Field studies were conducted for 3 yr near Mead, NE, to evaluate the effectiveness of seed safeners CGA-92194 [N-(1,3-dioxalon-2-yl-methoxy)iminobenzeneacetonitrile], NA (1,8-naphthalic anhydride), and R-29148 (2,2-dimethyl-5-methyldichloroacetyloxazolidine) to reduce herbicide injury to big bluestem (Andropogon gerardii Vitman), indiangrass [Sorghastrum nutans (L.) Nash], intermediate wheatgrass [Agropyron intermedium (Host.) Beauv.], sideoats grama [Bouteloua curtipendula (Michx.) Torr.], and switchgrass (Panicum virgatum L.) from preplant-incorporated butylate [5-ethyl bis-(2-methylpropyl)carbamothioate] and metolachlor [2-chloro-N- (2-ethyl-6-methylphenyl) -N- (2-methoxy-l-methylethyl)acetamide], applied at 4.5 and 2.2 kg ai/ha, respectively. Big bluestem stands were satisfactory, regardless of herbicide or safener treatment, although stands were reduced by NA treatment with either herbicide. Indiangrass stands varied by year, with protection from both herbicides by R-29148 in 1984 and by NA in 1985. All safeners reduced injury to intermediate wheatgrass from metolachlor and to a lesser extent from butylate; acceptable stands were obtained with metolachlor treatment when unsafened. Sideoats grama was nearly eliminated with either herbicide, regardless of safener. Switchgrass treated with NA produced stands two- to threefold higher than other safened or unsafened seed in metolachlor plots and equal to unsafened seed in the weeded control plots.

The impact of POST applications of fluazifop-P on sugarcane grown in Louisiana was determined for 3, 6,11, 22, and 44% of the lowest rate recommended for the control of johnsongrass in soybean (100 g ai ha−1). In field studies, sugarcane injury 4 WAT increased as the rate of fluazifop-P increased. Injury in excess of 80% was observed when fluazifop-P at 44 g ha−1 was applied in May and June and 54% when applied in August Sugarcane stalks treated with fluazifop-P were fewer in number, shorter and lighter, and immature at harvest This resulted in lower Brix and sucrose levels, higher fiber content, and ultimately lower sugar yields. Reductions in sugar yields associated with an application of fluazifop-P closely paralleled visual injury 4 WAT. Injury from application of fluazifop-P was also evident in the subsequent ratoon crop where reductions in spring shoot counts of 14 to 25% were obtained even when fluazifop-P had been applied at 6 g ha−1 the previous year. Greenhouse studies indicated that the response observed in the field with CP 70-321 sugarcane was indicative of the major cultivars grown, with the possible exception of CP 74-383.

This study investigated factors that influence occurrence and persistence of plant DNA in the soil environment in three crop rotations. In each rotation, soil was sampled in May before planting, in July and August while crops were growing, and in October after harvest. Total DNA was recovered from soil samples taken at two different depths in the soil profile and quantified. Three target plant genes (corn CP4 epsps, corn 10-kD Zein, and soybean CP4 epsps) also were quantified in these DNA extracts using species-specific quantitative real-time PCR assays. In general, total plant DNA content in the soil environment was greatest when the crop was growing in the field and decreased rapidly after harvest. Nevertheless, low levels of target plant DNA were often still detectable the following spring. Age of rotation did not influence target DNA quantities found in the soil environment. Data were collected for a combination of 10 location-years, which allowed for estimation of the variance components for six factors including time of sampling, year, location, crop, sampling depth, and herbicide to total and target DNA content in the soil samples. Mean target recombinant DNA content in soil was influenced most strongly by time of sampling and year (85 and 6%, respectively), whereas total soil DNA content was less dynamic and was most strongly influenced by location and year (49 and 25%, respectively). Over the duration of this study, no accumulation of transgenic plant DNA in the soil environment was observed.

