Winter Weeds Research Articles

Weed flora in the reclaimed lands along the northern sector of the Nile Valley in Egypt

Deserts comprise about 95% of the total land surface of Egypt; therefore, their potential for production must be assessed. Weed communities are mainly affected by the environment, and studies may increase our knowledge of the relationship among the weed flora, soil properties, crop rotation, soil management, fertiliser usage, and weed control. The area under study is one of the most recently reclaimed lands. The recorded 150 species in the monitored 19 sites were distributed within 33 families. The species-rich families were: Poaceae (31), Asteraceae (23), Brassicaceae (13), Chenopodiaceae (12), and Fabaceae (12). Chorological analysis revealed that the widely distributed species belonging to cosmopolitan, palaeotropical, and pantropical chorotypes constituted about 39.3% of the recorded flora. Pure Mediterranean species were very poorly represented, while biregional and triregional Mediterranean chorotypes constituted 28%. Saharo-Arabian chorotypes, either pure or penetrated into other regions, constituted 32%. Ubiquitous species with wide amplitude were Cynodon dactylon (L.) Pers. and Sonchus oleraceus L. Species richness varied from one crop to another. The winter weeds represented the main bulk of the recorded species within each crop, desert perennials exhibited notable variations, and margin species were the lowest. Redundancy analysis demonstrated the effect of soil organic matter, coarse sand, fine sand, silt, and soil saturation point on the spatial distribution of weed communities. The species-environment correlations were higher for the 4 axes, explaining 64.1% of the cumulative variance. The variations in soil pH, bicarbonates, ammonia, silt, and sulphate contents classified the vegetation into 4 site (vegetation) groups. Application of cluster analysis of species in crop-orchard farmlands resulted in 4 floristic groups (A-D). The weed species of the 2 winter crops, Egyptian clover and wheat, separated in Group A, tomato (winter/summer crop) in Group B, maize as a summer crop in Group C, and weeds of olive orchards and vineyards in Group D. This demonstrated high significant correlations between the olive and vineyard orchards (P < 0.01), and between the 2 winter crops, wheat and clover.

Influence of Winter Annual Weed Management and Crop Rotation on Soybean Cyst Nematode (Heterodera glycines) and Winter Annual Weeds: Years Four and Five

Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations by such species are common in no-till production fields in the midwestern United States of Indiana, Ohio, and Illinois. The objective of this research was to determine the influence of crop rotation and winter annual weed management on winter weed growth, SCN population density, and crop yield. Two crop rotations (SS and soybean–corn rotation) and six winter annual weed-management systems (autumn-applied herbicide, spring-applied herbicide, autumn + spring applied herbicides, autumn-seeded Italian ryegrass, autumn-seeded wheat, and a nontreated check) were evaluated in long-term, no-tillage systems at West Lafayette, IN, and Vincennes, IN. In the fourth and fifth years of these experiments, the 2-yr corn–soybean rotation generally resulted in increased soybean yield, decreased winter annual weed growth, and reduced SCN population density compared with SS. Autumn or spring herbicide applications or both were a more effective option than cover crops at reducing winter annual weed density. Cover-crop systems generally did not differ from the nontreated check in winter weed density. Between years three and five, winter annual weed SCN hosts in nontreated check plots increased approximately threefold to levels as high as 102 and 245 plants m−2 at West Lafayette, IN, and Vincennes, IN, respectively, which are infestation levels at or above those commonly observed in production fields. However, controlling winter annual weeds did not influence crop yields or SCN population density. The results of these studies suggest that winter weed management, even at the high levels of weed infestation present in these studies, appears to have little value as a tool for SCN management in corn and soybean production systems in the midwestern United States.

