Craig W. Bednarz

Yield, Quality, and Profitability of Cotton Produced at Varying Plant Densities

Modifying fruit distribution through varying plant density may impact cotton (Gossypium hirsutum L.) fiber quality. This study was conducted to determine how lint yield, fiber quality, and profitability of cotton may be manipulated through plant density. Two cotton cultivars were overseeded and hand-thinned to 3.6, 9.0, 12.6, and 21.5 plants m -2 at two University of Georgia experiment stations in 2001 and 2002. After the studies were machine-harvested each year, the seed cotton was shipped to the USDA-ARS Cotton Ginning Research Unit in Stoneville, MS, for ginning. While ginning, six lint samples were collected per plot and delivered to Cotton Incorporated (Cary, NC) for fiber quality analyses. Net returns were then calculated from yield, quality, and seed cost data. Lint yields were greatest at 12.6 plants m -2 and lowest at 3.6 plants m -2 . Of the fiber properties investigated, micronaire and fineness were most affected by plant density. In addition, quality adjustments in price were greatest for micronaire. Thus, avoidance of price discounts for high-micronaire fiber may occur through adjustments in seeding rate and plant density. Net returns above seed costs were greatest at 12.6 plants m -2 for both cultivars. One cultivar consistently outperformed the other in fiber quality. Results from this study support the findings of others that fiber properties are highly genetically influenced. Thus, to maximize fiber quality, cultivar selection is of greatest importance while management of plant density to maintain or maximize genetic potential is secondary.

Temperature response of whole-plant CO2 exchange rates of four upland cotton cultivars differing in leaf shape and leaf pubescence

It seems likely that CO2 exchange rates of cotton (Gossypium hirsutum L.) cultivars differing in leaf shape and leaf pubescence would respond differently to heat stress due to differences in boundary layer thickness. The objective of this study was to determine if CO2 exchange rates in commercially available cotton cultivars differing in leaf shape and leaf pubescence respond differently to heat stress under well-watered conditions. CO2 exchange rates of whole plants of four cultivars (‘FiberMax 832’, ‘Stoneville 474’, ‘DeltaPine 5690’ and ‘Paymaster 1220’) were measured at eight different temperatures (6 to 34°C) in 4°C steps. Net photosynthesis (Pnet) of the plants decreased at temperatures over 20C, while dark respiration (Rdark) increased exponentially with increasing temperature. Cotton cultivar did not influence the response of Pnet or Rdark to high temperature stress. Carbon use efficiency (CUE) and net assimilation rate (NAR) were highest at lower temperatures and became negative at temperatures higher than 32°C. The initial temperature response of CUE and NAR differed significantly between ‘FiberMax 832’ and the other cultivars. Carbon use efficiency and NAR of ‘FiberMax 832’ decreased at a greater rate with increasing temperature. Due to the fact that the okra leaf of ‘FiberMax 832’ is deeply lobed and smooth, one would expect this cultivar to possess a thinner boundary layer and enhanced heat tolerance under well-watered conditions, which was not the case.

Effects of foliar applied harpin protein on cotton lint yield, fiber quality, and crop maturity

Yield-enhancing compounds are among the many inputs used in cotton (Gossypium hirsutum L.) production systems across the United States Cotton Belt. Some of these products, however, have not been adequately tested in field settings and their impact on cotton yield and quality is unknown. Messenger, marketed by the Eden Bioscience Corporation (Bothell, WA), is a new product containing a protein that may stimulate the hypersensitive response of higher plants, resulting in increased yields. The objective of our investigation was to determine if Messenger applications would result in enhanced cotton crop maturity, lint yield or fiber quality. Messenger studies were conducted in Colquitt, Grady, and Tift Counties in South Georgia and at the University of Georgia Coastal Plain Experiment Station (UGA-CPES) in Tifton in 2000. Plot size at each location ranged from 1.2 ha (Grady County) to 0.01 ha (UGA-CPES). Messenger was applied as a foliar treatment at several stages of crop development at each location with either a John Deere (Moline, IL) high clearance sprayer or a CO2 backpack sprayer. Mid- and late-season plant maps at each location revealed no significant differences in crop maturity among the treatments. Lint yields in Colquitt, Grady, and Tift Counties and the UGA-CPES averaged 1159, 941, 1292, and 1654 kg ha− 1, respectively with no significant treatment differences within a location. Likewise, Messenger did not significantly affect fiber properties at any location. *Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the University of Georgia, the U.S. Department of Agriculture, or other cooperating agencies and does not imply its approval to the exclusion of other products or vendors that may also be suitable. Messenger, Eden, and Eden Bioscience are registered trademarks of the Eden Bioscience Corporation.

Cotton (Gossypium hirsutum) Response to Simulated Imazapic Residues

Field trials were conducted in 2000, 2001, and 2002 at Tifton, GA, and Plains, GA, to evaluate the effects of simulated imazapic residues on cotton growth and yield. Preemergence applications of imazapic at 1, 2, 5, 9, 18, and 36 g ai/ha were made to four different cotton varieties (two at each location) and included a nontreated control. There were no differences in cotton variety response to imazapic. Each cotton variety responded to imazapic in a similar manner. Analysis of cotton yield as a percentage relative to the nontreated control indicated no difference in variety for location, so data for varieties were combined. At Tifton, cotton injury was exponentially related to imazapic rate with a maximum injury of 44% for 35 g/ha. Seed cotton yields at this location were reduced 0, 6, 6, 14, 16, 34, and 61% at 1, 2, 5, 9, 18, and 36 g/ha, respectively. For Plains, cotton exhibited extreme sensitivity with injury exceeding 70% for imazapic at 5 g/ha and greater than 95% for 18 g/ha. Seed cotton yields at this location were reduced 60% or more from imazapic rates of 5 g/ha and greater. These results indicated that soil type is a key factor in the response of cotton to imazapic. Nomenclature: Imazapic; cotton, Gossypium hirsutum L. Additional index words: Carryover injury, herbicide persistence, residual herbicide, simulated carryover. Abbreviations: CEC, cation-exchange capacity; DAT, days after treatment.

