Evaluation of Weed Management and the Agronomic Utility of Cotton Grown on a 15-Inch Row Configuration and the Biology and Ecology of Doveweed

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Title: Evaluation of Weed Management and the Agronomic Utility of Cotton Grown on a 15-Inch Row Configuration and the Biology and Ecology of Doveweed
Author: Wilson, David Gaye, Jr.
Advisors: Dr. Michael G. Burton, Committee Member
Dr. J.R. Bradley, Committee Member
Dr. John W. Wilcut, Committee Member
Dr. Alan C. York, Committee Co-Chair
Dr. Keith L. Edmisten, Committee Co-Chair
Abstract: For more than a century, farmers planted cotton in rows spaced 91-cm or more apart. Row spacing was dictated primarily by equipment for cultivation, which was initially draft animals and later, tractors. Harvesting equipment also was designed to accommodate these wide row spacings. Recent advances in technology, especially herbicide-resistant cotton and the ability to spindle-pick cotton in 38-cm rows, have increased the potential for cotton production in narrow rows. Field experiments were conducted to evaluate weed management systems in glufosinate-resistant cotton planted in 38- and 97-cm rows. Greater than 90% control of annual grasses and Amaranthus spp. in 2004 and Ipomoea spp. in both years was obtained in narrow-row cotton receiving glufosinate applied early postemergence (EPOST) and mid-postemergence (MPOST) to 2- and 6-leaf cotton, respectively. With good early season control by glufosinate and rapid canopy closure, there was little benefit from pendimethalin, fluometuron, or pyrithiobac applied preemergence (PRE), S-metolachlor or pyrithiobac mixed with glufosinate applied MPOST, or trifloxysulfuron applied late postemergence (LPOST) to 11-leaf cotton. In 2005, glufosinate alone applied EPOST and MPOST did not adequately control annual grasses and Amaranthus spp. Pendimethalin applied PRE alone or mixed with fluometuron or pyrithiobac increased control to greater than 90% and increased yields 59 to 75%. Pendimethalin PRE followed by S-metolachlor or pyrithiobac mixed with glufosinate at MPOST was no more effective than pendimethalin alone. Without PRE herbicides, trifloxysulfuron applied LPOST increased Amaranthus but not annual grass control. Cotton row spacing had no effect on cotton yield and little effect on weed control. Weed control and yield in narrow-row cotton with a PRE herbicide plus glufosinate applied twice was similar to that in wide-row cotton with a PRE herbicide, glufosinate applied twice, and trifloxysulfuron plus prometryn plus MSMA applied postemergence-directed. Field experiments were conducted in 2004 and 2005 at Clayton and Rocky Mount, NC to determine weed management systems in 38-cm glyphosate-resistant cotton. Additionally, row spacing effects on weed management were also examined. Herbicide systems in the 38-cm row spacing controlled annual grasses more effectively when PRE herbicides or a mid-POST application of S-metolachlor was included. Control of Ipomoea spp. was more effective in systems including preemergence herbicides or glyphosate mixed with pyrithiobac POST. Programs containing sequential POST applications of glyphosate alone were effective in controlling Palmer amaranth and smooth pigweed. Cotton row spacing had little effect on weed control, and there were no differences in lint yield among herbicide systems in both row spacings. However, a 6% increase in lint yield was observed in the 38-cm rows compared to the 97-cm rows. There has been a recent technological advancement of glyphosate-resistant cultivars that allow topical applications of glyphosate up to 7 days prior to harvest. Studies were conducted to evaluate weed management systems in narrow-row cotton utilizing this new glyphosate-resistance technology. At least one herbicide system controlled annual grasses, Ipomoea spp., and Amaranthus spp. at least 96, 93, and 99% late in the season. Glyphosate applied alone to 1- and 6-leaf cotton provided excellent (≥ 93%) late-season control of all species present in this study. Systems including S-metolachlor provided more effective late-season control of annual grasses, while systems including pendimethalin plus fluometuron or pyrithiobac PRE tended to provide more effective late-season control of Ipomoea spp. There were no differences observed with respect to lint yield or fiber quality characteristics among herbicide systems. This research illustrates that excellent overall weed control can be obtained in narrow-row glyphosate-resistant cotton, but systems including the use of residual herbicides may be more beneficial. Studies were conducted to determine plant population effects on 38-cm cotton. The plant population