The phytotoxicities of three phenylurea herbicides applied annually to cotton at rates used for selective weed control were studied in irrigated soils of the southwestern United States. Yields of seed cotton were generally not affected by annual applications of 3-(p-chlorophenyl-1)-1,1-dimethylurea (monuron) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). Annual applications of 3-phenyl-1,1-dimethylurea (fenuron) often reduced seed cotton yields. Mild chlorosis of foliage of cotton seedlings was occasionally observed when monuron was used annually. Although diuron affected the growth of oats and barley 6 to 12 months after application, it caused no adverse effect on cotton seedlings. Monuron residues affected barley and oats more severely than did diuron residues. Accumulation of diuron and monuron from annual applications at rates used for selective weed control in cotton appears unlikely.

In greenhouse tests, temperature, humidity, drought stress, and concentration of surfactant influenced the foliar activity of spray mixtures containing a dodecyl ether of polyethylene glycol (Surfactant WK) and 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (diuron) or 3-(3,4-dichlorophenyl)-1-methoxy-1-methyl urea (linuron). In comparisons with other commonly used surfactants, Surfactant WK gave a superior performance when used in conjunction with diuron, linuron, and 5-bromo-3-sec-butyl-6-methyl uracil (bromacil). Increased water solubility of these herbicides in the presence of surfactant is only one factor among many involved in the enhanced activity of such combinations. Surfactant WK facilitated the deposition of high concentrations of linuron on leaf surfaces of Johnsongrass. Once a gradient was established, subsequent rapid movement of the herbicide into the leaf was noted.

Structural characteristics of surfactants and a herbicide were incorporated in the same molecule by forming long-chain alkylamine salts of 2,4-dichlorophenoxyacetic acid [2,4-D]. In water sprays, all of the 2,4-D salts showed surface activities characteristic of surfactants. The application rate of 2,4-D was held constant at 1/16 lb ae/A; salt concentration was varied by varying spray volume. Seventeen salts were herbicidally active on soybeans at a high concentration (1/16 lb ae in 10 gpa of spray) and a few were also active at a lower concentration (1/16 lb ae in 40 gpa). The remaining thirteen salts were relatively inactive in water. Structural features associated with water-active salts of 2,4-D were those which contribute to hydrophilic characteristics of surfactants. Lipophilic structural features contributed to inactivity in water.

The 2,4-D toxicity of fourteen water-active and water-inactive salts of 2,4-D was maximally and equally elicited in one or more of six water and oil spray systems. Differential activities of the salts permitted their classification into six distinct classes—three hydrophilic and three lipophilic. No one of five solution properties—surface tension, interfacial tension, turbidity, specific conductivity, or pH—could be correlated with herbicidal toxicity of a spray. However, a combination of three properties—interfacial tension, turbidity, and specific conductivity—provided some indication of the relative hydrophilic or lipophilic character of a salt and of the 2,4-D toxicity in different sprays. Data suggested that herbicides move into plants by two distinct pathways—one hydrophilic and the other lipophilic.

The discovery of the herbicidal properties of 2,4–dichlorophenoxyacetic acid (2, 4–D) created a great impetus in the search for new herbicides. As the herbicidal properties of 2,4–D became more generally known, it was obvious that many closely related chemicals and other organic compounds should be evaluated for their herbicidal properties.

Glyphosate-resistant (GR) horseweed has become an especially problematic weed in different crop production systems across the United States and the world. In this field study, we used a nondestructive measurement system to analyze the pollen production, deposition, and dispersion of a Tennessee glyphosate resistant (TNR) horseweed biotype in Knoxville, TN during the 2013 pollination season. We observed that the pollination season of TNR horseweed lasted about 2 mo (54 d). About 78.93% of horseweed pollen was released between 9:00 A.M. and 7:00 P.M. during each sampling day and the release peak was at about 1:30 P.M. The seasonal release of pollen grains was estimated to be 5.11 million grains plant−1. The release rate data indicated that the integrated horizontal flux density and deposition flux density contributed to 78.17% and 21.83% of the release rate, respectively. We also found that pollen concentration decreased with distance from the source field; the average pollen concentration decreased to 50.69% at a distance of 16 m from the source plot. This is the first result of a systematic, direct examination of the release rate (emission and deposition), release pattern (daily and seasonal), and dispersion pattern of GR horseweed pollen.

