Growers need to be aware that corn (Zea mays L.) develops leaf area slowly and competes poorly with early emerging weeds in the northeastern USA when planning a total postemergence program in glyphosate-resistant corn. We applied glyphosate at early postemergence (EPOST), third to fourth leaf stage (V3-V4) of corn growth; mid-postemergence (MPOST), V5 to V6 stage; and late postemergence (LPOST), V7 to V8 stage, in New York in 2003 and 2004 to determine how initial glyphosate timing affects growth, development, yield, and yield components of corn. The EPOST treatment, which received glyphosate when weeds were 10 cm or less in height, and a weed-free treatment silked on the same date, had similar dry matter (DM) accumulation (738 g m 22 ) and leaf area index (LAI) at silking (f3.50), kernels per plant (528-549), and grain yield (11.1 Mg ha 21 ). The MPOST treatment, which received glyphosate when some weeds were 18 to 35 cm tall, silked 2 d later, had 35% less LAI and 39% less DM accumulation at silking, 21% less kernels per plant, and 25% less grain yield. Although the LPOST and untreated control, which had 1363 and 653 weeds m 22 at the V5-V6 stage in 2003 and 2004, respectively, had the same LAI at silking (1.75-1.87), the LPOST treatment yielded higher (6.4 vs. 3.2 Mg ha 21 ). Results from this study indicate that growers in the northeastern USA should apply glyphosate by the V3-V4 stage to avoid yield losses from early season weed competition.

Vinegar can supplement the existing intrarow weed control options of organic farmers. However, there are two primary limitations to its use in vegetable crops. First, it is costly. Second, vinegar applications that contact the crop can cause injury and yield loss. The aim of this research was to use vinegar to control intrarow weeds in bell pepper and broccoli in a way that product costs would be reduced and crop injury would be minimized. Banded applications were shielded and directed below the crop canopy to reduce weed control costs and minimize contact with crop foliage. Organic paints applied to crop stems were evaluated as potential physical barriers to crop stem injury. Four field trials were conducted in 2009, two in transplanted bell pepper and two in transplanted broccoli. A single application of 200-grain vinegar (20% acetic acid) at 700 L ha−1was applied when weeds were in the cotyledon to six-leaf stage. Applications were made to crops with the lower stems coated in one of two stem protectants, or left uncoated. Hand-weeded and weedy treatments were included for comparison. One day after vinegar application, in-row weed control was 100% in both pepper trials and greater than 96% in the broccoli trials. Two weeks after application, 75% fewer weeds germinated in the vinegar-treated areas compared with the areas that were hand weeded. Neither stem protectant prevented crop injury. Despite pepper foliar injury of less than 5%, stem injury 2 wk after application contributed to a measurable yield reduction. Broccoli injury was limited to instances where overspray contacted the crop canopy. With vinegar, high levels of weed control and the extended duration of that control relative to hand weeding could facilitate improved organic intrarow weed control. However, crop injury must be reliably reduced. Alternative stem protectants may merit evaluation.

Dissipation of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) was greater in Sharpsburg silty clay loam soil than in Anselmo sandy loam soil and was faster in the topsoil than in the subsoil. Breakdown increased with increasing soil incubation temperatures. Phytotoxicity of dicamba and 3-amino-2,5-dichlorobenzoic acid (amiben) in aqueous solutions decreased upon exposure to sunlight. Amiben was more susceptible to photodecomposition than was dicamba. Aqueous dicamba solutions exposed to sunlight for 16 days decreased growth of cucumber (Cucumis sativus L.) seedlings, while amiben solutions caused no growth reduction after 2 days' sunlight exposure. Dicamba solutions exposed to 60 C showed increased phytotoxicity while amiben solutions were unaffected. Dicamba was most phytotoxic to corn (Zea mays L.) seedlings at pH 4 and to cucumber seedlings at pH 5. Dicamba solutions were taken up by both shoots and roots of corn and cucumber seedlings; however, root uptake resulted in greater growth reductions.

Residues in soil, following application of 0.25 lb/A of 4-amino-3,5,6-trichloropicolinic acid (picloram) to semi-arid rangelands, usually were restricted to the top 12 inches for 60 days. Five ppb or less picloram were detected below 12 inches at 120 to 180 days after application; but picloram usually dissipated from the soil profile within a year. More picloram was detected 5 months after application at 6 to 18 inches deep at the lower ends of plots with 3% slopes than in plots with 0, 1, or 2% slopes. Runoff water from plots irrigated 10 days after treatment contained 17 ppb picloram. Irrigation or rainfall at 20, 30, or 45 days after picloram application resulted in less than 1 ppb picloram in runoff water. No more than 1 or 2 ppb picloram were detected after dilution of runoff water in large ponds.

Three major hypotheses were examined in this study: (1) the density of summer annual weeds is reduced in crop rotation systems that include winter wheat compared to those with strictly summer annual crops, (2) the integration of a red clover in cropping systems reduces weed seedbank densities, and (3) changes in weed seedbanks due to crop rotation system have greater impact on future crops that are managed with cultivation alone, compared to those managed with herbicides. To test these hypotheses, five 3-yr rotation sequences were examined in central New York state: continuous field corn (FC); field corn with red clover (FC + CL); field corn–oats–wheat (FC/O/W); sweet corn–peas–wheat (SC/P/W), and SC/P/W with red clover (SC/P/W + CL). In the fourth year, sweet corn, snap beans, and cabbage were planted in subplots with three levels of weed management as sub-subplots: cultivation alone, reduced-rate herbicides (1/2×), and full-rate herbicides (1×). The trial was carried out in two separate cycles, from 1997 to 2000 (cycle 1) and from 1998 to 2001 (cycle 2). Crop rotations with strictly summer annual crops (FC) did not result in consistently higher weed seedbank densities of summer annual weeds compared to rotations involving winter wheat (FC/O/W; SC/P/W; SC/P/W + CL). Integration of red clover in continuous field corn resulted in higher weed seedbanks (cycle 1) or emergence (cycle 2) of several summer annual weeds compared to field corn alone. In contrast, integration of red clover in the SC/P/W rotation led to a 96% reduction in seedbank density of winter annuals in cycle 1, although this effect was not detected in cycle 2. Observed changes in weed seedbank density and emergence due to crop rotation resulted in increased weed biomass in the final year in only one case (sweet corn, cycle 2), and did not result in detectable differences in crop yields. In contrast, final year weed management had a strong effect on weed biomass and yield; cultivation alone resulted in yield losses for sweet corn (32 to 34%) and cabbage (0 to 7%), but not snap beans compared to either 1/2× or 1× herbicides.