Black medic (Medicago lupulina L.) infestations are a concern for Florida strawberry [Fragaria×ananassa (Weston) Duchense ex Rozier (pro sp.) [chiloensis×virginiana] producers. Current control techniques rely on hand weeding or clopyralid application. Coordinating POST control measures with emergence timing can reduce crop competition duration and increase control. The objective of this study was to evaluate M. lupulina emergence in response to burial depth and temperature and to model M. lupulina cumulative field emergence under subtropical Florida conditions using growing degree days (GDDs) as a predictor. Two studies were in controlled environments and looked at factors affecting emergence, burial depth, and temperature. A third experiment was a 2-yr emergence study conducted on four commercial strawberry fields in Hillsborough County, FL. Emergence was modeled as a function of accumulated standard and restricted daily GDD accounting, based on M. lupulina dormancy and germination. In Experiment 1, M. lupulina only emerged when seed was deposited on the surface. In Experiment 2, there was three-way interaction among temperature, burial depth, and measurement timing (P<0.0001). Medicago lupulina emerged from as deep as 2 cm at a temperature range between 15 and 25 C. Medicago lupulina field emergence was not consistent between years, although emergence was consistent across four sites in year 1, with 0 emergence in year 2. Dormancy and germination restrictions increased calibration and validation model fit and reduced GDD inflation, making models usable between years. Medicago lupulina primarily emerged during crop establishment, between mid-November and late-December, which corresponds to an ideal timing for control measures before the harvest period.

Planting peanut in narrow rows for weed control has not been investigated in recently released Virginia market peanut cultivars. Research was conducted in North Carolina from 2007 to 2009 to determine the effect of cultivar, planting pattern, and level of weed management inputs on weed control, peanut yield, and estimated economic return. Experiments consisted of three levels of weed management (clethodim applied POST, cultivation and hand-removal of weeds, and clethodim and appropriate broadleaf herbicides applied POST), three levels of planting pattern (single rows spaced 91 cm apart, standard twin rows spaced 20 cm apart on 91-cm centers, and narrow twin rows consisting of twin rows spaced 20 cm apart on 46-cm centers), and two Virginia cultivars (‘NC 12C’ and ‘VA 98R’). Weed management affected common lambsquarters, common ragweed, eclipta, nodding spurge, pitted morningglory, Texas millet, and yellow nutsedge control, irrespective of cultivar or planting pattern. Cultivar and planting pattern had only minor effects on weed control and interactions of these treatment factors seldom occurred. Weed control achieved with cultivation plus hand-removal was similar to weed management observed with grass and broadleaf herbicide programs. Pod yield did not differ among treatments when broadleaf weeds were the dominant species but did differ when Texas millet was the most prevalent weed. The highest yield with conventional herbicide weed management was in standard twin and narrow twin row planting patterns, although no differences among planting patterns were noted when cultivation and hand-removal were the primary weed management tactics. Differences in estimated economic return were associated with weed species, and interactions of treatment factors varied by year for that parameter.

Rates of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) up to 2.4 lb/A were applied as layby weed control treatments for cotton (Gossypium hirsutum L., var. Coker 100-A) in association with 0.0 or 1.0 lb/A of diuron as a preemergence treatment. Soybeans (Glycine max L. Merr., var. Lee) were grown as an alternate year rotational crop or as a rotational crop after cotton had been grown 3 years under diuron treatment. Similar rotational systems were evaluated in which corn (Zea mays L., var. Coker 71), tobacco (Nicotiana tabacum L., var. NC-95 or NC-2326), wheat (Triticum sativum Lam., var. Wakeland), cotton, and peanuts (Arachis hypogaea L., var. NC-2) served as the rotational crops in place of soybeans. In this mixed crop rotation, herbicidal treatments were 1.0 lb/A of diuron applied as a preemergence treatment plus 0.6 or 1.2 lb/A of diuron or 1.2 lb/A of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) applied as a layby treatment. Two soil types near Rocky Mount, North Carolina were used. Herbicidal residues were determined by bioassay analyses in the fourth year of the experiment and by evaluating crops grown in the years when no herbicides were applied. Diuron residues were greater on Duplin soil than on Norfolk soil, but residues on Duplin soil were less phytotoxic to crops than those on Norfolk soil. The higher organic matter content of Duplin soil (1.2 vs 0.6%) is cited to account for both of these observations. When diuron was applied to Norfolk soil as a preemergence treatment at 1.0 lb/A plus 0.6 lb/A as a layby treatment, the residues frequently injured wheat, peanuts, and tobacco grown subsequently. Soybeans sometimes were injured by this treatment, but corn and cotton tolerated it even when the layby rate was increased to 1.2 lb/A. At equal layby rates, linuron produced residues of less consequence than diuron. At the higher application rates, greater residues occurred following 3 years of application than where application had been on an alternate year basis.