In laboratory experiments, the effects of the herbicides HOE-39866 [ammonium (3-amino-3-carboxypropyl)-methylphosphinate] and SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate) on the incorporation of NaH14CO3, [14C]-leucine, [14C]-uracil, and [14C]-acetate into enzymatically isolated soybean [Glycine max (L.) Merr. ‘Essex’] cells were evaluated to assess the activity of these herbicides on CO2 fixation, protein, ribonucleic acid (RNA), and lipid syntheses. At low concentrations neither compound exhibited rapid or distinct inhibitions of any process as might be expected in the case of inhibition of a primary target site. Photosynthesis was the process least affected. At equimolar concentrations, protein and RNA syntheses were more sensitive to HOE-39866 than to SC-0224 while the reverse occurred in lipid synthesis. Protein synthesis appears to be a possible target site that may be involved in the herbicidal action of these two compounds.

The response of four growth stages of Setaria glauca (L.) Beauv. (yellow foxtail), Eleusine indica (L.) Gaertn. (goosegrass), and Dactyloctenium aegyptium (L.) Richt (crowfootgrass) to dimethylarsinic acid (cacodylic acid) applied at rates of 0.25, 0.5, and 1.0 lb/A was studied.

The four growth stages for chemical treatments were generally: (a) early tillering, (b) late tillering, (c) boot, and (d) post-heading. Seed production was reduced by as much as 96% in yellow foxtail, 80% in goosegrass, and 37% in crowfootgrass. Application of the chemical at the “boot” stage was most effective although earlier applications also were effective. Inflorescences often were malformed. Other growth effects suggested a growth regulator type activity.

Absorption and translocation characteristics of both root- and shoot-applied mefluidide N-[2,4-dimethyl-5-[[(trifluoromethyl) sulfonyl] amino] phenyl] acetamide were determined in soybean [Glycine max (L.) Merr. ‘Wells’], common cocklebur (Xanthium pensylvanicum Wallr.), and giant foxtail (Setaria faberi Herrm.). Absorption of 14C-mefluidide was greater through the foliage than the roots of all plant species. Rate of leaf absorption and translocation of 14C initially was greater in giant foxtail than in either soybean or common cocklebur, but these processes failed to increase greatly with time in giant foxtail. Absorption and translocation increased over time in soybean and common cocklebur. Soybean absorbed slightly greater quantities of 14C-mefluidide than common cocklebur, but by 8 days after labeling, common cocklebur translocated approximately 47% more radio-label out of the treated leaf than soybean. The foliar-applied 14C-label appeared to move in the phloem along with the assimilate stream in all species, mainly to areas of high metabolic activity. 14C was associated with the root systems and/or nutrient solutions of soybean and giant foxtail, but not of common cocklebur. Exuded material chromatographed as mefluidide. Movement of 14C-label in all root-treated plants appeared to be confined within the xylem with older tissue containing greater amounts of 14C than the younger tissue. Differences in selectivity between crop and weed species may be partially due to differential mefluidide absorption, translocation, and subsequent concentration in certain plant tissues.

Twenty accessions within 11 perennial Glycine species plus soybean were tested for tolerance to 2,4-D. Soybean was severely injured by 2,4-D, but 13 of the Glycine accessions had 15% or less injury 4 weeks after 2,4-D application. Greatest 2,4-D tolerance occurred with accessions of G. latifolia and G. microphylla. There was no difference among tolerant accessions of G. latifolia and G. microphylla and susceptible accessions of G. canescens in recovery or absorption of 14C-2,4-D 1, 3, 7, or 14 days after treatment (DAT). Distribution of 14C from 14C-2,4-D in various plant parts was similar among accessions. Metabolism of 2,4-D in the tolerant accessions (81 to 89% 1 DAT) was higher and more rapid than in susceptible accessions (approximately 50%, 1 DAT). The same five metabolites plus parent 2,4-D were extracted from the treated leaf of all accessions at all sampling dates. However, relative distribution between metabolites differed between tolerant and susceptible accessions. More rapid metabolism of 2,4-D in treated leaves of tolerant Glycine accessions can explain differential 2,4-D responses.