Nitrogen supply via internal nutrient cycling of residues and weeds in lowland rice farming

Development of alternative soil fertility management is opted to mitigate the side effects associated with the excessive use of synthetic fertilizer. Soil fertility management practice through strengthening internal nutrient cycling (agroecological management: AEM) was examined in lowland rice (Oryza sativa) farming in Tochigi Prefecture, Japan. The principal study fields were established AEM (EAEM), where AEM was established in 1999 and transitional AEM (TAEM), where AEM has been practiced since 2009 and the field is still in transient stage. A field with conventional nutrient management (CNM) was studied for reference purposes.In EAEM field, potential amount of soil N supply was estimated at 41.9gNm−2 in spring 2011. Components in AEM maintained labile N pool were basic mineralizable N (21.0gNm−2) and annually changing mineralizable N (20.9gNm−2). Annually changing mineralizable N include soil drying effect (3.6gNm−2), internal inputs (13.2gNm−2) such as rice straw, rice bran, spring and winter weed as well as external inputs (4.1gNm−2) such as biological N2 fixation, precipitation and guano. Estimated NH4–N released from soil during the cropping season was 28.5gNm−2 in 2011. As the N uptake of rice was 11.5gNm−2 in 2011, EAEM supplied sufficient N to satisfy N demand by the rice plants. Relatively large amount of NH4–N released in EAEM implies that the recycling of on-site N sources would supply substantial amount of N to rice plants. In TAEM (two and three year practice), limited amount of NH4–N (17.8gNm−2) available during the cropping season compared with EAEM emphasized the importance of long-term practice to ensure effects of AEM through increase of basic soil mineralizable N. The research result suggests that AEM might be a sustainable and appropriate soil fertility management option for lowland rice farming if measures such as adjusting application rate of rice bran are employed to control soil N supply.

Management of Winter Weeds Affects &lt;I&gt;Frankliniella fusca&lt;/I&gt; (Thysanoptera: Thripidae) Dispersal

Frankliniella fusca (Hinds) naturally disperses from winter weeds to crops in spring, causing direct and indirect damage. Field preparation before planting includes use of herbicides or cultivation to kill unwanted vegetation, which adversely affects F. fusca host plants and potentially influences F. fusca dispersal. Common chickweed, Stellaria media (L.), infested with F. fusca, was used as a model to study effects of timing and type of vegetation management on adult dispersal. Infested weeds were caged and F. fusca weekly dispersal was monitored using sticky traps. Weed management treatments performed at an early (14 April-11 May) or late (2 wk after early treatment) date consisted of glyphosate, paraquat, disking, hoeing, or untreated control. Late glyphosate and hoeing treatments resulted in cumulative dispersal statistically similar to or greater than from control plots. Compared with the control, significantly more F. fusca dispersed from the glyphosate and hoeing plots during the 3 wk after treatment. More thrips dispersed from the late paraquat treatment 1 wk post-application than from the control. Dispersal from the disked treatment and early paraquat treatment was similar to that of the control 1- to 3-wk post-treatment. Early treatments resulted in significantly smaller cumulative dispersal than the control in all but one instance. Late disking and paraquat treatments resulted in cumulative F. fusca captures that were statistically similar or less than that in the control. Winter weed management type and timing affect F. fusca dispersal magnitude and duration.

Evaluation of tall fescue (Festuca arundinacea) as a forage for sheep in the temperate high‐rainfall zone of south‐eastern Australia

AbstractTall fescue (Festuca arundinacea Schreb.) is currently seldom used in the high‐rainfall (&gt;600 mm) zone of south‐eastern Australia. To determine its potential to improve forage availability during the summer‐autumn feed‐deficit period, a field plot‐scale experiment with sheep evaluated a Continental cultivar of tall fescue (cv. Quantum) at Hamilton, Victoria, between September 2006 and January 2009. Four grazing treatments represented set stocking or rotational grazing at the two‐, three‐ or four‐leaf stage, in a completely randomized design with three replications. Grazing treatment effects on tall fescue tiller population dynamics, forage accumulation rates and consumption, sward nutritive value and botanical composition were measured. Results showed tall fescue can persist and support year‐round grazing by sheep, subject to water availability for summer growth from summer rain or on moisture retentive heavy soils. During the summer‐autumn (December–April) vegetative phase, grazing at the three‐leaf stage optimized forage consumption, with no difference in feed value or botanical composition between the grazing treatments during these months. During the reproductive phase (September–November), feed value was highest under set stocking and declined with the production of each successive leaf. Grazing at the three‐ or four‐leaf stage prevented winter weed invasion, but winter forage consumption was low in these treatments. Set stocking or grazing at the two‐leaf stage improved winter forage consumption rates, but these swards were invaded by winter growing weeds.

