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Strategies to steward and keep Provisia technology viable with threat of weedy rice outcrossing.

Farm Press Staff

December 8, 2022

4 Min Read
weedy rice
Red rice, or weedy rice, that crosses with herbicide resistant cultivated rice can become very difficult to manage. LSU AgCenter

With the Provisia Rice System threatened by weedy rice outcrosses in some areas of Louisiana, industry leaders and farmers in the state have formed a working group to implement strategies to steward and keep this important technology viable for years to come. 

Recently, ag retailers from the Coastal rice production region packed the Acadia Parish Extension Office auditorium in Crowley, La., to hear the working group’s recommendations for best management practices (BMPs) for limiting the development of weedy rice outcrosses to the ACCase-inhibiting herbicide technology. 

“ACCase-resistant rice is the only thing we have right now for controlling weedy rice that has outcrossed with Clearfield rice,” said Connor Webster, weed scientist at the LSU AgCenter. “If someone brought a new technology forward today, it would take several years before it could be commercially available. That’s why it is so important that we maintain this effective tool and prevent losing its effectiveness at the rate we are today.” 

The working group was organized earlier this year after weedy rice outcrossing was reported in at least 15 instances in Provisia rice in Louisiana. It’s made up of representatives from Horizon Ag, BASF, rice industry retail, and Louisiana State University and extension leaders. 

“Right now, we have a major problem with weedy rice,” said Ronnie Levy, Louisiana rice specialist and a member of the working group. “It is an economic hardship on producers trying to control these weeds that really rob yields. If we can control it and increase our yields while keeping costs down, it is a win-win for producers.” 

“This working group and attendance at this meeting for retailers is a unique deal,” said Tim Walker, Horizon Ag general manager. Horizon Ag markets PVL03, the rice variety for the Provisia Rice System.  

“We know our retail partners are going to have a lot of grower interaction in the weeks and months ahead, and they are going to play a vital role in getting this concise, consistent message to the field,” said Brad Guice, BASF biology area manager, who presented recommendations for Provisia herbicide. “We’re pleased to be working the industry to promote recommendations for this important technology.” 

Provisia best management practices  

The LSU AgCenter recommended the following practices to avoid outcrossing with weedy rice in a Provisia rice system. 

Use residual herbicides.  

Command, Prowl and Facet herbicides with grass activity control grass so that maximum coverage can occur with Provisia herbicide onto the weedy rice. Using residual herbicides for broadleaf activity PRE or DPRE (Sharpen, Prowl, Facet, or Gambit herbicides) will also reduce the need to tank-mix with the Provisia herbicide.  

 Be cautious of tank mixing herbicides that might lead to antagonism. 

Connor Webster, weed scientist at the LSU AgCenter, recommends having at least one application of Provisia herbicide alone, or two applications alone in a three-pass system. The size and population of weedy rice should always dictate follow-up applications. 

 Know which herbicides to mix – and which not to mix.  

ALS-inhibiting herbicides can antagonize Provisia herbicide, although a second Provisia herbicide application 28 days after initial treatment can overcome much of the antagonism. Grasp and Regiment herbicides should be avoided for a tank mix, while sulfonylurea herbicides are better choices. For contact herbicides, Stam herbicide severely antagonized Provisia herbicide activity, so propanil mixtures should be avoided. Basagran and Sharpen herbicides antagonized Provisia herbicide activity at 14 days after treatment but were not antagonistic at 28 days. 

 Be diligent and clean fields up late-season. 

If weedy rice is present, it needs to be taken out. This may mean using late-season herbicide applications, roguing, or spot spraying. 

 Consider crop rotation for success.  

Do not plant in the year following Clearfield rice or where an imidazolinone herbicide was used the previous year due to the risk of carryover damage from the herbicide. 

 Be aggressive in fallow ground and soybeans. 

Use tillage and Roundup herbicide with residuals to increase the time between applications. 

 BASF Recommendations 

Additional recommendations from BASF include, 

  • Use only Provisia herbicide over the top of Provisia rice. 

  • Start clean, with burndown and/or tillage. 

  • Let the size and population of weedy rice dictate follow-up applications. 

  • Use residuals like grass and broadleaf herbicides for broad-spectrum control. 

  • Do not mix Provisia herbicide with herbicides that have the potential to be antagonistic. 

  • Apply Provisia herbicide to actively growing grasses, red rice and volunteer rice. 

  • Make at least two (but no more than three) Provisia herbicide applications no later than panicle initiation. 

  • Use proper carrier volumes of 10-15 GPA by ground and by air. 

  • Clean equipment/combines. 

  • Harvest fields with weedy rice last. 

  Louisiana rice growers typically rotate between rice and crawfish production. Specific recommendations for crawfish production include: 

  • Don’t allow Provisia rice to go to seed in crawfish production. 

  • Don’t allow Provisia rice to go to seed in a non-rice year, including fallow or crawfish fields. Control weedy rice and red rice at pond edges with glyphosate or other chemical or cultural methods. 

  • Avoid using Provisia rice for green rice/crawfish forage production. 

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