Four field experiments were conducted in Oklahoma to measure full-season Palmer amaranth interference on cotton lint yield and fiber properties. Density of the weed ranged from 0 to 12 plants 10 m−1 of row. Cotton lint yield vs. weed density fit a linear model for densities ⩽ 8 weeds row−1 at Perkins and Chickasha in 1996 and at Alms in 1997. At Perkins in 1997, all densities fit a linear model. For each increase of 1 weed row−1, lint yield reductions were 62 kg ha−1 (or 10.7%) and 58 kg ha−1 (or 11.5%) at Perkins and at Chickasha in 1996, respectively. At Perkins and Alms in 1997, for each 1 weed row−1, lint yield was reduced 71 kg ha−1 (or 5.9%) and 112 kg ha−1 (or 8.7%), respectively. Lint yield vs. end-of-season weed volume fit a linear model except at Alms in 1997. For each increase of 1 m3 of weed plot−1, cotton lint yield in 1996 was reduced by 1.6 and 1.5% at Perkins and Chickasha, respectively. In 1997 at Perkins and Altus (⩽ 6 weeds), each increase of 1 m3 of weed plot−1 reduced lint yield 1.6 and 2.3%, respectively. Lint yield vs. end-of-season weed biomass fit a linear model in all four experiments. Lint yield was reduced 5.2 to 9.3% for each increase of 1 kg of weed biomass plot−1. Fiber analyses revealed significant differences for micronaire (fiber fineness) among weed densities in two experiments, marginal significance in a third, and none in a fourth. An intermediate number of weeds often resulted in improved fiber micronaires in these environments. No other fiber properties were influenced by weed density.

Field and laboratory experiments were conducted with unicorn-plant to determine conditions required for germination and to measure seed production. Field-grown plants produced an average of 122 pods/plant with an average of 71 seed/pod. The highest percent germination from seed harvested in 1980 occurred following a 2-week prechill treatment of 4 C. Germination increase was greater by removing the seed coat and the membrane enclosing the embryo than by removing the seed coat alone. Germination of seed from all pod compartments was similar. Aqueous extracts of unicorn-plant testa, leaf, stem, root, and exocarp were inhibitory in petri dish bioassays to cotton radicle growth. Extracts of stem, root, and exocarp were inhibitory to wheat radicle growth, and extracts of endocarp, leaf, and exocarp were inhibitory to unicorn-plant radicle growth. Seed buried in the field 10 cm deep for 1 to 8 months showed increased germination over time. Germination was lower when seed were stored at 4 C for 1 to 8 months in a soil having 25% (v/v) water.

Absorption of 2,4-D [(2,4-dichlorophenoxy) acetic acid], dicamba [3,6-dichloro-o-anisic acid], and the isopropylamine salt of glyphosate [N-(phosphonomethyl) glycine] by excised honeyvine milkweed [Cynanchum laeve (Michx.) Pers.] leaves was determined. Experimental variables included leaf position (terminal vs. basal), a surfactant, 4-isopropenyl-1-methylcyclohexane plus unspecified emulsifiers (SA-77), and leaf collection dates. Absorption of the three herbicides by terminal and basal leaves was increased by the addition of the surfactant. However, the surfactant increased absorption into basal leaves more than into terminal leaves. The surfactant reduced surface tension and increased drying time of water droplets on adaxial leaf surfaces by 50%. The pH of the herbicide solutions was reduced from about 5.8 to about 3.9 by SA-77. Absorption of all three herbicides was greater into terminal than into basal leaves when the surfactant was not present, but the difference disappeared when the surfactant was added. Generally, no differences were observed in the absorption of 2,4-D and dicamba. Glyphosate absorption was greater in terminal leaves collected after a period of adequate moisture than after a period of dry soil conditions.