Winter-applied Glyphosate Effects on Spring Green-up of Zoysiagrasses and ‘Yukon’ Bermudagrass in a Transition Zone

In transitional environments, turf managers and sod producers of warm-season grasses face the issue of winter annual weeds that can dominate dormant turf stands through the winter until late spring. The use of glyphosate to control weeds in dormant bermudagrass (Cynodon dactylon) has been well documented, but information is lacking about its effect on spring green-up of other warm-season grasses. A field study was conducted on two commercial sod farms in northern Italy (Expt. 1) to evaluate the effects of glyphosate applied on two different winter dates on weed control and spring green-up of ‘Zeon’ manilagrass (Zoysia matrella). A second study was carried out at the experimental agricultural farm of Padova University (Expt. 2) to assess the effects of a winter application of glyphosate on weed control and spring green-up of ‘Yukon’ bermudagrass and ‘Companion’ zoysiagrass (Zoysia japonica). Each experiment was conducted from Jan. to June 2011, and glyphosate was applied at 1.1 kg·ha−1 on 8 and 21 Feb. in Expt. 1 and on 8 Feb. in Expt. 2. Spring recovery was evaluated by periodical visual ratings of green turf cover and by collecting normalized difference vegetation indices (NDVIs). Weed injury was visually evaluated on all plots 7 weeks after the 8 Feb. glyphosate application. The visual ratings of green cover were strongly and positively correlated with NDVI measurements. Glyphosate applied in February as a single treatment effectively controlled winter weeds in ‘Zeon’ manilagrass (Expt. 1) and ‘Yukon’ bermudagrass (Expt. 2) without negatively affecting spring green-up. In contrast, spring green-up of ‘Companion’ zoysiagrass (Expt. 2) was delayed by the application of glyphosate.

Influence of Spring Herbicide Applications on Winter Weed Emergence in Corn and Soybean Production Systems

Experiments were conducted in Indiana to assess the densities of winter weed species at 180 and 310 days when the soil-applied residual herbicides were applied in combination with glyphosate in corn (Zea mays) and soybean (Glycine max) production systems. Weed densities were higher at 180 days compared to 310 days, irrespective of the weed species at SEPAC site. In corn systems, additional application of atrazine did not decrease the weed densities at both sites. However, in few instances, cloransulam-methyl reduced the shepherd’s purse and smallflower buttercup densities as compared to non-treated check in soybean systems. In most instances, the residual herbicides applied as PRE or POST did not decrease the weed densities significantly at 180 days or at 310 days after application compared to systems that did not utilize residual herbicides.

Towards machine vision based site-specific weed management in cereals

Arable weeds are generally distributed in patches, while herbicides are applied uniformly. Herbicides can be saved if only the patches are sprayed, i.e. patch spraying (PS). Bottlenecks for cost-effective PS are weed monitoring technology and valid technology-based decision rules for PS (thresholds). The novel machine vision algorithm Weedcer has been developed as an efficient weed monitoring tool for PS. Weedcer estimates the proportions of young weed leaves and cereal leaves in high resolution red–green–blue images. We conducted field trials to test relative weed cover (RWC) and relative mayweed cover (RMC) estimated by Weedcer as decision rules for PS . RWC is the total weed cover divided by the total plant cover and RMC is the mayweed cover divided by the total plant cover. The main criterion for evaluation and basis of these thresholds was the measured grain yield. Images (about 0.06-m 2) were acquired with a GPS guided autonomous field robot in spring, the normal time for spraying seed-propagated broadleaf weeds in both winter – and spring cereals in Norway. Three map-based trials (weed monitoring and spraying in two separate operations) showed that mean RWC per management unit (12.0 × 12.5-m) was generally adequate. In winter wheat heavily infested with scentless mayweed ( Tripleurospermum inodorum (L.) Sch.Bip.) and/or scented mayweed ( Matricaria recutita L.), the mean RMC per management unit was more adequate. Progress during the project allowed three additional trials conducted in real-time (weed monitoring and spraying in the same operation). These were conducted with the robot in spring cereals, and showed that a weighted moving average of RWC per image was adequate. The sprayed and unsprayed management units in these trials were minimum 3.0 × 3.0-m and 0.5 × 3.0-m, respectively. Results indicated that the Weedcer-based thresholds should be lower in wheat ( Triticum aestivum) than in barley ( Hordeum vulgare).

