Weed Control in Rice, 2015

 

Project Leader

Kassim Al-Khatib, professor & UCCE specialist, Weed Science Program, Dept. of Plant Sciences, UC Davis

he weed management project seeks to assist California rice growers in achieving economic and timely broad-spectrum weed control, the prevention and management of herbicide-resistant weeds, the development of new tools and technology to manage weeds in rice, and to comply with personal and environmental safety requirements.

Research in 2015 focused on the efficacy of new and existing herbicides, alternative crop establishment methods as a means of altering weed dynamics, and herbicide resistance strategies to deal with this problem in California rice fields.

Herbicide programs

Herbicides research was conducted in continuous flood, pinpoint flood, and drill-seeded rice at the Rice Experiment Station. Several herbicide combinations delivered near-perfect weed control. Following are highlights of this work.

CONTINUOUS FLOOD SYSTEMS

Continuous flood systems promote the suppression of weeds such as barnyardgrass and sprangletop. Predominant weeds in this system include early and late watergrass, followed by ducksalad, ricefield bulrush, smallflower umbrella sedge, redstem, and sprangletop.

Several granular into-the-water herbicides are available that can be applied early to provide good to excellent control, including Bolero®, Cerano®, Granite®, Halomax®, Londax®, and Shark® H20. Combining two of these herbicides can provide broad-spectrum control.

Foliar herbicides are often necessary to achieve excellent weed control in rice. Applied as a follow-up, these herbicides not only extend the spectrum of weed control, but also may help manage herbicide-resistant weeds. Herbicides available for foliar application include Abolish®, Clincher®, Granite® SC, Regiment®, RiceEdge®, Shark® H20, SuperWham!® or Stam®, Halomax®, and Londax®.

In studies of the efficacy of sequential and herbicide combinations, all Bolero®-based programs applied at the 2-leaf stage of rice provided 100% control of watergrass, sprangletop, and smallflower umbrella sedge. Inclusion of SuperWham!® with a crop oil concentrate at the 1-tiller stage or Regiment® at the 4-leaf stage of rice improved control of ducksalad. However, ricefield bulrush control was limited to 85%. A tank mix of Granite® SC and SuperWham!® applied at 4-leaf stage of rice provided 100% control of ricefield bulrush. Although Bolero®-based programs provided excellent control of grasses and ALS- and propanil-resistant smallflower umbrella sedge, a substantial level of stand reduction was observed.

Cerano® applied at the day of seeding provided more than 90% watergrass and sprangletop control. A foliar application of Super Wham! ® at 1-tiller stage following Cerano® provided perfect watergrass control, although control of ricefield bulrush and smallflower umbrella sedge was less than 75%. Cerano® followed by a granular application of Shark® H20 with Londax® or Halomax® at 3-leaf stage of rice, and then followed by a late foliar application of SuperWham!® at 2-tiller stage provided complete control of all weed species. An alternative with similar efficacy was Cerano® followed by Granite® GR at 3-leaf stage of rice, followed by a tank mix of Abolish® with Regiment® at 5-leaf stage of rice.

Granite® GR offers a broader spectrum of weed control compared to Bolero® and Cerano®, although it lacks efficacy on sprangletop and redstem. While a follow-up foliar application of SuperWham!® alone at 1-tiller stage offers overlapping control of some weed species, it does not control sprangletop and redstem. Granite® followed by a tank mix application of Abolish® with Regiment® at 5-leaf stage of rice provided 100% sprangletop control. The addition of Shark® H20 at the 2.5-leaf stage of rice maximized overall weed control.

The Shark® H20-based programs offer control of ALS- and propanil-resistant ricefield bulrush and smallflower umbrella sedge. A follow-up tank mix application of Abolish® with Regiment® at 5-leaf stage of rice controlled multiple-resistant watergrass escapes. Another option is to use Regiment® at the highest label rate at the 4-leaf stage of rice.

For Clincher®-resistant sprangletop, a program with a granular application of Cerano® day of seeding or Bolero® at 1-leaf stage of rice, followed by a foliar application of Abolish® at 5-leaf stage of rice, is recommended.

Butte® is a granular mixture of benzobicyclon and halosulfuron developed by Gowan® for use in water-seeded rice. It has good activity on sedges such as ricefield bulrush and is also effective on young watergrass seedlings. Rice is generally tolerant to this herbicide, although some stunting was observed in combinations with Cerano®. Butte® provides good broad-spectrum weed control. Combining it with herbicides such as Clincher®, Cerano®, and Granite® will improve grass weed control at later stages of rice development.

Butte® was evaluated at two rates—both alone and in combination with other herbicides. Applied early postflood, Butte® provided a broad spectrum of weed control with an exceptional level of crop safety. A follow-up 1-tiller stage application of SuperWham!® with Grandstand®, Granite® SC, or Regiment® provided 100% control of all weeds. While stand-alone applications of Butte® offer excellent weed control in water-seeded rice, a follow-up application or inclusion of a partner granular herbicide will improve weed control.

