Activity, adsorption, mobility, and field persistence of one emulsifiable concentrate (EC) and three microencapsulated (ME) formulations of alachlor were studied with petri dish bioassay, based on root response of oats grown in sand or soil. Both bioassays indicated that activity of all formulations was increased with increasing herbicide concentration. EC-alachlor in sand showed the highest activity, while ME-alachlorL and ME-alachlorA, the lowest; the activity of ME-alachlorC was intermediate. In silty clay loam soil, EC-alachlor had the highest activity, while ME-alachlorL had the lowest; and ME-alachlorA showed intermediate activity and was similar to that of ME-alachlorC More alachlor was adsorbed on the soil or remained encapsulated (not biologically available) after ME-alachlorL and ME-alachorA application compared to EC-alachlor. An intermediate amount of alachlor was adsorbed or remained inside the capsules when the ME-alachlorC formulation was applied. Greater amounts of alachlor were leached through a silty clay loam after EC-alachlor application compared to the three ME-alachlor formulations. Biologically available alachlor was not detected below 15 or 10 cm after application of EC- and ME-alachlor formulations, respectively. All alachlor formulations applied alone or in mixture with atrazine showed similar field persistence. Biologically available alachlor was not detected in the 0- to 10-cm soil depth 30 d after their application. All alachlor formulations applied alone gave excellent control of redroot pigweed and black nightshade, but only partial control of jimsonweed. None of the herbicide treatments showed any detrimental effect on corn, and all of them increased corn yield to the level of weed-free control.

Weed emergence models require biological parameters such as base temperature for germination, determination of which is costly and time-consuming. Transferability of these parameters across different populations may therefore represent one of the main constraints for the development and practical use of emergence models at a large scale. A collaborative project was undertaken to assess the interpopulation variability of base temperature for germination in different European populations of velvetleaf and jimsonweed and evaluate possible applicative consequences in terms of weed control. Seeds were collected in Italy, Portugal, and Spain, and each population was then sown in every country, obtaining nine seed batches named as experimental lots. Base temperature for germination was estimated for each experimental lot to calculate lot-specific accumulation of growing degree days (GDD) under three dissimilar climatic scenarios. Threshold date (TD50) was calculated as the date when GDD accumulation of a given experimental lot surpassed the values corresponding to 50% of cumulative field emergence of seedlings. GDD accumulation and TD50 were then used as indicators to identify differences among experimental lots within each climatic scenario. No significant differences were detected among base temperatures estimated for velvetleaf experimental lots or among their patterns of accumulation of GDD and TD50 values within climatic scenarios. Each value of base temperature determined for a single experimental lot could therefore be adopted to model germination for all the lots regardless of the population of origin or cultivation site. In contrast, the population of origin affected the base temperature for jimsonweed, with significantly higher values for experimental lots of the Portuguese population. From an applicative perspective, differences among patterns of accumulation of GDD and TD50 of several experimental lots within each climatic scenario suggest the need to use population-specific values as base temperature for germination and emergence modeling of jimsonweed.

Organic vegetable producers have limited options for managing weeds. They cite weed management as their number one research priority. Studies were conducted in 2004 and 2005 at the Black Sea Agricultural Research Institute, Samsun, Turkey, to determine the weed suppressive effects of summer cover crops in organic kale production. Treatments consisted of grain sorghum, sudangrass, hairy vetch, grain amaranth, pea, and fallow. Weed density and total weed dry biomass were assessed before and at 14, 28, and 56 d after incorporation (DAI) of the cover crops. Kale was transplanted 14 DAI and hand weeded once after last weed evaluation (56 DAI). All cover crops produced at least 1 ton/ha (t/ha) biomass; grain sorghum produced more dry matter than all other cover crops in both years. After incorporation of the cover crops, hairy vetch and sorghum treatments showed fewer species, lower weed density, and total weed dry biomass compared with other treatments. Cover crops suppressed emergence of common purslane, common lambsquarters, redroot pigweed, European heliotrope, field pennycress, annual sowthistle, black nightshade, shepherd's-purse, wild mustard, sun spurge, Persian speedwell, annual mercury, and jimsonweed up to 56 DAI. Total kale yield in hairy vetch treatments was more than double that of the no cover crop, and was significantly higher than yield from the other cover crop treatments. These results indicate that hairy vetch, grain sorghum, and sudangrass have ability to suppress early-season weeds in organic kale production.

