The Effect of Seeding Rate and Glyphosate Application Timing and Rate on Fruiting Patterns and Yield of Roundup Ready Cotton

Transcription

1 The Effect of Seeding Rate and Glphosate Application Timing and Rate on Fruiting Patterns and Yield of Roundup Read Cotton Oscar C. Sparks, Jim L. Barrentine, and Mariln R. McClelland 1 RESEARCH PROBLEM The advent of herbicide-resistant cotton (Gosspium hirsutum) cultivars has allowed foliar postemergence (POST) control of man problematic weed species in cotton; however, foliar applications of glphosate must be made before the fifth true leaf. Glphosate applications are also limited to 1.0 lb ai/acre or 0.75 lb ae/acre in a single application. There must also be 10 das and two nodes of growth between sequential applications. The in-crop total should not exceed 4 lb of glphosate/acre. If growers were able to appl glphosate over-the-top later in the season this might allow for eas weed control. The objective of this experiment was to see if increasing seeding rate would increase the number of nodes to the first fruiting branch thus allowing for later applications of glphosate. BACKGROUND INFORMATION Recommended applications of glphosate did not change plant height, nodes to first fruiting branch, or the location of cotton bolls (Murdock and Sherrick, 2000; Dotra and Keeling, 1997; Matthews et al., 1998). Off-labeled applications of glphosate shortened the anther column, resulting in increased distance from anthers to stigma (Pline et al., 2002), and in poorl pollinated breeding positions. Roundup Read cotton compensates for fruit loss from late applications of glphosate b setting fruit higher and/or at outer positions (Sanders et al., 2002; McCloske and Moser, 2002; Kalaher and Coble, 1998; Renolds et al., 1999). The question to answer is: can we somehow raise the node to the first fruiting branch? It was found b several researchers that the number of nodes to the first fruiting branch increases with an increase in seeding rate (Choudhar and Bordovsk, 2002). In contrast, plant height, number of nodes, and number of 1 Graduate research assistant, professor/head, and senior research associate, respectivel, Department of Crop, Soil, and Environmental Sciences, Faetteville. 60

2 Summaries of Arkansas Cotton Research 2002 fruiting branches decreased as plant population increases (Guthrie, 1991); however, the number of bolls per acre increases (McKnight, 2002) with increases in seeding rate. It was reported earlier that close spacing was conducive to earl maturit because of a higher percentage of first-position bolls. This is important in that first-position bolls contribute 50 to 80% of harvested ield, and this ield comes from nodes 8 through 12 (Burch and Krieg, 2002). We hpothesied that glphosate-resistant cotton grown under higher plant populations ma have a higher number of nodes to first fruiting branch, thus allowing for later applications of glphosate. RESEARCH DESCRIPTION An experiment was conducted in 2002 at the Cotton Branch Experiment Station, Marianna, AR, on a silt loam soil. The stud design was a randomied complete block with four replications with a factorial arrangement of treatments. The three factors were: 1) seeding rate with levels of 5, 10, and 15 lb/acre; 2) glphosate application rate with levels of 0, 1 and 2 lb ai/acre; and 3) glphosate application timing of four-, six-, and eight-leaf cotton. All plots received a preplant incorporated application of trifluralin at 0.5 lb ai/acre, and all plots were hand-weeded. All plots received a lab application of diuron at 0.8 lb ai/acre. The cotton cultivar used was DP 451BR with an in-furrow application of Temik at 4 lb/acre. Treatments were applied using a tractor-mounted spraer calibrated to deliver 20 gal/acre. Data collected consisted of number of monopodial branches, monopodial bolls, nodes to first fruiting branch, percent boll retention, highest smpodial node with first and second fruiting positions, and seed cotton ield. Data were subjected to analsis of variance, and treatment means were separated using Fisher s Protected Least Significant Difference (LSD) at the 0.05 level of significance. RESULTS AND DISCUSSION Seeding rate alone did not increase the number of nodes to first fruiting branch (Table 1). This finding was in direct contrast to what was expected. We found that increases in seeding rate decreased the number of monopodial branches and thus the number of monopodial bolls (Tables 2 and 3). This trend was seen over glphosate rates and application timings. Off-labeled applications of glphosate decreased retention of bolls on first five smpodia (Table 4). The increase in seeding rate alone did not affect the percent retention of first-position fruit; however, when glphosate applications where delaed past the four-leaf stage there was a trend for decreased fruit retention with increases in cotton leaf stage at application, glphosate rate, and seeding rate. When glphosate was applied at the labeled application timings (four-leaf stage) but off-labeled rates (2 lb/acre) were used, there was a substantial decrease in fruit retention at the high seeding rate (15 lb/acre); however, when lower seeding rates 61

