Absorption and translocation of 14C-fluazifop-butyl {butyl ester of (±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoate} was compared in susceptible quackgrass [Agropyron repens (L.) Beauv. ♯3 AGRRE] and tolerant soybean [Glycine max (L.) Merr.]. Foliar absorption was more rapid in soybeans with 75% of the recovered 14C absorbed 6 h after treatment compared to 36% in quackgrass. Translocation of the radiolabel occurred in both soybean and quackgrass with no significant difference between the species. Differential absorption and translocation did not contribute to the selectivity of fluazifop-butyl. Herbicidal activity was lower on quackgrass plants at the five- to six-leaf stage when compared to the two- to three-leaf stage. Greater quackgrass control was observed at 30 than at 20 C. Foliar absorption of 14C-fluazifop-butyl was significantly greater at 30 than at 20 C. Translocation of the radiolabel was greater in plants exposed to full light as compared to shade. Moisture stress significantly reduced quackgrass control with fluazifop-butyl.

The phytotoxicity of difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) applied to the three-leaf stages of hard red spring wheat (Triticum aestivum L. ‘Waldron’ and ‘Era’), barley (Hordeum vulgare L. ‘Beacon’) and wild oat (Avena fatua L. ♯ AVEFA) grown under constant, fluctuating, or alternating day-night temperatures was determined in controlled environment chambers. Difenzoquat injury to wild oat and Era wheat was greater at a constant 20 or 30 than at 10 C; however, injury to Waldron wheat was similar at 10, 20, and 30 C. Difenzoquat caused only slight injury to barley, and injury was similar at all temperatures. In Era wheat, selectivity of difenzoquat for wild oat was maximum with a 10-C night temperature in an otherwise 30-C-temperature environment; in Beacon barley selectivity was maximum with 3 or more days of 20- or 30-C posttreatment temperature; and in Waldron wheat selectivity was not adequate at any of the temperatures studied.

When applied in early February, simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], pronamide [3,5-dichloro-(N-1,1-dimethyl-2-propynyl)benzamide], secbumeton [N-ethyl-6-methoxy-N′-(1-methylpropyl)-1,3,5-triazine-2,4-diamine], and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] effectively removed weedy Bromus species from established alfalfa (Medicago sativa L.) and increased yields of alfalfa forage. Diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], terbacil (3-tert-butyl-5-chloro-6-methyluracil), and hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine- 2,4(1H,3H)-dione] had no adverse effects on yields of alfalfa when applied in late March. Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) was somewhat less effective for controlling weeds when applied in late March than when applied in February. When applied to weed-free stands of alfalfa after dormancy was broken, metribuzin, terbacil, hexazinone, and simazine, but not pronamide, significantly reduced yields of alfalfa. Terbacil applied immediately after the first cutting did not significantly reduce yields of the second cutting. Terbacil and bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] applied when alfalfa had 5 cm of regrowth significantly reduced yields.

A 3-yr study was conducted to compare the performance of several herbicides applied alone and in mixtures under three flooding conditions in dry-seeded rice (Oryza sativa L. ‘Labelle’). When the soil remained moist during the 2-week unflooded periods (1979 and 1981), weed emergence was slowed and no advantage with respect to enhanced weed control and increased rice yields could be demonstrated over that of the standard sequential propanil (3′,4′-dichloropropionanilide) application. However, in 1980 when drought stress may have reduced initial postemergence activity and weeds emerged during the 14-day unflooded periods, differences in weed control between herbicides were obtained. Results of this study also indicate that yield losses from weed competition resulted primarily from early season competition, and that the principal advantage of the residual herbicides in dry-seeded rice may be to eliminate the need for retreatment with propanil when flooding is delayed or fields are drained.

The basis for differences in response of eastern black nightshade (Solanum ptycanthum Dun.), a tolerant species, and velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH), a susceptible species, to foliar-applied chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide} was investigated by evaluating differences in spray retention and herbicide absorption, translocation, and metabolism. Based upon a foliar-applied rate causing a 50% reduction in dry weight, velvetleaf was greater than 20000 times more susceptible to chlorsulfuron than was eastern black nightshade. The differences detected in spray retention, absorption, and translocation were inadequate to account for the large response differences between the two species. The primary difference found was in the rate of chlorsulfuron degradation. In eastern black nightshade, 69.9% of the absorbed chlorsulfuron was metabolized within 24 h of application and 81.1% within 72 h of application. Only 7.1% of absorbed chlorsulfuron was metabolized in velvetleaf in a 72-h period.

