J.A. Still, J.K. Norsworthy, D.B. Johnson, E.K. McCallister, R.C. Scott, and K.L. Smith
ABSTRACT
Imazosulfuron is a new sulfonylurea herbicide being developed by Valent for use in rice (Oryza sativa). It is known to have preemergence (PRE) and postemergence (POST) activity on various weeds in rice. However, imazosulfuron has little grass activity so it is not considered a stand-alone herbicide. It must be incorporated into herbicide programs that contain grass herbicides. Experiments were conducted at Keiser and Stuttgart, Ark., in 2009 to evaluate herbicide programs containing imazosulfuron with clomazone, quinclorac, propanil, and halosulfuron compared with a standard herbicide program in drill-seeded rice. At Keiser, imazosulfuron provided good control of hemp sesbania (Sesbania herbacea) PRE and excellent control POST, and control improved as the imazosulfuron rate increased. At Stuttgart, late-season hemp sesbania control was
>99% across all programs. Preemergence imazosulfuron programs consistently provided better control of barnyardgrass (Echinochloa crus-galli) than POST programs. PRE and POST imazosulfuron programs helped control yellow nutsedge (Cyperus escluentus) but control was highly dependent on application rate. Programs containing the highest rate of imazosulfuron at 0.4 lb ai/acre provided season-long control of yellow nutsedge.
INTRODUCTION
The new sulfonylurea herbicide, imazosulfuron, being developed by Valent is a broadleaf herbicide intended for use in rice with an anticipated launch date of 2011.
Imazosulfuron provides excellent control of several broadleaf weed species common in rice when applied PRE or POST (Jones et al., 2009). Postemergence applications include
B.R. Wells Rice Research Studies 2009
those made early postemergence (EPOST) at 2- to 3-wk after planting and preflood (PREFLD). Because weed control from imazosulfuron is limited to broadleaf weeds, it must be incorporated into rice herbicide programs that contain herbicides that have activity on grasses. Hemp sesbania, barnyardgrass, and yellow nutsedge are included in the top 10 most problematic weeds in rice in Arkansas (Norsworthy et al., 2007).
Research is needed to determine where imazosulfuron fits into herbicide programs in rice for controlling these weeds. Our objective was to evaluate the effectiveness of imazosulfuron programs on control of six common rice weeds relative to a standard herbicide program in rice.
PROCEDURES
Field experiments were conducted at Keiser (clay soil) and Stuttgart (silt loam soil), Ark., in 2009. The design was a randomized complete block with four replications, and plots were 5 × 18 ft. ‘Wells’ rice was drill-seeded 19 May 2009, with various grass and broadleaf weed species being broadcast seeded the same day. Herbicide programs evaluated included imazosulfuron applied at 0.2, 0.3, and 0.4 lb ai/acre PRE with cloma-zone (Command) at 0.3 lb ai/acre followed by (fb) quinclorac (Facet) at 0.5 lb ai/acre plus propanil (Stam) at 4 lb ai/acre EPOST; imazosulfuron applied EPOST at 0.15, 0.2, and 0.3 lb/acre with clomazone at 0.3 lb/acre fb quinclorac 0.5 lb/acre plus propanil at 4 lb/acre PREFLD; imazosulfuron applied EPOST at 0.15, 0.2, and 0.3 lb/acre with quinclorac at 0.5 lb/acre fb thiobencarb at 3 lb/acre with propanil at 3 lb/acre applied PREFLD; imazosulfuron applied at 0.15, 0.2, and 0.3 lb/acre with clomazone at 0.3 lb/acre PRE fb quinclorac 0.5 lb/acre plus imazosulfuron at 0.15, 0.2, and 0.3 lb/acre PREFLD; and imazosulfuron applied PRE at 0.15, 0.2, and 0.3 lb/acre with clomazone 0.3 lb/acre fb imazosulfuron applied PREFLD at 0.15, 0.2, and 0.3 lb/acre with propanil at 4 lb/acre. The standard program for comparison consisted of clomazone 0.3 lb/acre plus quinclorac 0.5 lb/acre PRE fb propanil 4 lb/acre plus halosulfuron at 0.047 lb/acre PREFLD. All herbicides, excluding imazosulfuron, were applied at labeled rates.