The 14C-labeled herbicide, Sandoz 6706 [4-chloro-5-(dimethyl-amino)-2-α,α,α-trifluoro-m-tolyl-3(2H)-pyridazinone], was applied to soybean [Glycine max (L.) Merr. ‘Kent’] and sicklepod (Cassia obtusifolia L.) to evaluate differential species response in uptake and translocation. Liquid scintillation spectrometry and radioautographs indicated that in both species 6706 uptake was proportional to its concentration in the cultural solution and to transpiration, provided transpiration and the uptake mechanism were not limited. Translocation of the herbicide from roots to foliage followed the apoplastic route in both plants. A higher concentration of the herbicide accumulated in the upper leaves and apical meristem in sicklpod than in soybean.

Black medic (Medicago lupulina L.) is a problem weed species in Florida strawberry [Fragaria × ananassa (Weston) Duchesne ex Rozier (pro sp.) [chiloensis × virginiana]] production. It competes with the crop and hinders harvest efficiency. A reductionist approach is being undertaken to predict M. lupulina field emergence to coordinate control tactics. Germination is the first model component to be developed. The objectives were to study the effect of osmotic potential and temperature on seed germination and to develop the germination component for reductionist emergence modeling. Trials were initiated using petri dishes in incubators to test M. lupulina germination in response to osmotic potential (0 to −1 MPa) and constant (5 to 40 C) and fluctuating temperatures (35/25, 35/20, 25/15, and 25/10 C, 12/12-h duration). Medicago lupulina germinated between 5 and 35 C. Optimal germination was between 10 and 20 C. Germination was negatively impacted by temperatures above the optimum. Fluctuating temperatures did not influence germination compared with constant temperatures. A reduction in osmotic potential from 0 to −0.25 MPa reduced germination from 43% to 14%. Three temperature-mediated germination trends were identified: standard increases and plateau up to 20 C, reduced germination between 20 and 35 C, and no germination at 40 C. A novel restriction to daily growing degree-day (GDD) accounting was developed for heat-limited germination. The germination restriction accounted for the optimum and maximum temperature, diminishing returns of exposure to higher temperatures, and the negative impact of higher temperatures above the optimum range. Determination logic and the new daily GDD accounting formula aligned GDD accumulation across all temperatures to be described by a Weibull formula (R2 = 0.5199). Results establish the germination component for reductionist emergence modeling, but further study is required to account for dormancy and PRE growth.

Greenhouse experiments showed that yellow nutsedge shoot number and shoot and root dry weights were reduced by root-knot nematodes and chile peppers. Root-knot nematodes increased and chile peppers decreased the number of yellow nutsedge tubers. Yellow nutsedge tuber germination was reduced by chile peppers but not by root-knot nematodes. Yellow nutsedge established from root-knot nematode-infected tubers produced more tubers than noninfected tubers. Root-knot nematode populations became established on yellow nutsedge root systems when plants were established from tubers previously cultured with root-knot nematodes. Metolachlor stunted chile peppers, eliminated yellow nutsedge, and influenced root-knot nematode populations through reduction of host plant root mass. However, when root-knot nematodes were present, yellow nutsedge tuber germination was not affected by metolachlor. This research indicates that the pests do not exist independently and that their management may be interrelated.