Exposure to red light, temperature and exogenous gibberellins influenced germination of some winter weeds

Red light, temperature and gibberellins are well known for their capacity to induce higher germination in dormant seeds of several plant species. In the current study, we investigated the effect of various temperature (10, 13, 16, 19, 22 and 25°C) and gibberellic acid (GA 3 ) and GA 4+7 concentrations (0.1, 1, 10, and 100 uM) on germination of Poa annua, Alopecurus aequalis and Stellaria aquatica seeds incubated under continuous dark or treated with red light pulse of 80 mol m -2 s -1 red light (660 nm) for 10 min after 12 h of dark period. We found that incubation temperature and gibberellins (GAs) significantly enhanced seed germination in red light treated seeds, as maximum germination was observed for A. aequalis (67.3% at 13°C), P. annua (61.3% at 13°C), and S. aquatica (42% at 19°C) in such treatments. Exogenous GA 4+7 significantly promoted germination of P. annua and A. aequalis seeds, while GA 3 induced higher germination in S. aquatica seeds. It was observed that GAs were more effective in the presence of red light as least germination stimulation was recorded for GAs under dark condition and no germination was found in weed seeds at control and 0.1 mM GA 3 and GA 4+7 treatments. It can be concluded that lower temperature (13°C) and GA 4+7 in conjunctions with red light pulse, induced maximum germination in dormant weed seeds. Key words : Germination, temperature, nitrogen-containing compounds, red light, gibberellins.

A New Color-based Lawn Weed Detection Method and Its Integration with Texture-based Methods: A Hybrid Approach

We propose a color-based weed detection method specifically designed for detecting lawn weeds in winter. The proposed method exploits fuzzy logic to make inference from color information. Genetic algorithm is adopted to search for the optimal combination of color information, fuzzy membership functions, as well as fuzzy rules used in the method. Experimental results show that the proposed color-based method outperforms the conventional texture-based methods when testing with a winter dataset. In addition, we propose a hybrid system that incorporates both texture-based and color-based weed detection methods. It can automatically select a better method to perform weed detection, depending on an input image. The results show that the use of the hybrid system can significantly improve weed control performances for the overall datasets.

Influence of Winter Annual Weed Removal Timings on Soybean Cyst Nematode Population Density and Plant Biomass

Soybean cyst nematode (SCN) is one of the most yield limiting pathogens in U.S. soybean production. Henbit and purple deadnettle are winter annual weeds shown to facilitate SCN reproduction after crop harvest in the eastern Corn Belt. These weeds, along with volunteer soybean that germinates in autumn after harvest, are common to postharvest soybean production fields and provide an opportunity for SCN reproduction and population increase outside of the typical soybean production season. The objective of this experiment was to determine if autumn removal of these weeds and volunteer soybean can influence the winter weed seedbank, plant biomass, and SCN population densities. Microplots were established with or without Lamium spp. and volunteer soybean, and four winter weed removal timings (none, October, December, and May). Dry weights of autumn Lamium spp. were reduced 50% in October when grown in competition with volunteer soybean. SCN juveniles were found in henbit roots at higher densities in October (42 per gram of root) than December (5 per gram of root) and were also found in the roots of volunteer soybean (14 per gram of root) in October. SCN egg population densities were 50% lower in August after the summer fallow period. The results of this experiment suggest that autumn removal of winter annual weeds and volunteer soybean did not reduce SCN populations.

Winter Wheat and Weed Response to Postemergence Saflufenacil Alone and in Mixtures