Dryland and irrigated field experiments were established to measure differences in soil water relations throughout the growing season between plots in which cotton was grown with and without silverleaf nightshade interference. Soil moisture readings were taken weekly at 15-cm increments to a maximum depth of 120 and 150 cm during 1984 and 1985, respectively. When cotton was grown with silverleaf nightshade, soil water loss was greater at the lower portion of the soil profile earlier in the growing season than when cotton was grown alone. In the irrigated environment in 1985 when precipitation was higher than normal and the soil moisture content remained above normal, soil water loss did not differ. Cotton lint yield, plant height, and boll size reflected the amount of soil moisture available for growth and development of the crop. A statistical technique for quantifying soil water relations between the crop growing alone and growing with interference from the weed is demonstrated.

Barnyardgrass, large crabgrass, and Texas panicum were evaluated in field experiments over 3 yr to measure their duration of interference and density on grain sorghum yield. When grain yield data were converted to a percentage of the weed-free control, linear regression predicted a 3.6% yield loss for each week of weed interference regardless of year or grass species. Grain sorghum grown in a narrow (61-cm) row spacing was affected little by full-season interference; however, in wide (91-cm) rows, interference increased as grass density increased. Data from the wide-row spacing were described by linear regression following conversion of grain yield to percentages and weed density to log10. A separate nonlinear model also was derived which could predict the effect of weed density on grain sorghum yield.

Soil-water profiles of cotton, several weeds, and bare soil were compared in research conducted in 1989 and 1990 near Perkins, OK. Neutron probe access tubes were installed prior to plant establishment to facilitate nondestructive volumetric water content determinations at selected depths throughout the season. Planting was in a double-circle pattern concentric around each neutron probe access tube. Phenological and soil-water data were collected weekly. As plants began to senesce, aboveground biomass yield data were collected. In 1989, rainfall frequently replenished soil-water in the upper soil profile. The plants used the recharge water to varying degrees, particularly late in the season. Common cocklebur and johnsongrass extracted soil-water from greater depths than cotton and velvetleaf throughout the season. In 1990, the largest differences detected between bare soil and weeds early in the season were measured for common cocklebur, devil's-claw, and silverleaf nightshade. Later in the season, however, there was little difference in soil-water content in the upper soil profiles for all species. Johnsongrass emerged later than the other species in 1990 which affected its relative soil-water extraction.

Seed capsules of field-grown jimsonweed were harvested 2, 4, 6, and 10 weeks after anthesis. Degree day accumulation from anthesis and weeks after anthesis were equal in predicting the time required for nondormant jimsonweed seed production and seed dry weight. Seed germination increased as capsule age increased from 2 to 6 weeks. No additional increase in germination was observed in seed from capsules collected 10 weeks after anthesis. Maximum seed weight was obtained from capsules 6 and 10 weeks old in 1986 and 1987, respectively. Germination was correlated highly with seed weight.

Laboratory and field experiments were conducted to describe the root system of honeyvine milkweed [Cynanchum laeve (Michx.) Pers.], and to study factors affecting the growth of plants from root fragments of shallow, ascending roots. The root system of a typical plant was composed of lateral roots radiating from a sparsely-branched, vertical taproot. Laterals tended to concentrate in a boundary area between a loamy surface soil and a zone of clay accumulation, this boundary area being below the zone of cultivation. Vertical taproots were found to a depth of 2 m, with sections collected at this and shallower depths demonstrating the ability to produce aerial shoots. In laboratory studies, root sections were killed either by freezing for 2 h or by drying at either 20 or 30 C for 24 h. The optimum temperature for shoot development from root sections was between 20 and 30 C. Shoot emergence and growth from buried root sections were generally unaffected by either depth of planting or root length. As many as 45 daughter shoots were produced from a single plant originating from seed, and 27 daughter shoots were developed from a root section 131 days after planting. The maximum distance daughter shoots were observed from original plants 131 days after planting was 111 cm.

