Rice Weed Control with Penoxsulam (Grasp)

Transcription

1 PEST MANAGEMENT: WEEDS Rice Weed Control with Penoxsulam (Grasp) B.V. Ottis, R.E. Talbert, M.S. Malik, and A.T. Ellis ABSTRACT Two experiments were established in 2003 at the Rice Research and Extension Center near Stuttgart, Ark., to evaluate the potential of penoxsulam (Grasp) as part of a rice weed control program. In experiment one, penoxsulam applied alone and in tank mixtures early postemergence (EPOST) (two-leaf rice, one-leaf grass, two-leaf weeds) was evaluated, and experiment two evaluated penoxsulam applied alone and in tank mixtures mid-postemergence (MPOST) (four-leaf rice, three- to four-leaf grass, three- to four-leaf weeds). Plots were established in a randomized complete block design with four replications. Weeds evaluated were barnyardgrass (Echinochloa crus-galli), broadleaf signalgrass (Brachiaria platyphylla), hemp sesbania (Sesbania exaltata), northern jointvetch (Aeschynomene virginica), and pitted morningglory (Ipomoea lacunosa). In experiment one, yields ranged from 6357 to 7660 lb/acre, with rice treated with penoxsulam + propanil having a significantly higher yield than rice treated with penoxsulam alone, penoxsulam + clomazone, or propanil + quinclorac. In experiment two, rice yields ranged from 4571 to 7009 lb/acre, with treatments receiving MPOST applications having significantly higher yields than rice receiving only a PRE application. Penoxsulam applied postemergence appears to provide excellent barnyardgrass control and poor to moderate broadleaf weed control. Penoxsulam + cyhalofop-butyl did not result in reduced grass weed control. INTRODUCTION Penoxsulam (Grasp) was recently granted Reduced Risk Pesticide Status for use in rice from the USEPA. Penoxsulam is a member of the triazolopyrimidine 144

2 B.R. Wells Rice Research Studies 2003 sulfonamide family of herbicides. It is applied postemergence and inhibits the acetolactate synthase (ALS) enzyme similar to imidazolinone and sulfonylurea herbicides. However, it is thought that penoxsulam binds differently to the ALS enzyme, thereby having activity on known ALS-resistant species (Anonymous, 2003). Penoxsulam is applied at low use rates ranging from to lb ai/acre, and rice has shown good tolerance to postemergence applications (Anonymous, 2003). Penoxsulam will be marketed as a broadspectrum herbicide in rice. Summer 2003 was the first year that university and private researchers had the opportunity to evaluate penoxsulam in the field. The objectives of these experiments were to evaluate the potential of penoxsulam for rice weed control applied alone and in tank mixtures with other rice herbicides EPOST and MPOST. PROCEDURES Two studies were established at the Rice Research and Extension Center near Stuttgart, Ark., to evaluate the potential of penoxsulam for rice weed control. In experiment one, penoxsulam applied alone and in tank mixtures early postemergence (EPOST) (two-leaf rice, one-leaf grass, two-leaf weeds) was evaluated, and experiment two evaluated penoxsulam applied alone and in tank mixtures mid-postemergence (MPOST) (four-leaf rice, three- to four-leaf grass, three- to four-leaf weeds). Treatments were established in a randomized complete block with four replications. Plots were 5 by 15 ft and consisted of seven rows spaced 7 in. apart. The soil was a DeWitt silt loam with a ph of 5.8 and an organic matter content of 1%. The cultivar Francis was drill-seeded at a rate of 71 lb/acre. Herbicides were applied with a CO 2 backpack sprayer calibrated to deliver 10 gal/acre. Plots were fertilized with 42 lb N/acre as urea preflood followed by (fb) 25 lb N/acre as urea at panicle initiation. Hemp sesbania, northern jointvetch, and pitted morningglory were drill-seeded perpendicular to the Francis so control of these weeds could be evaluated along with natural populations of barnyardgrass and broadleaf signalgrass. Visual weed-control evaluations were made at two-week intervals following herbicide application on a scale between 0 to 100%, with 0% being no control and 100% being complete control. At maturity, plots were harvested, weighed, and adjusted to 12% moisture. All data were subjected to analysis of variance (ANOVA), and treatment means were separated by Fisher s least significant difference at P RESULTS AND DISCUSSION Experiment One Barnyardgrass and broadleaf signalgrass control was excellent 21 days after treatment (DAT) with all applications and timings (Table 1). Hemp sesbania, northern jointvetch, and pitted morningglory control was weak, possibly due to dry conditions 145

