Weed Control
in Rice - 2009

 

 

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Project Leader and Principal  Investigators

Albert Fischer, associate professor, Dept. of Plant Sciences, UC Davis

 

 

 

The weed control project seeks to assist California rice growers in the prevention and management of herbicide-resistant weeds, to achieve economic and timely broad-spectrum weed control, and to comply with personal and environmental safety requirements. Field testing in 2009 took place at the Rice Experiment Station, and in grower fields infested with late watergrass heavily resistant to multiple herbicides. Additionally, alternative rice establishment systems are under study.

Herbicide studies

Herbicide test plots in 2009 were located at the Rice Experiment Station and in Glenn County. These tests examined registered and potential new herbicides for effectiveness, safety and compatibility. Rice varieties used in this work were M-205 and M-206, which contribute to reduced lodging and improved harvest yield.

Prowl® (pendimethalin) is a selective herbicide for controlling annual grasses such as barnyardgrass and sprangletop and certain broadleaf weeds as they germinate and emerge. Prowl® H2O is a water-based capsule formulation that has been developed for use in dry- and drill-seeded rice. It needs to be applied to moist soil without any standing water. Flooding causes the chemical to degrade and lose efficacy.

Prowl® H2O applied alone as a delayed pre-emergent has in the past provided 46% watergrass/barnyardgrass control and 33% sprangletop control at 40 days after seeding. However, in 2009 testing this treatment did not control watergrass and provided 57% control of sprangletop.

Since Prowl® H2O does not control already emerged weeds, watergrass control was greatly improved when Prowl® H2O DPRE was followed by Super Wham®. Best performance with this compound can be expected when applied prior to weed emergence.

The combination of Granite® SC, Prowl® H2O, and Clincher® applied at the two- to three-stage of rice provided outstanding grass control, although yields were no better than other, less elaborate treatments. Prowl® H2O generally works better in dry/drill-seeded and aerobic conditions than in water-saturated soils.

Strada® WG (orthosulfamuron) is an ALS inhibitor for broad-spectrum control of watergrass and smallflower umbrellasedge that does not harm rice. Tests were conducted on two formulations – a water-dispersible granular form of this compound for pinpoint applications and a granular formulation for into-the-water treatments in continuously flooded rice.

Strada® was tested in a pinpoint system in a basin previously treated with Cerano® on day of seeding. Applications were made at the two- to four-leaf stage and five- to six- leaf stage of rice. Excellent weed control and good yields were reported in all treatments. Granular Strada® GR applied into-the-water following an early application of Cerano®, or followed by propanil, was also promising.

Granite® (penoxsulam) is an ALS-inhibiting herbicide applied after flooding for selective control of susceptible watergrass and barnyardgrass, broadleaf weeds, and sedges.

The granular formulation – Granite® GR – was commercially available for the first time in 2005. It was tested in combination with a follow-up application of Stam®4 SC. This treatment provided excellent broad-spectrum weed control.

Granite® SC is a fluid formulation for foliar application. It was labeled for California in 2006. It was tested in a pinpoint flood system with floodwater dropped at the three- to four-leaf stage of rice. High-yielding treatments included Clincher® tank mixed with Granite® SC followed by either Stam® or Super Wham®. Also, Granite® SC with Clincher® (or Clincher® EZ) provided good broad-spectrum control. Granite® SC will not control sprangletop; therefore Clincher® is generally needed for control of this weed.

V-10142 (imazosulfuron) is a Valent Corporation dispersible granule. Valent is pursuing registration of this formulation in California. It is intended as a tank-mix partner for follow-up spray treatments after an into-the-water herbicide. Treatments with Cerano® followed by a tank mix of this herbicide with propanil (Wham®) or Bolero® followed by a tank mix of V-10142 with Regiment® provided good weed control and yield. This compound is an ALS inhibitor, so it is not recommended for use with similar herbicides such as Granite® or Londax®.

V-10219 (thiobencarb plus imazosulfuron) is a Valent Corporation combination granule for into-the-water application. This compound was tested at three rates at the two-leaf stage of rice. Formulation of this product is still in development.

Stam® 4SC is a liquid suspension of propanil that was tested as a stand-alone treatment in a pinpoint system. It was also tested in the continuously flooded experiment alone following Cerano®. Weed control and yield were similar to Cerano® followed by Super Wham®.

Rice culture studies

Testing on the three major systems of rice culture – continuous flood, pinpoint flood, and dry or drill-seeded – continued in 2009. This research is seeking the best herbicide and management combinations for each of these systems.

