Information from 2000 Missouri Rice Research Update, February 2001.

2000 Summary Of Herbicide Evaluations In Rice

Andy Kendig and Anthony Ohmes

The 2000 season saw an increase in rice research. Twenty-seven research studies were conducted at two locations. Preemergence, postemergence grass and broadleaf, and conventional herbicide program studies were evaluated on a silt loam and clay soil. In addition, several experimental herbicides and programs designed around these experimental herbicides were evaluated. Many of these studies were funded by the Missouri Rice Council. Funding was also provided by The Rice Foundation for a study on a silt loam and clay soil.

The objectives of this report are to present a brief update of new herbicide chemistry and provide an overview of studies conducted this past year which evaluated new chemistry or newly labeled products for rice.

Section 1. The following is a brief summary of experimental herbicides that are currently being developed.

Aim was registered for POST use on rice. Aim provides control similar to Blazer of some rice weeds.

Aura, Clincher, Ricestar are postemergence grass herbicides for rice being developed by BASF, Dow ArgroSciences, and Aventis, respectively. These types of herbicides control no broadleaf weeds. The grass activity appears to be size sensitive (much like Stam) and further research is needed into how these herbicides will work into an overall weed control program. Ricestar is a new formulation of Whip 360 with the addition of a new "safening" compound. The addition of the safener has reduced rice injury as well as control of larger grass. Therefore, Ricestar should not be used as a salvage treatment.

Clearfield Rice. "Clearfield" is BASF's formerly American Cyanamid's new trademark for "IT", "IMI", or Pursuit-resistant crops. Research on Pursuit-resistant rice continues to show promise as well as complications. In Arkansas, POST applications of Pursuit have been injuring the "resistant" rice. In Missouri, PPI and PRE applications (potential benefits of this system) have been providing poor weed control. With Clearfield rice a grower could selectively control red rice in his/her crop. One concern will be the possibility that the herbicide resistant rice could cross breed with red rice and generate Pursuit-resistant red rice. Registration is expected in approximately two years.

Command has received a full section 3 label for use in rice. There were virtually no reports of crop injury nor off-target injury and growers have been pleased with the combination of good grass control at a low price and convenience of use. Over the last four years, Command has also been more consistent than Prowl.

Liberty Link Rice. Liberty is a fast-acting, non-selective herbicide and has performed similarly to Stam, including the fact that grass must be small and actively growing. With herbicide-tolerant Liberty rice, growers can selectively control red rice in rice. One concern will be the possibility the herbicide-resistant rice could cross breed with red rice and generate Liberty-resistant red rice.

Regiment is a POST herbicide for rice from Valent. This herbicide controls a number of troublesome rice weeds and is especially noted for killing very large barnyardgrass. However, it can be weak on broadleaf signalgrass, crabgrass, fall panicum and sprangletop. This herbicide will likely be used as a pre or postflood clean up application for grasses which escape Command, Prowl, Stam or Arrosolo-based programs.

Section 2. The following section is a brief overview of selected studies conducted this past season. Research of interest include Command programs, Liberty Link vs. Clearfield programs, total postemergence NewPath (Pursuit) programs on Clearfield rice, new chemistry (Aura, Clincher, Ricestar, Regiment) injury and tank-mix antagonism, sodium chlorate desiccation timing, and herbicide tolerance of Baldo rice.

Command programs were evaluated at the silt loam and clay locations. Like Bolero, Facet and Prowl, Command is PRE herbicide that could offer some residual activity to a Stam application. Research was conducted to investigate potential crop injury and barnyardgrass control with a Command + Stam tank mixture. Command was applied at 21.3 oz/A. No injury from Command + Stam POST was observed at the clay soil location. There was injury at the silt loam location. However, injury from the labeled rate of 21.3 oz/A was comparable to PRE applications at the same rate and did not negatively influence yield. Weed control was evaluated at the silt loam location. Command PRE at 21.3 oz/A followed by Grandstand or followed by Regiment provided good barnyardgrass and hemp sesbania control through the season.

A Clearfield versus Liberty Link rice study was conducted at the silt loam and clay locations. Clearfield and Liberty Link rice are tolerant to NewPath (Pursuit) and Liberty herbicides, respectively. Both herbicides provide red rice control. Research was conducted to assess potential crop injury and red rice as well as barnyardgrass control. NewPath programs included preplant incorporated (PPI) and PRE applications of 5 and 6 oz/A, alone and followed by POST applications of 2 and 3 oz/A. A sequential total POST program of 2 oz/A early POST followed by 2 oz/A pre-flood was evaluated. Blazer was added to POST NewPath applications for hemp sesbania control. Liberty programs included single applications early POST, pre-flood, and post-flood; sequential applications early POST followed by pre- or post-flood; and three applications at the three timings. Application rates were 30 oz/A for single, 30 and 60 oz/A for sequential, and 20 and 30 oz/A for three applications.

Clearfield. No crop injury was observed at either location. Two applications of Newpath provided more consistent control compared to single applications of both barnyardgrass and red rice. Single soil applications at 5 and 6 oz/A provided <85% barnyardgrass and red rice control. Single PPI and all sequential applications at the silt loam location provided >70% barnyardgrass control while single PPI (clay location) and PRE (both locations) applications provided <60% barnyardgrass control. Single PPI at 6 oz/A and sequential applications of Newpath at the silt loam location provided 80% to 90% control of red rice. There was a 10% or greater decrease in weed control in general at the clay location. One might argue that increased adsorption from increased clay content would explain the overall decrease in weed control. However, 80% to 90% barnyardgrass and red rice control at mid-season (8 weeks after planting) in the silt loam, under certain conditions, may not be enough for season long control.