The duration and intensity of unicorn-plant interference on lint yield of cotton were evaluated in the field. Random densities of 5.5 ± 1.1 unicorn-plant/m2 reduced lint yield by 41 kg/ha or about 5% for each week that unicorn-plant was present. Interference by 4, 8, and 12 weeds/10 m row decreased yield by 22, 49, and 56 kg/ha, respectively, for each week of weed interference. Each 1 kg/ha of unicorn-plant dry weight reduced lint yield by 0.26 kg/ha. Linear regression of weed dry weight could be used to predict cotton lint yield changes regardless of duration or intensity of weed interference.

The ability of honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.] to establish and develop from seed was studied in laboratory and field experiments. Optimum germination temperature was 30 C. Seed incubated at cooler temperatures and then transferred to 30 C germinated equally as well as seed incubated continually at 30 C. Germination was unaffected at moisture stress levels between 0 and −4.6 bars, but was decreased at levels between −4.6 and −12.8 bars. The optimum pH range for germination was between 5 and 7. The greatest emergence of seedlings occurred at a depth of 0.5 cm with no emergence occurring at depths greater than 5 cm. Greater emergence was obtained with a loam than sandy loam at all planting depths except 0.5 cm. Field plots seeded on May 1 gave maximum seed production. Seed production decreased with each 2-week delay in planting. Planting dates of July 10 or later produced no seed. Seed germination was affected little by delayed planting. The following spring, regrowth from plants seeded on June 12 or later was less vigorous than regrowth from plants seeded earlier.

Duration and density experiments were conducted in the field to measure horsenettle (Solanum carolinense L. # SOLCA) interference with Spanish and runner-type peanuts (Arachis hypogaea L. ‘Pronto’ and ‘Florunner′). Spanish peanut yield generally was higher with 6 to 8 weeks of weed-free maintenance. Horsenettle interference for 6 to 8 weeks did not decrease the yield of Spanish peanuts, and interference for 6 weeks did not decrease yields of runner peanuts. Weed-free maintenance for 2 or more weeks allowed increased runner peanut yield when compared to weedy plots. Linear regression predicted a 69 kg/ha Spanish peanut yield increase for each week of weed-free maintenance. Linear regression predicted a Spanish peanut yield reduction of 40 kg/ha for each week of weed interference in 1983, the only year in which the slopes of the regressions were statistically significant Curvilinear equations with the runner-type cultivar predicted an 81 kg/ha yield increase or 96 kg/ha decrease for each week of weed-free maintenance or weed interference, respectively. In 1 of 2 yr, Spanish peanut yield was reduced by horsenettle at a density of 32 plants/10 m of row.

Weed free field experiments were conducted for 3 yr at one location to measure the response of cotton to glyphosate spot applied once, twice, and three times. Glyphosate treatments frequently used for silverleaf nightshade control were applied at specified intervals after cotton emergence to in-row, uniformly spaced densities of “simulated” weeds. The number and application timing influenced cotton injury each year. Frequently, cotton lint yields following treatments applied once at four, six, or eight sites/9 m of row were not reduced significantly compared to the untreated plots; however, average yield reductions ranged from 10 to 14%. Glyphosate, applied more than once generally, caused more crop injury and reduced lint yields by 13 to 39%.

Plants started with seed, 'seedlings', and established plants of silverleaf nightshade (Solanum elaeagnifolium Cav.) were grown in the field under shade levels of 0, 47, 63, and 92% of full sunlight to determine vegetative, reproductive, and physiological responses to shade. Dry-matter production of both 'seedling’ and established plants declined markedly with increasing shade levels. Established plants did not bear fruit under 92% shade, and 63% shade prevented fruit production by 'seedlings'. Taproots of plants grown in full sunlight contained 16% more total non-structural carbohydrate (TNC) per gram dry weight than taproots of plants grown under 92% shade. Leaves of established plants grown under moderate shade had significantly more chlorophyll per unit leaf fresh weight than plants grown in full sunlight; however, plants under heavy (92%) shade had 35% less chlorophyll per unit leaf area than unshaded plants. The chlorophyll a/b ratio of the 92%-shaded plants was significantly less than with other treatments. Leaf area increased, with increasing shade; however, leaf weight per unit area decreased because of thinner leaves. Photosynthetic rates of recently expanded leaves were 10.4, 4.6, 3.3, and 0.9 mg CO2 · dm−2 · h−1 for the 0, 47, 63, and 92% shade treatments, respectively.

