Detached leaves and whole plants of quackgrass [Agropyron repens (L.) Beauv. # AGRRE] were used to study uptake and translocation of butyl esters of 14C-fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, with or without additional adjuvants. In the absence of adjuvants 3.2% of applied radioactivity entered detached quackgrass leaves by 6 h, and at the end of 24 h, 6.0% had penetrated. The presence of additives increased uptake by leaves significantly. In the presence of the nonionic surfactant Agral (nonyl phenol ethoxylate) at 0.2% (v/v) or the oil-additive Actipron (self-emulsifying adjuvant oil) at 2.0% (v/v), 17.2 and 12.9% of applied radioactivity, respectively, entered the leaves by 24 h. Evidence of dependence of phloem translocation of the radioactivity on source-sink relationships of the plant was obtained in the studies with whole plants. Translocation measured up to 7 days after treatment showed that radioactivity was concentrated in areas such as young developed leaves, young stems, and rhizome apices. Rhizomes appear to be major sinks for the accumulation of radioactivity and at 7 days 0.5% of applied radioactivity was found there. In wholeplant experiments the two adjuvants either individually or in mixture increased the uptake of 14C-fluazifop significantly. However, a corresponding increase in basipetal translocation was found only in one experiment. Much of the increased activity that had entered the leaves in the presence of adjuvants was found to have moved to areas distal to the treated zone or remained within the treated zones. In all experiments, applied 14C was not fully recovered. Evidence of significant volatility losses from treated surfaces was obtained and it is thought that this may be the main reason for the inability to recover all of the applied activity.

Sixty isolates of the plant pathogenic fungus Sclerotinia sclerotiorum (Lib.) de Bary and six isolates of Sclerotinia minor Jagger were evaluated in a controlled environment for virulence on leaves excised from 8-week-old dandelion plants. Significant negative correlations were obtained between the relative virulence of the isolates and the dry weights of dandelion plants inoculated in a controlled environment; and positive correlations were detected between the relative virulence of isolates and reduction in number of dandelion plants in turfgrass swards infested with inoculum of the isolates. In August 1988, an 80.7% reduction in the number of dandelion plants was detected in a turfgrass sward treated in 1987 with four applications of heat-killed seed of perennial ryegrass (100 g m−2 application–1) infested with isolate R30 of S. sclerotiorum, followed by six applications at the same rate in 1988. Populations of dandelions in untreated swards increased by 22.2% during the same period. Heat-killed seed of perennial ryegrass (100 g m−2) infested with isolate R30 applied simultaneously with dandelion seed (25 g m−2) onto a sward of Kentucky bluegrass reduced the establishment of dandelion seedlings by 85.5%. Necrosis or discoloration did not develop on Kentucky bluegrass, creeping bentgrass, annual bluegrass, or quackgrass treated with inoculum of Sclerotinia. Sclerotia of Sclerotinia spp. were found, on occasion, in crowns but not on the foliage of diseased dandelions.

Experiments were conducted at three locations to evaluate the efficacy of fall and spring herbicide treatments for vegetation control and enhancement of alfalfa (Medicago sativa L.) establishment. on a sward dominated by quackgrass [Agropyron repens (L.) Beauv.], fall and spring glyphosate [N- (phosphonomethyl) glycine] treatments were equally effective in reducing competition from quackgrass and in establishing alfalfa. on a mixed grass sward, spring and fall glyphosate treatment resulted in similar alfalfa yields with early spring seeding; however, alfalfa yields were lower with delayed seeding on fall-treated plots, compared with spring treatment, because of greater weed competition. Pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl) benzamide] applied in the fall controlled perennial grasses, and when it was followed by paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) in the spring controlled broadleaf weeds as well, resulting in greater alfalfa yields compared with pronamide alone. Alfalfa established more slowly in the paraquat-treated and check plots, than in glyphosate-treated plots.

Field studies of herbicidal antagonism were conducted in corn (Zea mays L.), soybeans (Glycine max L. Merr.), and on industrial sites. The addition of chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea], cyanazine {2-[[4-(chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile}, bifenox [methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate], or atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] wettable powder plus dicamba (3,6-dichloro-o-anisic acid) to glyphosate [N-(phosphonomethyl)glycine]-alachlor[2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] combinations reduced the activity of glyphosate on quackgrass [Agropyron repens (L.) Beauv.], common dandelion (Taraxacum officinale Weber), and Canada thistle [Cirsium arvense (L.) Scop.] in no-till corn. Reduced weed control from antagonism resulted in decreased corn yields. Linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], chlorbromuron, or metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], when added to glyphosate, reduced the control of quackgrass but not that of Canada thistle, alfalfa, or common dandelion in soybeans. Antagonsim was not evident in annual weed species. In perennial weeds, the degree of antagonism was often reduced with increased dosages of glyphosate. The inclusion of terbacil (3-tert-butyl-5-chloro-6-methyluracil), bromacil (5-bromo-3-sec-butyl-6-methyluracil), and simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] with glyphosate in mixes interfered with the control of smooth brome (Bromus inermis Leyss.), but not when applications of the residual herbicides were delayed. Quackgrass control was reduced when amitrole (3-amino-s-triazole) was mixed with glyphosate, or when applied separately.

