Propanil-resistant Barnyardgrass Research Articles

History and Management of Herbicide-resistant Barnyardgrass (Echinochloa Crus-galli) in Arkansas Rice

Arkansas has been the leading state in rice production in the United States for many years. Barnyardgrass is the dominant weed in Arkansas rice. Propanil was the first highly effective herbicide for weed control in rice and has been used in Arkansas since 1959 as the primary herbicide for rice weed control. By 1989, its continual use led to the development of propanil-resistant barnyardgrass, which had spread to 16 of the 38 rice-producing counties in Arkansas by 1992. Arkansas rice growers are dependent on herbicides for the control of weeds in this drill-seeded crop. The residual herbicides thiobencarb, molinate, and pendimethalin mixed with propanil applied early postemergence improved control of propanilresistant barnyardgrass. But it was quinclorac, introduced in 1992, that became the real replacement treatment for propanil-resistant barnyardgrass. Then in 1999, a barnyardgrass biotype with resistance to both quinclorac and propanil was confirmed in Craighead County, Arkansas. Additionally, problems with quinclorac drift to other crops, especially tomato, led to restrictions on application of quinclorac in Arkansas by 1994. Fortunately, alternative herbicides for barnyardgrass control were developed, and clomazone was introduced in 2000. Clomazone is currently the standard herbicide for annual grasses in rice, including barnyardgrass. Herbicides recently developed for rice allow a broad range of options for a resistance management program, based on rotational and sequential herbicide applications. These include fenoxaprop and cyhalofop (both acetyl-CoA carboxylase [ACCase] inhibitors), bispyribac and penoxsulam (acetolactate synthase [ALS] inhibitors), and imazethapyr and imazamox (also ALS inhibitors for imidazolinone-resistant rice). From a global standpoint, there is considerable evidence that barnyardgrass has the propensity to develop resistance to most of these herbicide groups. Therefore, efforts to manage and monitor for herbicide resistance in this species need to be diligently continued. Research on nonchemical options is in progress utilizing weed-suppressive rice breeding lines to control barnyardgrass. Nomenclature: 2,6-bis[(4,6-dimethoxy-2-pyrimidinyl)oxy]benzoic acid, proposed common name bispyribac-sodium; clomazone; cyhalofop; fenoxaprop; imazamox; imazethapyr; molinate; pendimethalin; {2-(2,2-difluoroethoxy)-6(trifluoromethyl-N-(5,8-dimethoxy[1,2,4]triazolo[1,5-c]pyrimidin-2-yl))benzenesulfonamide}, proposed common name penoxsulam; propanil; quinclorac; thiobencarb; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; rice, Oryza sativa L.; tomato, Solanum lycopersicum L.

Antagonism of Cyhalofop Grass Activity by Halosulfuron, Triclopyr, and Propanil1

Field experiments in 2001 and 2002 at Stuttgart, AR, demonstrated cyhalofop applied POST controlled propanil-susceptible barnyardgrass, propanil-resistant barnyardgrass, and broadleaf signalgrass 67, 65, and 71%, respectively 28 days after treatment (DAT). Halosulfuron applied 1 d before cyhalofop or applied in a tank-mixture reduced broadleaf signalgrass and propanil-resistant or propanil-susceptible barnyardgrass by 35 to 59 percentage points. Triclopyr applied 5, 3, or 1 d before, or mixed with, cyhalofop reduced control of propanil-resistant and propanil-susceptible barnyardgrass, 16 to 41 percentage points, respectively. Triclopyr applied 1 d before cyhalofop or combined with cyhalofop reduced broadleaf signalgrass control 38 and 18 percentage points, respectively compared with cyhalofop alone. Propanil reduced cyhalofop grass control only when mixed with cyhalofop. Application timings, averaged across halosulfuron, propanil, and triclopyr, made 1 d before cyhalofop or tank-mixed with cyhalofop reduc...