Ammannia multiflora Roxb. is a dominant broadleaf weed that is a serious problem in southern China rice fields, and acetolactate synthase (ALS)-inhibiting herbicides have been used for its control for more than 20 years. Excessive reliance on ALS-inhibiting herbicides has led to herbicide resistance in A. multiflora. In this study, 10 A. multiflora populations from the Jiangsu Province of China were collected, and the resistance levels and target site–resistance mechanisms to ALS-inhibiting herbicides bensulfuron-methyl and penoxsulam were investigated. The dose–response assays showed that eight populations evolved resistance to bensulfuron-methyl (9.1- to 90.9-fold) and penoxsulam (5.0- to 103.1-fold). Amplification of ALS genes indicated that there were three ALS genes (AmALS1, AmALS2, and AmALS3) in A. multiflora. Sequence analysis revealed amino acid mutations at Pro-197 in either AmALS1 (Pro-197-Ala, Pro-197-Ser, and Pro-197-His) or AmALS2 (Pro-197-Ser and Pro-197-Arg) in resistant populations, and no mutations were found in AmALS3. Moreover, two independent mutations (Pro-197-Ala in AmALS1 and Pro-197-Ser in AmALS2 or Pro-197-Ala in AmALS1 and Pro-197-Arg in AmALS2) coexisted in two resistant populations, respectively. In addition, the auxin mimic herbicides MCPA and florpyrauxifen-benzyl, the photosystem II inhibitor bentazon, and the protoporphyrinogen oxidase inhibitor carfentrazone-ethyl can effectively control the resistant A. multiflora populations. Our study demonstrates the wide prevalence of ALS inhibitor–resistant A. multiflora populations in Jiangsu Province and the diversity of Pro-197 mutations in ALS genes and provides alternative herbicide options for controlling resistant A. multiflora populations.

Dispersal mechanisms of the alien plant species buffalobur during its invasion of cold desert areas in Xinjiang, northwestern China, were investigated. Seeds and fruits were readily moved by water in irrigation canals in the transition zone between natural desert and a farmed oasis. Maximum flotation time in moving canal water was ∼ 4 h for seeds and > 48 h for fruits, and water moved fruits 279 m in 10 min. Also, 100% of the seeds remained viable during 8 wk of flooding in the laboratory. Mean dispersal distance was 3.4 m by wind-driven rolling of detached plants and 0.5 m by ants. Retention time for 50% of fruits on wool of live sheep was ∼ 4 h. Seeds and fruits that fall into the canals (which are without irrigation water from mid-October to April) are cold-stratified during winter, and then during canal cleaning in spring soil and germinable seeds are deposited along the sides of the canals. The disturbed soil is a highly favorable site for plants to grow. The local spread of buffalobur away from the sides of canals is facilitated by sheep, wind, and ants. We conclude that water in the irrigation canals is the primary dispersal agent for seeds of this invasive species and that the best way to control its spread is to prevent plants growing beside the canals from setting seed.

Mixed stands of big sagebrush (Artemisia tridentata Nutt.) and green rabbitbrush (Chrysothamnus viscidiflorus (Hook.) Nutt.) were sprayed with butyl ester of 2,4-dichlorophenoxyacetic acid (2,4-D) at 1, 2, 3, and 4 lb/A on six phenological dates in 1956, 1957, and 1958 at the Squaw Butte Experiment Station, Burns, Oregon. Data on soil moisture; soil temperature; growth development of herbaceous species; twig elongation of big sagebrush and green rabbitbrush; dry-matter, crude-protein, and total-carbohydrate contents of green rabbitbrush herbage; and crude-protein and total-carbohydrate contents of big sagebrush and green rabbitbrush roots were obtained at weekly to biweekly intervals in all 3 years to evaluate the ecological and physiological conditions that might indicate seasonal patterns of susceptibility to 2,4-D. Big sagebrush, a non-deciduous, non-sprouting plant, was easily killed with 2,4-D at 2 lb/A when soil temperatures and moisture contents were satisfactory for vigorous growth. The development of abundant leaf area on green rabbitbrush, a deciduous, sprouting plant, was important for spray interception and a photosynthetic rate sufficient to promote carbohydrate accumulation. Green rabbitbrush was controlled about 80% with a single application of 2,4-D butyl ester at 3 lb/A after the new twigs were 3 inches long and while soil moisture contents were sufficient for active growth. Differences in susceptibility between the two species are compared with morphological, phenological, and physiological differences, and seasonal patterns of susceptibility are further compared with environmental conditions.

