Experiments were conducted from 1979 to 1982 to determine whether selected herbicide treatments applied before or after harvest would provide adequate weed control without the use of tillage between crops in continuous winter wheat (Triticum aestivum L.) production systems. of the herbicide treatments evaluated, only oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) at 2.2 kg ai/ha applied prior to wheat maturity adequately controlled summer annual weeds each year. Populations of yellow nutsedge (Cyperus esculentus L. # CYPES) and/or clammy groundcherry (Physalis heterophylla Nees) increased from continued preharvest use of oryzalin in no-till treatments and were greater than those resulting from conventional tillage or various postharvest no-till treatments containing glyphosate [N-(phosphonomethyl)glycine]. After 4 yr, populations of winter annual Cruciferae spp. at one location were lower in treatments that had poorer control of summer annual weeds or volunteer wheat. At a second location, winter annual broadleaf species were more numerous in conventionally tilled than in no-till treatments. Wheat yields obtained with no-till treatments were lower than yields obtained with conventional tillage in seasons favorable for high yields.

Enhancement of the canker causing ability of Botryosphaeria ribis on melaleuca was studied with respect to stress from simulated drought, low temperature, and defoliation treatments. Low xylem water potential was related to increased level of canker development and subsequent tree mortality. Canker development was enhanced by low temperature treatments with alternating exposure to 6 C for 3 d followed by 4 d at 30 (±5) C for 8 wk. Partial defoliation did not affect canker development but complete defoliation of B. ribis-inoculated ramets resulted in tree mortality within 4 wk. Callusing of melaleuca wounds was either reduced or prevented in stressed trees. These observations suggest that stress induced on the tree enhances the tree-killing efficacy of this fungus.

Foliar sprays of the monoethanolamine salt, potassium salt, free acid, and 1-decyl ester of clopyralid were more effective in killing greenhouse-grown honey mesquite than the 2-ethylhexyl ester at rates of 0.28 ae/ha or less. More clopyralid was transported to the lower canopy from application of the monoethanolamine salt and potassium salt than the 2-ethylhexyl ester of clopyralid at 4 h or 1, 3, or 8 days after treatment. Application of the monoethanolamine salt and the 2-ethylhexyl ester to leaves with a pipet indicated that about twice as much clopyralid was absorbed within 15 min from the ester form (26%) than from the amine form (12%) of the total recovered. However, after 24 h, absorption of the ester was less than the amine. More than twice as much clopyralid was transported from the treated leaf after application of amine than the ester. Only the acid form of clopyralid was transported away from the site of application of either ester or amine.

This work was initiated to develop a method of sampling quackgrass populations. Shoot and bud distribution of 36 field populations was obtained. The results demonstrated that shoot count was inappropriate in assessing quackgrass bud populations and that bud sampling depth should be at least 20 cm if an accurate estimate is required. When shoot count is the only possibility, quadrat size should be as large as possible to minimize the error. Descriptive statistics of the field populations were used to generate a series of 24 simulated quackgrass bud populations. The field and simulated data were computer sampled with a program designed to compare the effects of varying sample size (number of quadrats) and sample shape (quadrat size and form). The intensity of sampling must be a function of resources and cost, since sampling precision increased linearly with sample size. Precision of sampling was generally higher when a large number of small quadrats were used compared to a small number of large quadrats. Sampling intensity per unit area must be increased when bud density increases to maintain a given degree of precision, but it can be decreased when plot size increases.

A method was developed for the quantitative determination of trace levels of the widely used herbicide sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} and its metabolites in an aqueous solution using reversed-phase high-performance liquid chromatography (HPLC). Optimum extraction of sethoxydim was with dichloromethane and was only 15% efficient at pH 3. The limit of detection by HPLC for sethoxydim was 5 ng on column and <5 ppb in soil. At least five different compounds were detected in the commercial formulation, in EPA reference standards, and in commercial sethoxydim standards. Sethoxydim undergoes a rapid decomposition in the presence of water to form more polar products, which accounts for the low extraction efficiency. Decomposition was greatest under alkaline conditions. Acid pH and soil inhibited decomposition and gave greater recoveries of parent compound. At least one breakdown product cochromatographed with a known sulfone derivative. The procedures are directly applicable to soils, environmental waters, and plant and animal tissues.

