EFFECT OF PALMER AMARANTH (AMARANTHUS PALMERI) SEEDBANK DENSITY ON THE PERFORMANCE OF PENDIMETHALIN AND FLUOMETURON

Transcription

1 Summaries of Arkansas Cotton Research 2003 EFFECT OF PALMER AMARANTH (AMARANTHUS PALMERI) SEEDBANK DENSITY ON THE PERFORMANCE OF PENDIMETHALIN AND FLUOMETURON O.C. Sparks, J.L. Barrentine, N.R. Burgos, and M.R. McClelland 1 RESEARCH PROBLEM Palmer amaranth (Amaranthus palmeri L.) is one of the most common and difficult-to-control weeds in agriculture (Gossett and Toler, 1999). High growth rate (Sellers, 2003), competitive water use efficiency and light interception (Massinga et al., 2003; Rowland et al., 1999), respiration under stress conditions (Stutte and Weiland, 1978), and high reproductive potential at low plant densities (Bensch et al., 2003) make Palmer amaranth an excellent competitor for crop resources. Palmer amaranth seed production has been estimated to be between 60,000 (Bensch et al., 1999) and 500,000 seed/m 2 (Sellers et al., 2003) depending upon plant density. Abundant seed production, resulting in increased Palmer amaranth seedbank densities, could present pre-emergence (PRE) weed control problems. BACKGROUND INFORMATION Increased seedbank populations have been implicated for decreased weed control with soil applied herbicides (Keeley and Thullen, 1991). The effect of seed populations on PRE herbicide efficacy has been investigated in several plant species including ryegrass (Lolium multiflorum) (Burrill and Appleby, 1978); soybean (Glycine max) (Hoffman and Lavy, 1978; Andersen, 1981; Dieleman et al., 1999); and velvetleaf (Abutilon theophrasti) (Dieleman et al., 1999). Seeding rate increases decreased effectiveness of PRE herbicides due to reduced amounts of herbicide available to each plant in the soil-water solution (Andersen, 1981; Burrill and Appleby, 1978; Hoffman and Lavy, 1978; Winkle et al., 1981). Increased weed populations also decrease performance of post-emergence (POST) herbicide programs (Dieleman et al., 1999), probably through inadequate spray coverage of susceptible weed species. 1 Graduate assistant, professor and head, assistant professor, and Senior Research Associate, respectively, Department of Crop, Soil, and Environmental Sciences Fayetteville. 167

2 AAES Research Series 521 Therefore, herbicide rate (Hoffman and Lavy, 1978; Winkle et al., 1981) and management levels (Dieleman et al., 1999) may need to be increased with increased seed densities in the soil seedbank. Uncontrolled competition from Palmer amaranth results in substantial yield reductions (Morgan et al., 1997; Rowland et al., 1999). Amaranthus species have traditionally been controlled with PRE herbicides, including dinitroanilines and ureas, post-emergence-directed herbicides, and cultivation. The advent of glyphosate-tolerant cotton has allowed for POST overthe-top control of Palmer amaranth in cotton. However, PRE herbicides may still be needed for controlling early infestations of Palmer amaranth, especially in conventional cotton. Pendimethalin and fluometuron efficacy may decrease with increased Palmer amaranth soil seed density. The objective of this research was to evaluate pendimethalin (Prowl) and fluometuron (Cotoran) PRE efficacy as affected by Palmer amaranth soil-seed density. RESEARCH DESCRIPTION Greenhouse studies were conducted to evaluate the effects of Palmer amaranth soil seed density on the efficacy of pendimethalin and fluometuron applied PRE. The study design was completely random with eight replications and studies were conducted twice. Styrofoam pots filled with 400 g of silt loam soil were overseeded with seed of Palmer amaranth at 33,000; 66,000; 128,000; 256,000; and 528,000 seed/m 2. These seeding rates cover the range of Palmer amaranth seed production reported by (Sellers et al., 2003) and (Bensch et al., 2003). Seeds where then covered with 100 g of soil resulting in a burial depth of approximately 3 mm. Pendimethalin and fluometuron tank mixtures at rates of 0, 0.28, 0.56, 1.12 (standard field rate), 2.24, and 4.48 kg ai/ha each, were applied PRE to individual pots. Pots were overhead irrigated with a fine mist of water, followed by subirrigation. Pots were then subjected to a 14/10 hours, 42/35 C day/night light and temperature regime. Palmer amaranth seedlings were counted and removed three and six weeks after treatment. Slope estimates of the effect of Palmer amaranth soil density and herbicide on Palmer amaranth survival were compared using 95% confidence intervals. Slope comparisons that differed by more than two times the standard error were considered different. All other data were subjected to analysis of variance, and means were separated using Fishers protected LSD at the 0.05 level of significance. RESULTS AND DISCUSSION At all Palmer amaranth soil densities pendimethalin plus fluometuron PRE at 0.28 kg/ha each was less effective than higher rates. Pendimethalin plus fluometuron at 0.56 kg/ha each controlled low Palmer amaranth populations (33,000 to 132,000 seed/m 2 ) equal to higher herbicide rates. Pendimethalin plus fluometuron rates less than 1.12 kg/ha each controlled Palmer amaranth less than higher rates when Palmer amaranth populations were greater than 132,000 seed/m

