Under light grazing, the reproductive capacity of wild carrot (Daucus carota L.) was reduced, but on pastures under heavy grazing, cattle prevented regrowth and seed production of flowering plants. To simulate the effects of cattle grazing, seedlings and flowering plants were clipped at different times during the summer on natural and experimental plots on different soil textures. Plants on fine textured soils were larger in size, regenerated more rapidly, and had a higher survival rate after clipping. The most efficient time for control by a clipping treatment, determined on the basis of prevention of seed production and mortality of plants, was in the latter part of August.

The magnitude of the problem created by wild oats (Avena fatua L.) is one that warrants intensive study not only from the practical but also from the biological standpoint. A knowledge of the entities or taxa present in the wild oats population is a logical beginning to more extensive phases of investigation. The purpose of this paper is to report taxonomic and genetics studies carried out on the wild oats population of the Prairie Provinces. It is hoped that the information obtained may be of use to other investigators interested in the biology of wild oats.

No effect was shown of 3-amino-l,2,4-triazole (amitrole) upon the incorporation of alanine or histidine into soluble protein in bean (Phaseolus vulgaris L.) hypocotyls grown in darkness. The metabolic derivative of amitrole, β-(3-amino-1,2,4-triazolyl-l-)α-ala-nine (hereinafter referred to as 3-ATAL), also had no effect upon histidine incorporation. Serine incorporation was increased 56% in the presence of amitrole, but this may result from a reduction of endogenous serine pools. No evidence indicates a general disruption of protein synthesis. Activity from amitrole-5-14C was readily incorporated into bean protein, but hydrolysis revealed no 3-ATAL. Most of the activity was recovered as amitrole. Amitrole in the presence of riboflavin and light attacked bovine serum albumin, probably by free radical formation. Hydrolysis of bovine serum albumin revealed mainly amitrole. Apparently, the entry of amitrole into bean protein is by free radical formation.

The small size and slow growth of legume seedlings make them susceptible to damage or elimination by weed competition. Various methods of establishment such as sowing in late summer, sowing with a small grain companion crop, or mowing have not been entirely successful. The increased use of weed-controlling chemicals has awakened considerable interest in the establishment of legumes with the aid of herbicides. Research workers are in agreement that 4-(2,4-DB) [4-(2,4-dichlorophenoxy)butyric acid] can be safely used to control broad-leaved weeds in legumes. However, there is some difference of opinion as to the rates of various formulations that can be safely used.

Four forage grasses and five forage legumes were grown in greenhouse cultures containing 0.12, 0.25, 0.50, and 1.0 ppm of atrazine and of simazine in the soil. They were also planted April 2 and 9 in field plots which had been treated the previous spring with 0, 1, 2, and 4 lb/A of the same herbicides. In the greenhouse, atrazine produced more injury to the plants than simazine. In the field, residual simazine produced more marked injury. Tall fescue and alfalfa were the most tolerant crops. Timothy was the most susceptible. Red clover, Korean lespedeza, ladino clover, sweet-clover, orchardgrass, and bromegrass were intermediate.

Some parasitic plants are major pests in agriculture, but how this might be affected by climate change remains largely unknown. In this study, we assessed this question for five generalist holoparasitic Cuscuta species (smoothseed alfalfa dodder [Cuscuta approximata Bab.], alfalfa dodder [Cuscuta europaea L.], soybean dodder [Cuscuta chinensis C. Wright], Peruvian dodder [Cuscuta australis R. Br.], and Japanese dodder [Cuscuta japonica Choisy]) and two of their main Leguminosae host crop species (soybean [Glycine max (L.) Merr.] and alfalfa [Medicago sativa L.]. For each of the five Cuscuta species and the two crop species, we ran MaxEnt models, using climatic and soil variables to predict their potential current distributions and potential future distributions for 2070. We ran species distribution models for all seven species for multiple climate change scenarios, and tested for changes in the overlap of suitable ranges of each crop with the five parasites. We found that annual mean temperature and isothermality are the main bioclimatic factors determining the suitable habitats of the Cuscuta species and their hosts. For both host species, the marginally to optimally suitable area will increase by 2070 for all four representative concentration pathway scenarios. For most of the Cuscuta species, the marginally to optimally suitable area will also increase. While the suitable areas for both the hosts and the parasites will increase overall, Schoener’s D, indicating the relative overlap in suitable area, will change only marginally. However, the absolute area of potential niche overlap may increase up to 6-fold by 2070. Overall, our results indicate that larger parts of the globe will become suitable for both host species, but that they could also suffer from Cuscuta parasitism in larger parts of their suitable ranges.

