Mayweed (Anthemis cotula L. # ANTCO) achenes and seed were germinated in the laboratory at constant temperatures ranging from 5 to 30 C. Maximum percent germination occurred at 20 C for both achenes and seed. Under all conditions tested, achene germination was less than seed germination. Both acid scarification for 15 min and soaking in 14 mM gibberellic acid (GA3) more than doubled achene germination. Pericarp leachate inhibited achene and seed germination only at high concentrations, indicating that inhibitors in the pericarp are not a primary cause of low germination in achenes. Optimum germination of achenes and seed occurred at pH 4.5 and over a range from pH 3 to pH 6. Achene germination was inhibited to a greater degree by moisture stress than was seed germination. It appears that structural integrity of the pericarp is the predominant factor affecting mayweed germination.

The influence of acid scarification on the responsiveness of curly dock (Rumex crispus L. ♯ RUMCR) seeds to physical and chemical factors was studied. Scarification made the seeds responsive to GA4+7 (a mixture of gibberellin A4 + A7) and markedly improved the responsiveness to light, moist-chilling, and a 1-h 40-C temperature shift. Scarification reduced the mechanical restraint of the seedcoat by 0.4 to 0.8 MPa. Removal of the entire pericarp induced 69% germination in the dark. Moist-chilling treatment of seeds reduced the soaking period needed for maximum response to the high-temperature shift from 24 to 6 h. The embryo growth potential generated by moist-chilling was less in magnitude than that by the reduction in seed coat restraint by scarification. Induction of secondary dormancy was prevented to a marked degree in scarified (chilled or unchilled) seeds during polyethylene glycol-6000 (PEG) treatment in light or in the presence of GA4+7 while intact seeds rapidly became secondarily dormant in light. The ability of scarified seeds to remain germinable or nondormant for a longer period than the intact seed in low water potential imbibing medium may be due to a net reduction (by 0.4 to 0.8 MPa) in the impact on the embryo of germination-preventing forces (low water potential plus mechanical restraint of the seed coat).

Herbicide injury to five coniferous species was determined for the butoxyethanol ester of 2,4-D [(2,4-dichlorophenoxy)acetic acid], the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine], and the triethylamine salt of triclopyr {[(3,5,6-trichloro-2-pyridinyl) oxy] acetic acid} throughout the growing season of 1981. The relationship of herbicide tolerance to growth rate, water stress, and photosynthesis was determined for Jeffrey pine (Pinus jeffreyii Grev. & Balif), sugar pine (P. lambertiana Dougl.), red fir (Abies magnifica A. Murr.), white fir [A. concolor (Gord. & Glend) Lindl.], and Douglas fir [Pseudotsuga menziesii (Mirb.) Franco]. Although most of the species showed a high correlation of injury to leader or needle growth rate and xylem pressure potential, the seasonal trend in the degree of injury and the relationship of herbicide tolerance to various physiological factors were unique for each species. Criteria for determining herbicide application periods depended on species and herbicide.

An annual weed, found in Minnesota in the summer of 1984, was identified as Polygonum bungeanum Turcz. This species is not included in floras of North America and may have been introduced from Asia as long ago as 25 yr. Because the stems of this weed are prickly, we propose “prickly smartweed” as a common name for this species. Currently, we know the weed to occur in six counties in southern Minnesota and one county in northern Iowa. Field observations suggest that this species may be at least as competitive as other annual smartweeds.

Cotton (Gossypium hirsutum L. ‘Stoneville 213’) was grown on Lucedale fine sandy loam with sicklepod (Cassia obtusifolia L. ♯ CASOB) and a complex of redroot pigweed (Amaranthus retroflexus L. ♯ AMARE) and smooth pigweed (A. hybridus L. ♯ AMACH) in all possible combinations of 0, 1, 2, 4, 8, and 16 weeds of each species per 7.5 m of row. Seed cotton yields decreased as a quadratic function of increasing weed density. One pigweed and one sicklepod plant per 7.5 m of row reduced yields by 9 and 9.7% in 1979 and 1980, respectively. At low levels of infestation (≤4 weeds/7.5 m of row), the competitive effect of pigweed and sicklepod was additive; however, at the high densities, the competitive effect was not additive. Mechanical harvesting efficiency and cotton maturity were not decreased by any weed density. Sicklepod was more competitive than pigweed in both years.