Information on weed spatial distribution could improve weed management decisions. Herbicide use could be reduced if applied only to field zones with an infestation level higher than a specific economic threshold. In this study, we surveyed 31 winter barley fields in different regions of Spain to describe the spatial distribution of sterile oat and to analyze the relationship between sterile oat infestation level and landscape and crop yield attributes. Elevation and slope angle, crop yield and slope aspect were the main factors in order of importance in explaining the distribution of sterile oat. In general, greater infestation levels were observed in flat lowland and concave landscapes, with a low crop yield, and on northern exposures (when slope ≥ 2%). We could define field zones with a higher risk (> 6 times probability) of having sterile oat problems. High-probability zones, defined by topographic attributes alone, occupied 24% of the total area and contained 46% of the high infestation levels, whereas zones defined by topographic and crop yield attributes constituted 14% of the total area and contained 31% of the infestation.

Postemergence applications of BAS 9052 OH {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one} and Ro-13-8895 {acetone-O-[d-2-[p-[(α,α,α-trifluoro-p-tolyl-oxy] phenoxy] propionyl]oxime} at 0.3 kg/ha selectively controlled four- to five-leaf-stage quackgrass [Agropyron repens (L.) Beauv. ♯3 AGRRE] 75 and 80%, respectively, 105 days after treatment (DAT). KK-80 {4-[4-[4-(trifluoromethyl)phenoxy) phenoxy]-2-pentenoic} at the same rate and stage of growth controlled quackgrass only 45%. None of the herbicides had preemergence activity on quackgrass. All herbicides applied at 0.8 kg/ha controlled two- to three- or four- to five-leaf-stage quackgrass an average of 88%, whereas applications at the six- to seven-leaf stage controlled quackgrass only 27%, 105 DAT. Cultivation alone 1 DAT provided quackgrass control that gave soybean [Glycine max (L.) Merr.] yields equal to any herbicide or herbicide plus cultivation treatment In a greenhouse experiment, BAS 9052 OH killed 50-bud rhizome systems in 1 day, whereas KK-80 and Ro-13-8895 required 14 and 7 days of translocation, respectively, to provide similar control.

Single applications of 4.48 and 22.4 kg/ha of the ester formulation of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T ester), 2,4,5-T amine, and 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) to the ground cover and soil under apple (Malus sylvestris Mill.) trees significantly reduced the proportion of broadleaf plants to grasses. After six annual applications of these herbicides, the ground cover consisted of almost pure stands of grasses. Six applications of 2-sec-butyl-4,6-dinitrophenol (dinoseb) + oil at 4.2 kg/ha + 374 L/ha and five times this rate decreased the proportion of broadleaf weeds to grasses, but one application did not change the proportion. One and six annual applications of dinoseb amine at 16.8 and 84 kg/ha significantly reduced the percentage of broadleaf weeds. One application of 3-amino-s-triazole (amitrole) at 4.48 kg/ha and six annual applications of amitrole at 22.4 kg/ha significantly decreased the percentage of broadleaf weeds. Six annual applications of 2,2-dichloropropionic acid (dalapon) + dinoseb amine at 47.6 + 84 kg/ha significantly increased the percentage of broadleaf weeds, especially mouseear chickweed (Cerastium vulgatum L.) and red sorrel (Rumex acetosella L.). Six annual applications of ammonium sulfamate (AMS) at 168 and 840 kg/ha increased the proportion of grasses to broadleaf weeds as did a single application at 168 kg/ha. AMS caused phytotoxic symptoms on young apple replants at the 168-kg/ha rate and also on mature trees at the 840-kg/ha rate. No phytotoxic symptoms were noted with the other herbicides applied.

