Experiments were conducted to determine the effect of triglycerides, free fatty acids (FFA), and fatty acid methyl esters (FAME) on the foliar absorption, translocation, and phytotoxicity of quizalofop. Absorption, translocation, and phytotoxicity of quizalofop in oats were greater when quizalofop was applied with FFA or FAME than with their respective triglycerides. Triglycerides and FFA generally enhanced quizalofop absorption and translocation more when they contained unsaturated than saturated fatty acids. Methylation of the fatty acids reduced differences among fatty acids, but methyl stearate and methyl linolenate enhanced absorption of quizalofop less than the other FAME for oats and yellow foxtail. Quizalofop absorption and phytotoxicity to oats were greater when applied with sunflower oil, sunflower oil FFA, and sunflower oil FAME than with the corresponding linseed oil derivatives. Emulsifier generally reduced differences between linseed oil and sunflower oil derivatives in their enhancement of absorption, translocation, and phytotoxicity of quizalofop.

Manure applied to cropland may serve as a source of weed introduction and dispersal. In 36 manure samples from 20 farms, apparently-viable seeds from 13 grasses and 35 broadleaf plants were found. Common lambsquarters was on more than half the farms, yellow foxtail on 35%, common chickweed and dandelion on 30%, and wild mustard, redroot pigweed, and barnyardgrass on 25%. Four farms had manure with no seeds at all; the remainder averaged 75 100 per 1000 kg manure. Twelve milking-cow and heifer barns on six farms with large velvetleaf infestations also were sampled with an average of 133 000 seeds per 1000 kg manure. Only one barn contained velvetleaf seeds. When compared to soil seedbank numbers, manure is not an important seed source for New York farms. However, problems may arise with imported feeds heavily infested with weed seed or which contain even small numbers of noxious weeds.

Dinitroaniline herbicides are major herbicides used to control annual grass weeds in cool-season turfgrasses. At least three herbicides, benefin, pendimethalin, and trifluralin are labeled preemergence to control weeds in established turfgrass. Prodiamine could be a competitive product. Benefin at 2.2 to 3.4 kg ai/ha, pendimethalin at 1.7 to 3.4 kg ai/ha, prodiamine at 0.6 to 1.7 kg ai/ ha, and benefin plus trifluralin at 1.1 plus 0.6 to 2.3 plus 1.1 kg ai/ha effectively control many annual grass weeds, including large and smooth crabgrass, yellow and green foxtail, barnyardgrass, goosegrass, fall panicum, and annual bluegrass. Most dinitroaniline herbicides provide residual preemergence weed control for the entire growing season. In general, Kentucky bluegrass, perennial ryegrass, tall fescue, red fescue, and other cool-season turfgrasses tolerate most of these herbicides, although higher-than-normal rates of any dinitroaniline herbicide could restrict root growth and cause stand thinning in turfgrass species.

Experiments were conducted in 1982, 1983, and 1984 to determine whether herbicides can effectively control weeds in annual statice (Limonium sinuatum Mill.) without reducing the marketability of the crop. A greenhouse evaluation of chlorpropham (1-methylethyl 3-chlorophenylcarbamate), napropamide [N,N-diethyl-2-(1-naphthalenyloxy)propanamide], EPTC (S-ethyl dipropyl carbamothioate), oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyi)-1,3,4-oxadiazol-2-(3H)-one}, and trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] indicated that preemergence applications of the latter three herbicides resulted in the most effective weed control and least statice injury. Oxadiazon was the most effective for broadleaf and grass ed control in field-grown statice. Yield and quality were greatest in oxadiazon-treated plots and exceeded those of the handweeded controls. Annual statice was most sensitive to trifluralin.

Intensive surveys were conducted in 2 fields in eastern Nebraska to determine the spatial stability of common sunflower, velvetleaf, green and yellow foxtail, and hemp dogbane over 4 yr (1992 to 1995). The 1st field was planted to soybean in 1992 and corn in 1993, 1994, and 1995. The 2nd field was planted to corn in 1992 and 1994 and soybean in 1993 and 1995. Weed density was sampled prior to postemergence herbicide application at approximately 800 locations per year in each field on a regular 7 m grid. The same locations were sampled every year. Weed density at locations between the sample sites was determined by linear triangulation interpolation. Weed seedling distribution was significantly aggregated, with large weed-free areas in both fields. Common sunflower, velvetleaf, and hemp dogbane patches were very persistent in diameter in the east-west and north-south directions and in location and area over 4 yr in the 1st field. Foxtail distribution and density continuously increased in each of the 4 yr in the first field and decreased in the 2nd field. A geographic information system was used to overlay maps from each year for a species. This showed that 36% of the sampled area was continuously free of common sunflower, 62.5% was free of hemp dogbane, and 11.5% was free of velvetleaf in the 1st field, but only 1% was free of velvetleaf in the 2nd field. The persistence of broadleaf weed patches suggests that weed seedling distributions mapped in one year are good predictors of future seedling distributions. Improved and more efficient sampling methods are needed.