Strada® is a granular formulation of orthosulfamuron (an ALS-inhibiting herbicide) developed by Nichino America Inc. Efficacy of this compound was evaluated in a Cerano®-based program tank-mixed with SuperWham!® or Shark® H20 at 35 days after seeding (2-tiller stage). Cerano® followed by a tank mix of Strada® with SuperWham!® or Shark® H20 provided more than 95% control of watergrass and more than 80% control of ricefield bulrush. Smallflower umbrella sedge control was more than 95% with the program containing SuperWham!®.

PINPOINT SYSTEM

In this system the field is completely drained during a foliar herbicide application (2- to 4-leaf stage of rice), exposing more of the weed foliage for control. Prevailing weeds in experiments were ricefield bulrush, ducksalad, early and late watergrass, smallflower umbrella sedge, redstem, and sprangletop.

SuperWham!® applied alone at 4-leaf stage of rice provided more than 97% control of watergrass, ricefield bulrush, and smallflower umbrella sedge. When tank-mixed with Clincher®, SuperWham!® at 4-leaf stage of rice was effective in controlling both watergrass and sprangletop. One week after this treatment, a tank mix of Clincher® and Granite® SC provided perfect control of all weeds. With two follow-up applications of Shark® H20 at 4-leaf stage of rice and Abolish® with Regiment® at 5-leaf stage of rice, the overall efficacy was 100%. The addition of Shark® H20 to the weed management program offers improved efficacy, including control of ALS inhibitor- and/or propanil-resistant sedges. The tank-mix application of Regiment® with Abolish® provides a synergism effect on watergrass and also helps in controlling multiple herbicide-resistant watergrass.

A single application of Clincher®, Granite® SC, and Abolish® at 2- to 3-leaf stage of rice provided 100% control of watergrass and sprangletop—and excellent control of ducksalad, ricefield bulrush, and smallflower umbrella sedge. This program will not control ALS-resistant ricefield bulrush and thiobencarb-resistant watergrass populations. However, it is a good alternative for fields with Clincher®-resistant sprangletop populations. Similar results were obtained when Regiment® or Granite® SC were applied at the 3- to 4-leaf stage of rice, followed by a tank mix of SuperWham!® with Clincher® at the 1-tiller stage.

Excellent control of watergrass, sprangletop, ricefield bulrush, and smallflower umbrella sedge was achieved by Clincher® alone at 3- to 4-leaf stage of rice, followed by a tank mix of SuperWham!® with Grandstand® at 1-tiller stage or Abolish® with SuperWham!® at 3- to 4-leaf stage followed by Granite® SC alone at the 1-tiller stage. Grandstand® effectively controls ricefield bulrush and redstem and is particularly useful in fields with herbicide-resistant populations of these weeds. Abolish® is a better choice than Grandstand® when ducksalad is predominant.

DRILL-SEEDED RICE

Drill-seeded systems offer flexibility for herbicide use when proximity to sensitive crops restricts aerial applications. Drill seeding favors weeds that are adapted to dryland seedbeds such as sprangletop and barnyardgrass and is less favorable to aquatic species such as ricefield bulrush, ducksalad, and redstem. In 2015 experiments, the prevailing weeds were early and late watergrass, barnyardgrass, smallflower umbrella sedge, and sprangletop.

Abolish® and Prowl® are valuable residual herbicides that provide early weed control up to the start of permanent flood. Both herbicides suppress watergrass and barnyardgrass. However, Abolish® is more active on smallflower umbrella sedge than Prowl®. Regular flushing before permanent flood activates these herbicides and also helps in the establishment of rice plants. For a delayed pre-emergence application of these herbicides, rice seed is first drilled into dry soil and then the field is flushed once before herbicide application. One or two follow-up foliar herbicide applications are necessary for effective control.

Prowl® provided 62% control of watergrass species and 31% control of smallflower umbrella sedge. Abolish® was less effective on watergrass than Prowl®, although it was exceptionally effective on smallflower umbrella sedge. All the foliar applications following the Prowl® treatments provided excellent control of smallflower umbrella sedge (98% to 100%). A foliar application of SuperWham!® alone, following Abolish® or Prowl® application, improved control of watergrass compared to Prowl® alone but was not adequate. Following the pre-emergent application with a tank mix of Abolish® and Regiment® at 5-leaf stage of rice, watergrass control was greatly improved. Foliar applications of Prowl® with SuperWham!® and Clincher® at 3-leaf stage of rice and Shark® H20 at 4-leaf stage of rice provided excellent control of watergrass species. In this program, the second application of Prowl® extends suppression of watergrass, whereas the tank mix of SuperWham!® and Clincher® provides overlapping efficacy on emerged barnyardgrass and watergrass. Shark® H20 supplements SuperWham!® for controlling smallflower umbrella sedge (including propanil-resistant types). This is an intensive program for controlling watergrass and sedge and is particularly suited for controlling herbicide-resistant populations of grasses and sedges. Similar levels of weed control may be achieved without Shark® H20 when Abolish® is used in a delayed pre-emergence application and watergrass and smallflower umbrella sedge are susceptible. Use of Abolish® and Prowl® in alternate years will help to limit the development of resistant watergrass.