Experimental adjuvants were tested to maximize herbicidal activity of sethoxydim on quackgrass and of bentazon on common lambsquarters. Efficacious adjuvants were identified by measuring the 14C-herbicide droplet spread and absorption, as influenced by various adjuvants, on the target weed. The absorption and droplet spreadability of sethoxydim and bentazon on quackgrass and common lambsquarters leaves were increased or were decreased depending on the type of adjuvant used. No correlation was found between sethoxydim droplet spread and absorption on quackgrass. With bentazon, the relationship between these two factors was greater. Thus, measurement of droplet spread, as affected by adjuvants, was useful only as a screening technique for bentazon. Blending surfactants with paraffinic oil or soybean oil to form a crop oil concentrate changed the efficacy of the surfactant compared to the surfactant by itself. Surfactants most effective as components of paraffinic-oil based crop oil concentrate were different from surfactants ideal for inclusion with soybean oil-based crop oil concentrate. Thus, the effectiveness of a crop oil concentrate depends on herbicide, surfactant, and oil types. In the field, several of the superior adjuvants identified in the laboratory enhanced sethoxydim and bentazon activity on grass and broadleaf weeds.

The phytotoxicity of the butyl ester of fluazifop to quackgrass was enhanced by the addition of a nonionic surfactant and an oil additive either alone or in mixture to the spray solution. The enhancement caused by the surfactant was consistently greater than that caused by the oil additive. A higher level of quackgrass control was achieved at the carrier volumes of 100, 200, or 400 L/ha, than at 800 L/ha. Quackgrass growth inhibition was greater following application of small herbicide droplets which averaged 0.25 μl compared to larger herbicide droplets at each herbicide application rate. When droplet concentration was varied and different doses of the herbicides applied to plants, no significant differences were noted at the highest dose. However, at intermediate dose treatments, the least concentrated droplets (2.5 μg/μl) were most phytotoxic. Herbicide droplets placed at basal areas of leaves were more phytotoxic than when placed at lamina apices and middle areas. This effect was most pronounced on adaxial rather than abaxial surfaces. In general, application of droplets to younger leaves resulted in greater phytotoxicity than treatment of older leaves.

The translocation pattern and distribution in rhizomes of 14C-glyphosate, 14C-quizalofop, and 14C-sucrose was examined in five quackgrass biotypes. Translocation of radioactivity in the different plant parts varied among biotypes. Translocation in the whole plant after treatment with the three 14C-chemicals varied among biotypes but was not correlated with their tolerance to herbicides. Detailed analysis of distribution of radioactivity in the primary rhizome showed that more 14C was found in the apical sections after treatment with 14C-sucrose. A similar pattern was observed after 14C-glyphosate application with all biotypes except one. Very low radioactivity was found in rhizomes after 14C-quizalofop application, but a preferential accumulation in apical sections of the primary rhizome was detected in two biotypes. The tolerance of one biotype to glyphosate was explained by the absence of radioactivity accumulation in the apical sections of the rhizome.

Laboratory, greenhouse, and field experiments were conducted at the Lacombe Research Station to determine if CCC, ethephon, or CCC/ethephon had direct activity on quackgrass rhizome buds, and to determine if foliar applications of CCC/ethephon could predispose quackgrass to more effective control with sethoxydim. CCC, ethephon, and CCC/ethephon had growth regulating effects on the axillary buds and the apex of detached quackgrass rhizomes. CCC increased rhizome bud sprouting on rhizomes with the apex excised, but not on rhizomes with an intact apex. Ethephon or CCC/ethephon inhibited bud sprouting on rhizomes with an intact or excised apex. CCC/ethephon, but not CCC or ethephon alone, increased rhizome elongation on rhizomes with intact apices. In the greenhouse, pretreatments of CCC/ethephon increased sethoxydim activity on quackgrass rhizome buds and caused lower shoot emergence from one-bud rhizome segments. Results of field experiments were less consistent than those in the greenhouse. However, sometimes CCC or CCC/ethephon pretreatments resulted in increased quackgrass control in the field with sethoxydim.