The presence of a soil seedbank facilitates the persistence of annual weed species in arable fields. Soil weed seedbank is replenished by many sources, but the largest one is the seeds produced by uncontrolled late-season weed escapes. The estimation of weed seed production potential from late-season escapes may allow farmers to make appropriate management decisions to minimize seedbank replenishment. The objective of this research was to evaluate the feasibility of using unmanned aerial vehicle–based RGB and multispectral imagery for estimating seed rain potential in late-season weed escapes in crop fields. Three case studies were used to capture images of weed escapes before crop harvest: common waterhemp [Amaranthus tuberculatus (Moq.) Sauer] in soybean [Glycine max (L.) Merr.], Palmer amaranth [Amaranthus palmeri (S.) Watson] in cotton (Gossypium hirsutum L.), and johnsongrass [Sorghum halepense (L.) Pers.] in soybean. Randomly selected quadrats with different density gradients of weed escapes were sampled at the time of crop maturity. High-resolution RGB and multispectral images of the experimental area were collected using drones immediately before ground sample collection. Normalized difference vegetation index (NDVI), excess green index (ExG), and canopy volume estimates derived from canopy height models were used to obtain weed biological measurements (biomass and seed production). Among the indices investigated, NDVI and ExG had very strong correlations (0.71 to 0.97) with weed biomass. No specific remote sensing variable was ideal across the three cases examined here, suggesting that a generalized remote sensing approach may not offer robust estimations and case-specific applications are imperative. Nonetheless, drone imagery is a powerful tool for estimating seed production from uncontrolled weed escapes and assisting with management decision making.

Herbicide options for selective control of monocot weeds in rice (Oryza sativa L.) have historically been limited to a few modes of action such as inhibitors of acetolactate synthase (e.g., penoxsulam, imazamox), photosystem II (e.g., propanil), and acetyl-CoA carboxylase (e.g., cyhalofop). Florpyrauxifen-benzyl (Rinskor™) is a synthetic auxin molecule introduced to the U.S. rice herbicide market in 2018, providing broad-spectrum weed control (monocots and dicots), including hard-to-control species such as barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], along with postemergence rice selectivity at very low use rates. Within the year of commercialization, field agronomists and academics identified E. crus-galli escapes in some areas where florpyrauxifen-benzyl had been sprayed. Further evaluation under controlled environments confirmed that those plants were able to survive florpyrauxifen-benzyl application at the label rate. Here, we identify the mechanism of resistance to florpyrauxifen-benzyl and penoxsulam in two E. crus-galli populations from Arkansas (AR-27) and Missouri (MO-18). Using high-resolution mass spectrometry, we compared the two resistant biotypes with known susceptible plants regarding their ability to metabolize florpyrauxifen-benzyl, florpyrauxifen-acid, and penoxsulam in planta. We discovered that the resistant plants share a common resistance mechanism to florpyrauxifen-benzyl and penoxsulam, involving hydrolysis of a methoxy group (likely mediated by a cytochrome P450 monooxygenase) followed by glucose conjugation. Given that penoxsulam has been widely used in rice fields for the past decade, these data suggest that some populations of E. crus-galli may have evolved resistance before the commercialization of florpyrauxifen-benzyl.

Herbicidal applications to mesquite in Arizona (17), New Mexico (21), and Texas (5) indicate that the low-volatile esters of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) are usually more effective than amine salt formulations, but there have been instances where the reverse was true. This inconsistency has occurred only in isolated cases, but was of interest in that factors which affect differential susceptibility to the ester and the amine formulations are important and should be more fully understood. The purpose of this study was to determine whether mesquite has a different period of susceptibility to the ester than to the amine. Various biological and meteorological factors were also determined to test their relation to mesquite susceptibility.

Growth regulating type herbicides have been found to be effective when applied in low volume sprays. Uniformity of spray application has become a paramount requirement because of the high concentration of the spray solution. Volumes of one to ten gallons of solution per acre are not uncommon. Low volume application requires good design, construction, and operation of equipment. Air movement, temperature, and humidity also influence the spray deposition.

