A glyphosate-resistant Palmer amaranth biotype was confirmed in central Georgia. In the field, glyphosate applied to 5- to 13-cm-tall Palmer amaranth at three times the normal use rate of 0.84 kg ae ha−1controlled this biotype only 17%. The biotype was controlled 82% by glyphosate at 12 times the normal use rate. In the greenhouse,I50values (rate necessary for 50% inhibition) for visual control and shoot fresh weight, expressed as percentage of the nontreated, were 8 and 6.2 times greater, respectively, with the resistant biotype compared with a known glyphosate-susceptible biotype. Glyphosate absorption and translocation and the number of chromosomes did not differ between biotypes. Shikimate was detected in leaf tissue of the susceptible biotype treated with glyphosate but not in the resistant biotype.

Final lint yield in cotton (Gossypium hirsutum L.) is relatively stable across a wide range of population densities. This study was conducted to determine (i) which components of final lint yield impart this yield stability across plant populations and (ii) how yield distribution is influenced by population density. Studies were conducted in 1997 and 1998 on a Tifton loamy sand (Fine‐loamy, kaolinitic, thermic Plinthic Kandiudults). Cotton was planted in each study on 91‐cm row widths at seeding rates ranging from 3.5 to 25.1 seeds m−2. At harvest, each plot was hand picked and boll numbers and weights were recorded at each monopodial branch and sympodial branch fruiting position. Lower population densities led to plants with more mainstem nodes and monopodial branches with increased fruit retention, resulting in greater fruit production per plant. Boll size was inversely related to population density. Mean net assimilation rate from first flower to peak bloom also was related inversely to population density. The mainstem node of peak boll set increased with population density. Fruit production on a ground area basis was greater in the first sympodial position as population density increased, while fruit production on a ground area basis in third positions and monopodial branches was greater as population density decreased. Accumulative seedcotton from sympodial branches also increased with population density. Total fruit number and seedcotton yield per area were not influenced by population density in these studies. Yield stability across population densities was achieved through manipulation of boll occurrence and weight.

One approach to improving cotton (Gossypium hirsutum L.) yield and quality is to identify crop management practices that may exploit the most basic (i.e., within-boll) yield components. One of the parameters that may influence within-boll yield components is plant density. Thus, the objectives of this investigation were to determine how yield components in cotton are altered through plant density management. Two cotton cultivars were overseeded and hand thinned to 3.6, 9.0, 12.6, and 21.5 plants m 22 in 2001 and 2002. Before machine harvest, plants from 6 m of one row were removed from each plot and hand harvested by fruiting position. After hand harvest, seed cotton from each fruiting position was ginned separately. Boll number, lint mass, seed number, seed mass, seed surface area, and fiber properties were determined for each fruiting position. These data were then used for yield component calculations. Lint mass boll 21 , individual seed mass, and seed number boll 21 decreased as plant density increased while total seed surface area m 22 of land area increased, which resulted in increased lint yield m 22 of land area. Lint mass cm 22 of seed surface area and fiber number seed 21 did not consistently respond to plant density. These results indicate that plant density management may influence total seed surface area per unit land area. Most within-boll yield components, however, appear to be controlled more by cultivar than crop management.Craig W. Bednarz, Texas Tech Univ. and the Texas Agricultural Experiment Station,

Cotton (Gossypium hirsutum L.) within‐boll yield components have changed throughout the last 30 yr of cultivar development. The question arises, how do within‐boll yield components differ in contemporary high yielding cultivars? Nine commercially available cotton cultivars were over‐seeded and hand‐thinned to 10.8 plants m−2 in 2001, 2002, and 2003. Before machine harvest, plants from 6 m of one row were removed from each plot and hand‐harvested by fruiting position. After hand‐harvest, seed cotton from each fruiting position was ginned separately. Boll number, lint mass, seed number, seed mass, seed surface area, and fiber properties were determined for each fruiting position. These data were then used for within‐boll yield component calculations. One of the top yielding cultivars in this investigation (DPL 33 B), characterized by a smaller seed mass, produced greater total seed surface area per unit of land area, but lower lint mass and fiber number per unit of seed surface area. The other two top yielding cultivars in this investigation (DPL 491 and STV 4892 BR), characterized by a larger seed mass, produced lower total seed surface area per unit of land area, but greater lint mass and fiber number per unit of seed surface area. These data indicate fiber number and lint mass per unit of seed surface area are linked to seed size, which should be considered when selecting for increased lint mass or fiber number per unit of seed surface area.

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