Weed Control in Rice 02

Weed Control in Rice - 02
Project Leader and Principal UC Investigators Albert Fischer, weed science professor, Dept. of Vegetable Crops, UC Davis	The objectives of this ongoing project have grown increasingly multi-faceted as issues concerning herbicide applications have grown more challenging. Scientists continue their work on fine-tuning best management strategies for herbicide use, including those of new compounds, combinations and sequential applications. However, work continues on many fronts. New herbicides Work continued on clomazone (Cerano^®), a herbicide with a new mode of action — a pigment synthesis inhibitor — that controls herbicide-resistant watergrass and sprangletop. Cerano has been repeatedly effective on watergrass from pre-seeding/post flood to the one-leaf stage of rice. Crop injury was reduced this season compared to last year, which is most likely related to improved uniformity of water depth at the Hamilton Road research site near the Rice Experiment Station (RES). This underscores the importance of a static four- to six-inch-deep flood during the 12 to 14 days after application. This reduces rice injury and maximizes weed control efficiency. Soil-active herbicides can be more active in light soils and perform at lower rates, as noted in research at a light red soils site near Pleasant Grove. Rice varieties Akitakomachi, Calmochi-101, Calhikari-201, Koshihikari and S-102 were slightly more susceptible to Cerano when pushed past the recommended rate; however, in 2002 tolerance was good at the recommended rate of 0.6 pounds/acre. Full registration for Cerano was anticipated for the 2003 season. Regiment (bispyribac-sodium) has been tested at the RES for several seasons and also in farmers’ fields where resistant watergrass is problematic. Regiment is a post emergent herbicide and when applied with a silicone surfactant is effective on watergrass, ricefield bulrush and demonstrates good activity on California arrowhead at the one- to three-tiller stage of rice. Water must be lowered to expose at least 70 percent of weed foliage in order for Regiment to function most effectively. Rates must be increased with resistant watergrass in order to be effective. Clincher has been tested at the RES for five years now. It is a post-emergent herbicide that is highly active on susceptible watergrass and sprangletop. It is very safe on rice and can be applied from the two- to four-leaf stage and from one tiller to just before panicle initiation at a higher rate. Unfortunately, the material is restricted to ground use only due to non-target activity on fruit trees. It can be applied in sequential applications for broad-spectrum control. Clincher will not control watergrass that is resistant to Whip (fenoxaprop). Shark (carfentrazone) is a useful sedge and broadleaf herbicide that can be applied at the two- to three-leaf stage, in combination with other into-water herbicides and in sequential weed control operations. Shark at the two to three tiller stage also yielded promising weed control. Ricestar (fenoxaprop plus safener) has repeatedly demonstrated that it is a good herbicide for the control of sprangletop but is weak against watergrass. It has been tested at the RES for three years. Promising combinations Weed scientists have also developed promising herbicide combinations to perform in various irrigation management schemes and to detect any potential problems with antagonistic mixtures. Regiment in tank-mix combination with propanil, for instance, was found to be antagonistic for watergrass control. But combinations of Regiment in tank mix with Abolish continue to be synergistic on watergrass control in the field and in greenhouse experiments. This mixture also controlled smallflower umbrellasedge and sprangletop and was safe to rice for applications not earlier than the four- to six-leaf stage with water drained. Mixtures of Regiment with either Clincher or Grandstand (trichlopyr) continue to be antagonistic for watergrass control. Clincher applied with SuperWham (propanil) was deficient on watergrass. However, Clincher applied at the five- to six-leaf stage, followed by a sequential application of Regiment or SuperWham at the one- to three-tiller stage of rice resulted in excellent weed control. Similarly, Clincher followed by Shark resulted in excellent broad-spectrum control. Cerano in sequential application with Shark, Londax, SuperWham and Regiment resulted in excellent weed control in continuous flood systems. Other Formulations Experimentation with new herbicides and formulations continue to be an important aspect of weed research. Duet (a combination of propanil and bensulfuron) exhibited fair to good watergrass control and excellent sedge and broadleaf control at the five- to six-leaf-stage of rice with lowered water. Sempra (halosulfuron) used as a foliar spray or as into-the-water application performed much like Londax, although Sempra appeared to be somewhat more active and thus allowing for lower rates. It is an ALS inhibitor that has been tested at the RES for three years. Sofit (pretilachlor plus safener) applied to the soil surface provided excellent watergrass and broadleaf weed control and was very good in controlling ricefield bulrush. This new herbicide contains new chemistry to California rice and may fit well into situations where herbicide resistance is present. Taipan (benzofenap), an early post-emergent broadleaf herbicide not yet being pursued for registration in California, performed well on broadleaf weeds but missed the sedges. Work on rate and timing may develop this herbicide for the California rice industry. Yukon is a formulated granular mixture of halosulfuron and dicamba for broadleaf and sedge control. This herbicide seems promising and will be tested again next season for a better assessment of rate and timing and its potential to control resistant weeds. Genetic Purity The recent development of herbicide-resistant rice may be a tool necessary to provide California rice farmers with a means to overcome the crippling effects of herbicide resistance and the limited weed control options available. However, concerns exist regarding the outcrossing or transfer of heritable traits through cross-pollination. Theoretically, herbicide-resistant rice could possibly transfer the trait for herbicide resistance to conventional rice. An option for maintaining identity preservation of rice could be to establish borders that exclude the potential for cross pollination. Isolation distances given by seed-certification agencies are for the most part educated guesses, so a large experiment was continued in 2002 to establish maximum distances of pollen flow from transgenic to non-transgenic rice. The experiment, conducted at the RES, examined the outcrossing potential of Liberty-Link M-202 to conventional M-202 rice. Thus far the potential for outcrossing appears to be in very low frequency (0.009 percent) and over very short distances (less than six feet). Stand establishment Another important objective in this project is to explore rice-weed competition, weed biology and cultural practices that hold promise to minimize herbicide costs and impacts to the environment. With that in mind, scientists established a new trial to look at two different methods of stand establishment — dry seeding, “stale” seedbed — and compared them to continuous flooding. Dry seeding resulted in excellent weed control. The other system, in which a seedbed is prepared and then flooded to encourage early weed growth for herbicide application before rice planting, was not as encouraging because of poor stand establishment. A larger experiment was planned for 2003. Weed seed testing As a service to growers, weed scientists also tested weed seed samples from rice fields with suspected herbicide resistance. They examined 85 barnyardgrass, 135 early watergrass and 41 late watergrass accessions against the herbicides Ordram (molinate) and Clincher (cyhalofop). Herbicide resistance was present in a high proportion of samples tested.