Growth chamber experiments were conducted in the fall of 2006 and spring of 2007 to determine winter wheat, flixweed, and henbit response to POST treatments of saflufenacil at 13, 25, and 50 g ai ha−1applied alone and in combinations with bentazon at 560 g ai ha−1or 2,4-D amine at 533 g ae ha−1and nonionic surfactant (NIS) at 0.25% v/v. Mixtures of saflufenacil and 2,4-D amine were also applied without NIS. Necrosis was observed on wheat leaves within 1 d after treatment (DAT) and peaked at 5 to 7 DAT. Saflufenacil at 13, 25, or 50 g ai ha−1applied alone or in combination with 533 g ae ha−1of 2,4-D amine plus NIS caused 19 to 38% (alone) and 24 to 40% (in combination) wheat foliar necrosis, respectively. Foliar necrosis of wheat was 14% or less when saflufenacil, at any rate, was mixed with bentazon or 2,4-D amine without NIS. Combinations of saflufenacil at any of the rates tested plus bentazon and NIS did not reduce wheat dry weight. Saflufenacil plus 2,4-D amine without adjuvant resulted in similar wheat dry weights as 2,4-D amine. Saflufenacil plus 2,4-D amine without NIS provided 99% control of flixweed at 21 DAT, but henbit control ranged from 81 to 88%. In comparison, saflufenacil at 50 g ha−1mixed with bentazon and NIS controlled flixweed at 92% and henbit at 63% at 21 DAT. This research indicates saflufenacil has potential for POST use in winter wheat to control winter annual broadleaf weeds when tank-mixed with 2,4-D amine without NIS, but additional research is needed to discover ways to improve crop safety without reducing weed control.

Biomass accumulation, weed dynamics and nitrogen uptake by winter cover crops in a warm-temperate region of South Africa

-1 . The results suggest that legumes such as grazing vetch and forage peas may be grown to maximise biomass yields with minimal fertilizer inputs. Amount of biomass produced was a major factor in controlling winter weeds, while there was a progressive decline in the winter weed burden from the first to the second season. The low C: N ratio of grazing vetch (<15) and its high N content may make it attractive for resource-limited farmers in warm-temperate climates.

Competitive Ability and Phytotoxic Potential of Four Winter Canola Hybrids as Affected by Nitrogen Supply

Low inputs in nitrogen may affect canola (Brassica napus L.) competitiveness and allelopathic potential as well as grain and oil yields. A 2‐yr study was conducted to assess nitrogen supply effect on the ability of four canola hybrids to compete with corn poppy (Papaver rhoeas L.) as well as its effect on canola seed and oil yields. Phytotoxic potential of canola hybrids on germination and growth of winter wild oat (Avena sterilis spp. ludoviciana L.), corn poppy, and wild mustard (Sinapis arvensis L.) was also determined using a perlite‐based bioassay. At canola blossom, corn poppy plant number in nitrogen‐treated plots was 23% less than that in the nitrogen‐untreated ones. Canola seed and oil yield was reduced 18.6 and 23.7%, respectively, by the competition of 100 corn poppy plants m−2, with ‘Elan’ and ‘Titan’ the most productive hybrids. Nitrogen supply did not increase in all cases the competitive ability or the seed and oil yields. In the laboratory, germination of the winter weeds was completely inhibited by the greatest extract concentration (5 g 100 mL−1) of all hybrids. Nitrogen supply did not affect, in most cases, the phytotoxicity of canola hybrids, while phytotoxicity did not significantly differ among hybrids. Conclusively, the hybrids Elan and Titan, cultivated without any herbicide or nitrogen fertilizer, could be viable as a short‐term alternative crop system for canola seed and oil production, especially in organic or low‐input fields infested by corn poppy.

Brassicaceous and rye cover crops altered free-living soil nematode community composition