3 Summaries of Arkansas Cotton Research 2003 Pendimethalin plus fluometuron PRE at 0.28 and 0.56 kg/ha each applied to Palmer amaranth seed densities of 132,000 to 528, 000 seed/m 2 were less effective than rates of 1.12 kg/ha each or greater. Palmer amaranth control with pendimethalin plus fluometuron at 1.12 kg/ha each did not differ from higher rates when Palmer amaranth soil density was 33,000 to 132,000 seed/m 2 ; however, when the seeding rate was increased from 264,000 to 528,000 seed/m 2, higher herbicide doses were needed. Palmer amaranth escapes were increased by 3- to 7-fold when seeding rate was doubled. Palmer amaranth decay rates were compared by doubling the standard error for the decay rate estimate to create estimated 95% confidence intervals (Table 2). Decay rates with non-overlapping confidence intervals were considered different. The decay rate was significantly different for only the highest soil seed density of Palmer amaranth 528,000 seed/m 2. Palmer amaranth survival followed a different trend at this seed density (528,000 seed/m 2 ) than at lower soil seed densities. Decay rates were similar in herbicide rates needed to produce similar reductions in survival; however, the level of survival was usually greater as soil seed density increased. Optimization of pendimethalin and fluometuron PRE based on zero Palmer amaranth emergence or survival at 3 and 6 WAP from soil seed densities of 33,000; 66,000; 132,000; 264,000; and 528,000 seed/m 2 were 1.12 and 1.12 for 33,000 seed/m 2 ; 1.23 and 1.23 for 66,000 seed/m 2 ; 1.45 and 1.68 for 132,000 seed/m 2 ; 1.68 and 2.46 for 264,000 seed/m 2 ; and 1.68 and 3.25 kg ai/ha for 528,000 seed/m 2 (Table 3). Pendimethalin plus fluometuron at approximately 1.12 to 1.23 kg/ha each (close to normal field rates) were required when soil densities were between 33,000 and 66,000 seed/m 2. Increasing soil seed densities from 132,000 to 264,000 seed/m 2 required pendimethalin and fluometuron at approximately 1.5 to 2.5 kg/ ha each for complete control of Palmer amaranth at 3 WAP (approximately cotyledon- to one-leaf cotton) to 6 WAP (approximately four- to six-leaf cotton). At 528,000 seed/m 2, more than 3 kg/ha of both pendimethalin and fluometuron were required for complete control of Palmer amaranth 6 WAP. PRACTICAL APPLICATION Normal field rates of pendimethalin plus fluometuron were as effective in preventing emergence of Palmer amaranth at 3 and 6 WAP at seeding rates of 33,000 through 264,000 seed/m 2. Increased soil seed density required increased rates of pendimethalin and fluometuron. Palmer amaranth soil seed density variation within or between fields should be considered when choosing PRE herbicide programs. PRE herbicide systems, depending upon herbicide rate and soil density of Palmer amaranth, may or may not be effective in controlling Palmer amaranth. Cotton phytotoxicity, a parameter not evaluated in this study, would certainly be a factor, especially at rates greater than 1.12 kg/ha of both pendimethalin and fluometuron. At normal field rates (1.12 kg/ha), in some instances, two-fold increases in soil density increased Palmer amaranth emergence and survival more than five-fold. Future research should consist of multiple regression models to 169