Corn, cotton, peanuts, and soybeans in various rotations received six separate herbicidal treatments in a 5-year rotation from 1959 through 1963. Several of the combination treatments were highly effective in controlling witchweed (Striga spp.). Land heavily infested with witchweed required 3 to 4 years of herbicidal treatments before the competition of witchweed was eliminated and normal corn yields were produced. The most effective treatment for the control of witchweed without crop injury was postemergence applications of ½ lb/A 2,4-dichlorophenoxyacetic acid (2,4-D) as needed in continuous corn.

At the end of the 5-year study, all plots were planted to corn, Using corn yields as a criteria, there were no differences in witchweed competition in herbicide treated plots with continuous corn and herbicide treated plots in which corn was rotated with other crops.

In agar cultures 1-naphthaleneacetic acid (NAA) reduced bud activity of quackgrass (Agropyron repens (L.) Beauv.) rhizomes, while indole-3-acetic acid (IAA) had little effect. Gibberellic acid (GA) acted antagonistically with NAA. Maleic hydrazide (MH) had less effect on bud activity than isopropyl N-phenylcarbamate (IPC), 2,3,6-trichlorophenylacetic acid (fenac), or phenoxy compounds at high rates. GA or its active metabolite was translocated throughout the plant. 2,3,5-Triiodobenzoic acid stimulated bud activity on intact rhizomes.

Ethiopian mustard (Brassica carinata A. Braun) is a biofuel crop recently introduced in the southeastern United States. For this crop to be successful, integrated weed management strategies that complement its rotation with summer cash crops must be developed. The objectives of this research were to evaluate the effect of previous season summer crops on winter weed emergence patterns during Ethiopian mustard growing season and to assess the impact of planting Ethiopian mustard on the emergence patterns of summer weed species. Gompertz models were fit to winter and summer weed emergence patterns. All models represented more than 80% of the variation, with root mean-square error values less than 0.20. The emergence pattern for winter weed species was best described using growing degree-day accumulation, and this model can be utilized for implementing weed control strategies at the critical Ethiopian mustard growth stages. The results also showed that summer weeds can emerge during the winter in northern Florida but do not survive frost damage, which might create off-season seedbank reductions before the summer crop growing season.

Lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and white mustard (Brassica hirta L.) were highly susceptible to 2-methyl-4-chlorophenoxyacetic acid (MCPA) regardless of the pretreatment light exposure to which they were subjected. These broadleaved weeds were slightly more susceptible to MCPA applied after a prolonged period of darkness. Neither total carbohydrate, reducing sugar, protein, nor amino acid contents at the time of spraying were associated with the susceptibility of mustard plants to MCPA. Floral bud development on Canada thistle was greatly reduced by MCPA applied at any time of the day to plants 9 and 12 inches tall and was prevented on plants 3 and 6 inches tall. The susceptibility of broadleaved annual weeds and Canada thistle to MCPA was not affected by variations in temperature and humidity at time of spraying.

Downy brome (Bromus tectorum L.), and rattail fescue (Festuca myuros L.) were controlled by 2-methoxy-3,6-dichlorobenzoic acid (dicamba) and 2,4-bis(isoproplyamino)-6-methylmercapto-s-triazine (prometryne). Both herbicides gave 70–100% control when applied soon after the first postharvest irrigation. Dicamba was somewhat less effective when applied before this irrigation. Neither herbicide reduced seed yields when applied before or immediately after the first postharvest irrigation, but both herbicides caused some significant seed yield reductions when treatments were delayed until after considerable crop regrowth had occurred.

Tillage plus trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and prometryn [2,4-bis (isopropylamino)-6-(methylthio)-s-triazine] and tillage plus trifluralin and fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] applied as soil-incorporated preplanting treatments were compared with tillage alone in cotton (Gossypium hirsutum L.) grown in 51-cm and 102-cm rows on fine sandy loam soil. Over 3 yr, cotton grown in 51-cm rows yielded 15% more than cotton grown in 102-cm rows. Final cotton emergence was not altered by weed-control treatment or by planting pattern. Weed-control treatments with herbicides provided essentially complete, season-long control of grass and broadleaf weeds. At cotton layby, more weeds were in no-herbicide plots with 51-cm rows compared with 102-cm rows, but at cotton harvest numbers of weeds in both row patterns were essentially equal.