Patterns of absorption and distribution of dalapon (2,2–dichloropropionic acid) were determined by radioautography and counting. Dalapon was absorbed through the cuticle and through the large open pores of hypostomatous leaves. Stomata were clearly the most expeditious routes of entry, but results were erratic when no surfactant was included. An anionic surfactant, sodium dioctylsulfosuccinate, enhanced both (a) cuticular and (b) stomatal plus cuticular penetration 3- to 4-fold during a 2-hr. absorption period. Studies confirmed the view that dalapon is translocated to regions of high metabolic activity and/or storage in association with and dependent upon the movement of food materials. Dalapon did not move appreciably out of albino leaves or green leaves previously depleted of food reserves, but was transported readily out of normal leaves in the light when a surfactant was used to enhance cuticular penetration.

Long-term compensation points in waterstargrass (Heteranthera dubia (Jacq.) Mac M), coontail (Ceratophyllum demersum L.), and duckweed (Lemna minor L.) were near 2–3% full sunlight during a 28-day period. Fresh weight of H. dubia increased as temperature increased from 15 to 30 C and as light intensity increased from 110 to 1000 foot-candles. Fresh weight of C. demersum increased as temperature increased above 20 C and as light intensity increased from 120 to 550 foot-candles. The L. minor strain used in this experiment was not temperature-dependent and increased in fresh weight and frond number at 25 and 30 C as light intensity increased from 77 to 550 foot-candles.

Three applications/yr of glyphosate [N-(phosphonomethyl)glycine] with a ropewick applicator (RWA), a roller applicator (RA), and a recirculating sprayer (RCS) were compared to hoeing and cultivation for the control of johnsongrass [Sorghum halepense (L.) Pers. ♯3 SORHA] in cotton (Gossypium hirsutum L. ‘Acala SJ-2′) in six field experiments from 1979 to 1981. Averaged over the 3 yr and dates of application, plots treated with glyphosate contained 78% fewer live johnsongrass shoots (15/m2) than cultivated-control plots (68/m2). Although applications of glyphosate with the RWA and RA improved or tended to improve yields of cotton, only plots treated with the RWA yielded significantly more seed cotton than cultivated control plots in all years. However, yields of plots treated with the RWA still averaged 38% less than hoed plots. Plots treated with the RA produced significantly more cotton than cultivated-control plots only in 1981.

Reports of unacceptable shattercane (Sorghum bicolor) control with acetolactate synthase (ALS)-inhibiting herbicides prompted the investigation of 29 fields in central and south-central Nebraska for ALS-resistant (ALSr) shattercane. These fields were located in three distinct geographical areas designated C, G, and P. Shattercane from 13 fields spanning all three areas was resistant to 80 g ai ha−1 (2 X field rate) primisulfuron. Accessions C and G were more resistant than accession P to primisulfuron and nicosulfuron. Accessions C and G were susceptible to imazethapyr, whereas accession P was resistant. The ALS resistance was associated with alterations in the ALS enzyme. Primisulfuron I50 values for ALS from ROX (forage sorghum), C, G, and P were 7, 8,510, 8,870, and 714 nM, respectively; nicosulfuron I50 values were 647, 4,110, 4,070, and 1,460 nM, respectively; and imazethapyr I50 values were 5,440, 13,100, 11,800, and 51,700 nM, respectively. Based on cross-resistance and enzyme sensitivities, at least two biotypes are represented in the three accessions of ALSr shattercane. Shattercane individuals from accessions C, G, and P were intercrossed to determine if the ALSr genes in each of the accessions were at independent loci. All the F2 populations were resistant to 80 g ai ha−1 primisulfuron, suggesting that the ALSr alleles in the three accessions are at the same locus or possibly linked loci. When the C, G, and P accessions were crossed with the wild type (WT), comparisons between the F1, susceptible, and resistant populations showed that primisulfuron resistance was expressed as a dominant, partially dominant, and additive trait for the C, G, and P accessions, respectively. The differences in ALSr allelic interactions indicate that primisulfuron resistance developed independently in each of the three accessions.