Chemical interactions with the herbicide propanil on propanil-resistant barnyardgrass

We are examining the interaction of compounds with the herbicide propanil to find synergistic or additive actions that can increase efficacy against propanil-resistant barnyardgrass [Echinochloa crus-galli] (R-BYG) without substantial injury to rice. Field tests (herbicidal injury) and laboratory tests (chlorophyll quantification in excised leaves; measurement of chlorophyll fluorescence to determine PSII inhibition) have been conducted on R-BYG and rice tissue exposed to various rates of propanil and additive. Important synergistic interactions on R-BYG in laboratory and field tests were found with propanil plus either the herbicides anilophos or piperophos, or the insecticide carbaryl. In laboratory tests, the insecticide methiocarb and PPG-124 (p-chlorophenyl N-methylcarbamate) were highly effective synergists with propanil on R-BYG. Other important interactions occurred with certain concentrations/application rates when propanil was combined with the herbicides quinclorac, thiobencarb, molinate, or pendimethalin (field tests). Combinations of these or other chemicals with propanil may provide additive or synergistic action useful to control R-BYG without increasing rice injury. Such mixtures might also prevent or delay the development of propanil resistance in this weed species.

Chemical interactions with the herbicide propanil on propanil‐resistant barnyardgrass

We are examining the interaction of compounds with the herbicide propanil to find synergistic or additive actions that can increase efficacy against propanil-resistant barnyardgrass [Echinochloa crus-galli] (R-BYG) without substantial injury to rice. Field tests (herbicidal injury) and laboratory tests (chlorophyll quantification in excised leaves; measurement of chlorophyll fluorescence to determine PSII inhibition) have been conducted on R-BYG and rice tissue exposed to various rates of propanil and additive. Important synergistic interactions on R-BYG in laboratory and field tests were found with propanil plus either the herbicides anilophos or piperophos, or the insecticide carbaryl. In laboratory tests, the insecticide methiocarb and PPG-124 (p-chlorophenyl N-methylcarbamate) were highly effective synergists with propanil on R-BYG. Other important interactions occurred with certain concentrations/application rates when propanil was combined with the herbicides quinclorac, thiobencarb, molinate, or pendimethalin (field tests). Combinations of these or other chemicals with propanil may provide additive or synergistic action useful to control R-BYG without increasing rice injury. Such mixtures might also prevent or delay the development of propanil resistance in this weed species.

Control of Propanil-Resistant Barnyardgrass (Echinochloa crus-galli) in Rice (Oryza sativa) with Carbaryl/Propanil Mixtures

Propanil and carbaryl mixtures, propanil formulated with carbaryl, the package mixture of propanil plus molinate (alone and plus pendimethalin), propanil plus quinclorac, and propanil plus pendimethalin were evaluated in field experiments for control of propanil-resistant and -susceptible barnyardgrass in 1995 and 1996 in Arkansas. Propanil alone at 3.3 kg ai/ha did not control propanil-resistant barnyardgrass when applied to two-leaf and repeated at four-leaf barnyardgrass. Propanil at 3.3 kg/ha with carbaryl at 0.1 to 0.3 kg ai/ha controlled propanil-resistant barnyardgrass at least 90% when applied at the two-leaf stage with no rice yield reduction. Applications repeated at the four-leaf stage also controlled propanil-resistant barnyardgrass, but rice injury was 66% with 0.3 kg/ha carbaryl in 1 of 2 yr, and rice yield was reduced. Control of resistant barnyardgrass with the commercial formulation of propanil plus carbaryl and propanil plus molinate was lower with a single application than with repeat applications. Propanil plus quinclorac, propanil plus pendimethalin, and propanil plus molinate plus pendimethalin controlled resistant barnyardgrass with one application at the two-leaf stage.

Chlorophyll fluorescence evaluation of agrochemical interactions with propanil on propanil-resistant barnyardgrass (Echinochloa crus-galli)

Resistance to propanil by a barnyardgrass (BYG) biotype has been reported, and its occurrence is becoming widespread in U.S. rice-producing regions. Interactions between propanil and the herbicides anilofos, molinate, pendimethalin, piperophos, quinclorac, and thiobencarb and the insecticide carbaryl were evaluated in laboratory studies for improved control of propanil-resistant barnyardgrass (R-BYG). Chlorophyll fluorescence measurements of BYG leaf segments were used to ascertain electron transport inhibition and to assess the synergy/antagonism of propanil (100 μM) with the various additives (50 μM). Synergistic effects on photosynthetic inhibition were found with anilofos, carbaryl, pendimethalin, and piperophos in combination with propanil. Such synergistic actions of chemicals with propanil may lead to chemical combinations useful for R-BYG control.