Sensitivity of Triploid Hybrid Bermudagrass Cultivars and Common Bermudagrass to Postemergence Herbicides1

The potential weediness of hybrid bermudagrass cultivars in nontarget areas is an important factor when considering the development of herbicide-resistant cultivars. Field studies evaluated the response of common bermudagrass, hexaploid hybrid ‘Tifton-10’, and two triploid hybrid bermudagrass cultivars (‘TifEagle’ and ‘TifSport’) to clethodim, fluazifop-p, glufosinate, glyphosate, and quizalofop-p. Glyphosate was more consistent than clethodim and clethodim plus glyphosate in controlling common bermudagrass. The triploid cultivars were equally sensitive to each of these treatments, whereas Tifton-10 control was highest with treatments that included glyphosate. Variability between years in control of common bermudagrass was attributed to differences in plant size at application, with greater control of smaller plants. All herbicides reduced common bermudagrass plant diameters ≥ 93% in 1999 when grown without a crop. However, in 2001, only herbicide treatments that included two applications of 1.1 kg ai/ha glyphosate reduced plant diameters 6 to 59%. None of the other treatments reduced common bermudagrass plant diameters compared with pretreatment values. When grown with cotton, fluazifop-p and 4.5 kg/ha glyphosate were the only treatments consistent across cultivars and years. All herbicide treatments reduced triploid hybrid bermudagrass plant diameters ≥ 90%, whereas Tifton-10 plant diameters were reduced > 86% by all treatments, with the exception of clethodim. As in the non-cropland study, common bermudagrass plant diameters were reduced ≥ 97% by herbicides in 1999, whereas in 2001, only fluazifop-p and glyphosate treatments reduced plant diameters compared with the nontreated control. Both the lack of aggressiveness and susceptibility to common herbicides of the triploid hybrid cultivars relative to common bermudagrass indicates that these non–pollen-producing or -receiving cultivars are reasonable candidates for the introduction of herbicide resistance. Nomenclature: Clethodim; fluazifop-p; glufosinate; glyphosate; quizalofop-p; common bermudagrass, Cynodon dactylon (L.) Pers. #3 CYNDA ‘Tifton-10’; hybrid bermudagrass, Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy ‘TifEagle’, ‘TifSport’; cotton, Gossypium hirsutum L. Additional index words: Transgenic turfgrass, turfgrass weed management. Abbreviations: fb, followed by; triploid hybrid cultivars, grouping of TifEagle and TifSport bermudagrass cultivars; WAP, weeks after transplanting.

Effect of Flower Bud Removal on Carbon Dioxide Exchange Rates of Cotton

Numerous fruit removal studies have demonstrated that reproductive sink removal enhances cotton (Gossypium hirsutum L.) vegetative growth and development. Few studies, however, have examined changes in CO2 exchange rates accompanying fruit removal. The objective of this study was to establish the effect of early season flower bud removal on whole plant CO2 exchange rates of cotton. The effect of flower bud removal on the CO2 exchange rates of cotton was investigated in a 31-day study conducted in a controlled environment. Differences in net photosynthesis, dark respiration, daily carbon gain, and carbon use efficiency were not observed in this study with flower bud removal. However, the rate of increase (or decrease in dark respiration) for these parameters was greater with flower bud removal with their maxima occurring later in the study period. All selected photosynthetic parameters also increased steadily with time for both treatments.

ALLEY EFFECT ON SEVERAL COTTON CULTIVARS IN SMALL PLOT RESEARCH

Small plot research often necessitates the use of alleys or fallow areas along plot ends. To determine if there is an interaction between cotton (Gossypium hirsutum L.) cultivars of differing maturity group and the alley effect on plant yield, field studies were conducted in 1997 and 1998 in northeast Louisiana and south central Georgia. A randomized complete block arrangement of treatments was used with the cotton cultivars “Stoneville LA887” (STV LA887), “Delta Pine 5690” (DPL 5690), and “Paymaster 1215RR” (PM 1215RR). Plots were approximately 15 m long with 3 m alleys and were hand harvested in 0.3 m increments. Overall plot yield increased 12–15% by inclusion of lint from plants bordering the alleys. Lint yields were increased for the first 0.6 m from the alley. There was no interaction between cultivar and distance from the alley for yield although the change in boll number and boll size from the alley was not the same among cultivars. Plant height and number of main stem nodes was negatively correlated with distance from the alley across cultivars. Micronaire and fiber length were affected by cultivar, distance from the alley and their interaction. These results suggest that end trimming is not necessary for studies investigating cotton cultivars if lint yield is the only factor of interest. However, if fiber quality or yield components are of interest, plants within 0.6 m of the alley should be removed or not included for measurement.

Surface Runoff and Lateral Subsurface Flow as a response to Conservation Tillage and Soil-WaterConditions

Surface runoff and lateral subsurface flow were measured on six 0.2 ha plots in South Georgia in order to quantify the effects of conservation tillage. Significant differences in water losses were observed between the conventionally and strip tilled plots. Surface runoff from the conventionally tilled plots exceeded that from the strip tilled plots while subsurface losses were reversed. Surface runoff losses from the conventionally tilled plots exceeded those from the strip tilled plots by 80%. Subsurface losses from the strip tilled plots exceeded those from the conventionally tilled plots by 67%. Overall, a net annual gain of 60 mm of water was observed for the strip till plots.