Velvetleaf, eastern black nightshade, wild mustard, common cocklebur, green foxtail, and yellow foxtail, grown for 4 weeks in nonaerated nutrient solution, developed satisfactorily compared to plants grown in soil. For experiments involving certain weed species grown in nutrient solution, aeration may be unnecessary.

A mathematical model describing the behavior of 14C-haloxyfop {2-[4-[(3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} and its methyl and ethoxyethyl esters on yellow foxtail [Seteria glauca (L.) Beauv. #3 SETLU] has been developed to evaluate volatility, penetration, ester transformation, metabolism, and transport of the chemical in the plant system. The effects of crop oil concentrate, temperature, structure of the molecule, and the addition of bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] to the application solution on the kinetic rate constants have been studied. Crop oil concentrate was found to dramatically increase penetration at an optimal level of approximately 0.3% (v/v). Significant increases in rate constants were observed at higher temperatures. Esters were rapidly converted to the acid in the plant with conversion of the ethoxyethyl ester being approximately twice as fast as the methyl ester. Subsequent metabolism of the acid proceeded at a moderate rate which was independent of the original ester form of the molecule. All kinetic processes were described by first-order rate constants with the exception of transport which appeared to slow a few hours after application even though acid levels in the plant were high. When bentazon was applied in combination with haloxyfop-methyl, penetration of the ester was somewhat inhibited, while transport of radioactivity associated with the molecule to other plant parts was dramatically reduced.

Spring-applied herbicides were evaluated in the field in 1982 through 1984 in western Nebraska for selective weed control in irrigated seedling alfalfa (Medicago sativa L. ‘Appollo’). Weed densities were least in plots treated preplant with benefin [N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)benzenamine] in combination with postemergence applications of 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid]. Combinations of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} with bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and fluazifop-butyl {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} with bromoxynil provided less grass control than sethoxydim or fluazifop-butyl applied alone. Annual weeds did not reduce alfalfa stand density.

Combinations of thifensulfuron with carbaryl, chlorpyrifos, malathion, and methomyl caused soybean injury that exceeded the expected injury based on effects of herbicide and synergists applied alone. Thifensulfuron-induced injury and growth reductions generally increased as insecticide rates increased from 140 to 560 g ai ha-1. TBPT and fenarimol also synergistically enhanced thifensulfuron injury in soybeans. Yellow foxtail control by thifensulfuron was enhanced slightly by all insecticides except carbaryl. Insecticides did not enhance kochia control by thifensulfuron.

Field experiments were conducted in 1982 through 1986 to evaluate the effect of six postemergence grass herbicides, clethodim, the methyl ester of diclofop, the butyl ester of fluazifop-P, the methyl ester of haloxyfop, the methyl ester of quizalofop, and sethoxydim, on 31 seedling grass species. All herbicides except diclofop controlled most of the species tested. None of the herbicides controlled rattail fescue or red fescue. Only clethodim and haloxyfop controlled annual bluegrass.

DPX-79406 was evaluated for POST annual grass weed control in both controlled environment and field experiments. In controlled environment experiments, green foxtail was most susceptible to DPX-79406; whereas yellow foxtail was least susceptible of the species evaluated. DPX-79406 at 12 g/ha completely controlled six leaf black-seeded proso millet, yellow foxtail, green foxtail, and barnyardgrass. In the field, DPX-79406 at 3.0 to 25.0 g/ha effectively controlled annual grass weeds without injury to three- to six-leaf corn. There was more variation in the effectiveness of DPX-79406 applied in the field. Early POST applications provided less weed control than the late application, especially for barnyardgrass, because of weeds emerging after application. As a result, higher doses were sometimes needed for effective control. In weed-free field trials at two sites in 1990 and 1991, corn tolerated doses up to 75 g/ha of DPX-79406 applied at the three- to six-leaf growth stage. However, doses as low as 18.8 g/ha applied at the six- to nine-leaf growth stage reduced grain yield. In 1991, corn tillering increases and height and yield reductions were related linearly to the dose of DPX-79406 applied during later growth stages. DPX-79406 should be applied early POST in order to avoid crop injury while providing effective weed control.