Field studies were conducted near Clayton, Goldsboro, Kinston, and Rocky Mount, NC in 2003 to evaluate weed control and cotton response to postemergence (POST) treatments of glufosinate applied alone or in tank mixtures with s-metolachlor, pyrithiobac, or trifloxysulfuron. Late-season control of common lambsquarters, common ragweed, entireleaf morningglory, ivyleaf morningglory, jimsonweed, pitted morningglory, purple nutsedge, and sicklepod with glufosinate early postemergence (EPOST) was ≥90%. The addition of S-metolachlor to glufosinate EPOST improved control of all weeds except sicklepod, ivyleaf morningglory, and entireleaf morningglory. When applied POST, glufosinate provided ≥90% late season control of common lambsquarters, common ragweed, entireleaf morningglory, ivyleaf morningglory, jimsonweed, large crabgrass, pitted morningglory, purple nutsedge, and sicklepod. Control of goosegrass and Palmer amaranth was 81 and 84%, respectively. When pyrithiobac or trifloxysulfuron were added in POST tank mixtures, control of Palmer amaranth improved 6 and 9 percentage points, respectively. Control of goosegrass remained near 80% regardless of herbicide treatment used. The addition of a late post-directed (LAYBY) tank-mixture of glufosinate plus prometryn provided ≥88% late season control of all weeds. Reduced control of goosegrass and Palmer amaranth was observed with the LAYBY tank mixture of glufosinate plus MSMA when compared to other LAYBY tank mixtures. Cotton lint yields in plots receiving any herbicide application were significantly higher than plots receiving no herbicide application for all application timings. Cotton lint yields were ≥ 740 kg/ha where an EPOST was applied and ≥ 680 kg/ha when a POST herbicide was applied. Cotton lint yields were at least 200 kg/ha greater on plots receiving a LAYBY application when compared to plots where no LAYBY treatment was applied.

Studies were conducted to evaluate weed management systems in nontransgenic, bromoxynil-resistant, and glyphosate-resistant cotton in strip- and conventional-tillage environments. Tillage did not affect weed control, cotton lint yields, or net returns. Early season stunting in strip-tillage cotton was 5% or less, regardless of herbicide system or cultivar and was transient. Excellent (> 90%) control of common lambsquarters, common ragweed, and Ipomoea species, including entireleaf, ivyleaf, pitted and tall morningglories, jimsonweed, prickly sida, and velvetleaf, was achieved with systems containing bromoxynil, glyphosate, and pyrithiobac early postemergence (EPOST). Glyphosate systems provided better and more consistent control of fall panicum and large crabgrass than bromoxynil and pyrithiobac systems. Bromoxynil and pyrithiobac EPOST did not control sicklepod unless applied in mixture with MSMA and followed by (fb) a late postemergence-directed (LAYBY) treatment of prometryn plus MSMA. Palmer amaranth was controlled (> 90%) with all glyphosate and pyrithiobac systems and with the bromoxynil system that included a broadcast soil-applied herbicide treatment. Bromoxynil systems without a broadcast soil-applied herbicide treatment controlled Palmer amaranth 87% or less. Herbicide systems that included glyphosate EPOST controlled sicklepod with or without a soil-applied herbicide treatment. The highest yielding cotton included all the glyphosate systems and bromoxynil systems that contained a soil-applied herbicide treatment. Nontransgenic systems that included a soil-applied herbicide treatment yielded less than a system with soil-applied treatment plus glyphosate EPOST. Net returns from glyphosate systems were generally higher than net returns from bromoxynil or pyrithiobac systems.

The noxious weed Benghal dayflower has become a severely troublesome agricultural weed in Georgia in the southeastern Unite States, and there are indications that it is moving northward. Benghal dayflower is glyphosate tolerant and possesses a high degree of reproductive elasticity, making it a formidable threat in many crop systems. The purpose of these experiments was to develop the first temperature response profiles for Benghal dayflower, and use them to evaluate whether temperature might limit its northward invasion into North Carolina and adjacent states on the U.S. east coast. Experiments focused on vegetative and early reproductive growth, stages considered crucial for establishment and competitiveness. Exposure to a range of aerial temperatures revealed that Benghal dayflower growth and production of aerial and subterranean reproductive structures were maximized at 30 C, with sharp declines occurring at cooler temperatures. When exposed to differing root temperatures in hydroponics, with a constant aerial temperature, Benghal dayflower growth did not show the same cool temperature sensitivity, but reproductive performance declined when temperatures decreased below about 29 C. The root temperature responses of several other weed species known to thrive in the climate of this geographic area also were determined. Growth of sicklepod, hemp sesbania, and jimsonweed was more sensitive than Benghal dayflower to cool temperatures, whereas the growth response of velvetleaf was similar. Based on the comparison of the Benghal dayflower temperature responses in controlled environments to (1) seasonal air and soil temperatures in the field, and (2) the temperature responses of agronomic weeds known to thrive in the region, it is concluded that cool temperatures will not restrain the northward spread of Benghal dayflower into North Carolina.