Effects of the imidazolinone herbicide AC243 997 [2-(5-isopropyl)-5-methyl-4-oxo-2-imidazolin-2-yl) nicotinic acid] on the growth of corn (Zea mays L. ‘Black Mexican Sweet’) cell suspension cultures were characterized. The herbicide caused half maximal growth inhibition at concentrations in the range of 10 nM to 30 nM. Significant reductions in protein synthesis were observed following treatment of cells with 10 μM herbicide. Analysis of free amino acid pool sizes indicated that levels of the biosyn-thetically related amino acids leucine and valine were substantially decreased in cells exposed to 10 μM herbicide. Supplementation of suspension culture growth media with leucine and valine plus isoleucine (1 mM each) reversed growth inhibitory effects of AC243 997 at levels ranging from 10 nM to 1 mM. The results suggest a specific interaction of this imidazolinone herbicide with leucine, valine, and isoleucine metabolism.

Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was superior to 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], dicamba (3,6-dichloro-o-anisic acid), picloram (4-amino-3,5,6-trichloropicolinic acid), and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} for control of honey mesquite (Prosopis glandulosa Torr. ♯ PRCJG) in the field. However, equal ratio mixtures of clopyralid + picloram or triclopyr (0.28 + 0.28 or 0.56 + 0.56 kg ae/ha) were as effective for honey mesquite control as clopyralid at rates of 0.56 and 1.12 kg/ha. Equal mixtures of picloram + 2,4,5-T, picloram + triclopyr, picloram + dicamba, triclopyr + 2,4,5-T, or triclopyr + dicamba were less effective in controlling honey mesquite than clopyralid alone or clopyralid + picloram or triclopyr in 1:1 mixtures. In the greenhouse, mixtures of clopyralid + 2,4,5-T, picloram, or triclopyr were highly effective for the control of honey mesquite. Mixtures of 2,4,5-T + picloram, 2,4,5-T + triclopyr, or triclopyr + picloram were also effective when applied at 0.28 + 0.28 kg/ha.

Interference studies utilizing manipulated and natural infestations of giant foxtail (Setaria faberi Herrm. ♯ SETFA) in soybeans [Glycine max (L.) Merr. ‘Williams’] were conducted at Urbana, IL, in 1982 and 1983. Giant foxtail clumps, each consisting of 3 to 6 plants per dm2, were used to determine the effect of clump density on giant foxtail dry weight and soybean seed yield. In both years, regression equations predicted a soybean seed yield loss of 0.8% for each giant foxtail clump per 9 m of row. The highest density of 30 clumps per 9 m of row reduced soybean yield 26%. In a second study, fluazifop {(±)-2-[4-[(5-(trifluoromethyl)-2-pyridinyl)oxy]phenoxy]propanoic acid} at 0.28 kg ai/ha or fluazifop + alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl)acetanilide] at 0.28 + 2.24 kg/ha applied 10 or 15 days after emergence gave maximum giant foxtail control with little or no reduction in soybean seed yield. Interference from uncontrolled giant foxtail began to reduce soybean dry-matter accumulation 15 days after emergence under favorable growing conditions in 1982. Under less favorable conditions in 1983, similar effects were not observed until 25 days after emergence.