The freezing resistance of overwintering buds of four perennial weed species was evaluated in artificial freezing experiments conducted in the winters of 1986 and 1987. Survival, dry weight of surviving shoots, and number of shoots produced/surviving section were determined at −4, −8, −12, −16, and −20 C for Canada thistle roots, leafy spurge roots, leafy spurge crowns, perennial sowthistle roots, and quackgrass rhizomes. The temperature required to reduce survival (LT50) and total dry weight (GR50) by 50% was determined. The response to freezing temperatures varied among species and in some cases between years. The LT50 was −7, −13, colder than −20, −17, and colder than −20, and the GR50 was −5, −11, −14, −15, and −13 for Canada thistle roots, leafy spurge roots, leafy spurge crowns, perennial sowthistle roots, and quackgrass rhizomes, respectively. The relative susceptibility to freezing among species appears to be directly related to the depth at which the overwintering buds generally are located.

An experiment was conducted to evaluate the translocation pattern of 14C-glyphosate and 14C-quizalofop in five quackgrass biotypes at two stages of growth. Whole plant translocation differed between stages for each herbicide. The percentage of 14C-glyphosate and 14C-quizalofop in the leafwash and in the treated leaf did not differ among biotypes, but differences occurred for the translocation to the underground parts. The partitioning of the 14C-glyphosate and 14C-quizalofop in the treated crown, other crowns, propagating rhizomes, and other rhizomes differed among biotypes. On a disintegration per minute (DPM) mg-1 basis, differences among biotypes were found with 14C-glyphosate but much less with 14C-quizalofop. Metabolism of 14C-quizalofop in the treated leaf was similar in the two biotypes tested except for the percentage of polar metabolites 1 d after treatment. The percentage of 14C-quizalofop available for translocation was the same in both biotypes.

Field experiments were conducted at the Lacombe Research Station from 1989 to 1991 to determine if short-term, split applications of grass-specific herbicides would improve quackgrass control relative to single applications. Quackgrass infested plots were planted to canola the first year and barley the following year. Glyphosate applied at 880 g/ha controlled quackgrass to a greater extent and for a longer time period than any of the grass-specific herbicides. In contrast to glyphosate, none of the grass-specific herbicides controlled quackgrass 1 yr after treatment. Quackgrass control with sethoxydim or fluazifop-P was usually similar when applied as single or short-term, split applications. In contrast, quizalofop often provided better quackgrass control and higher crop yields when short-term, split applications were compared to a single application with the same total amount of quizalofop. However, the extent of increased quackgrass control is difficult to justify due to increased application costs and inconvenience.

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.

In greenhouse and field studies, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid} controlled quackgrass [Agropyron repens (Beauv.) # AGRRE] in potato (Solanum tuberosum L. ‘Russet Burbank’). Quackgrass control with fluazifop at 0.25 and 0.5 kg ai/ha in the greenhouse was greatest with application at the two-leaf stage compared with the four-and six-leaf stages. Control was not affected by rhizome length, with similar control obtained of plants grown from 2- and 10-node rhizome pieces. Removal of quackgrass shoots at 6 or 24 h after treatment resulted in decreased control at application rates of 0.25 and 0.5 kg/ha. Fluazifop at 0.5 kg/ha controlled quackgrass treated at the four-leaf stage. The active enantiomer of fluazifop at half the rate of the racemic mixture controlled the quackgrass to the same extent. Fluazifop did not affect potato yield.

The effect of temperatures below 0 C and plant maturity on the phytotoxicity of glyphosate [N-(phosphonomethyl)glycine] on rapidly growing alfalfa (Medicago sativa L. ‘Vernal’) and quackgrass [Agropyron repens (L.) Beauv.] plants was studied in a controlled environment. Pretreatment at −4 C partially protected alfalfa from injury by 0.8 kg/ha of glyphosate at six alfalfa maturities. This same treatment had no significant effect on glyphosate phytotoxicity to quackgrass. Pretreatment at −4 C increased translocation of glyphosate in quackgrass but reduced its translocation in alfalfa. A greater reduction in translocation occurred in the smaller alfalfa plants.

Four field experiments were conducted during 1988 and 1989 to determine the effects of POST application of nicosulfuron on quackgrass control in conventional field corn. A single application of nicosulfuron at 35 to 70 g ha–1 applied to four- to six-leaf quackgrass controlled over 90% of quackgrass five weeks after treatment. Nicosulfuron at 35 g ha–1 applied at the one- to three-leaf stage was not as effective as the same rate applied at the four- to six-leaf stage. When nicosulfuron at 35 g ha–1 was applied to four- to six-leaf quackgrass, over 80% of the quackgrass regrowth was controlled one year later. Nicosulfuron did not injure ‘Agway 584S’ corn at the highest rate (140 g ha–1) tested and did not reduce silage or grain yield.