Chlorophyll fluorescence for rapid detection of propanil-resistant barnyardgrass (Echinochloa crus-galli)

Repeated use of propanil to control barnyardgrass (BYG) and other weeds in rice has led to the development of propanil-resistant barnyardgrass (R-BYG). R-BYG possesses elevated aryl acylamidase activity levels, which cause rapid metabolism of propanil analogous to propanil degradation in rice. The current screening method for determining propanil resistance in BYG requires about 10 mo. The present study examined the use of chlorophyll fluorescence as a more rapid method to identify propanil resistance in BYG soon after it is suspected. Chlorophyll fluorescence data from excised BYG leaf tissue (R-BYG and susceptible-BYG [S-BYG]; 13- to 41-d-old) exposed to 100 μM propanil for 2 h indicated a 95 to 100% inhibition of electron transport (photosynthesis inhibition) in both R- and S-BYG. However, when incubated in water in the dark for 22 h after the initial 2-h treatment, metabolism in R-BYG was sufficient to reduce levels of absorbed propanil and facilitate recovery. Lack of metabolism of propanil prevented recovery in S-BYG, thus allowing the two biotypes to be distinguished easily by the chlorophyll fluorescence assay. Further studies using this 2-h exposure to 100 μM propanil followed by a 22-h recovery period evaluated several assay parameters. A longer recovery time and the effects of various propanil concentrations were also evaluated. A herbicide dose-response curve showed the greatest difference in photosynthesis inhibition for both biotypes at about 100 μM propanil, but both biotypes were inhibited > 95% when treated with 400 μM propanil. Inhibition of photosynthesis in both biotypes was greatest when the recovery incubation temperature was 35 C compared to 20, 25, and 30 C. Fluorescence data from harvested tissue stored moist in plastic bags at 23 C (to simulate shipment) showed that biotypes could be differentiated even when received as late as 4 d after harvest. Thus, samples can be harvested from the field soon after propanil failure and resistance or susceptibility to propanil determined after only a few days. This technique can greatly reduce the time, space, and labor currently required to determine propanil resistance in BYG.

Resistance Mechanism of Propanil-Resistant Barnyardgrass: II. In-vivo Metabolism of the Propanil Molecule

Propanil-resistant barnyardgrass populations, previously verified in Arkansas rice fields and in greenhouse tests, were examined in the laboratory to ascertain if the resistance mechanism in this weed biotype was herbicide metabolism. Propanil-resistant barnyardgrass was controlled >95% in the greenhouse when carbaryl (an aryl acylamidase inhibitor) was applied two days prior to propanil. Laboratory studies with 14 C-radiolabelled propanil indicated that the herbicide was hydrolysed in propanil-resistant barnyardgrass and rice to form 3,4-dichloroaniline, but no detectable hydrolysis occurred in susceptible barnyardgrass. Two additional polar metabolites were detected in propanil-resistant barnyardgrass and rice and tentatively identified by thin layer chromatography. Overall, metabolites in the resistant barnyardgrass had R f values similar to those in rice, indicating similar metabolism for both species. These data, coupled with data from a previous report on the resistant biotype showing no differential absorption/translocation or molecular modification of the herbicide binding site in the resistant biotype, indicate that the resistance mechanism is metabolic degradation of propanil.