Liberty Link. No crop injury was observed at either location. Similar to the Clearfield technology, two or more applications of Liberty were more consistent than single applications. Although too late for beneficial control of barnyardgrass and red rice, the post-flood single application did provide control similar to multiple applications. Three applications at 30 oz/A provided >85% control of barnyardgrass and >90% control of red rice at both locations. At the clay location, sequential treatments that included a post-flood application provided 100% control of red rice 10 weeks after planting. These data suggest and support previous research which indicates that multiple applications which include a POST-flood application will be necessary for control of barnyardgrass and red rice.

POST sequential NewPath programs were evaluated for barnyardgrass and red rice control. One of the potential problems in Missouri that we have seen with this herbicide is the inconsistent and poor barnyardgrass control from PPI and PRE applications. Research was conducted to see if a total POST program would be more beneficial for Missouri. Application timings were early POST followed by pre-flood. NewPath rates of 2, 3, and 4 oz/A followed by 2, 3, and 4 oz/A were applied in all combinations for a total of nine treatments.

With the exception of 2 oz/A followed by 2 oz/A or 3 oz/A and 4 oz/A followed by 3 oz/A, sequential applications provided 90% or greater control of both barnyardgrass and red rice late in the season. NewPath at 4 oz/A followed by 3 oz/A provided 93% and 80% control of barnyardgrass and red rice, respectively. However, at the clay location only the 3 oz/A followed by 4 oz/A and 4 oz/A followed by 4 oz/A programs provided above 80% control of both barnyardgrass and red rice late in the season.

These data suggest that a total POST-sequential program could work for Missouri producers. The 3 oz/A or 4 oz/A followed by 4 oz/A NewPath programs have been most consistent over both soils.

Aura, Clincher, Ricestar and Regiment are four experimental herbicides being evaluated for crop injury and grass control. Regiment is the exception in the group because it is an ALS-inhibiting herbicide which has activity on selected broadleaves, as well. Since these products have a narrow weed control spectrum, the focus of most of our research is to fit these products in some sort of program.

A study was initiated in 1999 to evaluate these products and Whip 360 alone at various POST timings in order to determine what these products will bring to a weed control program. The treatments were 12.8 and 17 oz/A of Ricestar, 6.7 and 10 oz/A of Clincher, and 5 and 7.2 oz/A of Aura rates applied to 2- to 3-leaf, 4- to 5-leaf, 6- to 8-leaf (preflood), and 10- to 14-leaf (postflood) barnyardgrass in rice.

No significant injury was observed from the experimental products in 2000. Minor injury was observed from Whip 360. Weed control data collected in 1999 indicated that Aura, Clincher, and Ricestar should target small (2-3 inch) actively growing grass, much like Stam. Regiment has shown to have good activity on larger barnyardgrass, as well.

Since Aura, Clincher, and Ricestar are grass compounds, research, initiated in 1999, was conducted to evaluate various tank mixtures with broadleaf compounds in order to evaluate any potential antagonism problems. The study was conducted on a Crowley silt loam. The treatments were Ricestar at 17 oz/A, Clincher at 10 oz/A, and Aura at 7.2 oz/A applied alone and in tank mixtures with Basagran, Blazer, Grandstand, Londax, Permit, Aim, and Stam on 4- to 5 -leaf barnyardgrass. Results from 1999 and 2000 were mixed. Ricestar showed some antagonism to Permit and Aim in 1999. However, 2000 results showed no antagonism with these products. No antagonism was observed with Clincher tank mixes in 2000. Ricestar and Aura grass control was reduced when tank-mixed with Stam in 2000. The inconsistencies of these two years indicate that more research should be done in order to confirm any antagonism problems.

Sodium chlorate is a crop desiccant which can be used as a harvest aid in rice. Although it is labeled, many producers are reluctant to use sodium chlorate because of questions about sodium chlorate's effect on rice moisture, stand, harvest ability, and milling yield. Preliminary research in Louisiana has indicated that use of a harvest aid too soon before harvest could negatively influence milling yield. One potential benefit of using a harvest aid is the crop possibly drying down faster in the field resulting in quicker harvest and maybe reducing post-harvest drying costs.

Research was conducted in 2000 to evaluate sodium chlorate as a harvest aid in a conventional rice variety. Sodium chlorate was applied at 3 lb/A (1/2 X rate), 6 lb/A (X rate) and 9 lb/A (1 1/2 X rate). Sodium chlorate was applied every other day beginning at 12 days prior to harvest for a total of six application timings. Moisture, yield and milling yield were evaluated.

Although moisture was different prior to each application, at-harvest moisture was not affected by the sodium chlorate when compared to the untreated check. Yield and milling yield did not differ among application timings as well. The preliminary data suggest that 12 days up to 2 days before harvest does not greatly influence rice harvest. Perhaps application timings greater than 12 days before harvest would provide more information as to a beneficial application timing.

Baldo rice was evaluated for crop tolerance to currently labeled as well as experimental products. Research was conducted to evaluate the safety of both preemergence and postemergence herbicides on Baldo as compared to Jefferson. The objective of this study was to determine if Baldo rice has similar crop tolerance to rice herbicides as a standard variety. The PRE and delayed-PRE herbicides were Command, Prowl and Bolero. The labeled POST herbicides were Arrosolo, Whip, and Grandstand. Other POST herbicides, which have not received a label approval yet, were Ricestar, Aura, and Regiment. Herbicides were applied at standard and double use rates.

Baldo did not recover from Command injury as quick as Jefferson. However, yield was not significantly decreased from Command. Injury from other herbicides evaluated was similar in both varieties, none of which negatively influenced yield.

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