Greenhouse and laboratory investigations using four soils were conducted to determine the influence of seven herbicides on symbiotic nitrogen (N2) fixation by soybeans [Glycine max (L.) Merr. ‘Davis’]. Soils were treated with recommended rates of herbicides immediately after planting. After 8 to 10 weeks the nodulated root systems were assayed for nitrogenase activity using the acetylene (C2H2) to ethylene (C2H4) reduction technique, and total numbers and dry weights of nodules were determined. Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] (0.3 kg/ha) decreased nodule dry weight and C2H4 production per plant per hour in a Convent sandy loam. Alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl) acetanilide] (2.2 kg/ha) and prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] (0.6 kg/ha) also decreased C2H4 production per plant per hour in a Convent sandy loam, while metribuzin (0.6 kg/ha) increased C2H4 production per plant per hour and per milligram of nodule dry weight in a Mhoon silt loam. Prometryn (1.7 kg/ha) increased production of C2H4 per plant per hour in a Moreland silt loam. None of the herbicides affected C2H4 production, nodule number, or nodule dry weight in a Commerce silt loam.

The influence of sublethal levels of a number of herbicides and plant growth regulators on the germinability of the seeds and the growth and development of seedlings of mouseearcress [Arabidopsis thaliana (L.) Heynh. ♯ ARBTH] was determined. Only 7 of the 22 chemicals tested had a persistent effect on progeny. Amitrole (3-amino-s-triazole) was one of the most effective compounds. It caused a characteristic bleaching only in shoot tips and pods in parent plants and appeared to act directly on the progeny by accumulation in the seed. Two auxin transport inhibitors, TIBA (2,3,5-triiodobenzoic acid) and CPII (5-O-carboxyphenyl-3-phenylisoxazole), and four of the six photosynthetic electron transport inhibitors included in the study also affected progeny. They appeared to act indirectly by interfering with seed development.

The fate of 14C-sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} in an aqueous solution and on glass exposed to light was evaluated. Within 1 h, more than 80% of the 14C-sethoxydim was transformed to six major products. Qualitatively the transformations were similar for both systems, and a single end product constituted the majority of 14C after 72 h. Two transitory compounds were found to be phytotoxic to barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCG] and were more stable than sethoxydim. A nonphytotoxic compound isolated and identified by mass spectroscopy was desethoxy-sethoxydim.

The effects of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4 (1H, 3H)-dione] and its metabolites, A [3-(4-hydroxycyclohexyl)-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4 (1H,3H)-dione], B [3-cyclohexyl-6-(methylamino)-1-methyl-1,3,5-triazine-2,4 (1H,3H)-dione], C [3-(4-hydroxycyclohexyl)-6-(methylamino)-1-methyl-1,3,5-triazine-2,4 (1H,3H)-dione], D [3-cyclohexyl-1-methyl-1,3,5-triazine-2,4,6 (1H, 3H,5H)-trione], and E [3-(4-hydroxycy clohexyl)-1-methyl-1,3,5-triazine-2,4,6 (1H,3H,5H)-trione], on photosynthesis of loblolly pine primary needle segments were studied using a bioassay technique. Hexazinone, at concentrations equal to or greater than 1.0 × 10-6 M, inhibited photosynthesis, while 1.0 × 10-8 M and 1.0 × 10-7 M concentrations increased photosynthesis. Metabolite B at 1.0 × 10-4 M also inhibited photosynthesis. Metabolites A, C, D, and E did not affect photosynthesis at 1.0 × 10-4 in pine needle segments. The bioassay proved simple and useful for determining effects of certain herbicides and metabolites on photosynthesis.

Effects of fluazifop-butyl {(±)-butyl 2-[4-[(5-(trifluoromethyl)-2-pyridinyl)oxy] phenoxy] propanoate} on cellular uptake and incorporation of 14C-leucine, 14C-uridine, and 14C-thymidine into protein, RNA, and DNA, respectively, were evaluated in corn (Zea mays L.) coleoptiles and soybean [Glycine max (L.) Merr.] hypocotyls. Uptake of 14C-leucine in corn coleoptiles was inhibited by fluazifop-butyl at 10-4 to 10-7 M, which was related to reductions in incorporation of 14C-leucine into protein at 10-4 to 10-6 M. The effect of fluazifop-butyl on 14C-leucine uptake and incorporation was reduced by 2 × 10-6 M 2,4-D [(2,4-dichlorophenoxy)acetic acid], indicating antagonism between these herbicides. RNA and DNA synthesis were inhibited at 10-5 and 10-4 M. Protein synthesis in soybean hypocotyls was stimulated by 10-7 and 10-6 M fluazifop-butyl 33 and 27%, respectively, and inhibited by 10-4 M 50%. RNA and DNA synthesis were also inhibited by 10-4 M in soybean.