4 AAES Research Series 521 predict not only Palmer amaranth emergence and survival from different PRE herbicide systems, but also other agronomically important weeds in cotton, considering several factors, including soil type, rainfall, temperature, and microbial enrichment. This information would be a valuable addition to COTMAN or weedmanagement decision-aid programs. LITERATURE CITED Andersen, R.N Increasing herbicide tolerance of soybeans (Glycine max) by increasing seeding rates. Weed Sci. 29: Bensch, C.N., M.J. Horak, and D. Peterson Interference of redroot pigweed (Amaranthus retroflexus), Palmer amaranth (A. palmeri), and common waterhemp (A. rudis) in soybean. Weed Sci. 51: Burrill, L.C. and A.P. Appleby Influence of Italian ryegrass density on efficacy of diuron herbicide. Agron. Jour. 70: Dieleman, J.A., D.A. Mortensen, and A.R. Martin Influence of velvetleaf (Abutilon theophrasti) and common sunflower (Helianthus annuus) density variation on weed management outcomes. Weed Sci. 47: Gossett, B.J. and J.E. Toler Differential control of Palmer amaranth (Amaranthus palmeri) and smooth pigweed (Amaranthus hybridus) by postemergence herbicides in soybean (Glycine max). Weed Technol. 13: Hoffman, D.W. and T.L. Lavy Plant competition for atrazine. Weed Sci. 26: Keeley, P.E. and R.J. Thullen Biology and control of black nightshade (Solanum nigrum) in cotton (Gossypium hirsutum). Weed Technol. 5: Massinga, R.A., R.S. Currie, and T.P. Trooien Water use and light interception under Palmer amaranth (Amaranthus palmeri) and corn competition. Weed Sci. 51: Rowland, M.W., D.S. Murray, and L.M. Verhalen Full-season Palmer amaranth (Amaranthus palmeri) interference with cotton (Gossypium hirsutum). Weed Sci. 47: Sellers, B.A., R.J. Smeda, W.G. Johnson, A.J. Kendig, and M.R. Ellersieck Comparative growth of six Amaranthus species in Missouri. Weed Sci. 51: Stutte, C.A., and R.T. Weiland Gaseous nitrogen loss and transpiration of several crop and weed species. Crop Sci. 18: Taylor, K.L. and R.G. Hartzler Effect of seed bank augmentation on herbicide efficacy. Weed Technol. 14: Winkle, M.E., J.R. C. Leavitt, and O.C. Burnside Effects of weed density on herbicide absorption and bioactivity. Weed Sci. 29:

5 Summaries of Arkansas Cotton Research 2003 Table 1. The effect of pendimethalin and fluoreturon rate and Palmer amaranth seed density (seed m 2 ) on Palmer amaranth (AMAPA) emergence and survival. Palmer amarnath density (seeds/m 2 ) a Pendimethalin plus fluometuron kg ai/ha each Palmer amaranth emergence and survival /m f de d b a gh 625 gh 3593 fgh de c h 156 h 781 gh 4218 fg d h 0 h 156 h 937 gh 7031 ef h 0 h 0 h 0 h 0 h a Means followed by the same letter do not differ, (P =0.05). Table 2. Comparison of Palmer amaranth decay rates (Dr) six weeks after treatment (WAT) over rates of pendimethalin and fluometuron. Slope parameters ~Standard AMAPA D r estimate a error density seeds m 2 ~95% Confidence interval lower upper a a a a b a Slope estimates within a column followed by the same lower-case letter are not significantly different (95% confidence intervals do not overlap). 171

6 AAES Research Series 521 Table 3. Optimization of equivalent rates of pendimethalin and fluometuron at a specific seedbank population based on complete control of Palmer amaranth at 3 and 6 (WAP). Optimization of pendimethalin plus fluometuron rates AMAPA density 3 WAP ( R 2 =0.34) Prob> F=<0.001 Seed Herbicide WAP ( R 2 =0.65) Prob> F=<0.001 Seed Herbicide seeds/m kg ai/ha each