Weed composition may vary because of natural environment, management practices, and their interactions. In this study we presented a systematic approach for analyzing the relative importance of environmental and management factors on weed composition of the most conspicuous species in sugarcane. A data-mining approach represented by k-means cluster and classification and regression trees (CART) were used for analyzing the 11 most frequent weeds recorded in sugarcane cropping systems of northern Argentina. Data of weed abundance and explanatory factors contained records from 1976 sugarcane fields over 2 consecutive years. The k-means method selected five different weed clusters. One cluster contained 44% of the data and exhibited the lowest overall weed abundance. The other four clusters were dominated by three perennial species, bermudagrass, johnsongrass, and purple nutsedge, and the annual itchgrass. The CART model was able to explain 44% of the sugarcane's weed composition variability. Four of the five clusters were represented in the terminal nodes of the final CART model. Sugarcane burning before harvesting was the first factor selected in the CART, and all nodes resulting from this split were characterized by low abundance of weeds. Regarding the predictive power of the variables, rainfall and the genotype identity were the most important predictors. These results have management implications as they indicate that the genotype identity would be a more important factor than crop age when designing sugarcane weed management. Moreover, the abiotic control of crop–weed interaction would be more related to rainfall than the environmental heterogeneity related to soil type, for example soil fertility. Although all these exploratory patterns resulting from the CART data-mining procedure should be refined, it became clear that this information may be used to develop an experimental framework to study the factors driving weed assembly.

Wettable powder and granular formulations of pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide], applied at 1.7 kg/ha to the soil surface or incorporated to depths of 1.3 to 7.5 cm, controlled dodder (Cuscuta indecora Choisy and C. campestris Yunck.) completely in the greenhouse for periods of 6 to 16 weeks. Seedlings emerged in pronamide-treated soil, but did not elongate normally and did not twine. Pronamide had very little activity as a vapor. In the field, the same rate applied to the soil surface and sprinkler irrigated or mechanically incorporated with the soil usually controlled dodder for about 1 month longer than did the standard herbicide, chlorpropham (isopropyl m-chlorocarbanilate) at 6.7 kg/ha. Pronamide at 6.7 kg/ha did not injure established alfalfa (Medicago sativa L.).

The effects of buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} on the photochemical reactions of isolated pea (Pisum sativum L.) chloroplast thylakoids were analyzed. Buthidazole was found to inhibit electron transport at two distinct sites in the photosynthetic electron transport chain. The major site of inhibition was on the reducing side of photosystem II at the site of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] inhibition. Buthidazole also had a secondary site of electron transport inhibition on the oxidizing side of photosystem II. No evidence was found for buthidazole to act as an uncoupler or as an energy transfer inhibitor.

Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), IAA (indoleacetic acid), kinetin (6-furfurylamino purine), and their combinations in culture solutions did not affect cotton (Gossypium hirsutum L., var. Deltapine Smooth Leaf) germination but reduced primary root and shoot lengths of seedlings. Trifluralin alone and in combination with IAA or kinetin inhibited lateral root development. When IAA and kinetin were both applied with 5 ppmw trifluralin, lateral roots developed.

In greenhouse studies, magnesium-deficient tomato (Lycopersicon esculentum Mill.) plants were more susceptible to 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) than normal plants when grown under continuous light. Under a 12-hr photoperiod, magnesium-atrazine interactions were not significant. Magnesium deficiency and continuous light each caused reductions in chlorophyll content in tomatoes. A combination of these two conditions caused an additive reduction in chlorophyll content and also caused the greatest susceptibility to atrazine. The influence of magnesium on atrazine toxicity may be due to its effect on chlorophyll content rather than a direct effect on atrazine action.

Various populations of common lambsquarters (Chenopodium album L. # CHEAL) and late-flowering goosefoot (Chenopodium strictum Roth. # CHESG) plants were studied at the eight-to ten-leaf stage. Prior to measurement of fluorescence induction, the detached leaves were vacuum infiltrated with unformulated atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea], and pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone]. The fluorescence induction measurements were then made 1 h after adaptation in the dark. The fluorescence induction curves of intact leaves were recorded with a laboratorybuilt apparatus. A xenon lamp was used to produce the actinic beam. Cytological tests were done on meristematic cells of the root tips of the seedlings treated in 2 nM 8-hydroxyquinoline. The cytotypes were hexaploids (among which were atrazine-susceptible, pyrazon-susceptible, atrazine-resistant, and pyrazon-tolerant populations), and tetraploids (among which were atrazine-susceptible and atrazine-tolerant populations).

