Four synthetic multiring analogs of strigol (0.1 mM) were effective as germination stimulants of dormant, unchilled seeds of shepherdspurse (Capsella bursa-pastoris (L.) Medik. # CAPBP). The effect was concentration dependent and exceeded that produced by 0.1 mM gibberellic acid (GA). The analog treatments resulted in normal, unpigmented seedlings after 7 days, whereas GA treatment led to distorted, nongeotropic, yellow seedlings. The strigol analogs were also more effective in inducing shepherdspurse germination than 10 mM nitrate or 5.0 mM thiourea (ineffective in the dark) and 5.0 mM thiourea plus 4.5 mM ascorbate (germination stimulated, but seedling growth, inhibited). Chilling at 4 C for 11 days reduced the effectiveness of the strigol analogs, but not that of gibberellic acid and thiourea plus ascorbate. Ascorbate acts synergistically with thiourea in promoting shepherdspurse germination. Strigol and epistrigol had no effect on either chilled or unchilled shepherdspurse seeds. The stimulation of dormant shepherdspurse seeds by the synthetic strigol analogs is the first demonstration that these compounds have bioregulatory activity in dormant seeds of genera other than Striga.

The ether extract of small everlasting (Antennaria microphylla Rydb.) was phytotoxic to lettuce seed root growth and leafy spurge (Euphorbia esula L. # EPHES) root elongation and cell culture growth. Three phenolic compounds (hydroquinone, arbutin, and caffeic acid) were chromatographically isolated and characterized from the ether extract. Arbutin and caffeic acid were moderately phytotoxic to leafy spurge root growth at 300 ppm (w/v), and hydroquinone was strongly phytotoxic to leafy spurge root growth at 50 ppm (w/v). The observed phytotoxicity of hydroquinone and the high-yield natural occurrence of arbutin, a water soluble, easily hydrolyzed monoglucoside of hydroquinone, in small everlasting is consistent with the participation of these two compounds in the observed allelopathy of small everlasting against leafy spurge.

Absorption and translocation of 14C-ethalfluralin (N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine) were measured in cucumber plants in the field and greenhouse. In field enclosures, cucumbers treated with 1.68 or 3.36 kg ai/ha preemergence soil-surface applications of 14C-ethalfluralin accumulated significantly more 14C in leaves than in petioles, stems, or fruits. In greenhouse studies, 14C-ethalfluralin vapor was absorbed by both cucumber seedling stems and cotyledons. Seedlings absorbed 14C-ethalfluralin from a nutrient solution and translocated 14C into all plant parts. Cucumber absorbed 14C-ethalfluralin topically applied to the stem and translocated 14C acropetally, while only limited basipetal translocation occurred. Although cotyledons absorbed 14C-ethalfluralin, very little 14 C moved out of the treated tissue.

Field observations indicate that wheat (Triticum aestivum L.) is considerably more tolerant to soil residues of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} than barley (Hordeum vulgare L.). The basis for relative differences in tolerance was investigated by measuring herbicide dose response, uptake, movement, and metabolism using ‘Clark’ barley and ‘Marberg’ wheat. Barley root fresh and dry weights were significantly reduced when roots were exposed to nutrient solution containing 35 mM chlorsulfuron for 1 day. Wheat roots similarly exposed for 3 days to 1.1 mM chlorsulfuron displayed no growth reduction. The small differences in uptake and movement of chlorsulfuron detected in wheat and barley are inadequate to explain the large response difference between the two species. Both species rapidly metabolize chlorsulfuron in 1 day and there is no significant difference in the level of parent compound remaining in barley compared to wheat. A factor other than uptake, movement, or metabolism must account for barley roots greater sensitivity to root-applied chlorsulfuron.

Buried seeds of witchgrass (Panicum capillare L., # PANCA) exposed to natural seasonal temperature changes in Lexington, KY, for 0 to 35 months exhibited annual dormancy/nondormancy cycles. Seeds were dormant at maturity in early October. During burial in late autumn and winter, fresh seeds and those that had been buried for 1 and 2 years became nondormant. Nondormant seeds germinated from 76 to 100% in light at daily thermoperiods of 15/6, 20/10, 25/15, 30/15, and 35/20 C, while in darkness they germinated from 1 to 24%. In late spring, seeds lost the ability to germinate in darkness, and by late summer 63 to 100% of them had lost the ability to germinate in light. As seeds became nondormant, they germinated (in light) at high (35/20, 30/15 C) and then at lower (25/15, 20/10, and 15/6 C) temperatures. As seeds reentered dormancy, they lost the ability to germinate (in light) at 15/6 C and at higher thermoperiods 2 to 3 months later.