Clomazone use-rates were adjusted for soil type with 0.3 lb/acre applied on silt loam soil and 0.6 lb/acre applied on clay soil. All non-propanil POST treatments contained Dyne-A-Pak at 2.5% v/v, and a nontreated control was included. All applications were applied at 15 gal/acre. Weeds evaluated were hemp sesbania, barnyardgrass, yellow nutsedge, broadleaf signalgrass (Brachiaria platyphylla), pitted morningglory (Ipomoea lacunosa), and Palmer amaranth (Amaranthus palmeri). Visual ratings of rice injury and weed control were recorded at 8 and 12 weeks after planting (WAP) on a scale of 0 to 100 % with 100 % being complete weed control or rice injury. Rice yield data were recorded in bushels per acre (bu/acre). All data were subjected to analysis of variance, and means were separated using Fisher’s protected Least Significant Difference (LSD) test at the 5% level of significance.
RESULTS AND DISCUSSION
Herbicide programs containing imazosulfuron caused little or no injury to rice (data not shown). At Keiser, PRE and POST activity on hemp sesbania from
imazosul-furon herbicide programs ranged from 91% to 100% (Table 1). Programs that included PRE-applied imazosulfuron at 0.3 and 0.4 lb ai/acre, but no PREFLD herbicide resulted in >95% late-season (12 WAP) hemp sesbania control and was similar to programs that included PREFLD applications. Because of the clay soil at Keiser, it may be necessary to increase the imazosulfuron rate to 0.3 lb ai/acre when applied PRE in such treat-ments. The imazosulfuron rate of 0.3 lb ai/acre is the highest anticipated rate that will be labeled PRE in rice (Carey, personal communication). Control of barnyardgrass with all herbicide programs that included PRE- or EPOST-applied imazosulfuron fb quinclorac/propanil or thiobencarb/propanil POST was superior to other programs in-cluding the standard program (Table 1). Programs that included a POST application of a propanil/quinclorac or propanil/thiobencarb combination provided the highest pitted morningglory control at 8 WAP. Programs that included POST applications of quinclorac and propanil controlled Palmer amaranth at 8 WAP better than programs that contained POST applications of imazosulfuron. Imazosulfuron applied POST does not provide effective grass control (Jones et al., 2009) and must be used with grass herbicides. As a result, care must be given to controlling barnyardgrass in fields containing biotypes resistant to propanil and quinclorac.
On the Stuttgart silt loam soil, all treatments controlled hemp sesbania 99% to 100% and were comparable to the standard herbicide program (Table 2). Barnyardgrass and broadleaf signalgrass control was similar to the standard herbicide program when imazosulfuron was applied at rates greater than or equal to 0.2 lb ai/acre. Programs including EPOST fb PREFLD and PRE fb PREFLD applications provided >89% con-trol of yellow nutsedge, which was comparable to concon-trol with the standard treatment.
The soil types at the locations differed in clay content and subsequently affected the efficacy of imazosulfuron when applied PRE. Higher use rates of imazosulfuron than those evaluated here may be needed on clay soils. Because there was little or no injury to rice from imazosulfuron, yield from programs containing imazosulfuron were superior or equal to rice yield from the standard program (Table 3).
SIGNIFICANCE OF FINDINGS
The imazosulfuron-containing herbicide programs were highly efficacious on several weeds, but particularly on hemp sesbania and yellow nutsedge. Because of this, imazosulfuron appears to be an effective tool when coupled with grass herbicides for future weed management use in rice. In addition, adjustments in application rates depend-ing on soil type may be necessary based on observations from these experiments.
ACKNOWLEDGMENTS
The financial support for this project from the Arkansas Rice Research and Pro-motion Board and Valent is thankfully acknowledged.