Laboratory experiments with 14C-herbicides were conducted with grain sorghum as an indicator species to determine the effects of imposed moisture stress on absorption, precent recovery, and acropetal and basipetal translocation of the butyl ester of fluazifop, the methyl ester of haloxyfop, the ethyl ester of quizalofop, and sethoxydim. Haloxyfop was the only herbicide where recovery decreased between the 3-and 48-h interval. All plants absorbed more of the herbicide at the 48-h interval than at the 3- or 6-h interval under both stressed and non-stressed conditions. Increased drought stress caused more acropetal movement with fluazifop and sethoxydim and less acropetal movement with quizalofop at the 3-h interval. Basipetal transloation, although different among herbicides, responded similarly to imposed moisture stress, which decreased basipetal translocation approximately 19%.

Glyphosate, alone and in combination with other herbicides or additives, was evaluated as a spot or shielded treatment for the control of silverleaf nightshade in cotton in three experiments over four years. Glyphosate used at 10.8 g ae/L in 1985 on dryland cotton controlled 81 to 98% of the silverleaf nightshade, but cotton lint yields were reduced by all treatments compared to the weed-free check. Glyphosate used at 7.2 g ae/L in 1986 on irrigated cotton controlled 6 to 83% of the silverleaf nightshade, and lint yields were reduced only when multiple spot applications were made. Spot applications of glyphosate were effective for silverleaf nightshade control when applied 7 wk after crop emergence in 1988. Weed control and cotton injury were lower with shielded applications than spot applications. In 1989, retreatments during a season or the next year resulted in 95% or greater silverleaf nightshade control. Cotton yield increases from herbicide treatment were not observed in 1988; however, yield increases were observed in 1989 when spot treatments were applied to the more successful 1988 plots.

The distance-of-influence of an individual devil's-claw plant to cotton leaf, stem, boll (reproductive parts), and combined aboveground plant parts was determined in two field experiments. The distance-of-influence could not be detected for the first 6 weeks after emergence; by 9 to 12 weeks, it extended up to 25 cm or more; and by the end of the season, up to 50 cm on each side of the weed. Cotton leaf and stem weights were less sensitive than cotton boll weights for measuring distance-of-influence from devil's-claw. At maturity, cotton boll weight was reduced 62 and 51% in 1983 and 45 and 29% in 1984 for sampling intervals of 0 to 25 and 25 to 50 cm, respectively. Interference from cotton reduced devil's-claw stem weight, seed capsule weight, and whole plant biomass by 6 weeks after emergence and reduced leaf biomass by 9 weeks in 1983. All except stem biomass were affected in 1984. Distance-of-influence and weed-density interference studies predicted lint yield loss similarly.

Phytotoxicity of five substituted urea herbicides 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), 3-phenyl-1,1-dimethylurea (fenuron), 3-hexahydro-4,7-methanoindan-5-yl) −1,1-dimethylurea (norea), and 3-(m-trifluoromethylphenyl)-1,1-dimethylurea (fluometuron) at 0, 10, 100, and 1000 ppm were determined in factorial combination at four urea nitrogen levels of 0, 45, 450, and 900 ppm with three Aspergilli: A. niger, A. sydowi, and A. tamarii. Response interactions were apparent, with all three fungi most tolerant for fenuron and least for diuron. Apparent tolerance order of the three intermediates were: A. niger, norea > fluometuron > monuron; A. sydowi, fluometuron > monuron > norea; and A. tamarii, fluometuron > norea > monuron. Oat (Avena sativa L.) bioassay for residual herbicide toxicity indicated significant differences in herbicide degradation rates between these three fungi at 5, 10, and 20 ppm in Eufaula sand. Diuron was more rapidly degraded than monuron at these levels with fluometuron and norea somewhat intermediate. A. niger was most effective in degradation of these herbicides with A. tamarii greater than A. sydowi. High nitrogen levels in soil organic matter amendment generally favored increased rates of urea herbicide degradation.

