New rice herbicides on the horizon, Arkansas researcher reports

Jason Norsworthy says growers tell him he’s always bringing them bad news when he speaks at meetings around the state.

Most of the time, Norsworthy, professor of weed science at the University of Arkansas, is talking to farmers about resistance, the number of herbicides they need in their weed control program or a new weed that’s become resistant to one or more herbicides.

“Why can’t you give us a better message?” said Dr. Norsworthy, speaking at the Roy J. Smith Barnyardgrass Workshop in Stuttgart, Ark. “Growers tell me ‘Every time I see you, everything you’re going to tell me is about what’s wrong, about something that’s broken.’

“Part of the reason for putting this program together today is that I wanted to be the one to bring you some good news,” he said. “There are some exciting things happening in rice. If things go as expected over the next few years, we could have some exciting changes in our fight against barnyardgrass and other problem weeds.”

The key, Norsworthy and other speakers at the workshop said, is to make the tools currently available to rice producers battling herbicide-resistant barnyardgrass last until the new products can make it through the EPA approval process.

Norsworthy and other weed scientists at the University of Arkansas, Louisiana State University, Mississippi State University and Texas A&M University organized the workshop to provide growers and consultants with the latest information on the problem of barnyardgrass resistance to multiple herbicides.

Barnyardgrass, barnyardgrass...

According to surveys of growers and consultants, barnyardgrass is the No. 1 problem weed in rice. It’s the driver weed, so to speak, the weed that becomes the center of growers’ efforts to produce a weed-free rice crop.

“The No. 1 weed in rice is Barnyardgrass,” said Norsworthy. “What’s No. 2?”

Someone in the audience responded “Barnyardgrass.”

“That’s what I tell people,” said Norsworthy, who holds the Elms Farming Chair of Weed Science at Arkansas. “If you rank them by the amount of the weeds we see, it’s barnyardgrass, barnyardgrass and barnyardgrass.”

According to the survey of growers and consultants, sprangletop is the No. 2 problem weed in rice, followed by red rice; joint vetch; Palmer amaranth; coffeebean or hemp sesbania; smartweed; signalgrass; three sedges, yellow nutsedge, rice flatsedge and smallflower umbrellasedge; and three aquatics, ducksalad, arrowhead and roundleaf mud plantain.

“What’s interesting is that Palmer amaranth went from not even being considered an important weed in rice 10 years ago to where it’s now the fifth most troublesome,” said Norsworthy.

Besides being problem weeds, Norsworthy said, most of those – with one possible exception – can be controlled by the new compounds he tested in his university herbicide trials in 2014.

Most in a year

“Eight new herbicides. That is the most I have looked at in rice or I would say in any crop in one year,” he said. “Of those eight herbicides, seven had activity on barnyardgrass. That’s why I’m so excited about these herbicides.

“I will be honest with you,” he noted. “Of the herbicides that I evaluated in 2014, some will not make it past 2014. But there are some that did. I will be talking basically about the herbicides that did make it beyond 2014.”

Norsworthy said the new herbicides encompass four different herbicide modes of action. “That’s what really gets me excited – these are new chemistries, new modes of action which could be added to our arsenal.”

Included in the herbicides are:

Provisia – A new weed control system from BASF that will be centered on rice lines that are tolerant to quizalofop (Assure) grass herbicide.

Benzobicyclon – Anew grass, sedge and broadleaf herbicide that can be applied post-flood in rice.

Pethoxamid – a new rice herbicide with activity similar to Dual that will provide “excellent” control of annual grasses and suppression of sedges. Its best fit may be in a system that include clomazone or Command pre-emergence followed by pethoxamid and Newpath.

Rinskor Active – A new rice herbicide that controls barnyardgrass, broadleaf signalgrass, yellow nutsedge, pitted morningglory and coffeebean. Its best fit will probably also be in a tank mix with Newpath.

Norsworthy said Provisia and benzobicyclon could each be available in 2017 while pethoxamid and rinskor active could be approved by 2018. Another weed control system involving rice that is resistant to Callisto and Fusilade may also be in the mix, but no time table is available on when it might come to market.

“These are very exciting herbicides,” said Norsworthy. “But we – and I’m pointing to myself, to Extension, to consultants and growers – must do a better job of preserving the herbicides we have until we can reach the next stage.”

For more on controlling barnyardgrass, go to www.uaex.edue and click on publication number FSA2175.

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