In studies conducted from 1991 through 1994, researchers investigated the effects of several crop rotations and herbicide programs on crop yield and populations of common lambsquarters, common ragweed, Amaranthus spp., and jimsonweed at two sites. Crop rotations included continuous corn, continuous soybean, corn–soybean, and corn–tomato–soybean, and herbicide programs were the split-plots and included continuous use of acetolactate synthase (ALS)–inhibitor herbicides, continuous use of non–ALS-inhibitor herbicides, annual rotations between ALS- and non–ALS-inhibitor herbicides, combinations of ALS- and non–ALS-inhibitor herbicides in the same year, and no herbicide. Weed control and weed populations generally were affected by an interaction between crop rotations and herbicide programs. After 4 yr, common lambsquarters control was lowest, and populations were highest where fomesafen was used alone for four consecutive years or in rotation with other herbicides. Although common ragweed populations were low at site 2, control at both sites was generally lowest from treatments that included only ALS-inhibitor herbicides. Common ragweed populations were highest at site 1 in 1992 and 1993 following continuous applications of ALS-inhibitor herbicides. Jimsonweed populations were also low at site 2, but control at site 1 in tomato was low. Jimsonweed control from fomesafen and the combination of butylate plus atrazine in soybean and corn, respectively, was variable. Amaranthus spp. populations decreased as the study progressed, and in 1993, control was over 90% from all treatments, except in the case of the treatment combining butylate plus atrazine. Corn and soybean yields varied with year and site, and yields of these crops and tomato were related to rainfall and weed control.

Studies were conducted to evaluate absorption, translocation, and metabolism of 14C-CGA 362622 when foliar applied to cotton, peanut, jimsonweed, and sicklepod. Differential metabolism is the basis for tolerance in cotton and jimsonweed. In addition, cotton absorbs less herbicide compared with the other three species, thus aiding in tolerance. Only jimsonweed translocated appreciable herbicide (25%) out of treated leaves and acropetally to the meristematic tissue where the herbicide was quickly metabolized. No plant species translocated over 2% of applied radioactivity below the treated leaves. Most of the metabolites formed by the four species were more polar than CGA 362622 and averaged 51, 48, 30, and 25% of the radioactivity detected in the treated leaves of cotton, jimsonweed, peanut, and sicklepod, respectively. The half-life of CGA 362622 was estimated to be 0.8, 1.9, 4, and 6 d in treated leaves of cotton, jimsonweed, sicklepod, and peanut, respectively.

Potato exhibits adequate tolerance to preemergence applications of sulfentrazone at rates up to 0.28 kg ai ha−1. Sulfentrazone also controls several troublesome weeds such as common lambsquarters but may be less effective against jimsonweed. Laboratory experiments were conducted to investigate differential tolerance to root-absorbed [14C]sulfentrazone by potato, common lambsquarters, and jimsonweed. Common lambsquarters and jimsonweed absorption of [14C]sulfentrazone g−1 fresh weight was more than twofold that in potato after 24-h exposure. After 48-h exposure, sulfentrazone absorption by common lambsquarters was nearly twofold that in jimsonweed and nearly threefold that in potato. Sulfentrazone movement from roots to shoots was also greater in common lambsquarters than in jimsonweed and potato after 6 h. Both weed species exhibited nearly a twofold increase in sulfentrazone translocation from roots to shoots compared with potato after 12, 24, and 48 h. Minor differences in sulfentrazone metabolism in roots were noted among species after 6 h. Metabolism in roots and shoots was similar in all species after 12, 24, and 48 h. Because the enzyme on which sulfentrazone acts, protoporphyrinogen oxidase, is located in shoot tissue, translocation to shoots is essential for sulfentrazone toxicity. Therefore, differential root absorption and differential translocation of sulfentrazone from roots to shoots are the proposed primary mechanisms of differential sulfentrazone tolerance among potato, common lambsquarters, and jimsonweed.

Studies were conducted to evaluate weed management programs in nontransgenic, bromoxynil-resistant, and glyphosate-resistant cotton in nontilled and tilled environments. Tillage did not affect weed control provided by herbicides. Early-season stunting in nontilled cotton was 3% regardless of the herbicide system and was no longer evident at midseason. Cotton yield was 10 to 15% greater, on an average, under tilled conditions than that under nontilled conditions. Excellent (> 90%) common lambsquarters, entireleaf morningglory, ivyleaf morningglory, jimsonweed, pitted morningglory, prickly sida, tall morningglory, and velvetleaf control was achieved with treatments containing pyrithiobac, bromoxynil, and glyphosate. Preemergence (PRE) or postemergence-directed (PD) herbicide inputs were necessary for adequate large crabgrass and goosegrass control. Bromoxynil and pyrithiobac postemergence did not control sicklepod unless supplemented with MSMA and followed by a late-postdirected treatment of cyanazine plus MSMA. Treatments that included glyphosate controlled sicklepod regardless of the late-PD treatment. Economic returns were at least $930 ha−1 and not different from the higher yielding programs in nontransgenic cotton when fluometuron applied PRE was included in the bromoxynil programs. Late-season weed control was usually greater than 90% from glyphosate programs, and net returns from glyphosate programs were as high or higher than the net returns from programs that used midseason treatments of bromoxynil, pyrithiobac, or fluometuron plus MSMA.