Improving the Management of Dicot Weeds in Peanut with Narrow Row Spacings and Residual Herbicides W. Carroll Johnson III,* Eric P. Prostko, and Benjamin G. Mullinix, Jr. ABSTRACT ment strategies in peanut is important because of the Narrow row spacings in peanut (Arachis hypogaea L.) production high cost of weed control, reduced profit margins, and suppress spotted wilt and promote rapid canopy closure, improving continued large losses due to weeds. competitiveness with weeds. Trials were conducted from 1999 to 2001 That reassessment should also include the potential to determine if weed suppression in narrow row spacings, in conjunc- role of cultural weed controls in peanut, and narrow row tion with new residual herbicides supplemented with nonresidual her- spacings in particular. This concept for cultural weed bicides, improved weed control and reduced herbicide use. Within each control has been proposed in peanut (Cardina et al., row spacing were three levels of weed management using the residual 1987; Wehtje et al., 1984). Buchanan and Hauser (1980) herbicides imazapic {(Ϯ)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)- showed that peanut seeded in multiple groupings of 5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid}, diclosulam narrowly spaced rows suppressed weed resurgence bet- [N-(2,6-dichlorophenyl)-5-ethoxy-7-fluoro[1,2,4]triazolo[1,5-c]pyrimi- ter than peanut seeded in wide rows. In their initial trials, dine-2-sulfonamide], sulfentrazone {N-[2,4-dichloro-5-[4-(difluoro- methyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]phenyl]meth- however, the in-row seed spacing was the same between anesulfonamide}, and flumioxazin {2-[7-fluoro-3,4-dihydro-3-oxo- wide- and narrow-row spacings, which resulted in higher 4-(2-propynyl)-2H-1,4-benzoxazin-6-yl]-4,5,6,7-tetrahydro-1H-iso- seeding rate in narrow-row spacings than in wide-row indole-1,3(2H)-dione}. Minimal weed management was ethalfluralin spacings. In follow-up trials, the in-row seed spacing [N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)ben- was altered such that seeding rate remained the same zenamine] alone for annual grass control. Moderate weed management among all row spacings (Hauser and Buchanan, 1981). was ethalfluralin, a residual herbicide, and 2,4-DB [4-(2,4-dichloro- This is critical for the practicality of multiple groupings phenoxy)butanoic acid]. Intense weed management was the moderate of narrowly spaced rows since peanut seed are costly system for each residual herbicide, plus paraquat (1,1؅-dimethyl-4,4؅- (approx. $148 haϪ1), accounting for 15% of the input bipyridinium ion), bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothia- costs in peanut production (Smith et al., 2003). diazin-4(3H)-one 2,2-dioxide], and acifluorfen {5-[2-chloro-4-(triflu- The enhanced competitiveness of peanut seeded in oromethyl)phenoxy]-2-nitrobenzoic acid}. Peanut seeded in narrow narrow row spacings reduced the biomass of Florida rows had quicker canopy closure than peanut seeded in wide rows. beggarweed [Desmodium tortuosum (Sw.) DC] and sickle- Densities of individual weeds species were not affected, although total weed densities were lower in narrow rows than wide rows. Narrow pod [Senna obtusifolia (L.) Irwin and Barneby], two of row spacings with residual herbicides did not reduce herbicide use the most troublesome weeds of peanut in the southeast- compared with wide row spacings. Yields were 12% greater in narrow ern USA (Hauser and Buchanan, 1982). Researchers rows than wide rows. While narrow row spacings did not affect individ- concluded that the greatest weed suppression was pro- ual weed species and reduce herbicide use, narrow row spacings sup- vided by peanut seeded in a cluster of seven rows spaced plement herbicides by reducing the total number of weed escapes. 20 cm apart on a raised seedbed. Given the subterranean fruiting of peanut and difficulties of digging and in- verting peanut seeded using this cluster of narrow rows, roducers in Georgia commonly spend more than Ϫ1 it was concluded that a pattern of paired rows, with P$86 ha for weed control in peanut (Smith et al., rows spaced 18 cm apart in the pair and each pair spaced 2003), which accounts for approximately 8% of the vari- 75 cm apart, would give similar levels of weed suppres- able costs of peanut production. Similar expenditures sion and be easier to dig and invert at harvest. Colvin have been reported for other southeastern peanut pro- et al. (1985) evaluated six levels of weed control intensity ducing states (Webster, 2001a). Despite these investments among various row spacings, including the paired-row in weed control, annual losses from weeds in peanut were configuration. In their trials, narrow row spacings sup- recently estimated to be $11.2, $6.4, and $47.7 million in pressed weed growth, but not enough to reduce herbi- Alabama, Florida, and