3 AAES Research Series 507 (5 and 10 lb/acre) were used there was no decrease in boll retention when glphosate was applied at the four-leaf stage regardless of glphosate rate (Table 4). We saw the same tpe of trend with respect to percent retention of first-position bolls on higher smpodial branches; however, the decreases were more subtle (Table 5). There was also a trend for greater retention of outer bolls under lower plant densities when offlabeled applications of glphosate are made (Table 6). The potential for compensation b setting fruit higher on the cotton plant was less in high plant densities (15 lb/acre) than in low plant densities (5 lb/acre) (Table 7). Seed cotton ield was not affected b application timing under low seeding rates and labeled rates of glphosate. However, ield was decreased when glphosate applications were made after the four-leaf stage at the higher seeding rates. There was no reduction in cotton ield when higher seeding rates were used and no glphosate was applied. In fact seeding rates of 10 and 15 lb/acre had significantl higher ields than seeding rates of 5 lb/acre (Table 8). In this stud, increases in seeding rate did not significantl increase the nodes to first fruiting branch. In direct contrast with our hpothesis, it appears that cotton at lower seeding rates was able to compensate or tolerate off-labeled applications of glphosate better than higher cotton seeding rates. This phenomenon ma have been due to fruit being set at higher positions, or more retained outer bolls. It is also possible that lower concentrations of glphosate are translocated to potential fruiting positions allowing for greater dispersion of glphosate through sink competition for glphosate because of more fruiting positions per plant. The main point gained from this research is to follow the Roundup Read cotton label. There was no advantage to increasing seeding rate to overcome the incomplete tolerance of Roundup Read cotton to foliar applications of glphosate. There ma be some usefulness in reducing seeding rate; however, issues such as inconsistent stands from reduced seeding rates and lateseason weed control ma be limiting factors. PRACTICAL APPLICATION If off-labeled applications of glphosate are ever labeled as a salvage treatment, there ma be greater ield loss under higher seeding rates (15 lb/acre) and higher glphosate rates (2 lb /acre) as compared to lower seeding rates (5 lb/acre) and labeled rates. Again, the main message from this experiment is to follow the Roundup Read cotton label. LITERATURE CITED Burch, K.M. and D.R. Krieg The relative contribution of individual fruiting sites to cotton ield and qualit. Proc. Beltwide Cotton Conf., National Cotton Council, Memphis, TN CD-Rom. 62

4 Summaries of Arkansas Cotton Research 2002 Choudhar, M. and D.G. Bordovsk Seeding rate for drland cotton in the Texas Rolling Plains. Proc. Beltwide Cotton Conf., National Cotton Council, Memphis, TN CD-Rom. Dotra, P.A. and J.W. Keeling Roundup Read cotton tolerance to Roundup Ultra applied at various growth stages. Proc. Beltwide Cotton Conf., National Cotton Council, Memphis, TN. Vol. 1:778 Guthrie, D.S Effect of plant population and variet on cotton fruiting profile. Proc. Beltwide Cotton Conf., National Cotton Council, Memphis, TN. Vol. 1:844. Kalaher C.J. and H.D. Coble Fruit abscission and ield response of Roundup Read cotton to topical applications of glphosate. Proc. Beltwide Cotton Conf., National Cotton Council, Memphis, TN. Vol. 1:849. McCloske, W.B. and H.S. Moser Tolerance of Roundup Read cotton to topical and post-directed glphosate. Proc. Beltwide Cotton Conf., National Cotton Council, Memphis, TN CD-Rom. McKnight, L.A Influence of high plant densities on ield, row qualit and earliness in ultra-narrow cotton in the San Joaquin Valle of California. Proc. Beltwide Cotton Conf., National Cotton Council, Memphis, TN CD-Rom. Matthews, S.G., G.N. Rhodes, Jr., T.C. Mueller, and R.M. Haes Effects of Roundup Ultra on Roundup Read cotton. Proc. Beltwide Cotton Conf., National Cotton Council, Memphis, TN. Vol. 1:850. Murdock, E.C. and S.L. Sherrick Tolerance of Roundup Read (glphosatetolerant) cotton to postemergence and postemergence-directed applications of Roundup Ultra. Proc. Beltwide Cotton Conf., National Cotton Council, Memphis, TN. Vol. 2:1477. Pline, W.A., R. Viator, K.L. Edmisten, J.W. Wilcut, J. Thomas, and R. Wells Glphosate inhibits pollen and anther development in glphosate resistant cotton. Proc. Beltwide Cotton Conf., National Cotton Council, Memphis, TN CD-Rom. Renolds, D.B., S.L. File, R.E. Blackle, and C.E. Snipes The effect of Roundup on Roundup Read cotton. Proc. Beltwide Cotton Conf., National Cotton Council, Memphis, TN. Vol. 1:732. Sanders, J.C., D.B. Renolds, K.M. Bloodworth, and L.T. Barber Fruit retention of Roundup Read cotton. Proc. Beltwide Cotton Conf., National Cotton Council, Memphis, TN CD-Rom. 63