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.

Field experiments were conducted to determine the effect of nitrogen fertilization on competition between wild oat (Avena fatua L. # AVEFA) and spring wheat (Triticum aestivum ‘Anza’). Nitrogen fertilizer treatments were applied over several wild oat-wheat density combinations. Wheat grain yield in wild oat-infested plots generally declined with fertilization while the density of wild oat panicles increased. Apparently, in competition with wheat, wild oat was better able to utilize the added nitrogen and thus gained a competitive advantage over the wheat. The increased competitiveness of wild oat resulted in reduced crop yields. Under the conditions of these experiments, nitrogen fertilization resulted in positive wheat yield response only when the wild oat plant density was below 1.6 percent of the total plant density.

Hydrilla [Hydrilla verticillata (L.f.) Royle # HYLLI] was grown for 4 to 16 weeks in pans filled with either an organic muck-sand soil, sand, or sand mixed with Osmocote, Esmigran, and dolomite under outdoor conditions in plastic-lined pools with flowing pond water. Dry weight for plants cultured in sand plus the fertilizers was dependent on the concentration of fertilizer and was from 6 to 14 times that of plants cultured in sand alone. Dry weight was also higher for three treatments of sand amended with fertilizer than for plants cultured in the organic muck-sand soil. Water temperature for different growth periods influenced dry weight of hydrilla cultured with all three root media. Tuber production was independent of three levels of fertilizer for 16 weeks of plant growth, but plant weight was dependent on the concentration of nutrients in the root zone. Of nine plant tissue nutrients measured, only phosphorus in both the shoots and roots was dependent on the level of fertilizer in the root zone. This suggests that growth of hydrilla is controlled by nutrients in the root zone. The use of sand amended with various levels of fertilizers may be a way to simulate fertility levels of sediments as a method to study aquatic sites for their potential to support growth of hydrilla.

Greenhouse-grown kochia [Kochia scoparia (L.) Schrad. # KCHSC] seedlings from populations having either a 13-yr triazine history or no triazine history were sprayed postemergence with 0, 2, or 20 kg/ha atrazine [6-chloro-N-ethyl-N′-[1-methylethyl)-1,3,5-triazine-2,4-diamine]. Fresh weight was reduced 20% in triazine history kochia treated with 20 kg/ha atrazine. Seedlings with no triazine history were killed by 2 kg/ha atrazine. Biotypes resistant to atrazine were also resistant to five other triazine herbicides. Biotypes susceptible to atrazine were susceptible to the other triazines. Atrazine-resistant biotypes were more susceptible to 2,4-D [(2,4-dichlorophenoxy)acetic acid] than atrazine-susceptible biotypes, but atrazine history had no effect on response to diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea].

Germination of dormant wild oat (Avena fatua L. # AVEFA) seed was examined in response to various concentrations of ethephon (2-chloroethylphosphonic acid), KNO3, or both together in the dark at temperatures ranging from 7 to 32 C. Both chemicals significantly (P = 0.05) promoted germination and their effects were additive. Maximum stimulation of germination in response to all treatments occurred at 7 C, with a gradual decrease in reponse as temperature or duration of after-ripening, the seed that retained dormancy during storage remained responsive to ethephon also occurred during storage of mature seed at 3 to 32 C. The rate and extent of this dormancy loss increased with an increase in storage temperature. Regardless of the temperature or duration of after-ripening, the seed that retained dormancy during storage remained responsive to ethephon and KNO3 treatments. Suitable combinations of after-ripening, ethephon, and KNO3 induced over 90% germination of seed that was dormant at maturity. Experimental evidence has been obtained that suggests that this percentage may represent the total number of viable seed in the population. While ethephon promoted seed germination, it severely stunted root and shoot growth of the resulting seedlings. It appears that strategies could be developed to combine the use of ethephon and nitrate with the natural process of after-ripening to enhance and synchronize wild oat germination.

Red clover (Trifolium pratense L.) was direct seeded into a grass sod after spraying with dalapon (2,2-dichloropropanoic acid), glyphosate [N-(phosphonomethyl) glycine], or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at rates of 5.6, 2.2, and 0.6 kg ai/ha respectively. Dalapon applied a few days prior to planting did not improve red clover stands in comparison to seeding in unsprayed sod. Applying glyphosate a few days prior to seeding in spring and summer invariably increased red clover stands, but paraquat was effective in only one of four spring or summer applications. Glyphosate applied the fall preceding a spring or summer seeding produced red clover stands superior to those after all spring treatments. Where glyphosate or paraquat was applied, water content of the upper 20 cm of the soil profile was greater during the first 10 days after treatment, relative to unsprayed plots or those treated with dalapon. By 30 days after application, the glyphosate-treated sods used less soil water than those treated with paraquat. Applications of glyphosate and paraquat greatly suppressed water utilization by oats (Avena sativa L.) in the greenhouse, based on water potential of the potting soil. Dalapon had little effect on water use by oat seedlings in the greenhouse.