Sethoxydim {2-[1-(ethoxyimino)-butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one}, KK 80 {ethyl-4-[4-[4-(trifluoromethyl)phenoxy] phenoxy]-2-pentenoate}, and RO-13-8895 {acetone-0-2-[D-2-[δ,δ,δ-trifluoro-p-tolyl)-oxy] phenoxy] propionyl] oxime} did not injure plants visibly or reduce the yield of tomatoes (Lycopersicon esculentum L.). Diclofop LC [2,4-(2,4-dichlorophenoxy)phenoxy] propanoic acid] and diclofop HC in combination with oil or surfactant reduced tomato yield because tomatoes retained more of these spray solutions. No herbicide treatments injured onions (Allium cepa L.). All compounds controlled most grass weeds. Tomato plants grown at 29/18 C were injured more by some diclofop treatments than plants grown at 18/7 C. Cell membrane permeability of tomato plants treated with diclofop alone or in combination with adjuvants increased as visual injury symptoms became more severe.

Studies were conducted to measure the foliar activity of sethoxydim (BAS 9052 OH) {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl-3-hydroxy-2-cyclohexen-1-one} and RO-13-8895 {acetone-O-[D-2-[p-[(α,α,α-trifluoro-p-tolyl)-oxy] phenoxy] propionyl] oxime} as affected by adjuvants, soil moisture, and growth stage of grasses, and to compare the responses of three grass species to these herbicides. The activity of both herbicides was increased by adjuvants. The activity of sethoxydim was not significantly affected by soil moisture. Goosegrass [Eleusine indica (L.) Gaertn. ♯3 ELEIN] and broadleaf signalgrass [Brachiaria platyphylla (Griseb. ♯ BRAPP) Nash] control was greater with RO-13-8895 at the high than at the low soil moisture level. Soil moisture did not influence large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA] control, since it was relatively tolerant to RO-13-8895. Both herbicides gave greater control at early than at late growth stages. When averaged over all variables, sethoxydim gave greater large crabgrass control than RO-13-8895, but RO-13-8895 gave greater goosegrass and broadleaf signalgrass control than sethoxydim.

The efficacy of siduron [1-(2-methylcyclohexyl)-3-phenylurea] on bermudagrass [Cynodon dactylon (L.) Pers. CYNDA3] in bentgrass (Agrostis spp.) golf greens was evaluated. In field trials, the frequency of bermudagrass occurrence in most treatments either remained unchanged or increased. Cultural treatments such as vertical mowing and aerifying did not improve the efficacy. Dry-weight measurements showed no significant differences due to chemical treatments. In pot trials, differential susceptibility of collections of bermudagrass was evident, supporting the hypothesis that selection of tolerant strains over several years' use of the herbicide has caused the poor efficacy seen in the field. Differences in the development of shoot, root, and rhizome systems between treated and untreated were evident.

Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} was evaluated on three Wyoming soil types for control of big sagebrush (Artemisia tridentata Nutt.), silver sagebrush (Artemisia cana Pursh.), and phytotoxic effects on associated vegetation. Big sagebrush was controlled with tebuthiuron at application rates of 0.6 to 1.1 kg ai/ha, whereas silver sagebrush was not completely controlled. Prairie junegrass [Koeleria pyramidata (Cam.) Beauv.], western wheatgrass (Agropyron smithii Rydb. ♯3 AGRSM), needleandthread (Stipa comata Trin. ♯ STDCO), and green needlegrass (Stipa viritdula Trin. ♯ STOVI) were not significantly reduced with tebuthiuron up to 1.1 kg ai/ha. Blue grama (Bouteloua gracilis H.B.K. ♯ BOBGR), downy brome (Bromus tectorum L. ♯ BROTE), plains pricklypear (Opuntia polyacantha Haw. ♯ OPUPO), and broom snakeweed [Gutierrezia sarothrae (Pursh.) Britt. and Rugsby, ♯ GUESA] were tolerant to tebuthiuron at rates up to 1.1 kg ai/ha.

In greenhouse studies, control of common ragweed (Ambrosia artemisiifolia L. ♯ AMBEL) and common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE) was achieved whether or not soybeans [Glycine max L. (Merr.) ‘Ransom’] partially shielded the weeds from foliar applications of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}. Excellent control (> 90%) of common ragweed was obtained in the greenhouse 2 and 4 weeks after plant emergence. Best control (> 90%) of common cocklebur was obtained 2 weeks after plant emergence. A simulated rainfall of 0.6 cm occurring 1 min after acifluorfen application did not decrease control or fresh weight of common ragweed in greenhouse studies. The weed control efficiency of acifluorfen on common cocklebur was reduced when the herbicide was applied intermittently within 6 h of the 0.6-cm simulated rainfall. The weed control efficiency of acifluorfen on both weed species was also reduced when the herbicide was applied intermittently within 6 to 12 h of a 1.3-cm simulated rainfall in greenhouse studies. In field studies, 2.5 cm of simulated rainfall within 12 to 24 h after acifluorfen application reduced control of common ragweed.