Georgia, respectively (Webster, cide use. It was the general consensus that greater yields 2001a). Reasons for the continued large losses from and net returns of paired row spacings compared with weeds in peanut is subject to considerable debate, espe- wide row spacings were due to optimum conditions for cially since 18 effective herbicide active ingredients are crop growth that increased yield, not necessarily better registered for peanut (Prostko, 2003). Some of the re- weed control (Colvin et al., 1985; Cox and Reid, 1965). cent herbicide registrations provide improved residual Despite the proven yield increase, only 3% of the control of troublesome dicot weeds and perennial nut- Reproduced from Agronomy Journal. Published by American Society of Agronomy. All copyrights reserved. Georgia peanut hectarage was planted to narrow or sedges (Cyperus sp.). Reassessing current weed manage- paired rows in 1981 (Anonymous, 1981). Planter tech- nologies in the early 1980s did not allow for accurate W.C. Johnson III, USDA-ARS, Coastal Plain Exp. Stn., P.O. Box 748, Tifton, GA 31793-0748; and E.P. Prostko and B.G. Mullinix, Jr., and consistent metering of low seed numbers through Coastal Plain Exp. Stn., Tifton, GA 31793-0748. Received 21 Aug. each planter unit, often resulting in wide skips due to 2003. *Corresponding author ([email protected]). planter malfunction or seedling mortality. Increasing Published in Agron. J. 97:85–88 (2005). © American Society of Agronomy Abbreviations: DAE, days after emergence; EPOST, early postemer- 677 S. Segoe Rd., Madison, WI 53711 USA gence; PRE, preemergence; VE, vegetative emergence. 85 86 AGRONOMY JOURNAL, VOL. 97, JANUARY–FEBRUARY 2005 the seeding rate in each planter unit hedged against that programs. Subplots were three beds wide (5.4 m) and 6.1 m risk but increased production costs. long. In the early 1990s, spotted wilt of peanut (tomato Sub-subplots of the experimental design were levels of dicot spotted wilt tospovirus) became epidemic in the south- weed management intensity for each of the residual herbicides; eastern USA. Current management of spotted wilt con- minimal, moderate, and intensive efforts for weed control. Sub-subplots were one bed wide (1.8 m) and 6.1 m long. Minimal sists of production practices that either reduce incidence Ϫ weed management consisted of ethalfluralin (0.8 kg a.i. ha 1) of the disease or minimize losses (Brown et al., 2003). PRE for annual grass control. Ethalfluralin had no effect on One of the production practices used to manage spotted the dicot weeds of interest in this study (Prostko, 2003). Mod- wilt is seeding peanut in narrow or paired-row spacings. erate weed management was a system of ethalfluralin PRE, Consequently, 32% of the 2002 peanut hectarage in one of the residual herbicides, and a single early postemer- Georgia was planted in narrow or paired-row spacings gence (EPOST) application of 2,4-DB at 0.28 kg a.i. haϪ1. (N.B. Smith, personal communication, 2003). Intensive weed management was the moderate system for With the recent increase in using narrow or paired- each residual herbicide, supplemented with a tank-mix appli- row spacings is renewed interest in integrating the en- cation of paraquat (0.14 kg a.i. haϪ1), bentazon (0.56 kg a.i. Ϫ Ϫ hanced competitiveness of peanut seeded in narrow ha 1), and acifluorfen (0.28 kg a.i. ha 1) at vegetative emer- rows with residual herbicides that were not available gence (VE) of peanut. The weed management systems were when similar trials were conducted in the 1970s and designed according to the unique weed control spectrum for early 1980s. These herbicides generally provide long- each of the residual herbicides, which were applied at optimum term residual control of a broad-spectrum of dicot weeds rates and time of application. Treatments were applied with a tractor-mounted plot sprayer and perennial nutsedges. We hypothesize that the im- Ϫ1 pressurized with CO2, calibrated to deliver 234 L ha using proved competitiveness of peanut seeded in narrow row low-drift Turbo TeeJet spray tips (Spraying Systems Co., P.O. spacings combined with the versatility of current resid- Box 7900, Wheaton, IL) treating a swath 1.8 m wide. Excluding ual herbicides may improve weed control efficiency, weed management, pest and crop management practices were reduce herbicide use, and increase yield. held constant over the experiment and based on Georgia Co- operative Extension Service recommendations. MATERIALS AND METHODS Parameters measured were midseason weed counts taken approximately 70 days after emergence (DAE) and peanut Irrigated field studies using the C99R peanut cultivar were yield. Weeds were counted in two 0.5 m2 quadrats (1.0 by conducted from 1999 to 2001 at the Attapulgus Research and 0.5 m) randomly placed adjacent to the crop drill in the center Education Center in Decatur County near Attapulgus, GA.