Four experiments (three in Macedonia, Greece and one in Holtville, CA) were conducted in 1988 and 1989 to evaluate foliar applications of picloram, glyphosate alone and with adjuvant, and triclopyr for the control of established silverleaf nightshade. Silverleaf nightshade control was determined by comparing stem population at the time of herbicide application to stem population 6 to 11 mo after application. Picloram, averaged over rate and location, controlled silverleaf nightshade consistently, restricting regrowth to less than 5%. Silverleaf nightshade control with glyphosate alone or with adjuvant varied with location, regrowth ranged from 0 to 69%. Regrowth of silverleaf nightshade treated with triclopyr approached that of the untreated control.

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.

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.

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%.

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.

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.

Field experiments were conducted in 1985 and 1986 under eight environments to evaluate the population dynamics of a range of silverleaf nightshade densities and to measure the effects of those populations on cotton lint yield. Dry weed weights of silverleaf nightshade stands were influenced by growing conditions among years, but were positively related to initial densities as long as 2 yr after establishment. Stem numbers increased as initial densities and stand age increased. A negative linear relationship existed between cotton lint yield and weed biomass and between cotton lint yield and stem number from both 1- and 2-yr-old weed stands. For each 1 kg/10 m of row increase in dry weed weight from 1- and 2-yr-old stands, a 9 and 21% lint yield loss/ha was predicted, respectively. For each stem/10 m of row, a 0.35 and 0.31% yield loss was predicted, respectively. Late-planted cotton was less vulnerable to yield reductions by silverleaf nightshade; however, its yield potential was also less.