The phytotoxicity of postemergence propanil (3′,4′-dichloropropionanilide) to hard red spring (HRS) wheat (Triticum aestivum L.) was determined in the field and controlled environmental chamber. HRS wheat tolerance to propanil was influenced by cultivar, crop growth stage at time of application, and posttreatment temperature. Injury to wheat from propanil was greater at the five- than two-leaf stage of application and at 30- than at 10- or 20-C posttreatment temperatures. ‘Butte’ wheat was the most susceptible HRS wheat cultivar to propanil, with yield reductions ranging from 15 to 40% depending upon year and crop growth stage at application.

In greenhouse and field studies, sethoxydim {2-[1-(ethoxyimino)-butyl]-5-(2-ethylthio)-propyl]-3-hydroxy-2-cyclohexen-1-one} provided good control of quackgrass [(Agropyron repens L. (Beauv.) ♯ AGRRE] in potato (Solanum tuberosum L. ‘Russet Burbank’). Level of control with sethoxydim at 0.6 kg ai/ha in the greenhouse was improved by the addition of a surfactant at 1.0% (v/v) of spray volume. Removal of quackgrass shoots at 6 or 24 h after treatment resulted in decreased control at application rates of 0.6, 1.0, and 1.6 kg ai/ha. Application of sethoxydim at 1.2 or 1.6 kg ai/ha in the field gave excellent control of quackgrass when applied at either the three- or six-leaf stage. Cultivation at 2 days after treatment did not adversely affect level of control obtained. Sethoxydim did not cause any adverse effect on potato yield, but delaying application until the six-leaf stage of quackgrass resulted in yield loss due to quackgrass competition.

In greenhouse studies, postemergence applications of 0.1 or 0.3 kg ai/ha mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} as a tank mixture with 0.3, 0.4, or 0.6 kg ai/ha acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, or as a pretreatment 3, 5, or 7 days prior to acifluorfen treatment, often increased injury to ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. ♯3 IPOHE], velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH), and common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE), compared to the injury from either herbicide alone. All sequential treatments with 0.1 kg ai/ha mefluidide and 0.3 kg ai/ha acifluorfen increased injury and decreased dry weight of ivyleaf morningglory and velvetleaf when compared with 0.6 kg/ha acifluorfen alone.

Seed size and weight significantly affected witchweed [Striga asiatica (L.) Kuntze = S. lutea Lour. ♯4 STRLU] seed germination, witchweed emergence, and host-parasitization. Witchweed seed were divided into four groups for testing; large (> 149 microns in diameter) and heavy (specific gravity greater than one) (LH), large and light (specific gravity less than one) (LL), small (< 125 microns in diameter) and heavy (SH), and small and light (SL). Germination percentages were 87, 84, 58, and 26 for LH, LL, SH, and SL, respectively. Corn (Zea mays L.) was planted in pots containing soil infested with these four seed categories. The total number of witchweed plants (submerged plus emerged) per pot containing LH, LL, SH, and SL witchweed seed was 65, 12, 0, and 0, respectively, and the number of witchweed plants that emerged was 19, 4, 0, and 0 per pot. There were no significant differences in shoot weights of corn grown in the pots either between kinds of witchweed seed infesting the soil or between plants grown in infested soil and plants grown in soil that did not contain witchweed seed. Roots of corn plants grown in soil infested with LH seed were significantly heavier than those grown in soil infested with any other seed class and heavier than those from soil that did not contain witchweed seed. No other seed class significantly affected root weight.

Twenty-nine wild oat (Avena fatua L. ♯3 AVEFA) and Avena sterilis L. ♯ AVEST accessions having various areas of origin and/or growth characteristics were grown to maturity in controlled environmental chambers. The four environments consisted of a 16-h photoperiod until 3 weeks after emergence, when the photoperiod was decreased (DP) 1 h per week for 8 weeks at a constant 14, 20, or 26 C (DP 14, DP 20, or DP 26); and an 8-h photoperiod until 3 weeks after emergence, when the photoperiod was increased (IP) 1 h per week for 8 weeks at a constant 20 C (IP 20). The relative growth rate of the accessions was similar in each environment. The length of the second leaf was up to 15 cm greater under 8- than 16-h day length at 20 C for some accessions, but was similar under both day lengths for other accessions. The width of the second leaf was greater under 14 than 20 C and was narrower with a 16-h than an 8-h photoperiod. Tiller initiation was slower in the DP 14 and IP 20 than in the DP 20 and DP 26 environments. Days to panicle emergence for individual accessions ranged from 10 to 57 days higher in the DP 14 than in the DP 20 environment. Seed produced on plants grown at 14 C had lower germination in water and 1500 ppm gibberellic acid than seed from plants grown at 20 C. Wild oat accessions varied in morphological characteristics, days to panicle emergence, and dormancy, and responded differently to changes in photoperiod and temperature. Wild oat morphological characteristics, days to panicle emergence, and dormancy did not consistently relate to species or area of origin.