Populations of large-flowered taxa of Carduus from many locations in the United States and Canada were grown in a common nursery from 1975 to 1983 at Lincoln, NE. Dates of first bloom and associated degree-day accumulation data exhibited some consistent relationships. Four species appeared to be represented in the collection. These included Carduus thoermeri Wein., C. macrocephalus Desf., and musk thistle (C. nutans L. ♯ CRUNU). A collection from British Columbia should be accorded species status but apparently has not been named in the literature. Interbreeding has taken place in the nursery and these combinations are intermediate between C. thoermeri and C. macrocephalus and between C. thoermeri and the British Columbia material. Some morphological characteristics supported these separations.

The dispersion of ethylene in the soil after application from a backpack ethylene applicator (BPEA) was determined using a bioassay of witchweed [Striga asiatica (L.) Kuntze # STRLU] seed germination. Witchweed seed were buried in packets in ridged seedbeds under field conditions. Ethylene dispersion was better when injected into the furrow than into the ridge top. Injections 30 cm deep were more effective in causing seed germination than injections 15 cm deep. Seed germination induced by ethylene injection into the furrow 30 cm deep was 13% more than that obtained from the ridge top injection 15 cm deep. Seed germination as high as 90% was obtained at soil depths to 75 cm at a horizontal distance of 100 cm from the point of ethylene injection. Ethylene diffused up to 300 cm horizontally and to 75 cm vertically to cause at least 45% seed germination in a field of Lakeland soil (Typic Quartzisamment). The BPEA was found to be an effective application tool in witchweed control operations.

Experiments were conducted in the field and controlled-environment chambers to determine wild oat (Avena fatua L. # AVEFA) control with difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) as influenced by applications at 4-h intervals during the day. Difenzoquat phytotoxicity was significantly higher in four of the six field experiments when applied at 1300 and 1700 h than at other times and was increased in the other two experiments. Difenzoquat phytotoxicity increased with temperature at treatment in the field experiments. Wild oat control was not increased by 8 h of 28 C before or after difenzoquat application compared to a constant 18 C in controlled-environment chambers. In controlled-environment chambers, wild oat control with difenzoquat was not influenced by the time of application during the day when humidity and temperature were kept constant.

The influence of relative planting date on the growth of common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANST), common ragweed (Ambrosia artemesiifolia L. ♯ AMBEL), sicklepod (Cassia obtusifolia L. ♯ CASOB), and redroot pigweed (Amaranthus retroflexus L. ♯ AMARE) grown in competition with soybean [Glycine max (L.) Merr. ‘Bragg’] was studied in the greenhouse. Increases in dry matter and height were slower for the five weed species than for soybean throughout the period of the study. The root: shoot ratio of soybean was the highest of any plant in the study, while common ragweed, common cocklebur, common lambsquarters, and sicklepod were intermediate, and redroot pigweed was the lowest. Soybean dry weight was always reduced when grown in competition with a weed. Soybean dry-matter production was reduced most when weeds were planted 2 weeks before soybean, especially with common cocklebur and common lambsquarters. Weed dry-matter content was severely reduced when the weed seed were planted simultaneously with or following soybean. Soybean height was usually reduced by competition with the weeds. The height of common ragweed was increased, however, when planted simultaneously with soybean. Common lambsquarters, redroot pigweed, and common ragweed heights were increased when planted 2 weeks prior to soybean.

Field studies were established in 1974 and 1975 at various locations in San Diego County, CA, to evaluate several herbicides for the control of chamise (Adenostoma fasciculatum H.&A.) and redshank chamise (Adenostoma sparsifolium Torr.). Herbicide effects on vegetation were reevaluated in 1982. Plots originally treated with 2.2 or 4.5 kg ae/ha of glyphosate [N-(phosphonomethyl)glycine] had virtually no chamise regrowth 8 yr after treatment. The herbicides 2,4-D [(2,4-dichlorophenoxy)acetic acid], combinations of 2,4-D with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] or dichlorprop [2-(2,4-dichlorophenoxy) propionic acid], fosamine [ethyl hydrogen (aminocarbonyl)phosphonate], triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and picloram (4-amino-3,5,6-trichloropicolinic acid) had no long-term effects on chamise. Soil collected in 1982 from glyphosate-treated plots contained similar numbers of chamise seeds but fewer seeds of other species compared to untreated plots. Canopy cover of redshank chamise was similar in treated and untreated plots after 8 yr. These results document the effectiveness of glyphosate in killing the underground root-crown of chamise, which prevented sprouting, but not redshank chamise.

