Research studies evaluated effects of the auxin transport inhibitor, diflufenzopyr, on the biokinetics and efficacy of aminocyclopyrachlor-methyl ester (AMCP-ME) applications to black nightshade and large crabgrass. Absorption, translocation, and metabolism of 14C-AMCP-ME was quantified with and without diflufenzopyr (35 g ai ha−1). Diflufenzopyr had minimal effects on translocation of radioactivity in either species. Accumulation of radioactivity in aboveground plant sections of black nightshade was greater than or equal to that in large crabgrass by 72 h after treatment (HAT). In both species, metabolism of 14C-AMCP-ME was rapid, as 60 to 78% of the extracted radioactivity was the free acid metabolite 8 HAT. In the greenhouse, black nightshade and large crabgrass were treated with AMCP-ME (9, 18, and 35 g ai ha−1) alone and in combination with diflufenzopyr (35 g ha−1). Mixtures of AMCP-ME plus diflufenzopyr did not increase large crabgrass control compared with AMCP-ME alone at any time. Diflufenzopyr (35 g ha−1) increased black nightshade control with AMCP-ME (18 and 35 g ha−1) 7 d after treatment (DAT). However, this increase in control was not observed 14 or 28 DAT. All treatments containing AMCP-ME controlled large crabgrass 70 to 79% 28 DAT compared with > 93% for black nightshade at the same time point.

There is an urgent need to accelerate the development and implementation of effective organic-compliant herbicides that are environmentally safe and that help the producer meet increasing consumer demand for organic products. Therefore, greenhouse experiments were conducted to evaluate the effectiveness of acetic acid (5%), acetic acid (30%), citric acid (10%), citric acid (5%) + garlic (0.2%), citric acid (10%) + garlic (0.2%), clove oil (45.6%), and corn gluten meal (CGM) compounds as natural-product herbicides for weed control. The herbicides were applied to the broadleaf weeds stranglervine, wild mustard, black nightshade, sicklepod, velvetleaf, and redroot pigweed and to narrowleaf weeds crowfootgrass, Johnsongrass, annual ryegrass, goosegrass, green foxtail, and yellow nutsedge. The herbicides were applied POST at two weed growth stages, namely, two to four and four to six true-leaf stages. CGM was applied PPI in two soil types. Citric acid (5%) + garlic (0.2%) had the greatest control (98%) of younger broadleaf weeds, followed by acetic acid (30%) > CGM > citric acid (10%) > acetic acid (5%) > citric acid (10%) + garlic (0.2%), and clove oil. Wild mustard was most sensitive to these herbicides, whereas redroot pigweed was the least sensitive. Herbicides did not control narrowleaf weeds except for acetic acid (30%) when applied early POST (EPOST) and CGM. Acetic acid (30%) was phytotoxic to all broadleaf weeds and most narrowleaf weeds when applied EPOST. Delayed application until the four- to six-leaf stage significantly reduced efficacy; acetic acid was less sensitive to growth stage than other herbicides. These results will help to determine effective natural herbicides for controlling weeds in organic farming.

Row orientation in vineyards can affect the quantity of light intercepted by the crop's canopy. Consequently, the light available to weeds growing under the canopy might also be affected, with potential implications for their physiology, growth, and productivity. This hypothesis was tested in 2003 and 2004 in a central California vineyard having rows oriented east–west (EW) and north–south (NS) in a randomized complete block design. In April of both years, potted black nightshade seedlings were placed under grapevines of both row orientations and grown for about 10 wk. Photosynthetically active radiation (PAR) at the weed canopy zone (WCZ) of NS rows was bimodal, with peaks occurring at about 09:30 A.M. and 4:30 P.M. At those times, PAR approached 500 μmol m−2 s−1 (between 30 and 40% of full sun). In contrast, maximum PAR in the WCZ of EW rows was generally less than 75 μmol m−2 s−1 throughout the day. The ratio of red to far-red light was also greater in NS than EW rows in the morning and afternoon. In both row orientations, PAR was suboptimal for nightshade because maximum net photosynthesis occurred at light levels ≥ 500 μmol m−2 s−1, but nightshade in the NS rows had higher net photosynthetic rates than those in EW rows when subjected to higher ambient PAR. Stem extension and phenology of nightshade was not affected by vine row orientation, but plants in EW rows had greater leaf areas, leaf area ratios, leaf weight ratios, and lower specific leaf weights than plants in NS rows. Berry mass, seeds per berry, and estimated seed production was 40, 7, and 20% lower, respectively, for plants in the EW than in the NS rows. Dry mass and total nonstructural carbohydrates (TNC) of nightshade roots were also 25 and 45% lower, respectively, in EW than in NS plants. Thus, grapevine row orientation may affect nightshade fecundity by reducing light in the WCZ.