An experiment was established at three sites to determine the longevity and distribution of rhizome buds of two quackgrass biotypes in the soil profile under two tillage systems (no-till or fall-plow). The experiments were established in May 1987 at sites initially free of quackgrass. Rhizome segments with three nodes were planted 2 to 5 cm deep to give an initial density of 21 buds m-2. Production of new buds was prevented in subsequent years. Rhizome bud populations were sampled every 6 mo between October 1987 and October 1989. Buds were produced until snow cover, indicating the need to control quackgrass until late fall to prevent a bud population increase. Under no-till conditions, 94% of quackgrass buds occurred in the top 10 cm of soil while 68 and 19% were found below 10 and 20 cm, respectively, in the fall-plow treatments. A control program against quackgrass should aim at keeping the majority of rhizomes in the top 10 cm in order to facilitate control by having most shoots emerging at the same time. There was no statistically significant difference in bud longevity between biotypes, sites, and tillage systems. Viability of the rhizome buds declined rapidly during the first year. In most cases it took 2 yr for the bud populations to reach extinction although 0.6% of buds of one biotype survived as long as 30 mo in one of the three sites. Therefore, a minimum of 2 yr of total control would be required to eradicate quackgrass from most locations.

The effect of the isopropylamine salt of glyphosate and the ethyl ester of quizalofop on the rhizome bud viability of five quackgrass biotypes was tested. Two bioassays used were: direct measure of the growth of the bud on an agar medium and determination of the respiratory activity with tetrazolium chloride. The response to herbicide treatments differed among biotypes. The growth bioassay showed lower viability than the tetrazolium bioassay. Quizalofop reduced viability more than glyphosate. Viability of untreated buds increased with increasing distance from the base of the rhizome. The viability of herbicide-treated buds was more or less equal regardless of the position. It appeared that both herbicides were translocated to all the rhizome buds.

Photosynthesis decreased 32% in quackgrass infected with rust. Photoassimilate transport in rust-infected quackgrass, assessed by autoradiography, was less than that of control (no rust) leaves 35 min after exposure to 14CO2. Greenhouse-grown quackgrass height, foliar and rhizome dry weights, rhizome length, and bud numbers decreased 11, 25, 28, 19, and 21% in rust-infected plants, respectively, compared to control plants. Foliar and rhizome biomass decreased 31 and 39%, respectively, in field-grown rust-infected plants. Rhizome bud death 48 h after treatment (HAT) in both control and rust-infected plants increased as glyphosate rate increased from 0.13 to 1 kg ae ha−1; however, control plant bud death was significantly greater than that of rust-infected plants.

The antagonistic effect of bentazon on sethoxydim adsorption and activity was studied in quackgrass. The diffusion of 14C-sethoxydim into and through an isolated tomato fruit cuticle was inhibited in the presence of the sodium salt of bentazon. Bentazon also increased the partitioning of 14C-sethoxydim into CH2Cl2 and water; however, it decreased partitioning into ethyl acetate. Removal of epicuticular wax from quackgrass leaf surfaces did not prevent the antagonism. Addition of sodium acetate or sodium bicarbonate to the sethoxydim spray solution at 10 mM reduced uptake of 14C-sethoxydim by quackgrass similar to the effect of bentazon. Sodium ions in the bentazon formulation appeared responsible for the antagonism by exchanging with the H+ of the sethoxydim hydroxyl group to form a more polar sodium salt of sethoxydim. The addition of Li+, K+, Cs+, Ca++, and Mg++ cations associated with a weak acid also reduced 14C-sethoxydim absorption. Addition of organic acids to the spray solution overcame the antagonism by preventing the formation of sodium salt of sethoxydim. In the field, the addition of a 3000 ppm sodium acetate solution delivering 0.56 kg/ha produced the same antagonism as bentazon on quackgrass control with sethoxydim.

14C-Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} was rapidly metabolized by quackgrass [Agropyron repens (L.) Beauv. ♯ AGRRE], barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCG], alfalfa (Medicago sativa L. ‘Saranac’), and navy bean (Phaseolus vulgaris L. ‘Seafarer’). One hour after application, 46, 27, 38, and 46% of the total 14C in the ethyl acetate-soluble fraction from treated leaves was sethoxydim, respectively. After 24 h, less than 2% was sethoxydim in any species. Nine metabolites were found, seven of which cochromatographed with photo- and thermal-transformation products of sethoxydim. Two metabolites, previously shown to be phytotoxic to barnyardgrass, contained the majority of 14C up to 24 h after application. Quantitative or qualitative differences in the metabolites of treated leaves could not account for the observed differences in selectivity.