Studies were conducted to evaluate seed and root reproduction and herbicide sensitivity of maypop passionflower (Passiflora incarnata L. ♯ PAQIN). Water-leached seeds that were not exposed to light had the greatest germination (53%). Depending on soil type, seedlings emerged from depths of 10 to 12 cm. Most rapid germination and seedling development occurred between 30 and 35 C. Plants rapidly produced an extensive system of lateral roots and rhizomes that had regenerative capability at maturity. Root or rhizome sections of only 0.5 cm in length had a 20% regeneration rate. Desiccation effectively reduced viability of root and rhizome pieces. Effective herbicide control was limited to the triethylamine salt of triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} at 2.2 ai kg/ha, alkanolamine salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 1.7 kg/ha, and dicamba (3,6-dichloro-o-anisic acid) at 0.3 to 0.6 kg/ha.

Cotton (Gossypium hirsutum L. ‘Westburn M’) was grown for 2 yr at two locations with full-season interference from buffalobur (Solanum rostratum Dunal ♯ SOLCU) at densities ranging from 0 to 64 plants/10 m of row. Dry weight of buffalobur harvested increased by 0.063 to 0.303 kg/plot for each additional weed/10 m of row. Intraspecific competition among buffalobur plants was observed at the higher weed densities. Cotton plant height was reduced by 16 and 32 buffalobur plants/10 m of row (or more) at Tipton and Perkins, OK, respectively, when compared with cotton grown under weed-free conditions. The threshold densities at which initial lint yield reductions occurred were 8 buffalobur plants/10 m of row in 1982 and 1983 at Tipton and 32 and 2 plants/10 m of row at Perkins in 1982 and 1983, respectively. Lint yields were reduced curvilinearly from 6 to 18 kg/ha for each additional buffalobur plant/10 m of row. Fiber quality was not significantly influenced by weed density when analyzed over all experiments; however, 50% span length, uniformity index, and micronaire were adversely affected in some environments.

In greenhouse and controlled-environment tests, velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH) and prickly sida (Sida spinosa L. ♯ SIDSP) control with Fusarium lateritium Nees ex Fr. was affected by inoculum concentration and plant growth stage at the time of inoculation, by postinoculative air temperature, and by dew period duration and temperature. A higher level of control of both weeds was obtained with inoculum concentrations of 7.5 × 105 and 1.5 × 106 macroconidia/ml when the weeds had fewer than seven true leaves. Postinoculative air temperatures above 25 C significantly reduced control of both weeds. Mortality of both species was higher at dew temperatures of 25 C than at temperatures of either 15 or 35 C. At least 12 h of dew at 25 C was required to achieve satisfactory control of prickly sida, while a dew period of 16 h was required to achieve a comparable level of control of velvetleaf.

Twenty herbicides were applied to a rangeland pasture in the Post Oak Savannah Resource Area of Texas in April 1978 and May 1979. At time of treatment, total vegetation cover was 88 to 100%, with 36% grasses and 52 to 64% broadleaf cover. From May 31 through September, total, grass, and broadleaf covers were 89 to 100, 51 to 65, and 27 to 44%, respectively. One to 2 months after treatment, grass cover generally increased except where certain herbicides, particularly bromacil (5-bromo-3-sec-butyl-6-methyluracil), dalapon (2,2-dichloropropionic acid), glyphosate [N-(phosphonomethyl)glycine], or hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4 (1H, 3H)-dione] had been applied. By September or October in the year of application only dalapon consistently reduced grass cover. In the year following treatment, grass cover was still reduced on the dalapon-treated plots. Most herbicides reduced broadleaf cover in the year of treatment. Broadleaf cover returned most rapidly to those areas treated with dalapon. During the year following treatment, broadleaf cover remained low on plots treated with picloram (4-amino-3,5,6-trichloropicolinic acid), 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and picloram + 2,4,5-T. For plots treated in 1978, the grass and broadleaf standing-crop weights of untreated plots were 490 and 450 kg/ha, respectively, in October 1978, and 2707 and 1033 kg/ha in October 1979. In 1978, grass weight increased with several herbicide treatments whereas only dalapon increased the broadleaf weight. For plots treated in May 1979 and harvested in September 1979, grass and broadleaf standing-crop weights of untreated plots were 2629 and 607 kg/ha, respectively.

Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, CGA-82725 {2-propynyl 2-[4-[(3,5-dichloro-2-pyridinyl)oxy]phenoxy]propanoate}, RO 13-8895 {acetone-O-[D-2-[p-(α,α,α-trifluoro-p-tolyl)oxy]phenoxy]propionyl oxime}, and difenopenten {4-[4-[4-(trifluoromethyl)phenoxy]phenoxy]-2-pentenoic acid} were evaluated as single and/or split applications for postemergence control of johnsongrass [Sorghum halepense (L.) Pers. ♯ SORHA] grown from rhizomes in soybeans [Glycine max (L.) Merr.]. Good to excellent control, crop safety, and yield enhancement were achieved with all herbicides evaluated. Antagonism between postemergence grass and broadleaf herbicides was evaluated by applying sethoxydim, CGA-82725, RO 13-8895, and difenopenten alone to soybeans infested with johnsongrass grown from seed, and applying these herbicides as mixtures with acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], or benazolin (4-chloro-2-oxobenzothiazolin-3-ylacetic acid). Acifluorfen was most antagonistic to the activity of postemergence grass herbicides, with difenopenten and sethoxydim the most susceptible to antagonism. Reductons in johnsongrass control were attributed to antagonism by broadleaf herbicides, which caused soybean yield reductions of up to 67%.

A sorghum-sudangrass hybrid [Sorghum bicolor (L.) Moench. x Sorghum sudanense (P.) Stapf. ‘DEKALB SX17+’] (SSH) and foxtail millet [Setaria italica (L.) Beauv.] (FM) were evaluated for their effects on weed populations when grown for forage and as land conditioners prior to late-summer, no-till planting of alfalfa (Medicago sativa L. ‘Arc’). Both grasses established well in no-till situations, except for FM when excessive mulch impeded seed placement or seedling summer-annual weeds were not destroyed at planting time. SSH was the better competitor; after both were planted into a dense stand of seedling summer-annual weeds, SSH outyielded the weeds while FM did not. Both grasses suppressed weeds and enhanced subsequent alfalfa establishment. Obtaining adequate alfalfa stands was not a problem in no-till seedings: seedling populations often exceeded 300/m2 3 to 6 weeks after planting. Lack of adequate weed control was associated with stand losses in which disease was also a factor. Biennial and perennial broadleaf species were the predominant weeds. Prior cropping of SSH or FM is a valuable option for growers wishing to establish alfalfa without tillage, particularly when summer forage is useful.

In four tests conducted in 2 years, Alternaria cassiae Jurair and Khan effectively controlled sicklepod (Cassia obtusifolia L. ♯ CASOB) as indicated by stand counts of the weed and by soybean [Glycine max (L.) Merr.] yields. The number of sicklepod seedlings was reduced more than 90% within 14 days after foliar applications of A. cassiae conidia were banded (46 cm) at rates of 4.2 and 2.1 kg/ha (9.4 and 4.7 kg/ha broadcast, respectively). One banded application of 0.04 or 0.4 kg/ha (0.09 or 0.9 kg/ha broadcast, respectively) did not satisfactorily control sicklepod. These results indicate that sicklepod control may be enhanced by multiple applications of A. cassiae.