Field research was conducted at two locations in 1982 and 1983 to evaluate the competitiveness of coffee senna (Cassia occidentalis L. # CASOC) with cotton (Gossypium hirsutum L.). With season-long competition, each increase of 1 coffee senna plant/7.5 m of row reduced seed cotton by 9 to 117 kg/ha. Each additional week of competition from a dense stand (40 plants/m of row) of coffee senna reduced seed cotton yield by 118 kg/ha and cotton main stem height by 1.25 cm. Neither cotton stand density nor fiber properties were affected by coffee senna density or duration of competition. Seed cotton yields and main stem heights obtained when cotton was kept weed free for 6 weeks after cotton emergence were not significantly different from those kept weed free for 8, 10, or 14 weeks. Coffee senna dry-matter production was essentially zero when cotton was maintained weed free for 8 or more weeks.

Soil characteristics, elevation, annual precipitation, potential evapotranspiration, length of frost-free season, and mean maximum July temperature were estimated for 116 established infestations of spotted knapweed (Centaurea maculosa Lam. # CENMA) in Montana using basic land resource maps. Areas potentially vulnerable to invasion by the plant were delineated on the basis of representative edaphic and climatic characteristics. No single environmental variable was an effective predictor of sites vulnerable to invasion by spotted knapweed. Only a combination of variables was effective, indicating that the factors that regulate adaptability of this plant are complex. This technique provides a first approximation map of the regions most similar environmentally to infested sites and, therefore, most vulnerable to further invasion. This weed migration prediction technique shows promise for predicting suitable habitats of other invader species.

Several herbicides were toxic to barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] when applied as a soil treatment at 0.56 kg ai/ha to a sandy loam soil with 0.8% organic matter. At this application rate, haloxyfop {methyl ester of 2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, CGA-82725 {2-propynyl ester of 2-[4-[(3,5-dichloro-2-pyridinyl)oxy] phenoxy] propanoate}, and DPX-Y6202 {ethyl ester of 2-[4-[(6-chloro-2-quinoxalinyl)oxy]-phenoxy] propanoate} provided the greatest persistence of activity. At 31, 28, and 25 days after treatment with these herbicides, respectively, barnyardgrass growth was still inhibited by 50%. Soil activity and persistence of fluazifop {butyl ester of (±)-2-[4-[[5-trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} increased following soil sterilization. Covering the soil surface with vermiculite prior to treatment intercepted the spray and significantly reduced control of 4- to 6-cm-tall barnyardgrass plants with fluazifop.

Greenhouse and field experiments, at two locations in Georgia, evaluated the tolerance of several soft red winter wheat cultivars (Triticum aestivum L.) to postemergence applications of metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one]. In the greenhouse, none of the cultivars growing in pots tolerated a 0.6 kg ai/ha treatment of metribuzin applied at the two-to three-tiller, six- to nine-tiller, or early-stem elongation growth stages. In nutrient culture, ‘McNair 1003’ was more tolerant to a 0.15 μg/ml concentration of metribuzin than other cultivars. Significant injury and yield reductions of wheat cultivars treated in the field with 0.6 and 1.1 kg/ha of metribuzin occurred. Differences between the cultivars were not uniform over all experiments. Increased injury was accompanied by higher rainfall and low temperatures subsequent to application. None of the wheat cultivars evaluated in the field experiments was injured by the 0.3 kg/ha rate of metribuzin. Acceptable selective weed control was obtained with this rate, indicating that metribuzin could be used in these soft red winter wheat cultivars.

A fiber system for controlled delivery of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} was evaluated for its potential use in the management of the submersed aquatic weed hydrilla [Hydrilla verticillata (L.f.) Royle # HYLLI] in slow-moving water. The release of fluridone from the fibers was first order and could be extended over several days simply by using fibers of larger diameters. Fibers of 0.8- and 1.2-mm diam released fluridone over a period of 40 and 50 days, respectively. Both effectively controlled hydrilla at a rate of 2.2 kg ai/ha in a 4-month study in replicated pools with water flow adjusted to provide one volume change every 24 h. Under the same conditions, the conventional liquid formulation was ineffective and a pellet formulation provided only marginal control.