The degradation kinetics of propylene glycol butyl ether (hereafter referred to as PGBE) ester of 2-(2,4,5-trichlorophenoxy) propionic acid (silvex) and the persistence of silvex in water and sediment were studied under impounded conditions. PGBE ester of silvex was applied to the surface of three ponds at the rate of 9 kg/ha/A. Water and sediment samples were collected at 4, 12, 24, and 48 hr after treatment and were extracted for PGBE ester of silvex immediately after collection. The concentrations of PGBE ester of silvex and silvex present in the water and sediment samples were determined by gas chromatography. Physico-chemical and mineralogical characteristics of the sediment samples collected prior to treatment were determined. The hydrolysis of PGBE ester of silvex to silvex obeyed first order reaction kinetics, the specific reaction rate constants for the three ponds being 0.09 hr−1, 0.10 hr−1, and 0.14 hr−1. Fifty percent hydrolysis of PGBE ester of silvex occurred in 5 to 8 hr, 90% hydrolysis occurred in 16 to 24 hr, and 99% hydrolysis occurred in 33 to 49 hr. The concentration of silvex in water initially increased, but decreased to zero by the end of 3 weeks. Adsorption of both the PGBE ester of silvex and silvex appeared to occur on the sediment; essentially complete disappearance of both occurred by the fifth week following treatment. Under laboratory conditions, silvex adsorption by the sediments conformed to the Freundlich adsorption equation.

Several herbicides were applied to drainage ditchbanks in sugarcane (Saccharum officinarum L.) to control johnsongrass (Sorghum halepense (L.) Pers.) from rhizomes and seed. Five post-emergence applications of monosodium methanearsonate (MSMA) at 3.6 lb/A or 2,2-dichloropropionic acid (dalapon) at 7.4 lb/A controlled rhizome johnsongrass as effectively as 600 lb/A of sodium chlorate, the standard treatment. Johnsongrass seedlings infested ditchbanks 1 year after applying sodium chlorate. But preemergence treatments with mixtures of (2,3,6-trichlorophenyl)acetic acid (fenac), 5-bromo-3-sec-butyl-6-methyluracil (bromacil), or trichloroacetic acid (TCA) with MSMA, or postemergence applications of MSMA, dalapon, and sodium chlorate controlled these seedlings. Bermudagrass (Cynodon dactylon (L.) Pers.) rapidly vegetated ditchbanks treated with MSMA, but other herbicide treatments suppressed vegetation with desirable species to the point where erosion could become a problem.

Field experiments were established to determine the dose and timing of DPX-A7881 applied postemergence for control of weeds in winter rapeseed. Wild mustard and shepherdspurse were effectively controlled by DPX-A7881. Control of these weeds by DPX-A7881 was dependent upon growth stage. The later the growth stage at time of herbicide application the poorer the control. Fall applications of DPX-A7881 provided greater control of wild mustard and shepherdspurse seedlings compared to spring applications. The 0.010 kg ai ha-1 dose was as effective in controlling susceptible weed species as 0.030 kg ai ha-1. Control of common lambsquarters and redroot pigweed by DPX-A7881 was poor. Regardless of timing or amount of herbicide applied, DPX-A7881 did not significantly reduce dry weights of either barnyardgrass or green foxtail. Doses of DPX-A7881 ranging from 0.010 to 0.030 kg ai ha-1 did not injure or adversely affect winter survival of rapeseed seedlings. Rapeseed yield and seed quality were not affected by DPX-A7881 applied postemergence.

The influence of soil moisture on the competitive relationship between yellow nutsedge and cotton was determined in an additive competition experiment where main plots were irrigation regimes and subplots were nutsedge densities. Increasing nutsedge density caused a significant linear decrease in seed cotton yield. Regression analysis indicated that approximately 9 (1993), 12 (1994), or 37 (1995) kg ha−1 of seed cotton yield was lost for each additional initial nutsedge tuber per meter of crop row. Both postharvest stem biomass, an indicator of total aboveground biomass, and seed cotton yield increased with increasing soil moisture in all 3 yr of the study. Increasing yellow nutsedge density reduced midseason cotton height in both wet and dry soil moisture regimes but only slightly reduced postharvest stem biomass in the wet treatment in 1995. There was an interaction between soil moisture regime and yellow nutsedge density only with respect to midseason cotton leaf water potentials. Soil moisture availability did not interact with the effect of yellow nutsedge density with respect to end of the season stem biomass or seed cotton yield.