B.R. Wells Rice Research Studies 2009
LITERATURE CITED
Jones, G.T., J.K. Norsworthy, S.K. Bangarwa, D.B. Johnson, and J.D. DeVore. 2009.
Effect of imazosulfuron rate and timing on weed control in rice. Arkansas Crop Prot. Assoc. 13:15.
Norsworthy, J.K., N.R. Burgos, R.C. Scott, and K.L. Smith. 2007. Consultant perspec-tives on weed management needs in Arkansas rice. Weed Technol. 21:832-839.
Table 1. Late-season (12 WAP) hemp sesbania and barnyardgrass control at Keiser. Palmer amaranth and pitted morningglory control at 8 WAP at Keiser.
Control
Hemp Barnyard- Palmer Pitted Herbicide Rate Timing sesbania grass amaranth morningglory
(lb ai/acre) --- (%)
Table 1. Continued.
Control
Hemp Barnyard- Palmer Pitted Herbicide Rate Timing sesbania grass amaranth morningglory
(lb ai/acre) --- (%)
z PRE = preemergence, EPOST = early postemergence, and PREFLD = preflood.
B.R. Wells Rice Research Studies 2009
Table 2. Late-season (12 WAP) hemp sesbania, barnyardgrass, broadleaf signalgrass, and yellow nutsedge control at Stuttgart.
Control
Hemp Barnyard- Broadleaf Yellow Herbicide Rate Timing sesbania grass signalgrass nutsedge
(lb ai/acre) --- (%)
Table 2. Continued.
Control
Hemp Barnyard- Broadleaf Yellow Herbicide Rate Timing sesbania grass signalgrass nutsedge
(lb ai/acre) --- (%)
---Imazosulfuron 0.3 PRE 100 99 95 99
clomazone 0.3 PRE
quinclorac 0.5 PREFLD
imazosulfuron 0.3 PREFLD
Imazosulfuron 0.15 PRE 99 91 92 97
clomazone 0.3 PRE
imazosulfuron 0.15 PREFLD
propanil 4 PREFLD
Imazosulfuron 0.2 PRE 99 92 96 94
clomazone 0.3 PRE
imazosulfuron 0.2 PREFLD
propanil 4 PREFLD
Imazosulfuron 0.3 PRE 99 98 94 99
clomazone 0.3 PRE
imazosulfuron 0.3 PREFLD
propanil 4 PREFLD
Clomazone 0.3 PRE 100 100 100 100
quinclorac 0.5 PRE
halosulfuron 0.047 PREFLD
propanil 4 PREFLD
LSD = 0.5 7.7 7.3 10.8
z PRE = preemergence, EPOST = early postemergence, and PREFLD = preflood.
B.R. Wells Rice Research Studies 2009
Table 3. Rice yields at Keiser and Stuttgart, Ark., as influenced by herbicide programs.
Yield
Herbicide Rate Timing Stuttgart Keiser
(lb ai/acre) - (bu/acre)
Imazosulfuron 0.15 EPOST 191 129
clomazone 0.3 EPOST
Imazosulfuron 0.15 EPOST 181 190
quinclorac 0.5 EPOST
Table 3. Continued.
Yield
Herbicide Rate Timing Stuttgart Keiser
(lb ai/acre) - (bu/acre)
---Imazosulfuron 0.15 PRE 178 137
clomazone 0.3 PRE
imazosulfuron 0.15 PREFLD
propanil 4 PREFLD
Imazosulfuron 0.2 PRE 176 113
clomazone 0.3 PRE
imazosulfuron 0.2 PREFLD
propanil 4 PREFLD
Imazosulfuron 0.3 PRE 176 166
clomazone 0.3 PRE
imazosulfuron 0.3 PREFLD
propanil 4 PREFLD
Clomazone 0.3 PRE 161 153
quinclorac 0.5 PRE
halosulfuron 0.047 PREFLD
propanil 4 PREFLD
LSD = 26.7 48.6
z PRE = preemergence, EPOST = early postemergence, and PREFLD = preflood.