densities under investigation ranged from 34,400 to 310,400 plants ha-1. All plant populations in the 38-cm rows were compared to 97-cm rows with a population density of 115,800 plants ha-1. Plant height, number of mainstem nodes, number of bolls per plant, and seed cotton weight per boll decreased as plant populations increased. However, when plant populations ranged from 102,800 to 301,400 plants ha-1, a higher percentage of first position bolls and total seedcotton weight in the lower and middle portion of the canopy was noted for the 38-cm rows compared to 97-cm rows. Therefore, an earlier crop could possibly achieved in 38-cm rows by using populations of at least 120,000 plants ha-1 compared to the 97-cm rows. The amount of photosynthetically-active radiation (PAR) penetrating through the plant canopy at 10 wk after planting (WAP) averaged 19% less with a population density of at least 60,300 plants ha-1 in the 38-cm rows compared to the 97-cm rows. This could lower the probability of late-season weed resurgence in cotton planted in 38-cm rows. There were no differences in lint yields with plant populations ranging from 60,300 to 301,409 plants ha-1. However, decreases in lint yield with plant populations above or below those levels were observed. All fiber quality characteristics were within acceptable levels to avoid price discounts regardless of plant population density or row spacing. Our findings indicate that higher plant population densities than what is utilized in wide-row cotton production systems are not warranted in narrow-row cotton if it is to be spindle-picked. An experiment was conducted at five locations during 2004 and 2005 to determine if MC application strategies currently recommended for wide-row cotton are valid for cotton planted in 38-cm rows. Cotton planted in 38- and 97-cm rows received MC in three application strategies. The low rate multiple (LRM) strategy consisted of MC at 12 g a.i. ha-1 applied three times at 2-wk intervals beginning at the first square stage. The modified early bloom (MEB) strategy consisted of MC at 24 g ha-1 applied 2 wk prior to early bloom and repeated at early bloom. The early bloom (EB) strategy consisted of MC at 24 g ha-1 applied at early bloom and repeated 2 wk later. Cotton in 38- and 97-cm rows responded similarly to MC, as indicated by lack of a MC application strategy by row spacing interaction for plant height, fruiting characteristics, fruit retention, lint yield, and fiber quality. Cotton in 38-cm rows was shorter, produced more bolls per unit area, had greater boll retention on first position sympodial sites, and yielded 10% more than cotton in wide rows. Except for plant height, which was reduced more by MC in the LRM and MEB strategies than in the EB strategy, cotton response was similar with each MC application strategy. Averaged over row spacings, MC increased lint yield 5%. Minor increases in fiber length were noted in MC-treated cotton, but MC did not affect micronaire, fiber strength, or fiber length uniformity. The results suggest current MC recommendations for wide-row cotton in North Carolina are appropriate for cotton in 38-cm rows. The LRM or MEB strategies would be preferred. Laboratory and greenhouse experiments were conducted to determine the effect of temperature and seed burial depth on doveweed germination and emergence. Germination at constant temperature was well defined by a Gaussian model, which estimated peak germination at 28 C. However, based upon t-tests the effect of temperature treatments between 25 and 30 C did not differ (P > t = 0.08). The mean base temperature for germination (50%) was between 20 and 25 C. Similar maximum percent germination was observed for optimal treatments under both constant and alternating temperatures. Among alternating temperature treatments, 35/25 C regime gave the highest germination (77%). Germination was higher with alternating temperature regimes of 40/30 and 40/35 C (65 and 30%, respectively) than constant temperatures of 36 and 38 C (4 and 0%, respectively). No germination was observed at constant temperature of 38 C and alternating temperature regimes of 20/10 and 25/15. Light did not facilitate germination. In depth of emergence experiments, peak emergence was reached 2 wk after planting regardless of burial depth. Peak emergence was between 0 and 1 cm at 4 weeks after planting, and occurred from as deep as 4 cm. The mean emergence depth was 3.2 cm. Knowledge gained from this research will aid in an integrated weed management strategy for doveweed.
Date: 2006-08-07
Degree: PhD
Discipline: Crop Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/5594

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