5 AAES Research Series 507 Table 1. The effect of seeding rate, glphosate rate, and glphosate application timing on the nodes to first fruiting branch, Marianna, AR, Glphosate rate and timing cf 6.2 df 6.0 ef 5.9 f 6.4 bf 6.6 ad 6.2 df cf 6.5 bf 6.6 ad 7.1 a 6.2 df 6.4 cf 6.6 ad bf 7.0 ab 6.4 cf 6.5 bf 6.3 cf 6.3 cf 6.8 ac Means followed b the same range of letters are not significantl different (P=0.05). Table 2. The effect of seeding rate, glphosate rate, and glphosate application timing on the number of monopodial branches, Marianna, AR, Glphosate rate and timing ac 2.13 ac 2.40 ab 2.13 ac 2.40 ab 2.67 a 2.60 a be 1.27 df 1.87 bd 1.80 be 1.67 cf 1.87 bd 1.60 cf df 1.87 bd 1.60 cf 1.06 f 1.20 ef 1.47 df 1.60 cf Means followed b the same range of letters are not significantl different (P=0.05). Table 3. The effect of seeding rate, glphosate rate, and glphosate application timing on the number of monopodial bolls, Marianna, AR, Glphosate rate and timing ab 2.70 b 4.80 a 4.30 ab 3.30 ab 4.50 a 4.30 ab c 0.13 c 1.00 c 0.80 c 0.53 c 0.86 c 0.67 c c 0.20 c 0.33 c 0.20 c 0.00 c 0.07 c 0.27 c Means followed b the same range of letters are not significantl different (P=0.05). 64

6 Summaries of Arkansas Cotton Research 2002 Table 4. The effect of seeding rate, glphosate rate, and glphosate application timing on percent retention of first position bolls on smpodial branches 1 through 5, Marianna, AR, Glphosate rate and timing (%) ad 68 a 40 ej 35 gk 49 bg 29 il 12 mn bg 45 ch 17 ln 25 jm 47 ch 11 mn 8 n ch 57 ad 32 hl 36 fj 20 kn 7 n 12 mn Means followed b the same range of letters are not significantl different (P=0.05). Table 5. The effect of seeding rate, glphosate rate, and glphosate application timing on percent retention of first position bolls on smpodial branches 6 through 10, Marianna, AR, Glphosate rate and timing (%) ad 72 ac 76 a 73 ae 73 ae 63 de 76 ae ae 65 ad 59 be 59 be 65 ad 64 ad 69 ac be 59 be 71 ac 60 ae 71 ac 56 ce 59 be Means followed b the same range of letters are not significantl different (P=0.05). Table 6. The effect of seeding rate, glphosate rate, and glphosate application timing on the number of outer bolls retained, Marianna, AR, Glphosate rate and timing ef 1.80 cf 2.20 ae 1.93 bf 1.60 df 2.47 ad 2.93 ab f 1.20 ef 1.80 cf 2.07 be 1.33 ef 2.73 ac 3.27 a fg 0.93 f 2.20 ae 1.13 ef 1.13 ef 1.67 cf 1.20 ef Means followed b the same range of letters are not significantl different (P=0.05). 65

7 AAES Research Series 507 Table 7. The effect of seeding rate, glphosate rate, and glphosate application timing on the highest smpodial node with first and second fruiting positions, Marianna, AR, Glphosate rate and timing be 10.9 ac 10.5 ae 10.6 ad 10.1 ae 10.7 ac 11.3 ab ae 11.0 ac 10.8 ac 10.6 ad 9.9 ce 11.4 a 11.1 ac ef 8.3 f 9.3 df 9.1 ef 10.0 be 10.1 ae 9.9 ce Means followed b the same range of letters are not significantl different (P=0.05). Table 8. The effect of seeding rate, glphosate rate, and glphosate application timing on the seed-cotton ield, Marianna, AR, Glphosate rate and timing eg 3145 e 3274 bd 3203 ce 3274 bd 2827 fg 2898 f bd 3527 a 3327 bc 3115 e 3339 b 2727 fh 2851 fg bd 3203 ce 3145 e 2815 fg 3162 de 2762 fh 2662 h Means followed b the same range of letters are not significantl different (P=0.05). 66