Seedlings from golden delicious apples (Malus domestica Borkh. ‘Smoothee’) were grown in the greenhouse with orchardgrass (Dactylis glomerata L. # DACGL), Kentucky bluegrass (Poa pratensis L. # POAPR), red sorrel (Rumex acetosella L. # RUMAA), and Korean lespedeza (Lespedeza stipulacea L. # LESSL) at four densities and four fertility levels. Orchardgrass and red sorrel inhibited tree growth more than Kentucky bluegrass on a per plant basis. Korean lespedeza inhibition of apple growth was associated with the amount of root nodulation on the Korean lespedeza. Apple shoot dry weight over all fertility levels, ground cover species, and densities was predicted by a regression model based on increase with fertility and decrease with ground cover dry weight. These results indicate that the competitiveness between equal number of ground cover species is due to differences in biomass production. Addition of nitrogen to the system increased nitrogen levels in apples but did not completely overcome apple growth inhibition.

Imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} was evaluated in the field for weed control in flue-cured tobacco (Nicotiana tabacum L.) during 1983 and 1984. The 75 DG formulation of imazaquin was used at 0.28 and 0.42 kg ai/ha. Methods of application were: preplant incorporated, over the top immediately after transplanting, postbed incorporated, and early postemergence. Imazaquin controlled 90%, or better, of common lambsquarters (Chenopodium album L. # CHEAL), common ragweed (Ambrosia artemisiifolia L. # AMBEL), redroot pigweed (Amaranthus retroflexus L. # AMARE), spiny amaranth (Amaranthus spinosus L. # AMASP), ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. # IPOHE], sicklepod (Cassia obtusifolia L. # CASOB), and prickly sida (Sida spinosa L. # SIDSP) with all application methods except early postemergence. It controlled 80 to 89% of large crabgrass (Digitaria sanguinalis L. # DIGSA) by the soil-applied methods. Postemergence applications of imazaquin controlled common ragweed, pigweed spp., ivyleaf morningglory, prickly sida, and sicklepod. Imazaquin was less effective postemergence on lambsquarters and large crabgrass. Tobacco tolerated use of imazaquin by all methods of application except preplant incorporation.

The phytotoxicity of difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) applied to the three-leaf stages of hard red spring wheat (Triticum aestivum L. ‘Waldron’ and ‘Era’), barley (Hordeum vulgare L. ‘Beacon’) and wild oat (Avena fatua L. ♯ AVEFA) grown under constant, fluctuating, or alternating day-night temperatures was determined in controlled environment chambers. Difenzoquat injury to wild oat and Era wheat was greater at a constant 20 or 30 than at 10 C; however, injury to Waldron wheat was similar at 10, 20, and 30 C. Difenzoquat caused only slight injury to barley, and injury was similar at all temperatures. In Era wheat, selectivity of difenzoquat for wild oat was maximum with a 10-C night temperature in an otherwise 30-C-temperature environment; in Beacon barley selectivity was maximum with 3 or more days of 20- or 30-C posttreatment temperature; and in Waldron wheat selectivity was not adequate at any of the temperatures studied.

The northern New England region includes the states of Vermont, New Hampshire, and Maine and encompasses a large degree of climate and edaphic variation across a relatively small spatial area, making it ideal for studying climate change impacts on agricultural weed communities. We sampled weed seedbanks and measured soil physical and chemical characteristics on 77 organic farms across the region and analyzed the relationships between weed community parameters and select geographic, climatic, and edaphic variables using multivariate procedures. Temperature-related variables (latitude, longitude, mean maximum and minimum temperature) were the strongest and most consistent correlates with weed seedbank composition. Edaphic variables were, for the most part, relatively weaker and inconsistent correlates with weed seedbanks. Our analyses also indicate that a number of agriculturally important weed species are associated with specific U.S. Department of Agriculture plant hardiness zones, implying that future changes in climate factors that result in geographic shifts in these zones will likely be accompanied by changes in the composition of weed communities and therefore new management challenges for farmers.

The herbicide isopropyl N–(3–chlorophenyl)carbamate (CIPC) has been found to be effective in controlling annual grasses when applied as a pre-emergence treatment. This herbicide is also very effective in controlling chickweed (1, 9, 12) and grasses in dormant alfalfa (11).