Full-season interference of silverleaf nightshade (Solanum elaeagnifolium Cav. # SOLEL) with dryland and irrigated cotton (Gossypium hirsutum L. ‘Paymaster 145′) was evaluated in five field experiments during 1984 and 1985, Weed densities ranged from 0 to 32 plants/10 m of crop row. Dry weight of silverleaf nightshade increased from 0.08 to 0.39 kg/plot for each additional weed/10 m of row. Intraspecific competition among silverleaf nightshade plants was not evident. However, cotton height was reduced at weed densities of 4 plants/10 m of row or more. The densities at which initial lint yield reductions occurred ranged from 4 to 32 weed plants/10 m of row. Irrigated cotton more effectively competed with the weed than did dryland cotton, suggesting that soil water was a primary competition factor between the two species. Boll size was reduced at densities of 2 weeds/10 m of row and above. Silverleaf nightshade reduced mechanical harvest efficiency only at densities of 16 and 32 plants/10 m of row. Fiber properties were not affected. Linear regression predicted that lint yield would be reduced 1.54% for each silverleaf nightshade plant/10 m of cotton row. The distance silverleaf nightshade was established from the crop row did not affect the weed's interference with cotton within a range of 0 to 30 cm.

Benazolin (4-chloro-2-oxobenzothiazolin-3-ylacetic acid) formulated as the dimethylamine salt was evaluated for common cocklebur (Xanthium pensylvanicum Wallr.) and prickly sida (Sida spinosa L.) control in soybeans [Glycine max (L.) Merr.] between 1977 and 1979. Benazolin was applied alone or in admixtures with acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4 (3H)-one 2,2-dioxide], dinoseb (2-sec-butyl-4,6-dinitrophenol) plus naptalam (N-1-naphthylphthalamic acid), and 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] over-the-top of soybeans {V3 to V12 [V(N); vegetative stage with “N” nodes on the main stem beginning with the unifoliolate node]}. Benazolin effectively controlled common cocklebur at rates of 0.2 and 0.4 kg/ha. Soybean tolerance was acceptable even with a repeat application of 0.4 kg/ha. Early-season (July) control was less than late season (August) because it took 2 to 3 weeks for benazolin to kill common cocklebur. Prickly sida control was poor with benazolin even at 0.6 kg/ha. Soybean tolerance and seed yields were higher when soybeans were treated with admixtures of benazolin plus bentazon than with benazolin alone. Antagonism was observed with this admixture for prickly sida and late-season common cocklebur control. Antagonism was eliminated with ratios of benazolin to bentazon of 1 to 3 applied in a single application or a 1 to 1.5 ratio repeated.

Controlled – environment studies were conducted to determine the influence of temperature, light, seed weight, depth of planting, substrate pH, and salinity on the germination and emergence of silverleaf nightshade (Solanum elaeagnifolium Cav.). The effects of planting date, top removal, and root-cutting length on establishment were studied in the field. Fluctuating temperatures of 20 to 30C produced 57% germination. Maximum germination, 59%, occurred between pH 6 and 7. NaCl concentrations greater than 2500 ppmw caused germination to decrease 85% or more compared to the control. Light was not important for germination. Mean seedling emergence was 46% from depths of 1.0 to 2.5 cm. Silverleaf nightshade seedling emergence from a 2-cm depth was 31% greater in a sandy soil than a loam. Delayed seeding caused a decline in dry-weight accumulation of above-ground parts. Fifteen percent of seedlings clipped 15 days after emergence were capable of regrowth, and after 30 days or more, 90% of the clipped plants regrew.