Nematode community analysis was utilized to evaluate the biofumigant or allelopathic effects of brassicaceous and rye winter cover crops on non-target nematodes in three experiments (two sites) in Maryland. The cover crop treatments included mustard blend ( Sinapis alba and Brassica juncea) ‘Caliente’, rapeseed ( B. napus) ‘Essex’/’Humus’, forage radish ( Raphanus sativus) ‘Dichon’, oilseed radish ( R. sativus) ‘Adagio’/’Colonel’, rye ( Secale cereale) ‘Wheeler’ and a no cover crop (winter weeds) control. Soil samples (0–15 cm) were collected two or three times per year and extracted nematodes were identified to genus or family. Nematode response parameters were genus, family, trophic group population density, and percent distribution of trophic groups in the entire nematode community divided into colonizer-persister ranks. The parameters refer only to free-living nematodes, however facultative hyphal-root hair feeding Tylenchidae were included. Cover crops had unique impacts on nematode communities, but these impacts appeared to be associated more with quality of organic matter inputs rather than biofumigation or allelopathy. Across all dates and seasons, and four to nine months after winter-kill, dormant bacterivore (dauer larvae) nematode populations in the forage radish (C/N shoots ∼10) plots ranged from 3.5 to 15.7 times higher ( P < 0.10) than in the control plots. Plant-associate (Tylenchidae) nematodes were 4–6.5 times higher ( P < 0.10) in rapeseed or rye (C/N shoots ∼25) plots compared to the control in June of two experiments. Across experiments fungivore nematode abundance was increased in either rapeseed ‘Essex’ or rye compared to radishes or the control. Correlations of nematode community groups with cover crop and soil parameters suggested that dauer larvae abundance was associated with soil moisture in radish plots, and tissue quality and quantity at the time of cover crop termination was associated with nematode community response. Canonical discriminant analysis suggested that rapeseed and rye had similar effects on the nematode community composition, as did the two radish cultivars, though distinct from the effect of rye and rapeseed. Overall, results suggest that radishes stimulated a bacterial decomposition pathway, while rapeseed and rye stimulated a proportionally greater fungal-based food web.

The response of ACCase‐resistant Phalaris paradoxa populations involves two different target site mutations

Summary Phalaris paradoxa (awned canary‐grass) is an aggressive annual winter weed in wheat and other arable crops that is controlled mainly by ACCase‐inhibiting herbicides: cyclohexanediones (DIMs), aryloxyphenoxypropionates (FOPs) and phenylpyrazolines (DENs, e.g. pinoxaden). The selection pressure imposed on the weed populations by repeated use of these herbicides has resulted in the evolution of increased numbers of ACCase‐resistant populations of P. paradoxa in Israel and other countries. Two populations, Revadim (RV) and Mishmar Ha’emek (MH) that were exposed to differing weed and crop management tactics were investigated. Both populations were highly resistant to all FOPs, pinoxaden and cycloxydim, but responded differently to some DIMs. RV plants exhibited much higher resistance to tralkoxydim than MH plants, while showing similar low levels of resistance to tepraloxydim and clethodim. Both populations were equally susceptible to graminicides with other modes of action. The mutations responsible for the observed resistance were identified using PCR‐RFLP and by sequencing the carboxyl transferase domain of the chloroplastic ACCase gene. RV plants possess a substitution of Asp2078 to Gly, whereas in MH population a mixture of Ile2041 to Asn or Asp2078 to Gly was found. Our study demonstrates that lack of herbicide and crop rotation may result in the evolution of diverse target site mutations and differential response of the whole plant to ACCase inhibitors.

Weed infestation structure and biomass productivity of winter wheat and weeds depending on crop sequence system and protection method

Weed infestation structure and biomass productivity of winter wheat and weeds depending on crop sequence system and protection method

Winter Cover Crops and Vinegar for Early-Season Weed Control in Sustainable Cotton

ABSTRACT Weeds may be suppressed by winter cover crops and the use of organic herbicides such as vinegar. Black oat (Avena strigosa) and hairy vetch (Vicia villosa) winter cover crops were planted for 2 years as part of a sustainable production system for cotton in the Lower Rio Grande Valley of Texas, and were till-killed each spring prior to cotton planting. Palmer amaranth (Amaranthus palme ri), common purslane (Portulaca oleracea), and sunflower (Helianthus annuus) were frequently-encountered winter and spring weeds. Both cover crops controlled winter weeds as well as did winter tillage without cover. Black oats plots had 8% and 17% more total winter weed cover than no-cover and hairy vetch plots, respectively. Seven weeks after cotton planting, cotton cover was 10% to 15% less in former winter hairy vetch and no-cover sustainable plots than in former black oats plots, but cotton height did not vary by winter cover crop. Total spring weed, pigweed, and purslane cover did not vary between former hairy vetch, black oats, and no-cover plots. All sustainable plots had higher spring weed cover than did conventional plots maintained with cultivation and synthetic herbicides. Breakdowns in the sustainable spring weed management system (withholding of spring cultivation) or insect pest management system (failure of alfalfa strips) led to increases of 60% or more in weed cover in sustainable plots. Cotton lint yield (kg/ha) did not differ between sustainable and conventional weed management systems. When evaluated as a cover crop and weed management tool, vinegar containing 9% acid (1,550 L/ha) reduced live hairy vetch cover to less than 5% in one of two trials, but was not effective as a burndown herbicide on black oats. Vinegar at this concentration (2,980 L/ha) killed >80% of 30-day-old or younger cotton and sunflower and 10-day-old Palmer amaranth and purslane in field trials, but caused <50% mortality to mature Palmer amaranth and purslane. More dilute vinegar solutions (0.9% to 4.5% acid) caused little or no mortality. Black oats and hairy vetch covers controlled winter but not spring weeds in this production system. With more prolonged use, winter covers could become a key spring weed control component in sustainable cotton production. Vinegar could be useful in controlling young weed seedlings in non-crop areas, or as a follow-up to cultivation.