The residual effect of three cotton (Gossypium hirsutum L.) herbicide programs, including the use of no herbicides, a minimum program consisting of fluometuron {N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl] urea} and MSMA (monosodium salt of methylarsonic acid), and an intensive program consisting of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine], fluometuron, MSMA, and linuron [N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea], were evaluated from 1976 to 1982. Herbicide injury to wheat (Triticum aestivum L.) and hairy vetch (Vicia villosa Roth.) on three soils showed carryover effects in the following sequence: Sharkey silty clay > Dundee silt loam > Loring silt loam. The intensive program was the most injurious on the Sharkey silty clay. The effects of the two herbicide programs were nearly equal on the Dundee and Loring silt loams. Possible replacement crops for cotton, such as grain sorghum [Sorghum bicolor (L.) Moench.] and corn (Zea mays L.) suffered the least damage from carryover; rice (Oryza sativa L.), soybeans [Glycine max (L.) Merr.] and cucumber (Cucumis sativis L.) suffered severe damage. Greenhouse bioassays generally confirmed field results, and fluometuron appeared to be the major component of carryover.

Yellow nutsedge (Cyperus esculentus L. # CYPES) was treated with unlabeled and 14C-labeled glyphosate [N-(phosphonomethyl)glycine] to study the toxicity and translocation of glyphosate into parent tubers of this weed. When plants of 2 and 4 weeks of age were treated with 0.6 kg ai/ha of glyphosate, fewer parent tubers from treated plants resprouted (14 and 32%) than tubers from control plants (73 and 59%, respectively) of equal age. Also, fewer tubers resprouted from 2-week than from 4-week-old treated plants. The radioactivity of parent tubers from plants treated at 2 weeks of age, which exceeded that of tubers from plants of 4 and 6 weeks of age, indicated that translocation of 14C into parent tubers decreased as the treated plants increased in age. The differential amounts of 14C translocated appear to explain why applications of glyphosate were more effective in suppressing resprouting of parent tubers from 2-week than 4-week-old plants.

Crownbeard [Verbesina encelioides (Cav.) Benth. & Hook. f. ex. A. Gray # VEEEN (Compositae)] exhibited rapid seedling, vegetative, and reproductive growth. Seed germination under ideal conditions was high and occurred in varying soils except in gravel. It was significantly suppressed under drought and waterlogged conditions and was maximum at 21% moisture regimes. Larger and heavier seeds which exhibited higher germination were produced by the plants growing in open and sand dune habitats. Seedling emergence was highest from surface-sown seeds and least in those sown at 2.5-cm soil depth, beyond which no emergence occurred. High phenotypic plasticity, ecological variability, phenological diversity, seed germination in varied soils and under diverse moisture regimes, quick seedling growth and subsequent establishment, coupled with versatile breeding system, contribute to the successful growth, propagation, and spread of this species in nature in India.

Weeds are a major constraint to crop production in smallholder farms in tropical Africa. The weed seedbank and annual recruitment are the main sources of weed infestation in crops. This study was carried out in Ibadan, Nigeria, to evaluate the effect on the seedbank of two types of planted fallow (alley cropping with leucaena and live mulch with tropical kudzu) and a natural bush fallow under four land-use intensities. Type of fallow was the main plot. Land-use intensities, consisting of continuous cropping of maize intercropped with cassava, 1 cropping yr of maize–cassava followed by 1, 2, and 3 yr of fallow, were the subplots. Averaged over a 3-yr period, the seedbank was 55% lower in the tropical kudzu plots and 43% lower in the leucaena plots compared with natural bush. The difference in seedbanks between plots cultivated after leucaena and natural fallow was 23%. Seed density of annual broadleaf weeds was high and dominated the seedbank of both planted and natural fallow. Overall, seeds of grasses occurred at low densities in all plots cultivated after 2 to 3 yr of fallow, whereas seeds of sedges occurred more in continuously cultivated plots and plots cultivated after 1 yr of fallow in all the fallow types. Seed density of perennial broadleaf weeds increased as land-use intensity decreased. Live mulch with tropical kudzu, especially when combined with 2 to 3 yr of fallow, lowered the seedbank more than the leucaena and traditional bush fallow systems.