The commercial use of herbicides formulated on granular carriers has expanded rapidly and in many instances has preceded research on their development and properties. Experimental studies have been concerned primarily with field problems involving the control of weeds in a particular weed-crop situation. Conflicting results obtained in both the experimental and the practical use of granular herbicides have emphasized the need for basic information on the mode of action of granular-herbicide formulations and the effect of environment and cultural techniques on their use.

Disodium endothal (3,6 endoxohexahydrophthalic acid) was applied to a number of emergent and submerged aquatic species and was found to be particularly effective in controlling pondweeds, Potamogeton spp. On P. foliosus, P. crispus, and P. pectinatus, liquid and granular preparations appeared to be equally effective. Endothal was not very effective on some species, such as waterwillow, Justicia americana, and creeping waterprimrose, Jussiaea repens L. var. glabrescens, although defoliation did occur.

One of the major characteristics limiting the usefulness of pre-emergence herbicide applications concerns the persistence of chemical activity in the soil. In many instances, the herbicides break down too quickly to obtain satisfactory weed control. On the other hand, there is the possible hazard that a chemical may be too persistent and thus endanger the growth of succeeding crops. Another closely related factor is susceptibility to leaching. It is especially important when chemicals are used that are toxic to the crop plants as well as the weeds.

During the past several years, pre-emergence herbicides for crabgrass control in turf have come into prominence. Some herbicides are relatively new; others, such as lead arsenate, calcium arsenate, and chlordane, have been used as herbicides for a number of years. Research workers have included the old as well as the newer herbicides in experiments under controlled conditions to determine their effectiveness as pre-emergence herbicides. However, information on the effect of these herbicides on the germination and growth of turfgrass species is limited. Application of lead arsenate as orchard sprays over the years had a toxic effect on the soil after the orchards had been removed and the areas planted to other crops due to arsenic accumulation. The poor condition of young alfalfa and barley in the affected fields was roughly proportional to the concentration of readily soluble arsenic in the surface soil.

Leguminous crops for hay, seed, pasture or soil improvement occupy a large portion of the total crop acreage. Plantings of legumes, particularly alfalfa, are often maintained long after production has dropped below an economic level. The reason may be reluctance of farmers to attempt establishment of new stands. In areas where fall seeding is possible but where mosture is often scant, spring seedings with the attendant hazard of annual weeds, must be relied upon for establishment of new stands.

In studies of the effect of root temperature on the toxicity of 2,4-dichlorophenoxyacetic acid (2,4-D) to rubber rabbitbrush (Chrysothamnus nauseosus (Pall.) Britton), 75 F resulted in the highest mortality following 2,4-D treatment. Root temperatures had no effect on leaf cuticle thickness. In similar studies with Canada thistle (Cirsium arvense (L) Scop.) and Russian knapweed (Centaurea repens L.), little injury resulted from 2,4-D treatment at 45 F whereas at 90 F in Canada thistle and at 60, 75, and 90 F in Russian knapweed, severe injury and/or death resulted.

Itchgrass [Rottboellia cochinchinensis (Lour.) Clayton] is recognized as one of the most noxious and troublesome annual weeds in tropical and subtropical regions. Acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides have been frequently used for managing R. cochinchinensis POST in a variety of crops, resulting in evolved resistance to these herbicides. Recently, resistance to fluazifop-P-butyl has been demonstrated for this weed, as the result of a G-to-C single-nucleotide polymorphism (SNP) that leads to the Trp-2027-Cys substitution in the ACCase enzyme. This study was conducted to develop a high-resolution melting analysis (HRMA) for the detection of the mutation underlying the Trp-2027-Cys substitution. The HRMA assay allowed differentiating between fluazifop-P-butyl–resistant (C mutant) and susceptible (G wild type) R. cochinchinensis plants. HRMA accuracy was confirmed with DNA sequencing of the target-site mutation, and no false positives or negatives were observed. Our results illustrated how HRMA is effective detecting the Trp-2027-Cys substitution in an R. cochinchinensis resistance, and how this technique can be of great value for developing high-throughput programs for monitoring evolution and dispersion of target site–based herbicide resistance at large scales.