistant to herbicides is a potential concern for all Georgia peanut farmers.




Eric Protsko, a weed scientist with the University of Georgia College of Agricultural and Environmental Sciences said that.

Sicklepod weeds look similar to peanut plants, though the leaves are a little wider and a lighter green than those of the peanut plant, Clint Thompson of University of Georgia writes for AG Professional.

The weed is a concern for peanut farmers every year because the seed remains viable in the soil for at least five years and can germinate from a 5-inch soil depth. This makes the weed almost impossible to control with residual herbicides, and there are no peanut herbicides that provide adequate residual control.

Sicklepod is especially threatening, considering it is self-pollinating, meaning it doesn't require additional plants or insects to spread throughout a field. Approximately 14,000 seeds are produced per plant, far fewer seeds than Palmer amaranth.

Cotton farmers have struggled to contain Roundup-resistant Palmer amaranth in recent years, and now some peanut farmers are having difficulty managing sicklepod.

Through greenhouse research on the UGA Tifton Campus, Prostko is studying whether this is a production problem or a resistance issue.

"Now that our senses are heightened because of our problems with Palmer amaranth, we are looking at whether every failure we've had has been a true herbicide resistance problem. That's the issue," Prostko said. "Enough people start talking about it, a couple of good growers tell you they're experiencing management concerns, then maybe we do need to take a closer look at it."

To complete this research, Prostko, UGA graduate student Wen Carter and fellow UGA weed science researcher Bill Vencill are studying the effects of the herbicide Cadre, which may be farmers' best treatment option against sicklepod. The research project has more than a year left before it's complete, as 30 populations need to be screened.

In some preliminary screenings, Vencill identified a few suspect sicklepod populations, according to Prostko.

"However, we don't know how widespread it is or how much of a problem it is. I think there are other issues that might be going on, such as delayed applications or reduced spray coverage at faster tractor speeds. The only way to know for sure is for us to do what we're doing and come up with a better picture of what might be out there."

Timing is crucial for the researchers as they don't want to allow the test plants to produce seeds.

"If we let them go to seed, you've just made a big deposit in the soil seed bank, which could be a potential problem," Prostko said.

Farmers' best mode of action is to treat with Cadre; however, those actions may be futile if resistance is truly an issue.

"I wouldn't be surprised if we had a lot of resistance because it (the herbicide) has been around a while," Prostko said.

Sicklepod and Foetid Senna are aggressive invaders of pasture and can completely dominate grass species, eradicating pasture growth and excluding stock. Carrying capacities can be reduced by as much as 85%. It is conceivable that properties could become completely unproductive.

Although it is generally unpalatable to stock, if eaten, sicklepod is toxic to cattle. If left to grow in a sugar cane crop, Sicklepod can have a significant effect on yield. Processing contaminated cane can cause machinery breakdowns at sugar mills because of the woody nature of Sicklepod.

Sicklepod is also causing concern as an environmental weed in some native ecosystems in Far North Queensland. Its current distribution suggests that it may be able to invade open native plant communities.

Feral cattle, feral pigs and the occurrence of natural events such as cyclone, which open up the forest canopy, are likely to enhance the possibility of invasion into pristine areas and it is currently threatening small remnant areas of native grassland in the Wet Tropics.

While there is no evidence that Sicklepod is currently an aggressive environmental weed in Australia, this may be because its impact is not yet evident. The information available suggests that its environmental impacts may increase in the future.

Sicklepod is native to the Caribbean region and tropical America while Foetid Senna is native to Asia, from India to China and Polynesia.

Sicklepod is one of the most difficult weeds to control in soybeans. Although less competitive on a per-plant basis than many other common annual broadleaf weeds, heavy infestations can reduce soybean yields 60 to 70 percent or more. In addition, a price dockage may occur because of foreign matter (sicklepod seed) in the harvested product.

There are numerous benefits to be obtained from planting soybeans in narrow rows. Adequate sicklepod control can often be obtained in narrow-row soybeans.

Planting soybeans in wide rows may be less risky than planting in narrow rows where sicklepod is a major problem. Planting soybeans in wide rows provides more options for sicklepod control. Planting in wide rows makes it possible to cultivate and to make postemergence-directed herbicide applications.

Research in Alabama has shown that reductions in sicklepod infestations can be obtained only when intensive management systems providing virtually complete control are followed for a number of years. Maintaining sicklepod populations at the economic threshold level resulted in tremendous increases in the sicklepod seedbank over time.


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