Continuous flood

In the continuous flood trial, good weed control was achieved with early treatments. Best results were obtained when herbicide programs provided at least 95% broad-spectrum weed control in the first month after seeding.

Continuous flood rice systems are particularly helpful in suppressing barnyardgrass and sprangletop when a minimum 4-inch water depth can be maintained.

Granular formulations applied early into-the-water are excellent nondrift tools for this system. Cerano® applied early is a very good grass herbicide. It also provides good broad-spectrum weed control when followed by propanil or Strada® followed by Stam®, Shark® H2O, or Shark® H2O with Londax®.

Another successful follow-up application for Cerano® was the mixture of the new Valent Corporation compound V-10142 (imazosulfuron) with Wham® (propanil). Granite® GR followed by Stam® 4SC provided excellent broad-spectrum control of rice weeds. Some stunting was observed after the Granite® GR treatment.

Other treatments that worked well included the experimental into-the-water granular herbicide V-10219 (thiobencarb and imazosulfuron), Bolero® Ultramax followed by Super Wham®, Abolish® followed by Super Wham®, Regiment®, or Cerano® followed by propanil tank-mixed with Granite® SC.

Pinpoint system

The pinpoint system used in California requires early draining to expose emerging weeds to foliar herbicides. However, this exposure of soil surface to air also favors the establishment of other weeds – smallflower umbrellasedge, barnyardgrass and sprangletop. Thus, it is important that fields be rapidly reflooded within 48 hours of herbicide application.

Follow-up applications can be made at the one-to-two tiller stage of rice with water lowered to expose 70% of weed foliage to the spray. Some of the best broad-spectrum treatments were Clincher® tank-mixed with Granite® SC followed by propanil – or propanil alone. Other good broad-spectrum treatments included Regiment® alone or Regiment® followed by propanil, Granite® SC by itself or in tank mixtures with propanil and then followed by Clincher®, or Prowl® plus propanil as an early post-emergent treatment. The new cyhalofop formulation, Clincher® EZ, performed similarly to Clincher® in all combinations.

Drill-seeded system

The drill-seeded plot was flushed with water three times for establishment. A permanent flood was applied when rice was at five-leaf stage. Significant yield losses were associated with infestations by the main weeds in this system—watergrass, barnyardgrass, and sprangletop.

There were no stand-alone treatments that provided sufficient weed control and good yield in the drill-seeded trial in 2009. Several combinations that did provide excellent weed control and good yield were a tank mix of Prowl® H2O with Granite® SC and Clincher®, Clincher® followed by Super Wham®, Granite® SC plus Clincher® followed by Super Wham®, Granite® SC followed by Clincher®, Regiment® plus Abolish® followed by Super Wham® plus Clincher®, Super Wham® plus Whip®, Prowl® H2O followed by Super Wham®, or a tank mix of Prowl® H2O with Super Wham® and Clincher®.

Alternative stand establishment

Alternative stand establishment techniques developed the past five years at the Rice Experiment Station have been implemented in the fields of several cooperating growers.

For the second year, a cooperating grower in Glenn County used a spring-tilled, stale seedbed technique on a field plagued with resistant late watergrass or “mimic.” Glyphosate eliminated weeds germinated with an early irrigation prior to flooding and seeding rice. Follow-up applications in this system included Super Wham®, Granite® SC, or Regiment®. 

Again, this technique has proven very successful in reducing or eliminating watergrass and sprangletop competition during the growing season. Researchers hope that using this technique for multiple years will deplete the weed seed bank sufficiently to allow a rotation back into a conventional production system with high yields.

A fall-tilled field on the same farm did not have as many rice weeds emerge, but rice stand establishment was not as good.

Several other growers also implemented the spring-tilled stale seedbed technique with good success in controlling resistant late watergrass. More detail on this work is reported in the section “Scaling Out Alternative Rice Establishment Practices to Control Herbicide-Resistant Weeds.”

Organic alternatives

Several compounds were tested for use by organic growers in stale-seedbed rice production and for potential use in conventional production to control herbicide-resistant weeds.

Currently available compounds certified for organic rice production are strictly contact herbicides. They burn plant tissue upon application and do not translocate in the plant. Since they do not necessarily kill the weed, the potential for regrowth exists.

Four organic products were tested on a spring-tilled, stale seedbed trial at a resistant watergrass site and at the Rice Experiment Station. Control by these compounds was poor when reflooding was delayed by five days. However, control improved for some treatments when reflooding occurred within a day of application. The best results in these trials were obtained with the product Green Match.

 

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