Greenhouse experiments were conducted to determine the effect of mixing bromoxynil with clethodim, sethoxydim, fluazifop-P, fluazifop-P plus fenoxaprop-P, or quizalofop-P on annual grass control. Antagonism with mixtures of bromoxynil and graminicides was dependent upon species and the graminicide in the mixture. Goosegrass control was unaffected by mixing bromoxynil with any graminicide. Mixing bromoxynil with clethodim, sethoxydim, fluazifop-P, or fluazifop-P plus fenoxaprop-P had no effect on control of Texas panicum, but the rate of quizalofop-P required for 80% control was increased 240%. Mixing bromoxynil with clethodim or sethoxydim had no effect on control of large crabgrass or yellow foxtail, but the rate of fluazifop-P, fluazifop-P plus fenoxaprop-P, or quizalofop-P required for 80% control was increased 180 to 290%. Antagonism of large crabgrass and yellow foxtail control with mixtures of quizalofop-P and bromoxynil increased as the rate of bromoxynil increased. Antagonism toward large crabgrass and yellow foxtail was alleviated by applying bromoxynil 6 d before the graminicides or 3 or 6 d after the graminicides.

Triazine-resistant (TR) biotypes of weeds normally susceptible (S) to triazine herbicides first were documented in Ontario in 1974. By 1988, at least nine weed species had TR biotypes, and at least 50% of the corn-producing areas were infested. Corn has been grown the longest in the southwestern Ontario, but TR weeds are only a minor problem there. Predominant agronomic practices in the southwest include crop rotation, atrazine use on 60% of corn land, use of other postemergence herbicides, interrow cultivation, little silage corn, and little manure returned to the land. Corn, particularly grain corn, is new as a large hectareage crop in eastern Ontario. However, more than 75% of corn land in that area is infested with two or more TR weed species. Predominant agronomic practices in the east include continuous corn, nearly all fields are atrazine treated, use of postemergence herbicides is not common, cultivation is rare, 25% of the corn is for silage, and manure from corn silage is returned to all cultivated land. Adequate herbicide programs exist to control TR weeds in corn and other crops. However, the spread from field to field and from farm to farm is often rapid, particularly in eastern Ontario.

The effect of nonionic surfactant, crop oil concentrate, organosilicone surfactant, methylated seed oil, and a blend of organosilicone surfactant and methylated seed oil on absorption of 14C-clethodim was evaluated in barnyardgrass (Echinochloa crus-galli). Absorption of 14C-label was greatest during the first 40 min after application when 14C-clethodim was applied with methylated seed oil or a blend of methylated seed oil and organosilicone surfactant. These adjuvants increased the rate of absorption more than crop oil concentrate, organosilicone surfactant, or nonionic surfactant. Crop oil concentrate was more effective than organosilicone or nonionic surfactant in increasing absorption, with nonionic surfactant being more effective than organosilicone surfactant. These results generally agreed with the order of increasing efficacy of clethodim on barnyardgrass as affected by adjuvants in field experiments. Another study was conducted to determine the effect of bromoxynil on absorption and translocation of 14C-clethodim in yellow foxtail (Setaria glauca). Bromoxynil reduced absorption of 14C–clethodim 4, 8, and 24 h after application and also reduced the amount of 14C-label translocated from the treated leaf. These data suggest that antagonism of clethodim control of yellow foxtail by bromoxynil observed in previous research can be attributed partially to decreased absorption and translocation of clethodim.

Spring-applied herbicides were evaluated in field studies conducted in 1985 through 1987 in western Nebraska for selective weed control in irrigated established alfalfa. Imazethapyr, norflurazon, pendimethalin, and prodiamine did not injure alfalfa but varied in their weed control spectrums. Overall weed densities were lowest in plots treated with norflurazon at 2.8 kg ai/ha and diuron at 1.8 kg/ha.

Tolerance of direct-seeded pepper under clear plastic mulch to herbicides applied pre- and post-emergence was investigated in 1991 and 1992. Weed control of herbicides applied preemergence was also studied. Paprika cultivar ‘Buketen’ and canning cultivars ‘Piquillo de Lodosa’ and ‘Pico de Mendavia’ were seeded in the field in Zaragoza, Spain, in a loamy soil. Percent emergence, plant mortality after the postemergence treatment, dry weight of plants, and fruit weight were recorded. Pepper was tolerant to diphenamid and napropamide applied preemergence but these herbicides did not control broadleaf weeds. Clomazone, when applied preemergence resulted in chlorotic seedlings and at 2 kg ai/ha reduced the final stand, but was selective when applied at the 6 to 8-leaf stage of the crop. Pepper was tolerant to diethatyl-ethyl when applied preemergence. However, diethatyl-ethyl applied postemergence caused severe phytotoxicity symptoms, and when mixed with diphenamid, fruit ripeness in 1992 was delayed. Weed control during the crop emergence period was better when diethatyl-ethyl was used mixed with diphenamid or napropamide.

