The effect of the bleaching and non-bleaching phenylpyridazinones, norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] and BAS 29095 [4,5-dimethoxy-2-phenyl-3(2H)-pyridazinone], on chlorophyll fluorescence of the green alga, Scenedesmus acutus, was investigated and compared to other bleaching herbicides, difunon3 [EMD-IT 5914, 5(dimethylamino-methylene)-2-oxo-4-phenyl-2,5-dihydrofuranecarbonitrile-(3)] and the diphenyl ether, oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene]. Following chlorophyll fluorescence during short-term cultivation in the presence of herbicides and comparing it to physiological parameters such as chlorophyll content and packed cell volume allowed for rapid screening to detect different primary herbicidal modes of action. Two primary bleaching effects caused by either inhibition of carotene biosynthesis (certain substituted pyridazinones and difunon) or peroxidative degradation of membrane lipids (certain diphenyl ethers) led to completely different fluorescence signals. Growth of algae in the presence of a carotene biosynthesis inhibitor resulted in a rapid rise to maximum fluorescence, followed by a single decay phase, whereas bleaching diphenyl ethers led to a rapid loss of total fluorescence. Non-bleaching phenylpyridazinones, which act as weak electron transport inhibitors, inhibited variable fluorescence. Detoxication during algal growth became evident by recovery of the fluorescence induction.

The herbicide 3,6-dichloropicolinic acid was more effective than 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] or equal-ratio combinations of 2,4,5-T with picloram (4-amino-3,5,6-trichloropicolinic acid) or dicamba (3,6-dichloro-o-anisic acid) when aerially applied as broadcast sprays for control of honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell]. Applied at 0.56 kg/ha, 3,6-dichloropicolinic acid controlled 60 and 68% of the honey mesquite at two locations; whereas, the mixture of 2,4,5-T and picloram controlled only 21 and 30% of the honey mesquite at the same rate of application. The herbicide 3,6-dichloropicolinic acid was equally effective when applied alone or in 1:1 mixtures with 2,4,5-T, picloram, or triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} at equivalent rates. Applying 3,6-dichloropicolinic acid at 1.12 kg/ha resulted in an absolute increase in mortality of 26% over the 0.56-kg/ha rate.

Interactions of nine dosage rates each of chloramben (3-amino-2,5-dichlorobenzoic acid) and diphenamid (N, N-dimethyl-2,2-diphenylacetamide) were studied using Italian ryegrass (Lolium multiflorum Lam.) as a test species. Injury score, estimated percent stand reduction, height, and fresh weight data were taken 1 week after seeding. Techniques for developing linear regression models based on these data and evaluating them graphically in terms of completeness and statistical validity are discussed. Three-dimensional graphs of these models indicate areas of possible herbicide interaction.

The herbicides glyphosate [N-(phosphonomethyl)glycine], hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], and pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynl)benzamide] were evaluated for effectiveness in quackgrass (Agropyron repens L. Beauv.) control when applied in the fall, a time that is desirable in a short-growing-season area such as Atlantic Canada. Glyphosate at 1.12 kg/ha applied to quackgrass in grain stubble gave good control. Glyphosate at 1.12 kg/ha in late October gave better control than the same rate applied in late September. At low rates of 0.56 and 1.12 kg/ha, glyphosate gave better quackgrass control when fall-applied than when spring-applied. No differences were noted between seasons at the 2.24-kg/ha rate of glyphosate. Pre-treatment with nitrogen at 35 kg/ha 30 or 15 days before application, or on the day of application, did not improve quackgrass control with glyphosate. Pronamide gave fair to good control. Hexazinone at 2.24, 4.48, or 6.72 kg/ha gave poor control when fall-applied, but excellent control when spring-applied.

Combinations of MSMA (monosodium methanearsonate) with bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide], DCPA (dimethyl tetrachloroterephthalate), or prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} were applied at various dates of treatment to bermudagrass [Cynodon dactylon (L.) Pers.] and Kentucky bluegrass (Poa pratensis L.) in the spring for large crabgrass [Digitaria sanguinalis (L.) Scop.] control. Bensulide controlled a higher percentage of weeds than did DCPA, regardless of treatment dates. When treatments were delayed until late April in Griffin and mid May in Blairsville, Georgia, large crabgrass control was improved from combinations of MSMA with bensulide compared to bensulide alone. Combinations of MSMA with DCPA improved large crabgrass control when applied in March and April at Griffin and in May at Blairsville. Combinations of MSMA with either bensulide or DCPA performed equally well whether applied as a single tank-mix treatment or as separate applications on the same day. Large crabgrass control was not improved at any date from combinations of MSMA with prosulfalin when compared with prosulfalin alone.