Weed Control in Rice - 02

Project Leader and Principal UC Investigators

Albert Fischer, weed science professor, Dept. of Vegetable Crops, UC Davis

The objectives of this ongoing project have grown increasingly multi-faceted as issues concerning herbicide applications have grown more challenging. Scientists continue their work on fine-tuning best management strategies for herbicide use, including those of new compounds, combinations and sequential applications. However, work continues on many fronts.

New herbicides

Work continued on clomazone (Cerano^®), a herbicide with a new mode of action — a pigment synthesis inhibitor — that controls herbicide-resistant watergrass and sprangletop. Cerano has been repeatedly effective on watergrass from pre-seeding/post flood to the one-leaf stage of rice. Crop injury was reduced this season compared to last year, which is most likely related to improved uniformity of water depth at the Hamilton Road research site near the Rice Experiment Station (RES). This underscores the importance of a static four- to six-inch-deep flood during the 12 to 14 days after application. This reduces rice injury and maximizes weed control efficiency. Soil-active herbicides can be more active in light soils and perform at lower rates, as noted in research at a light red soils site near Pleasant Grove. Rice varieties Akitakomachi, Calmochi-101, Calhikari-201, Koshihikari and S-102 were slightly more susceptible to Cerano when pushed past the recommended rate; however, in 2002 tolerance was good at the recommended rate of 0.6 pounds/acre. Full registration for Cerano was anticipated for the 2003 season.

Regiment (bispyribac-sodium) has been tested at the RES for several seasons and also in farmers’ fields where resistant watergrass is problematic. Regiment is a post emergent herbicide and when applied with a silicone surfactant is effective on watergrass, ricefield bulrush and demonstrates good activity on California arrowhead at the one- to three-tiller stage of rice. Water must be lowered to expose at least 70 percent of weed foliage in order for Regiment to function most effectively. Rates must be increased with resistant watergrass in order to be effective.

Clincher has been tested at the RES for five years now. It is a post-emergent herbicide that is highly active on susceptible watergrass and sprangletop. It is very safe on rice and can be applied from the two- to four-leaf stage and from one tiller to just before panicle initiation at a higher rate. Unfortunately, the material is restricted to ground use only due to non-target activity on fruit trees. It can be applied in sequential applications for broad-spectrum control. Clincher will not control watergrass that is resistant to Whip (fenoxaprop).

