Greenhouse hydroponic and field experiments were conducted to determine the effect of nitrogen (N) fertilizer on eastern black nightshade growth and N content. After 4 wk in hydroponics, the greatest shoot dry mass occurred in the 5 or 10 mM nitrate treatments. An exponential model was strongly correlated with eastern black nightshade root and shoot growth in the 5 or 10 mM nitrate treatments. Eastern black nightshade reached the exponential stage of growth approximately 21 d after transfer to the nitrate treatments. Root dry mass was only 10% of shoot biomass. There was a substantial increase in height and growth rate when plants were fertilized with 168 kg N ha−1. Eastern black nightshade was at its maximum growth 12 wk after planting, and fresh mass increased with N up to 336 kg N ha−1, the greatest N concentration in the study. The greatest N content was in the upper leaves and the least in the lower stem. These results indicate that eastern black nightshade growth is favored by high rates of N.

Studies were conducted to determine the effect of in-row eastern black nightshade establishment and removal timings in plasticulture tomato on tomato yield loss and nightshade berry production and seed viability. Eastern black nightshade was transplanted at 1, 2, 3, 4, 5, 6, and 12 wk after tomato planting (WAP) and remained until tomato harvest, or was established at tomato planting and removed at 2, 3, 4, 5, 6, 8, and 12 WAP to determine the critical weed-free periods. Eastern black nightshade seed viability increased with berry size and with length of establishment or removal time. The critical weed-free period to avoid viable nightshade seed production was 3–6 WAP. Tomato yield decreased with early weed establishment or with delayed time of weed removal. The critical weed-free period to avoid greater than 20% tomato yield loss for the sum weight of extra large and jumbo grades was 28 to 50 d after tomato transplanting.

Greenhouse studies were conducted to determine the effect of soil dust on glyphosate efficacy. Eastern black nightshade and hairy nightshade were affected similarly by glyphosate, regardless of whether plants were or were not treated with dust, but glyphosate phytotoxicity decreased when dust accumulated on plants. Silty clay dust at 2, 4, 6, 8, and 10 kg ha−1 on nightshade plants decreased the efficacy of glyphosate at 80 g ae ha−1 by 1, 5, 12, 21, and 32 percentage points, respectively. The adverse effect of dust on glyphosate efficacy occurred regardless of whether dust settled before or immediately after herbicide spraying and varied with dust type, which was silty clay ≥ silty clay loam > loamy sand. Glyphosate efficacy was slightly influenced by dust pH, with a trend toward increased efficacy as pH increased. Glyphosate applied at 280 L ha−1 spray volume controlled dust-treated plants better than when applied at 94 or 190 L ha−1. Three adjuvants (ammonium sulfate, nonionic surfactant, and organosilicone surfactant) only partially overcame the adverse effect of dust on glyphosate efficacy in eastern black and hairy nightshade control. Methylated seed oil or petroleum oil adjuvants did not improve glyphosate control of dust-treated or untreated plants.

Greenhouse and growth-chamber experiments were conducted to determine the influence of the ratio of red to far-red (R:FR) radiation and of neutral filtration of plant-available radiation on the vegetative and reproductive growth of selected nightshade species. Exposure of eastern black nightshade and black nightshade to far-red radiation resulted in greater partitioning of resources to stem tissue, resulting in taller plants. Number of flowers, timing of flowering, branching, and biomass production of black nightshade and eastern black nightshade were not influenced by the ratio of red to far-red radiation. Eastern black nightshade shoot and berry dry weight decreased as neutral density shading increased from 0 to 71%. Shoot dry weight decrease was associated with lower stem weight and production of fewer berries per plant. Neutral shading did not reduce leaf weight or leaf area per plant but increased the specific leaf area of eastern black nightshade. Internode elongation of nightshade species into a soybean canopy should primarily be associated with exposure to low R:FR irradiance ratios, whereas the thinner leaves of eastern black nightshade growing under shade should be associated with lower irradiance levels. Both responses are common adaptations of shade-avoiding plants.

The efficacies of bentazon and fomesafen in controlling annual weeds in dry and edible pod beans in New York State were investigated in greenhouse and field experiments. Dose responses to bentazon and fomesafen were studied for four weed species (ragweed, velvetleaf, eastern black nightshade, and hairy nightshade) under greenhouse conditions. Herbicides were applied at cotyledon to two-, two- to four-, and four- to six–true leaf stages, both with and without a crop oil concentrate (bentazon) or a nonionic surfactant (fomesafen). Field studies were conducted for 2 yr for all weed species except eastern black nightshade, for which no adequate field populations were found. Field studies confirmed greenhouse results, indicating that weed control could be improved by the use of an adjuvant, but there were exceptions. In general, adjuvant usage improved the efficacy of fomesafen more than it did with bentazon. The minimum rates of herbicide required for effective and consistent control was dependent on the particular combination of weed species, herbicide and its rate of application, growth stage at which the application was made, and adjuvant usage.

Plant model systems have contributed greatly to the dramatic progress in understanding the fundamental aspects of plant biology. Using model weeds will also help facilitate focused funding and research in the weed science community. Criteria for developing model weeds require attention to weedy characteristics that impart economic losses and a wide geographic distribution, attributes that present the potential for political and scientific support. Expressed sequence tag (EST) databases for model weeds are the most practical approach to identifying new genes and obtaining data on the gene expression underlying weedy characteristics. Weeds such as Canada thistle, eastern black nightshade, johnsongrass, jointed goatgrass, leafy spurge, waterhemp, and weedy rice are proposed as model systems.