Tall ironweed (Vernonia altissima Nutt.) is a perennial with underground, axillary vegetative buds from which new shoots are produced. In a 2-yr study, tall ironweed plants averaged 6115 seeds/plant. Germination of buried seeds increased with increased time of burial. Foliar herbicide applications were evaluated for control of tall ironweed plants in the pre- to early-bud stages of growth. The triethylamine salt or ethylene glycol butyl ether ester of triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} was the most effective, providing 93 to 90% control of top growth and regrowth of tall ironweed. The butoxyethanol and propylene glycol butyl ether esters of 2,4-D [(2,4-dichlorophenoxy) acetic acid] alone and in combination with the amine salt of triclopyr also provided excellent control.

Reduced-tillage practices have allowed leafy spurge to infest cropland. The reduction in leafy spurge infestation and winterhardiness by fall tillage, N application, or herbicide treatment was evaluated. Cultivating leafy spurge twice each fall for 3 yr provided complete control. Cultivation followed by N application at 225 kg ha−1 reduced the stand by 85% after 3 yr, whereas N applied alone had little effect. Picloram plus 2,4-D at 0.6 plus 1 kg ha−1 reduced the infestation to 65% of the untreated control after 2 yr but then the infestation declined rapidly to 1% after a third application. Leafy spurge cold tolerance decreased as root depth increased. The GR50 and LT50, the temperatures required to reduce total dry weight and survival, respectively, by 50% varied by root depth and treatment. For example, the LT50 and GR50 for untreated leafy spurge averaged −19 and < −20 C for crowns, respectively, compared to the −16 and −18 C for roots from 0 to 15 cm deep and −13 and −12.5 C for roots from 15 to 30 cm deep. The GR50 and LT50 temperature after 2 yr of treatment was reduced to 0 C by two cultivations in fall or picloram plus 2,4-D. Carbohydrate content was not a good indicator of winterhardiness. Cultivation reduced the leafy spurge root system faster than herbicide treatment especially at the 15- to 30-cm depth.

Purple nutsedge (Cyperus rotundus L.) control with (2,4-dichlorophenoxy)acetic acid (2,4-D) and 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) was increased in greenhouse and growth chamber studies by application of these herbicides in an undiluted isoparaffinic oil carrier rather than water. Two applications of 2,4-D at 2.2 kg/ha in the oil carrier inhibited tuber and shoot production and reduced the number of viable tubers present, but two applications of linuron at 0.6 or 2.2 kg/ha in the oil inhibited only shoot production from repotted tubers. Studies with labeled 2,4-D showed an increase in both rate and quantity of penetration of this herbicide into purple nutsedge when applied in oil rather than water. Labeled linuron was applied to purple nutsedge and to beans (Phaseolus vulgaris L. ‘Improved Tendergreen’) and also showed an increase in penetration with the oil rather than water. Translocation out of treated leaves was not increased for either 2,4-D or linuron by application in the oil carrier.

Fenac [(2,3,6-trichlorophenyl)acetic acid] and its sodium salt were incorporated in polyethylene matrices under varied conditions to afford a series of herbicide-polyethylene formulations. Diffusion within the matrix determined the rates at which the herbicides were released from the formulations into water. Release rates of the herbicides were altered significantly if (a) the formulation curing conditions were varied, (b) the initial amount of herbicide in the matrix was varied, (c) the solubility of the herbicide was changed, or (d) if an additive was used. The results indicate that herbicide diffuses from the matrix through water-filled cracks and capillary channels.

Nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene] are 2 diphenylether herbicides which are phytoactive on common purslane (Portulaca oleracea L.). The stomata of common purslane are normally open during the day and closed at night. Nitrofen and oxyfluorfen applications to common purslane leaves cause the stomata to close which is a result of increased membrane permeability. A slight increase (0.6 C) in leaf temperature and a decrease (2 bars) in the apparent water potential was evident after 6 h. Membrane degradation caused some cells to collapse and caused the leaves to appear pitted. Ethylene synthesis was stimulated (0.9 ppmv) causing a loss of plastids from the bundle sheath cells and finally leaf abscission, 8 to 24 h after treatment.