Large quantities of viscous, non-crystalline epicuticular waxes were observed on leaves of three goldenweed (Isocoma) species. Based on weights of residues from single 15-s chloroform extractions, wax on leaves of field-grown plants of the least herbicide-susceptible species, common goldenweed [I. coronopifolia (Gray) Greene], increased from 71 mg/dm2 in March to 286 mg/dm2 in October, which was two to four times greater than the amount present on other goldenweed species. Similar quantities were produced by leaves of glasshouse-grown plants, but maximum wax production occurred during summer months. The epicuticular wax of fully expanded leaves decreased with age. The amounts of epicuticular wax on individual plants growing within a field population varied by a factor of four.

Tomatoes (Lycopersicon esculentum ‘Roma VF’) and four weeds were grown in various combinations in field plots in 1973 and 1974. Season-long interference by jimsonweed (Datura stramonium L.), tall morningglory [Ipomoea purpurea (L.) Roth], and common cocklebur (Xanthium pensylvanicum Wallr.) at densities of 11, 43, and 86/m2 reduced tomato yields in 1973. In 1974, tomato yields were reduced by these three broadleaf weeds at densities of 2.7, 5.4, 8.1, and 11/m2. Season-long interference by large crabgrass [Digitaria sanguinalis (L.) Scop.] reduced tomato yield at densities of 55, 215, and 430/m2 in 1973 and 11, 22, 33, and 55/m2 in 1974. The fresh weight of tomato shoots decreased with all weed densities in both years. Total weed shoot weight increased with density and individual weed weights decreased with increasing densities. Tomato fruit quality, as measured by soluble solids, acidity, and color, was not influenced by the various weeds and densities.

Toxicity of non-radiolabeled and absorption and translocation of 14C-activity of applied 14C-acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} in showy crotalaria (Crotalaria spectabilis Roth) were evaluated in the growth chamber at air temperatures of 18, 27, or 35 C and 40 or 100% relative humidity (RH). Four days after treatment, acifluorfen applied over-the-top at 0.1 kg/ha resulted in 64 to 95% injury, but did not kill showy crotalaria. Acifluorfen was more toxic at 100% than at 40% RH. At either 40 or 100% RH, acifluorfen was more toxic at 27 and 35 C than at 18 C. Plants were placed in the greenhouse 4 days after treatment. At 6 weeks after treatment, there was extensive regrowth, and injury to all plants was less than 32%, except for those plants initially treated at 18 C and 40% RH for 4 days. These plants showed 76% injury. Acifluorfen applied to a single leaf midway up the stem caused 80 to 100% injury to the immature leaves near the apex, but less than 30% injury to lower leaves. Absorption of 14C-activity from 14C-acifluorfen applied to a single leaf midway up the shoot varied from 8 to 76% after 2 days. At either 40 or 100% RH, absorption was approximately four-fold greater at 27 and 35 C than at 18 C. At all temperatures tested, absorption was three- to four-fold greater at 100% than at 40% RH.

The effect of postharvest storage temperature (–15, 5, 20, and 30 C) on seed dormancy of red rice [Oryza sativa L. ‘strawhulled (SH)’], an annual species, was studied. Intact and dehulled (by hand) seeds were dormant at harvest. Intact seeds were nondormant (greater than 90% germination at 30 C) after dry storage at 20 or 30 C for 4 weeks after harvest. In intact seeds stored dry at 5 C, the degree of dormancy was dependent upon postharvest exposure time at 20 C prior to storage. Dormancy of intact seeds decreased at 5 C as this initial postharvest exposure to 20 C was increased from 2 to 7 days. This effect of initial 20 C exposure was independent of seed moisture content (11 to 12%). After dry storage of intact seeds at 5 C, dehulling promoted germination. Germination of such dehulled seeds increased with increasing storage time at 5 C up to 11 months when complete germination occurred. The response of seeds dehulled immediately after dry storage at 5 C was independent of prior exposure time (2 to 7 days) at 20 C. Storage at −15 C prevented all forms of dry-afterripening for 1 yr.