Experiments were conducted to determine the efficacy, absorption, and translocation of glyphosate, glufosinate, and imazethapyr with selected weed species. In the greenhouse glyphosate, glufosinate, and imazethapyr were applied at 0.25, 0.5, and 1 times their label rates of 1,121, 410, and 70 g ha−1, respectively, on 10- to 15-cm black nightshade, common waterhemp, eastern black nightshade, field bindweed, giant ragweed, ivyleaf morningglory, prairie cupgrass, velvetleaf, and yellow nutsedge. Glyphosate applied at the 1-time rate caused injury greater than or similar to injury from the 1-time rate of glufosinate or imazethapyr on black nightshade, common waterhemp, eastern black nightshade, field bindweed, giant ragweed, prairie cupgrass, and velvetleaf. The 1-time rate of glufosinate injured ivyleaf morningglory and yellow nutsedge more than did the 1-time rate of glyphosate or imazethapyr. Under field conditions glyphosate caused the greatest injury to common waterhemp, prairie cupgrass, and velvetleaf across plant growth stages. Giant ragweed and ivyleaf morningglory injury was more dependent on growth stage, with the 15- and 30-cm growth stages more susceptible to glyphosate than to glufosinate or imazethapyr. Differential response of these weed species may be caused by differences in herbicide translocation. Glyphosate was translocated more in both giant ragweed and ivyleaf morningglory, and these species were injured more by glyphosate than by glufosinate or imazethapyr at the larger growth stages.

Effects of environmental factors, especially light, on eastern black nightshade seed germination were studied under growth chamber conditions. Germination occurred only when temperatures were 20 C or higher for 12 to 24 h d−1. Optimum germination occurred within the constant temperature range of 28 to 33 C or with alternating temperatures of 30/25 and 35/30 C. In the dark, eastern black nightshade germination was poor except at high alternating temperatures of 30/25 and 35/30 C. Seed germination was enhanced by light when temperatures were suboptimal. Imbibition was a prerequisite for response of eastern black nightshade seed to light. The light requirement for eastern black nightshade germination was partially overcome by cold stratification, gibberellic acid (GA3), and high or alternating temperatures. Germination of eastern black nightshade seed was promoted by short exposure to sunlight but was inhibited by prolonged exposure, especially when irradiance was high.

Reducing seeding rates in 19- or 76-cm row soybean below the optimum rate may reduce soybean competitiveness with weeds, and indirectly increase production costs to the grower. Field studies in 2001 and 2002 evaluated the effect of soybean seeding rate and row spacing on the emergence, growth, and competitiveness of eastern black nightshade (EBN) in soybean. EBN emergence ceased within 45 d after planting (DAP), and was similar across soybean seeding rates and row spacing. EBN control by glyphosate was not affected by soybean population or row spacing. Soybean planted in 19-cm rows was more competitive with EBN, regardless of seeding rate. Increasing the soybean seeding rate in 76-cm rows from 185,000 seeds/ha to 432,000 seeds/ha reduced EBN dry weight threefold at East Lansing and nearly twofold at Clarksville in 2002. There was no increase in EBN density or dry weight in 19-cm row soybean planted at 308,000 seeds/ha compared with 556,000 seeds/ha, whereas a seeding rate of 432,000 seeds/ha in 76-cm row soybean did not suppress EBN dry weight or increase soybean yield in the presence of EBN compared with a seeding rate of 308,000 seeds/ha.

A 2-yr experiment assessed the potential for using soil degree days (DD) to predict cumulative weed emergence. Emerged weeds, by species, were monitored every 2 wk in undisturbed plots. Soil DD were calculated at each location using a base temperature of 9 C. Weed emergence was fit with logistic regression for common ragweed, common lambsquarters, velvetleaf, giant foxtail, yellow foxtail, large crabgrass, smooth pigweed, and eastern black nightshade. Coefficients of determination for the logistic models fit to the field data ranged between 0.90 and 0.95 for the eight weed species. Common ragweed and common lambsquarters were among the earliest species to emerge, reaching 10% emergence before 150 DD. Velvetleaf, giant foxtail, and yellow foxtail were next, completing 10% emergence by 180 DD. The last weeds to emerge were large crabgrass, smooth pigweed, and eastern black nightshade, which emerged after 280 DD. The developed models were verified by predicting cumulative weed emergence in adjacent plots. The coefficients of determination for the model verification plots ranged from 0.66 to 0.99 and averaged 0.90 across all eight weed species. These results suggest that soil DD are good predictors for weed emergence. Forecasting weed emergence will help growers make better crop and weed management decisions.

Weed species respond to the cumulative effect of multiple practices employed within weed management systems. However, this response is rarely studied at the system level, and the relationships between weed communities and management systems in crops are not well understood. We used multivariate analyses to assess relationships among tomato management systems and weed species identified through on-farm sampling of 59 fields. Giant foxtail, common lambsquarters, prickly sida, and carpetweed were common in all systems. Eastern black nightshade was common in the conventional processing and mixed fresh-market systems but largely absent from the organic system. Barnyardgrass and goosegrass were common in the organic fresh-market system but not in the other systems. Canonical correspondence analysis identified distinct associations between specific species and the management systems. Common purslane was strongly associated with the rain-fed, mixed fresh-market system, and barnyardgrass, goosegrass, yellow nutsedge, and green foxtail were associated with the irrigated, organic fresh-market system. Indicator species analysis identified five species that were significant indicators of the organic, fresh-market system and one species that was a significant indicator of the rain-fed, mixed fresh-market system. Weed populations persist or increase when a set of species-specific environmental conditions are met. The association of weed species in this study with particular systems supports the hypothesis that weed communities are strongly affected by management systems.