3 AAES Research Series 517 at time of application and late emergence of these weeds following application. Plot yields ranged from 6360 to 7660 lb/acre, with penoxsulam + propanil providing significantly higher yields than plots treated with EPOST applications of penoxsulam alone and penoxsulam + clomazone. All treatments provided higher yields than the nontreated check. Experiment Two Barnyardgrass control with penoxsulam alone and in tank mixtures with other herbicides following clomazone PRE was greater than 98% (Table 2). Broadleaf signalgrass control was less than 85% when clomazone was applied alone PRE or fb penoxsulam, but at least 99% when quinclorac or propanil was included in the MPOST application. Cyhalofop-butyl, propanil, or quinclorac improved broadleaf signalgrass control when applied with penoxsulam following clomazone PRE. Clomazone alone or fb penoxsulam or penoxsulam + cyhalofop-butyl did not provide adequate control of hemp sesbania or pitted morningglory. Applications of penoxsulam + propanil or quinclorac provided excellent control of hemp sesbania. Lack of pitted morningglory control with penoxsulam may have been due to large weed size at time of application. Rice yields ranged from 4570 to 7010 lb/acre with all treatments. There were significant differences in rice yields between treatments receiving MPOST applications and those receiving only PRE applications. There were no significant differences in rice yields among treatments having an MPOST herbicide application. SIGNIFICANCE OF FINDINGS Penoxsulam applied postemergence provides excellent barnyardgrass control and poor to moderate broadleaf-weed control. Penoxsulam does not appear to provide PRE broadleaf-weed control. Poor broadleaf-weed control in experiment one may have been due to dry conditions at time of application. Penoxsulam + cyhalofop-butyl did not result in reduced grass weed control, unlike results found in a study comparing applications of cyhalofop-butyl plus a herbicide with a mode of action similar to penoxsulam (Scherder et al., 2002). ACKNOWLEDGMENTS Funding for this research was provided by Dow AgroSciences and by grower check-off funds through the Arkansas Rice Research and Promotion Board. We appreciate the help of Mr. Jamie Branson, Mr. Jon Wright, and Mr. Danny Boothe, and the staff at the Rice Research and Extension Center. 146

4 B.R. Wells Rice Research Studies 2003 LITERATURE CITED Anonymous Penoxsulam broad spectrum herbicide for rice. Global Technical Bull. Dow AgroSciences Publication L Scherder, E.F., R.E. Talbert, M.L. Lovelace, F.L. Baldwin, K.L. Smith, and R.B. Lassiter Timing of broadleaf rice herbicides for reduced antagonism with cyhalofop-butyl. Proc. South. Weed. Sci. Soc. 55:

5 AAES Research Series 517 Table 1. Weed control 21 days after treatment and rice yields with EPOST tank mixtures of penoxsulam (Experiment 1). Rice Broadleaf Hemp Northern Pitted Rice Treatment Rate stage Barnyardgrass signalgrass sesbania jointvetch morningglory yield (lb/acre) (%) (lb/acre) Nontreated Penoxsulam leaf COC z 2.5 % 1-2 leaf Penoxsulam leaf clomazone leaf COC 2.5 % 1-2 leaf Penoxsulam leaf clomazone leaf cyhalofop- butyl leaf COC 2.5 % 1-2 leaf Penoxsulam leaf propanil leaf COC 1.25 % 1-2 leaf Clomazone leaf cyhalofop-butyl leaf COC 2.5 % 1-2 leaf Propanil leaf quinclorac leaf Clomazone leaf quinclorac leaf COC 1.25 % 1-2 leaf Clomazone leaf propanil leaf Penoxsulam PRE y clomazone 0.4 PRE Clomazone 0.4 PRE LSD (P=0.05) z COC = crop oil concentrate. y PRE = preemergence. 148

6 B.R. Wells Rice Research Studies 2003 Table 2. Weed control 21 days after treatment and rice yields with MPOST applications of penoxsulam following clomazone PRE (Experiment 2). Broadleaf Hemp Pitted Rice Treatment Rate Rice stage Barnyardgrass signalgrass sesbania morningglory yield (lb/acre) (%) (lb/acre) Nontreated Clomazone 0.22 PRE z Clomazone fb 0.22 PRE COC y 2.5% 4-leaf Clomazone fb 0.22 PRE cyhalofop-butyl leaf Clomazone fb 0.22 PRE quinclorac leaf Clomazone fb 0.22 PRE propanil leaf Clomazone fb 0.22 PRE triclopyr leaf Clomazone fb 0.22 PRE triclopyr leaf propanil leaf Clomazone fb 0.22 PRE bispyribac sodium leaf NIS x 0.125% 4-leaf continued 149

7 AAES Research Series 517 Table 2. Continued. Broadleaf Hemp Pitted Rice Treatment Rate Rice stage Barnyardgrass signalgrass sesbania morningglory yield (lb/acre) (%) (lb/acre) Clomazone fb 0.22 PRE quinclorac leaf propanil leaf Clomazone fb 0.22 PRE triclopyr leaf halosulfuron leaf COC 1.25% 4-leaf Penoxsulam 0.03 PRE Penoxsulam PRE Clomazone PRE penoxsulam 0.03 PRE Clomazone 0.4 PRE LSD (P=0.05) z PRE = preemergence. y COC = crop oil concentrate. x NIS, non-ionic surfactant. 150