Herbicide research

Five experiments were conducted in 2015 to evaluate different formulations, adjuvants, and new active ingredients in a continuous flood system.

Butte®—A new formulation of Butte® that more rapidly releases in water slightly improved early and late watergrass control compared to the existing formulation. The new formulation provided equal control of ducksalad, ricefield bulrush, and smallflower umbrella sedge compared to the existing formulation. It was found to be safe on rice. Grain yields for both formulations was equal.

Rice Edge®—Rice Edge® 60 DF is a formulation of propanil with halosulfuron from RiceCo LLC for use as an alternative to SuperWham!®. Tested under both continuous and pinpoint flood systems, it provided good to excellent control of grasses, sedges, and broadleaf weeds when applied at 5-leaf stage of rice. Weed control was not as effective at 3-tiller stage.

NAI-1777—NAI-1777 is a granular formulation of pyraclonil from Nichino America Inc. that has a similar mode of action to Shark®. A rate and timing study showed that this compound has excellent activity on sedges (ricefield bulrush, smallflower umbrella sedge). It also has good activity on ducksalad. It demonstrated excellent crop safety when applied at 1-leaf stage of rice.

NAI-1444—NAI-1444 is a granular formulation of ipfencarbazone from Nichino America Inc. that has a similar action to metolachlor (Dual®). It showed good activity on early and late watergrass and also showed good activity on smallflower umbrella sedge. This herbicide has good crop safety on rice.

OR-009—OR-009 is a nonionic surfactant by Oro-Agri that increases the efficacy of propanil (SuperWham!®). SuperWham!® was applied alone and with OR-009 at different concentrations at the 1- to 2-tiller stage of rice. OR-009 slightly improved early watergrass and ricefield bulrush control. Smallflower umbrella sedge and ducksalad control with SuperWham!® and OR-009 was equal to SuperWham!® alone. Further research is needed to optimize OR-009 with SuperWham!® or other foliar-applied herbicides

Developing management alternatives

To establish appropriate timing of weed control interventions, it is necessary to be able to predict the dynamics of weed germination and emergence. Current models combine information about irrigation method and soil temperature to provide species-specific emergence and growth curves. A model is being updated and validated for smallflower umbrella sedge and ricefield bulrush.

The dynamics of weed emergence are also under study in three different irrigation systems: water-seeded alternate wet and dry, drill-seeded alternate wet and dry, and water-seeded conventional. Evaluations of weed dynamics are in their final stages.

Herbicide resistance

Propanil-resistant smallflower umbrella sedge and ricefield bulrush populations have been confirmed in California rice fields. Resistant lines have shown a remarkable 14-fold increase in resistance to propanil, as well as increased resistance to other herbicides. The propanil-resistant lines, however, displayed a four-fold increased susceptibility to bentazon (Basagran®). Research results suggest that elevated propanil metabolism is not the resistance mechanism.

A field study evaluated the efficacy of different rates of bentazon applied alone or in combination with SuperWham!®. Bentazon provided excellent control of smallflower umbrella sedge and ricefield bulrush. Bentazon did not provide adequate control of ducksalad and did not provide any watergrass control (not surprising since bentazon is an herbicide for broadleaf weed control).

Ricefield bulrush resistance to propanil was similar to smallflower umbrella sedge. It also displayed increased susceptibility to bentazon. Propanil and bentazon mixtures can thus be used for efficient control of both propanil-resistant and susceptible ricefield bulrush.

ALS-inhibiting herbicides such as Londax®, Regiment®, Granite®, Strada®, and imazosulfuron (a component of League® MVP) are used in California rice fields to control sedges and broadleaf weeds. Research was initiated to investigate the response of ALS-resistant smallflower umbrella sedge and ricefield bulrush to different ALS herbicides and to determine the molecular mechanism of resistance. A similar project is under way on the watergrass complex. Results of these projects will help growers manage ALS-resistant weeds.

Testing of suspected herbicide-resistant weeds in grower fields is under way in the greenhouse at the Rice Experiment Station. Approximately 80 samples were collected by growers and PCAs. Specimens include barnyardgrass, early and late watergrass, smallflower umbrella sedge, sprangletop, ricefield bulrush, and redstem. Herbicide testing should give growers options and recommendations if they have resistance in their fields.