Shark (carfentrazone) is a useful sedge and broadleaf herbicide that can be applied at the two- to three-leaf stage, in combination with other into-water herbicides and in sequential weed control operations. Shark at the two to three tiller stage also yielded promising weed control.

Ricestar (fenoxaprop plus safener) has repeatedly demonstrated that it is a good herbicide for the control of sprangletop but is weak against watergrass. It has been tested at the RES for three years.

Promising combinations

Weed scientists have also developed promising herbicide combinations to perform in various irrigation management schemes and to detect any potential problems with antagonistic mixtures.

Regiment in tank-mix combination with propanil, for instance, was found to be antagonistic for watergrass control. But combinations of Regiment in tank mix with Abolish continue to be synergistic on watergrass control in the field and in greenhouse experiments. This mixture also controlled smallflower umbrellasedge and sprangletop and was safe to rice for applications not earlier than the four- to six-leaf stage with water drained. Mixtures of Regiment with either Clincher or Grandstand (trichlopyr) continue to be antagonistic for watergrass control.

Clincher applied with SuperWham (propanil) was deficient on watergrass. However, Clincher applied at the five- to six-leaf stage, followed by a sequential application of Regiment or SuperWham at the one- to three-tiller stage of rice resulted in excellent weed control. Similarly, Clincher followed by Shark resulted in excellent broad-spectrum control. Cerano in sequential application with Shark, Londax, SuperWham and Regiment resulted in excellent weed control in continuous flood systems.

Other Formulations

Experimentation with new herbicides and formulations continue to be an important aspect of weed research. Duet (a combination of propanil and bensulfuron) exhibited fair to good watergrass control and excellent sedge and broadleaf control at the five- to six-leaf-stage of rice with lowered water.

Sempra (halosulfuron) used as a foliar spray or as into-the-water application performed much like Londax, although Sempra appeared to be somewhat more active and thus allowing for lower rates. It is an ALS inhibitor that has been tested at the RES for three years.

Sofit (pretilachlor plus safener) applied to the soil surface provided excellent watergrass and broadleaf weed control and was very good in controlling ricefield bulrush. This new herbicide contains new chemistry to California rice and may fit well into situations where herbicide resistance is present.

Taipan (benzofenap), an early post-emergent broadleaf herbicide not yet being pursued for registration in California, performed well on broadleaf weeds but missed the sedges. Work on rate and timing may develop this herbicide for the California rice industry.

Yukon is a formulated granular mixture of halosulfuron and dicamba for broadleaf and sedge control. This herbicide seems promising and will be tested again next season for a better assessment of rate and timing and its potential to control resistant weeds.

Genetic Purity

The recent development of herbicide-resistant rice may be a tool necessary to provide California rice farmers with a means to overcome the crippling effects of herbicide resistance and the limited weed control options available. However, concerns exist regarding the outcrossing or transfer of heritable traits through cross-pollination. Theoretically, herbicide-resistant rice could possibly transfer the trait for herbicide resistance to conventional rice.

An option for maintaining identity preservation of rice could be to establish borders that exclude the potential for cross pollination. Isolation distances given by seed-certification agencies are for the most part educated guesses, so a large experiment was continued in 2002 to establish maximum distances of pollen flow from transgenic to non-transgenic rice. The experiment, conducted at the RES, examined the outcrossing potential of Liberty-Link M-202 to conventional M-202 rice. Thus far the potential for outcrossing appears to be in very low frequency (0.009 percent) and over very short distances (less than six feet).

Stand establishment

Another important objective in this project is to explore rice-weed competition, weed biology and cultural practices that hold promise to minimize herbicide costs and impacts to the environment. With that in mind, scientists established a new trial to look at two different methods of stand establishment — dry seeding, “stale” seedbed — and compared them to continuous flooding. Dry seeding resulted in excellent weed control. The other system, in which a seedbed is prepared and then flooded to encourage early weed growth for herbicide application before rice planting, was not as encouraging because of poor stand establishment. A larger experiment was planned for 2003.

Weed seed testing

As a service to growers, weed scientists also tested weed seed samples from rice fields with suspected herbicide resistance. They examined 85 barnyardgrass, 135 early watergrass and 41 late watergrass accessions against the herbicides Ordram (molinate) and Clincher (cyhalofop). Herbicide resistance was present in a high proportion of samples tested.