Over 20 experiments comparing glyphosate [N-(phosphonomethyl)glycine], dicamba (3,6-dichloro-2-methoxybenzoic acid), fosamine [ethyl hydrogen (aminocarbonyl)phosphonate], and 2,4-D [(2,4-dichlorophenoxy) acetic acid] for control of field bindweed (Convolvulus arvensis L. # CONAR) were conducted from 1976 to 1982 at various times of the year and different stages of weed growth. In three of the studies, 1.7, 3.4, and 5.0 kg ae/ha of glyphosate gave 54, 72, and 80% control, respectively, 1 yr after application. Control with glyphosate at 3.4, 2,4-D at 1.1, dicamba at 1.1, and fosamine at 13.7 kg ae/ha in the 20 studies was 71, 55, 57, and 73%, respectively, 1 yr after application. Glyphosate, 2,4-D, and fosamine gave good control at any time of the year if weed growth was lush. Dicamba gave good control anytime if growth was good and in the fall regardless of growing conditions. Control with mixtures of dicamba and picloram, picloram and 2,4-D, or glyphosate and picloram was higher than with the other herbicides. Dicamba at 1.1 kg/ha, applied after August caused some injury to wheat planted the same fall. Herbicide combinations with picloram at 0.28 kg/ha applied after June injured wheat planted in the fall.

Laboratory photolysis rates of 2,4-D [(2,4-dichlorophenoxy)acetic acid], bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], and haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} in dilute aqueous solution were enhanced by the presence of adjuvants. Addition of 1.0% (v/v) petroleum oil concentrate (POC), 1.0% (v/v) soybean oil concentrate (SBOC), and 0.15% (v/v) emulsifier package (EP) enhanced herbicide photolysis rates more than addition of 0.15% (v/v) oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate). Bioassays showed that phytotoxicity of photolyzed herbicide solutions was negatively correlated with time of exposure to ultraviolet light. Addition of 0.85% (v/v) acetophenone to aqueous herbicide solutions containing 0.15% (v/v) oxysorbic strongly sensitized photodegradation of 2,4-D, and to a lesser extent, haloxyfop. Acetophenone had no effect on bentazon photolysis in the presence of oxysorbic. In another study, herbicides were dissolved in white mineral oil or once-refined soybean oil and exposed to ultraviolet light. After a 6-h exposure, there was 92% loss of haloxyfop in mineral oil and 36% loss in soybean oil. There was no difference between oils in affecting the photolysis rate of 2,4-D or bentazon.

Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} at 2 or 4 ppmw placed 0 to 3, 8 to 11, or 15 to 18 cm deep in soil columns reduced root and shoot weights of buffelgrass [Pennisetum ciliare (L.) Link # PESCI] 30 days after emergence. Plains bristlegrass (Setaria macrostachya H.B.K.) seedling shoot weights were not reduced when 2 ppmw tebuthiuron was placed 8 to 11 cm deep or deeper. Effects of tebuthiuron at 0.13 to 0.50 ppmw on buffelgrass shoot and net tiller production were not moderated by the presence of honey mesquite (Prosopis glandulosa # PRCJG) in the pots. However, regardless of tebuthiuron dosage, average height and shoot weight of buffelgrass seedlings were greater when seedlings were grown in soil collected from beneath honey mesquite canopies compared to growth in soil from interspaces. Therefore, spatial variations in buffelgrass response to applications of tebuthiuron for control of invading shrubs may largely be attributed to soil changes induced by woody plants rather than to presence of shrubs.

Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, RO-13-8895 {acetone-O-[d-2-[p-[α,α,α-trifluoro-p-tolyl-oxy]phenoxy] propionyl] oxime}, and KK-80 {4-[4-[4-(trifluoromethyl)phenoxy] phenoxyl]-2-pentenoic} were evaluated for potential use for controlling quackgrass [Agropyron repens (L.) Beauv., # AGRRE] in perennial ryegrass (Lolium perenne L. ‘NK200’), smooth bromegrass (Bromus inermis Leyss. ‘Sac’), orchardgrass (Dactylis glomerata L. ‘Nordstern’), timothy (Phleum pratense L. ‘Climax’), Kentucky bluegrass (Poa pratensis L. ‘Park’), Reed canarygrass (Phalaris arundinaceae L. ‘Rise’), meadow fescue (Festuca elatior L.), and red fescue (Festuca rubra L.). The three herbicides, when applied postemergence at 1.1 kg ai/ha, caused severe injury to all species except red fescue. ‘Pennlawn’, ‘Ruby’, ‘Dawson’, MN67123, MN673, and MN6354 red fescue entries were tolerant to the three herbicides in both greenhouse and field experiments. Sethoxydim and RO-13-8895 effectively controlled quackgrass in Pennlawn red fescue, but KK-80 was not effective.