Verification and Distribution of Propanil-Resistant Barnyardgrass (Echinochloa crus-galli)in Arkansas

Propanil-resistant barnyardgrass was reported in Poinsett County, AR, in 1990. Greenhouse studies were initiated to determine the distribution of propanil-resistant barnyardgrass in the state and to characterize the resistance. Barnyardgrass seeds were obtained in 1991 and 1992 from fields in 19 of the 38 rice producing counties in Arkansas where propanil treatment at recommended rates gave unsatisfactory barnyardgrass control. Barnyardgrass seedlings from the various sources were treated with propanil at 4.5 kg ai/ha and seedling injury response was compared to the response of seedlings collected from known resistant and susceptible barnyardgrass populations. Propanil-resistance of varying levels was confirmed in 115 (16 counties) out of the 138 Arkansas barnyardgrass seed sources. Propanil I50values (rate of herbicide required to provide 50% injury/control) were determined to be 14, 20, and 39 kg/ha for slightly, moderately, and highly resistant barnyardgrass, respectively. A resistance factor of 20® was found in the highly resistant barnyardgrass category. Development of resistance was highly correlated with crop rotations where rice was grown one out of two, or two out of three years.

Propanil-Resistant Barnyardgrass (Echinochloa crus-galli) Control in Rice (Oryza sativa)

Six experiments were conducted in three rice fields near Harrisburg, AR in Poinsett County in 1991 and 1992 to confirm barnyardgrass resistance to propanil and to compare herbicide treatments for control of propanil-resistant barnyardgrass. In all experiments, standard treatments of thiobencarb applied delayed PRE or tank mixtures of propanil + thiobencarb applied POST controlled propanil-resistant barnyardgrass. In five of six experiments, propanil failed to control barnyardgrass at 6 to 8 kg ai/ha (three times use rates) and in three experiments it provided inconsistent control at 11 kg/ha. Emulsifiable propanil at 11 kg/ha frequently controlled resistant barnyardgrass better than the dry flowable formulation. Treatments that consistently controlled propanil-resistant barnyardgrass included propanil tank-mixed with pendimethalin or quinclorac applied POST to two-leaf grass; quinclorac applied alone delayed PRE or POST or applied POST tank-mixed with thiobencarb, pendimethalin, or a formulated mixture of molinate and propanil; a formulated mixture of propanil and molinate applied POST in tank mixtures with thiobencarb or pendimethalin; and fenoxaprop or fenoxaprop-P alone applied POST to four-leaf grass prior to flood establishment. Herbicide treatments that failed to control resistant barnyardgrass included POST applications of a formulated mixture of propanil and molinate alone and propanil in tank mixtures with bromoxynil or triclopyr. These studies confirm that barnyardgrass from several farms in Arkansas have resistance to propanil and identified treatments that control propanil-resistant barnyardgrass.

Rice weed control: current technology and emerging issues in temperate rice

Among temperate rice areas, the United States and Australia are most similar in climate and in the mechanisation of rice culture. Many weed problems, even weed species invading rice, are common to both countries; and the present technology for weed control as well as concern for the impact of these technologies to environmental quality, herbicide resistance, and other weed-related issues bear many similarities. Application of current, and any new, technologies to emerging issues in US rice weed control will therefore be directly relevant to rice production in Australia and all other temperate areas struggling with the same challenges. Weeds are a significant problem in temperate rice culture. In the United States, rice is mechanically direct-seeded, allowing weeds to germinate and establish with the crop. In the last 15 years weed growth and competition has been increased by the adoption of semi-dwarf cultivars, high N fertilisation, and, in water-seeded rice, shallow flooding. High rates, and often multiple applications, of herbicides have been necessary to maximise the yield potential of these cultural systems. Advances in cultural practices and herbicide technology have maintained, if not improved, weed control; but nearly 30 years of propanil use in the southern USA resulted in propanil-resistant barnyard grass Echinochloa crus-galli (L.) Beauv., and after 4 years of continuous use, bensulfuron resistance to 4 aquatic weed species was discovered in California. Although herbicides with different mechanisms of action are needed for alternation in resistance management strategies, fewer are likely to be available. Social and environmental concerns have slowed the development and registration of rice herbicides and increased the cost of controlling weeds. Water quality deterioration from ricefield tailwaters, drift to sensitive crops, the cost of renewing registration in aquatic systems, and weed resistance all forecast reduced herbicide use in rice. Neither cultural practices nor herbicides alone can solve weed problems in direct-seeded, mechanised rice culture. With fewer herbicides and a cultural system highly vulnerable to weed losses, integrated management strategies with better information on which to base weed control decisions will be needed to solve weed problems in temperate rice.