The decline in the natural soil population of seeds of wild mustard [Brassica kaber (DC.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler ♯ SINAR] under nine cultural and chemical practice treatments was studied under field conditions. Wild mustard plants were not allowed to produce seeds in any treatment. After seven growing seasons, treatments in which the soil was not disturbed (continuous grass sod or continuous chemical fallow) had approximately 50% of the original population of wild mustard seeds remaining. In contrast, less than 3% of the original population of wild mustard seeds remained in a treatment that involved plowing three times a year with additional tillage throughout the growing season. This 3%, however, was equivalent to 2.4 million seeds/ha in the plow layer. Eradication of wild mustard from an infested field may be impractical with currently available techniques.

Growth and competition of barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCG] and redroot pigweed (Amaranthus retroflexus L. ♯ AMARE) were studied at different seed proportions, seed burial depths, and soil moisture levels. After 7 days, emergence from 1-, 2-, 4-, and 8-cm depths was 96, 90, 83, and 27% for barnyardgrass and 84, 73, 62, and 0% for redroot pigweed, respectively. Barnyardgrass was more competitive than redroot pigweed. Intraspecific competition of barnyardgrass was greater than interspecific competition from redroot pigweed. Increasing planting depth from 1 to 4 cm and increasing soil moisture from 30 to 50% (low) to 100% (high) of field capacity reduced the competitive ability of redroot pigweed.

Freshly harvested Drummond rattlebox [Sesbania drummondii (Rydb.) Cory ♯3 SEBDR] seed germinated best after 2.5- to 4-h acid scarification in concentrated sulfuric acid. Optimum temperature for germination was 30 to 35 C. At 10 and 45 C no germination occurred for up to 7 days. Six days after planting in a silt loam soil there was 95 and 80% emergence of Drummond rattlebox from depths of 0.5 and 1 cm, respectively. No emergence was observed from depths of 11 cm or greater 12 days after planting.

Field studies were conducted to evaluate the effect of quackgrass [Agropyron repens (L.) Beauv. ♯ AGRRE] density and soil moisture on corn (Zea mays L.) growth and yield. Quackgrass densities ranging from 65 to 390 shoots/m2 reduced corn yield 12 to 16%. A quackgrass density of 745 shoots/m2 reduced corn yields an average of 37% and significantly reduced corn height, ear length, ear-fill length, kernels/row, rows/ear, and seed weight. In the soil moisture study, quackgrass was shorter than corn throughout the growing season, and analyses of corn leaf tissue indicated that quackgrass did not interfere with the nutrient status of the corn. In 1979, soil moisture was not limiting and corn yields were similar in all treatments regardless of irrigation or the presence of quackgrass. In 1980, soil moisture was limited and irrigation increased the yield of quackgrass-free corn. Irrigation also increased the yield of quackgrass-infested corn to a level similar to irrigated corn. When light and nutrients are not limiting factors, an adequate supply of soil moisture can eliminate the effects of quackgrass interference on the growth, development, and yield of corn.

An assessment was made of various parameters to measure growth of soybean [Glycine max (L.) Merr. ‘Wilkin’] and einkorn (Triticum monococcum L.) cell suspension cultures to establish convenient methods of screening the effects of chemicals. Methods assessed were settled cell volumes, packed cell volumes, absorbance at 525 nm of sonicated aliquots, dry weights (of aliquots or entire flask contents), and electrical conductivity and pH of the culture medium. Settled cell volumes, conductivity, and dry-weight changes were the most useful of the methods tested for determining the phytotoxicity of a nonionic linear alcohol ethylene oxide detergent (an adduct of 1-dodecanol containing eight ethylene oxide units) and the methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}. Because 3 to 4 weeks were required to assess whether the cultures could grow out of the initial inhibition by the detergent or herbicide, none of the methods was rapid. Advantages and disadvantages of the various methods and their relative values for screening compounds are described.