Nitrogen Storage with Cover Crops and Nitrogen Fertilization in Tilled and Nontilled Soils

Improved crop and N management practices are needed to increase soil N storage so that N fertilization rate and the potential for N leaching can be reduced in tilled and nontilled soils. We examined the influence of cover crops and N fertilization rates on N inputs from cover crops, cotton (Gossypium hirsutum L.) and sorghum [Sorghum bicolor (L.) Moench] and soil total N (STN) content at the 0‐ to 120‐cm depth in no‐tilled, strip‐tilled, and chisel‐tilled Dothan sandy loam (fine‐loamy, kaolinitic, thermic, Plinthic Kandiudults) from 2000 to 2002 in central Georgia. Cover crops were legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secale cereale L.)], biculture of legume and nonlegume (vetch + rye), and winter weeds and N fertilization rates were 0, 60 to 65, and 120 to 130 kg N ha−1. Nitrogen inputs in above‐ and belowground plant biomass varied with the season and were greater in vetch and vetch + rye with N rates than in rye and weeds with or without N in tilled and nontilled soils. The STN concentration varied with sampling times and decreased with depth. The STN content at 0 to 90 cm was greater in vetch and vetch + rye with N rates than in weeds with or without N in no‐tilled and chisel‐tilled soils. Similarly, STN content at 0 to 30 cm was greater with vetch and vetch + rye than with weeds in strip‐tilled soil. As a result, N storage at 0 to 30 cm gained at 71 to 108 kg N ha−1 yr−1 in vetch and vetch + rye with N fertilization compared with a loss at 110 kg N ha−1 yr−1 to a gain at 40 kg N ha−1 yr−1 in weeds with or without N fertilization in no‐tilled and chisel‐tilled soils. In strip‐tilled soil, N storage gained at 101 to 103 kg N ha−1 yr−1 with vetch and vetch + rye compared with a loss at 91 kg N ha−1 yr−1 with weeds. Nitrogen storage in tilled and nontilled soils can be increased by using legume or a biculture of legume and nonlegume cover crops compared with no cover crop with or without N fertilization. Because of similar levels of soil N storage and cotton and sorghum N uptake, legume can be replaced by biculture cover crop and N fertilization rate can be reduced to reduce the cost of N fertilization and the potential for N leaching.

Biological activity of pyribenzoxim in winter wheat and associated weeds

Pot and field tests were conducted to evaluate the efficacy of pyribenzoxim for winter weeds in wheat. In the pot tests, pyribenzoxim, at 50 g ha−1, controlled certain biotypes of blackgrass, including a fenoxaprop‐P‐ethyl‐resistant biotype (the “Notts” biotype). A chlorotoluron‐resistant blackgrass (the “Peldon” biotype) was not controlled. Cleaver, at the three‐to‐four‐leaf stage, was completely controlled by pyribenzoxim at 30 g ha−1. In the field, the application in December gave good control of common chickweed, but did not control other weeds. No damage to wheat was observed with this rate of pyribenzoxim in December. The application in March gave complete control of blackgrass, hairy chess, and soft brome at 70 g ha−1, and cleaver at 140 g ha−1. The partial control of corn poppy and field violet was achieved. The March application scorched the wheat at 50–70 g ha−1, with prolonged stunting at 100–140 g ha−1. In conclusion, it was shown that pyribenzoxim had potential as a wheat herbicide, but needed further fine‐tuning to find an optimum dosage.