Greenhouse studies were conducted to evaluate the effectiveness of Kinetic, a silicone adjuvant that appeared to increase the efficacy and rainfastness of the isopropylamine salt of glyphosate on velvetleaf, sicklepod, barnyardgrass, guineagrass, yellow foxtail, and yellow nutsedge. Simulated rainfall of 1.3 cm in 5 min at 15 and 60 min after herbicide treatment reduced glyphosate efficacy on all weeds. Kinetic enhanced glyphosate efficacy when yellow nutsedge and guineagrass were subjected to post-spray rainfall at 60 min. On velvetleaf, sicklepod, and yellow foxtail, Kinetic improved glyphosate efficacy when the critical rain-free period was reduced to 15 min. Kinetic failed to provide rainfastness for barnyardgrass, thereby indicating a specificity of Kinetic for certain weed species.

Behavior of 14C-haloxyfop-methyl {methyl 2-[4-[(3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoate} was examined in intact plants of soybean [Glycine max (L.) Merr. ‘Mead’], shattercane [Sorghum bicolor (L.) Moench. ♯ SORVU], and yellow foxtail [Setaria glauca (L.) Beauv. ♯ SETLU] and in cell cultures of soybean and yellow foxtail. Foliar absorption of 14C-haloxyfo-methyl by intact plants was almost complete within 48 h. Significant translocation occurred within 48 h of treatment, with soybean and shattercane plants translocating more 14C than yellow foxtail. Metabolism of 14C-haloxyfop-methyl in intact plants was similar among species. Haloxyfop-methyl was rapidly hydrolyzed to haloxyfop in treated leaves and then translocated to metabolically active areas within the plants. Significant quantities of polar products were also isolated. Soybean cells in suspension culture contained higher levels of 14C than did yellow foxtail cells. Most of the 14C in soybean cells was haloxyfop-methyl, while yellow foxtail contained mostly haloxyfop.

Field experiments were conducted to evaluate postplant crop residue, green and yellow foxtail control, and wheat grain yield after fall application of trifluralin granules in undisturbed small grain stubble. Levels of postplant residue were at least 48% cover (line transect method) and 2750 kg/ha of aboveground dry matter where herbicide granules were left unincorporated or were incorporated with conservation-till methods, including an undercutter, rotary hoe, or undercutter followed by a rotary hoe. Trifluralin at 0.56 kg/ha applied as granules in mid October in untilled stubble and incorporated with conservation-till methods controlled foxtail 81 to 88%, with control appearing slightly lower when granules were not incorporated. The 81 to 88% foxtail control in conservation-till treatments was comparable to control achieved with trifluralin at 0.56 kg/ha applied in mid October on conventionally-tilled soil and incorporated by a field cultivator. Foxtail control improved somewhat as trifluralin rate was increased to 0.84 and 1.12 kg/ha in conservation-till treatments. Slight wheat stand reductions at 1.12 kg/ha of trifluralin did not appear to reduce wheat yield. Fall application of trifluralin granules in these high-residue conditions apparently minimizes herbicide losses by photodecomposition and volatility, thereby facilitating good trifluralin efficacy the following season.

Site-specific weed management recommendations require knowledge of weed species, density, and location in the field. This study compared several sampling techniques to estimate weed density and distribution in two 65-ha no-till Zea mays–Glycine max rotation fields in eastern South Dakota. The most common weeds (Setaria viridis, Setaria glauca, Cirsium arvense, Ambrosia artemisiifolia, and Polygonum pensylvanicum) were counted by species in 0.1-m2 areas on a 15- by 30-m (1,352 points in each field) or 30- by 30-m (676 points in each field) grid pattern, and points were georeferenced and data spatially analyzed. Using different sampling approaches, weed populations were estimated by resampling the original data set. The average density for each technique was calculated and compared with the average field density calculated from the all-point data. All weeds had skewed population distributions with more than 60% of sampling points lacking the specific weed, but very high densities (i.e., > 100 plants m−2) were also observed. More than 300 random samples were required to estimate densities within 20% of the all-point means about 60% of the time. Sampling requirement increased as average density decreased. The W pattern produced average species densities that often were similar to the field averages, but information on patch location was absent. Weed counts taken on the 15- by 30-m grid were dependent spatially and weed contour maps were developed. Kriged maps presented both density and location of weed patches and could be used to establish management zones. However, grid-sampling production fields on a small enough scale to obtain spatially dependent data may have limited usefulness because of time, cost, and labor constraints.