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Title: VERIFICATION AND DISTRIBUTION OF PROPANIL RESISTANT BARNYARDGRASS ECHINOCHLOA CRUS GALLI (L) BEAUV IN ARKANSAS

Author
item CAREY, V - UNIV OF ARKANSAS
item Hoagland, Robert
item TALBERT, ROBERT - UNIV OF ARKANSAS

Submitted to: Weed Technology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Barnyardgrass [Echinochloa crus-galli (L.) Beauv] is the most important grass weed in rice throughout the world, and it occurs in all rice- growing areas in Arkansas. Propanil was one of the first herbicides for the control of barnyardgrass in rice, and was first used in Arkansas in 1962. In 1989, rice producers in one Arkansas county experienced problems with barnyardgrass control using the standard application rate of propanil (3.4 to 5.6 kg/ha). Barnyardgrass seedlings from these fields were found to be resistant to propanil at levels as high as 11.2 kg/ha in 1990, which confirmed the first reported case of propanil- resistant barnyardgrass in Arkansas. Concern of this weed resistance prompted this study to examine the distribution of this herbicide- resistant weed in Arkansas rice-producing counties. Results from a 2- year study (1991 and 1992) of field samples from 19 of 38 rice-growing counties in Arkansas indicated that propanil-resistant barnyardgrass was confirmed in 115 (16 counties) of the 138 samples tested. Propanil injury response of the barnyardgrass samples indicated several levels of resistance of this herbicide, with the most resistant group controlled only 80% by propanil concentrations 20 times the recommended rate required to control susceptible barnyardgrass. Propanil-resistant barnyardgrass is a widespread problem and will spread unless rice producers rotate crops and/or herbicides

Technical Abstract: Propanil-resistant barnyardgrass was reported in Poinsett County, Arkansas, in 1990. Greenhouse studies were initiated to determine the distribution of propanil-resistant barnyardgrass in Arkansas 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 I50 values (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 20X 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