Integrated Approach Aims to Preserve the Provisia and Max-Ace Technologies
⋅ BY FORD BALDWIN ⋅
My career as a rice weed scientist began at the University of Arkansas in 1974. While barnyardgrass was the No. 1 weed problem in rice, weedy rice (Oryza sativa L.) was the most difficult-to-control weed. Before the introduction of Clearfield rice in the early 2000s, the primary means of managing weedy rice was through crop rotation and striving for the complete prevention of seed production in the rotated crop. This zero-tolerance principle comes full circle in this article.
I have participated in developing and using the Clearfield and FullPage rice technologies, which made weedy rice management in the cultivated rice crop relatively easy until recent years. I am now witnessing an expansion in the types of weedy rice along with the widespread failure of the Clearfield and FullPage systems on this weed. The recent introduction of the quizalofop-tolerant rice technologies, Provisia and Max-Ace, offer an effective control option. However, unless the quizalofop-tolerant technologies are better managed, they will be very short-lived, with no new weedy rice control technologies on the foreseeable horizon.
The Problem
Data from Dr. Jason Norsworthy, distinguished professor at the University of Arkansas, provides a graphic description of the weedy rice problem. Dr. Norsworthy stated in a recent presentation that of 140 weedy rice populations tested since 2022, only one population was controlled by the herbicides used in Clearfield and FullPage rice. While the Clearfield and FullPage technologies offer residual and post-emergence control options for other weeds, these systems have become ineffective for weedy rice control.
Horizon Ag commercialized Provisia in 2018, with Max-Ace rice from RiceTec following in 2021. Many growers viewed these technologies as a tool they could rotate with Clearfield or FullPage rice to solve their weedy rice problem. Recent resistance screening data suggests otherwise. Of the 140 weedy rice samples tested by Dr. Norsworthy over the past three years, 15 samples were resistant to quizalofop (Provisia or Highcard) herbicide. Of those 15 positive samples, 11 were from fields where continuous rice had been grown, and no field history accompanied sample submission for the other four resistant samples.
No resistant samples came from fields rotated to soybean within a two- to three-year period. Perhaps the big hammer is that all 15 quizalofop-resistant samples were also resistant to the imidazolinone herbicides used in Clearfield and FullPage rice. Therefore, relying only on rotation from quizalofop-tolerant rice (Provisia or Max-Ace) to one of the imidazolinone technologies (Clearfield or FullPage) for weedy rice control is futile.
Throughout my career, I have frequently made the statement, “The weeds are talking, is anybody listening?” The weeds will tell you what you need to do. The first thing the weeds are telling us is the weedy rice problem is greatest in continuous rice. Much of this is in zero-grade fields that were constructed for the purpose of growing continuous rice. There are situations where this is no longer sustainable.
The second thing the weeds are telling us is the Provisia and Max-Ace technologies are prone to fail quickly without proper stewardship — more so than what occurred with the imidazolinone-tolerant rice technologies. Since the quizalofop-resistant weedy rice is also resistant to the imidazolinone herbicides, rotation between Provisia or Max-Ace with Clearfield or FullPage is destined to fail quickly, rendering all technologies useless. The obvious answer is an integrated approach to weedy rice management utilizing all tools in the toolbox.
The Integrated Approach
The program outlined here targets fields where weedy rice has become enough of an issue for farmers to switch to Provisia and Max-Ace rice. The components in the program have been thoroughly researched by Dr. Norsworthy and others with the University of Arkansas Division of Agriculture. They have been successfully put into practice by Terry Gray, a zero-grade rice farmer at Delaplaine, Arkansas, who had created and has now solved a severe weedy rice problem.
The first component of an integrated system involves crop rotation. Yes, that means growing soybeans in zero-grade fields, when most growers either do not wish to, or they believe they will be unsuccessful doing so. Terry Gray recently told me “it can be done — we aren’t setting records, but we are being successful growing soybeans, and we are cleaning up fields.” Therefore, before depending heavily on Provisia or Max-Ace rice, plant the field to soybean or, as an alternative, fallow it.
In the soybean crop (or fallow), the goal is 100% control of weedy rice — as in 1974, none must go to seed! Overlap residuals such as metolachlor (Dual) or pyroxasulfone (Zidua). Both are highly effective on weedy rice. Use high rates of glyphosate (Roundup) and glyphosate plus glufosinate (Liberty) mixtures — whatever it takes for 100% prevention of seed production. While glufosinate can struggle on some grasses, it is highly effective in controlling weedy rice.
The second component is to plant Provisia or Max-Ace rice the following year and meticulously follow the recommendations on the Provisia or Highcard labels. The key to success here is early timing. Both Dr. Norsworthy and Terry Gray emphasize that the first Provisia or Highcard application be made to two-leaf rice. In both programs, soil residual herbicides should be overlapped for grass control to maximize the weedy rice coverage and control with Provisia or Highcard. A second application of Provisia or Highcard should be made immediately before flooding, and the field should be flooded as soon as possible.
Quizalofop herbicide has no residual activity, meaning that every day between application and flood establishment is an opportunity for weedy rice to emerge. Furthermore, the lack of residual control with quizalofop makes grass control more challenging than in the Clearfield/FullPage systems, where imidazolinone herbicides have provided residual control up to flood establishment. Dr. Norsworthy even suggests a third application of Provisia be made as soon as the flood is established to control any weedy rice above the flood. Both Dr. Norsworthy and Terry Gray emphasize moving the flood date up at least a week. Terry says “begin trying to flood three-leaf rice and hope you get it done by four-leaf.”
The third component in this system is utilizing Rogue SC herbicide applied as soon as the flood is stabilized. The Rogue SC will control susceptible strains of weedy rice at most any stage and will suppress all strains that are completely covered with the flood water. Rogue SC is a key component in controlling any weedy rice missed by the Provisia or Highcard and other weeds such as sprangletop, aquatics, and annual sedges.
Following this year of Provisia or Max-Ace rice, consider rotating back to soybean. Soybean provides the potential for three years of zero tolerance for weedy rice seed production before rotating back to the rice of your choice. If ANY weedy rice produces seed in the Provisia or Max-Ace system, the chances for outcrossing are very high, and outcrossing will render these technologies useless.