The effects of weed density on the phytotoxicity of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] to white mustard (Brassica hirta Moench) and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] to foxtail millet [Setaria italica (L.) Beauv.] were determined in the greenhouse. The fresh weight of both plants was reduced by the herbicide treatments, but as the weed density (plants per pot) increased, the herbicide rate required to cause equivalent fresh weight reductions per pot also increased. White mustard and foxtail millet grown in pots absorbed less 14C-atrazine or 14C-alachlor per plant from the soil at high weed density than low, regardless of herbicide rate. Foxtail millet seedlings grown in petri dishes absorbed less 14C-alachlor per plant from aqueous solution as the number of seedlings per petri dish increased. Data from field experiments in 1977 and 1979 indicated that more alachlor or metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] was required for equal control of a high than low density of forage sorghum [Sorghum bicolor (L.) Moench ‘Rox Orange’] interseeded in maize (Zea mays L.). Rox Orange sorghum was used to simulate shattercane [Sorghum bicolor (L.) Moench], a problem weed in Nebraska. At the higher Rox Orange sorghum seeding rate used, both alachlor and metolachlor treatments decreased Rox Orange sorghum plant populations but not yield.

The effects of various densities and durations of wild oat (Avena fatua L.) competition in soybean [Glycine max (L.) Merr. ‘Evans’] were determined in the field during a 2-yr period. Season-long competition by densities of 1, 3,9, and 30 wild oat plants/m of row reduced soybean seed yield an average of 6, 17, 32, and 51%, respectively. An infestation of 30 wild oat plants/m of row did not reduce soybean yield if the period of competition was limited to 4 weeks after crop emergence; however, yields were reduced 29, 50, 63, 58, and 63% when wild oat competed for 5, 6, 7, and 8 weeks, or season long, respectively. Wild oat competition reduced soybean pods per plant and seeds per plant more than seeds per pod or seed weight.

The response of several spring wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and oat (Avena sativa L.) cultivars to preemergence and postemergence applications of chlorsulfuron (tested under code number DPX-4189) {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl] benzenesulfonamide} was evaluated in the field and greenhouse in 1979. In greenhouse experiments, ‘Butte’ spring wheat was less susceptible than six other spring wheat cultivars to chlorsulfuron at 1.0 kg/ha applied preemergence or postemergence. ‘Morex’, ‘Conquest’, and ‘Bonanza’ barley cultivars were less susceptible than six other barley cultivars to preemergence chlorsulfuron, but barley cultivars were similar in response to postemergence chlorsulfuron. The eight oat cultivars responded similarly to preemergence and postemergence chlorsulfuron at 1.0 kg/ha. Data from two field experiments, which included evaluation of durum wheat [Triticum durum (Desf.)] cultivars, indicated that the four small grains had adequate tolerance to postemergence chlorsulfuron at 0.125 and 0.25 kg/ha, except that durum wheat grain yield was reduced by 0.25 kg/ha at the Rosemount location. No differential cultivar responses to chlorsulfuron occurred among the small grains in the field.

Extensive variability in total lipid composition was observed in seeds of different plant species as well as cultivars within the same species. Susceptibility of plants to soil-incorporated trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and oryzalin (3,5-dinitro-N4,N4-dipropyisulfanilamide) under greenhouse conditions decreased as the percentage of total lipid in dry seeds increased. Species with high seed lipid levels such as jimsonweed (Datura stramonium L.), soybean [Glycine max (L.) Merr.], and velvetleaf (Abutilon theophrasti Medic.) were less susceptible to these herbicides than were oat [Avena sativa (L.), giant foxtail (Setaria faberi Herrm.), and sorghum [Sorghum bicolor (L.) Moench.] with low seed lipid levels. Velvetleaf was the most tolerant to the herbicides. Corn (Zea mays L.) cultivars with a wide range of seed lipid content (4.45 to 17.0% of dry weight) were germinated in herbicide-free soil, but their roots were allowed to grow through trifluralin- or oryzalin-treated soil. Roots of seedlings from seeds with high lipid content had higher lipid contents than those from low-lipid seeds. There was a significant correlation between root lipid content and sensitivity to trifluralin or oryzalin. Roots high in lipids were less susceptible than those with low amounts of lipids. Similar results were obtained for oat cultivars. The fatty acid composition of plant roots differed among plant species and also among cultivars of the same species. The individual fatty acids did not significantly correlate with susceptibility of roots to trifluralin or oryzalin. Root lipid and fatty acid compositions were not significantly altered by trifluralin or oryzalin treatment.

Methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy) phenoxy] propanoic acid} (diclofop as used herein refers to the methyl ester) added to nutrient solution inhibited adventitious root development and reduced the mitotic index in adventitious root tips of wheat (Triticum aestivum L. ‘Neepawa’) and wild oat (Avena fatua L.). Elongation of wild oat roots was significantly inhibited by 0.15 μM diclofop 24 h after treatment; whereas, wheat roots were unaffected at concentrations less than 1.5 μM even at 12 days, indicating at least a 10-fold difference in sensitivity. Initiation of new adventitious roots was reduced in both species by 0.30 μM diclofop. Mitotic index was more severely reduced at lower concentrations and after a shorter exposure in wild oat than in wheat. Histological studies showed that 24 h after wild oat roots were treated with 0.30 μM diclofop for 24 h, severe damage occurred to tissues within the developing central cylinder, close to the root apex. Disruption of cortical and epidermal cells generally was not as severe until 4 to 7 days after treatment. By 12 days the entire root tip was almost completely obliterated, with only the epidermal cell walls remaining intact.

Effects of 16 herbicides representing 14 herbicide classes on growth and extractable phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) were examined in light- and dark-grown soybean [Glycine max (L.) Merr. ‘Hill’] seedlings. High purity (96 to 100%) herbicides were supplied via aqueous culture at various concentrations: 0.5 mM amitrole (3-amino-s-triazole), 0.1 mM atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], 0.07 mM diclofop-methyl {methyl ester of 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoicacid}, 0.5 mM DSMA (disodium methanearsonate), 0.2 mM fenuron (1,1-dimethyl-3-phenylurea), 0.05 mM fluridone {1-methyl-3-phenyl-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, 0.5 mM MH (1,2-dihydro-3,6-pyridazinedione), 0.5 mM metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], 1.8 μM nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], 0.5 mM norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone], 0.05 mM paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), 0.15 mM perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide}, 0.2 mM propanil (3′,4′-dichloropropionanilide), 0.1 mM propham (isopropyl carbanilate), 0.5 mM TCA (trichloroacetic acid), and 0.05 mM 2,4-D [(2,4-dichlorophenoxy)acetic acid]. Dark-grown soybean seedlings (3-day-old) were transferred to control solutions (2 mM CaSO4) or to herbicide solutions (in 2 mM CaSO4) and grown at 25 C in continuous white light (200 μE•m-2•s-1) or continuous darkness until harvested 24 or 48 h after transfer. After 48 h, growth (fresh weight, dry weight, elongation) was inhibited by most of the chemicals. Other signs of toxicity (necrosis, secondary root stunting, and root tip swelling) were noted for some treatments. Roots were most affected, although hypocotyls were generally not changed. Hypocotyl elongation was stimulated by atrazine, fluridone, and norflurazon after 48 h light. Extractable PAL activity from soybean axes was decreased by atrazine, fenuron, metribuzin, norflurazon, propanil, propham, and 2,4-D. Amitrole and paraquat were the only herbicides that increased extractable PAL activity. Other compounds tested had no effect on the enzyme. None of the herbicides significantly affected in vitro PAL activity.

Different Saskatchewan soils were studied to determine their populations of 2,4-D [(2,4-dichlorophenoxy) acetic acid] degraders and gross aerobic bacteria. Soil from Indian Head field plots receiving relatively high field rates (1.12 or 1.68 kg/ha) of 2,4-D amine or ester applied annually over the previous 32 yr contained the highest population of degraders, ranging from 103 to 104 degraders/g soil. Control plots recorded lower populations of degraders (2.5 ± 0.5 × 103 degraders/g soil). Five soils from around the province were also studied, and a relationship was found between the rate of breakdown of 14C-2,4-D in the soil and the number of degraders. Another soil from a different site at Indian Head, but of a similar type to that in the field plots, displayed a much slower rate of 2,4-D degradation and also a much lower degrader population (7 ± 2 degraders/g soil) when compared to the other four soils (4 × 102 to 9 × 102 degraders/g soil). The ratio of degraders to the total bacterial flora varied in all studies between 1:6.5 × 102 and 1:3 × 105. When 1030 soil isolates were screened for their ability to degrade 2,4-D using an agar-block extraction technique, none possessed this feature. This would support the hypothesis that the ratio of 2,4-D degraders to the total microbial flora was indeed large (at least 1:103).

Ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] applied postemergence in November at rates from 1.4 to 4.5 kg/ha eliminated all annual bluegrass (Poa annua L.) that had survived application of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] in fall carbon-planted perennial ryegrass (Lolium perenne L.) seed fields. Ethofumesate also eliminated all annual bluegrass in established perennial ryegrass seed fields when applied in late October at rates from 1.1 to 3.4 kg/ha or when applied as sequential treatments with atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] at 1.4 kg/ha or with simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 2.2 kg/ha. In most experiments, perennial ryegrass seed yields were not adversely affected by applications of ethofumesate alone or by sequential treatments with diuron, atrazine, or simazine.

Salt rabbitbrush [Chrysothamnus nauseosus (Pallas) Britt., ssp. consimilis (Greene)] and greasewood [Sarcobatus vermiculatus (Hook.) Torr.] grow slowly in early spring until mid to late May. They then begin a period of rapid growth, at which time susceptibility to foliar herbicides is probably greatest. Greasewood ceases rapid growth in mid June to early July, but salt rabbitbrush continues to grow rapidly until early August. Greasewood that resprouts after herbicide application has a longer rapid-growth period than shrubs in an untreated stand. An average leader length of 4 cm indicates that rapid growth of salt rabbitbrush is underway, and first opening of the flower buds indicates that rapid growth is over. Appearance of greasewood staminate spikes indicates that rapid growth has begun, and the first appearance of dried spikes indicates that growth has ceased. Simultaneous control of these shrubs with a single application of phenoxy herbicides may only be possible during the relatively short period when both are growing rapidly. This period may only occur from late May to mid June in some stands and years, but may occur from mid May to early July in other cases.

Six species of 2- or 3-yr-old woody nursery stock were planted in the field in May 1976. Glyphosate [N-(phosphonomethyl) glycine] at 2.2 or 4.5 kg/ha or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at 0.6 or 1.1 kg/ha were applied one or two times as directed sprays in 1976 and one, two, or three times each season in 1977 and 1978. Three applications of glyphosate or paraquat were required to control weeds during the entire growing season. When late-season applications of glyphosate were made during 1977, residual weed control was observed during early 1978. When glyphosate was applied twice a year for 3 yr at 4.5 kg/ha, four of the previously dominant perennial weeds were controlled, including common dandelion (Taraxacum officinale Weber), broadleaf dock (Rumex obtusifolius L.), buckhorn plantain (Plantago lanceolata L.), and red sorrel (Rumex acetosella L.). Three applications provided 100% control of seven of the eight remaining broadleaf perennials, including hedge bindweed (Convolvulus sepium L.) and Canada thistle [Cirsium arvense (L.) Scop.]; six of seven species of broadleaf annuals, including Pennsylvania smartweed (Polygonum pensylvanicum L.) and tumble pigweed (Amaranthus albus L.); and all of the remaining grass weeds. Crop size, crop quality, and marketability of the six ornamental species were not adversely affected by either herbicide. Two or three applications of glyphosate at 2.2 kg/ha or two treatments at 4.5 kg/ha increased plant size of andorra junipers (Juniperus horizontalis Rend.). Three treatments of glyphosate at 2.2 kg/ha also increased the size of dwarf Japanese yews (Taxus cuspidata Sieb. & Zucc.) and two treatments at 4.5 kg/ha increased the size of boxleaf Japanese holly (Ilex crenata Thunb.).

In field and greenhouse studies, alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] was found to antagonize buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} injury to corn (Zea mays L.) when both herbicides were preplant incorporated. Similar results were found with five of seven other acetanilide herbicides tested. The antagonism between buthidazole and alachlor also occurred with common cocklebur (Xanthium pensylvanicum Wallr.) and ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.] but not with five other weed species. Preplant-incorporated applications of alachlor had little to no effect on the response of corn to postemergence applications of buthidazole, but alachlor increased the susceptibility of ivyleaf morningglory to postemergence applications of buthidazole. No antagonism was observed when alachlor was included in postemergence applications of buthidazole to corn or ivyleaf morningglory.