Effects of soil pH on growth, competitive ability, and leaf nutrient content of corn (Zea mays L.), Powell amaranth (Amaranthus powellii S. Wats. ♯ AMAPO), velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH), and green foxtail [Setaria viridis (L.) Beauv. ♯ SETVI] were measured in the field. Corn yields were significantly reduced by weed competition at all pH levels, but leaf nutrient content, as a percentage of dry weight, was not affected. Aboveground dry weights of Powell amaranth and velvetleaf were significantly lower at pH 4.8 than at pH 6.0 or 7.3, whereas growth of green foxtail was greater at pH 4.8 than at pH 7.3. Weed competitive ability, as evidenced by reductions in dry weight, varied with soil pH and companion plant. Powell amaranth and velvetleaf had higher levels of S, Zn, and especially Mn, at pH 4.8 than at pH 7.3. N and K in the leaf tissue were greater in the weed species than in corn at all soil pH levels. The dicot species had higher percentages of Ca and Mg in leaf tissue at all soil pH levels and accumulated higher percentages of Mn at low pH than the monocot species.

Mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl) sulfonyl] amino] phenyl] acetamide} was evaluated for effects on corn [Zea mays (L.) ‘Pioneer 3535’] coleoptile elongation. Mefluidide at 10-8 M, 10-7 M, and 10-6 M stimulated elongation approximately equal to growth stimulations with 10-6 M indoleacetic acid (IAA). Polar transport of 14C-IAA from donor agar blocks through corn coleoptiles and into receiver agar blocks after 12 h was increased 246% by 10-4 M mefluidide and inhibited 82% by 10-3 M mefluidide. Mefluidide-related chemicals (10-4 M) lacking a trifluoromethyl-sulfonyl-amino chain at the 1-position of the phenyl ring did not alter 14C-IAA transport. IAA transport was increased 97% when the acetamide chain at the 5-position was absent and 255% when the methyl in the 4-position was absent, and it decreased 65% when the methyl at the 2-position was absent. Polar transport of 14C-IAA through soybean [Glycine max (L.) Merr. ‘Williams’] hypocotyls was not altered by 10-4 M mefluidide; however, 10-3 M mefluidide increased IAA transport 116%. After 6 h, corn coleoptiles metabolized 14% of the mefluidide absorbed and soybean metabolized 54% of the mefluidide absorbed from 14C-mefluidide solutions (10-6 M). Differences in the rate of metabolism of mefluidide in meristematic tissue of corn and soybean may explain differences in mefluidide effects on auxin transport in corn and soybean.

The effect of soil disinfestation with methyl bromide (MB) or by soil solarization (solar heating) and the fungicides TMTD (tetramethylthiuram disulfide) and fentin acetate (triphenyltin acetate) on the degradation of terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-methylthio)-s-triazine] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] were investigated. The degradation of terbutryn appeared to follow first-order kinetics with a half-life of about 2 weeks and was much slower in MB-treated or solarized soils, i.e. half-life of about 11 weeks. Suppression of terbutryn degradation in the MB-treated soil was still evident 8 months after soil fumigation, similar to that found in autoclaved soil. TMTD and fentin acetate at 20 μg/g soil strongly inhibited degradation of terbutryn in soil. Degradation of atrazine was affected to a lesser extent by soil disinfestation. Results from the present study suggest that biocidal soil treatments may slow herbicide degradation. Thus, herbicide dosages in disinfested soil should be adjusted in order to avoid phytotoxicity. Moreover, lower dosages might be sufficient to attain weed control, and combined disinfestation or fungicides with herbicide treatments might be intentionally used to extend herbicide activity.

Chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl]-benzenesulfonamide} applied preemergence or postemergence as a soil drench retards the growth of four corn (Zea mays L.) genotypes in soil with 50% inhibition in each case at a rate of approximately 5 g ai/ha. R-25788 (N,N-diallyl-2,2-dichloroacetamide), applied at 1.0 kg ai/ha to the soil preemergence with chlorsulfuron or postemergence 2 days prior to chlorsulfuron treatment, reverses shoot growth inhibition induced by the herbicide in varying degree in ‘XL25A’ and ‘XL72B’ corn hybrids and ‘FRM017’ and ‘FR619’ inbreds, but not in soybean [Glycine max (L.) Merr., var. ‘Amsoy-71’]. Under similar conditions, flurazole [2-chloro-4-(trifluoromethyl)-5-thiazolecarboxylic acid (phenylmethyl ester)] and CGA-92194 [α-(1,3-dioxolan-2-yl-methoxy)-imino-benzeneacetonitrile] are less effective than R-25788 in protecting corn genotypes from chlorsulfuron injury. R-25788 also partially reverses chlorsulfuron-induced root growth inhibition in XL25A and FR619 corn but not in pea (Pisum sativum L. var. ‘Dwarf Gray Sugar’). Acetohydroxyacid synthase (AHAS) is higher in both activity and the proportion that is very sensitive to in vitro chlorsulfuron inhibition when prepared from XL25A shoots than from the roots. R-25788 does not reverse the in vitro inhibition of corn acetohydroxyacid synthase (AHAS) by chlorsulfuron. Pretreatment of 5-day-old XL25A corn with R-25788 at 24 or 48 μM significantly increases AHAS activity by approximately 25% in both shoots and roots but does not change its in vitro sensitivity to chlorsulfuron. This antidote also increases the glutathione (GSH) content in roots and etiolated shoots. The R-25788-induced elevation of AHAS activity may contribute to its antidotal effect in corn.

The herbicide AC 252 214 {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl] 3-quinoline-carboxylic acid} was absorbed by the roots and foliage of soybean [Glycine max (L.) Merr. ‘Williams’], common cocklebur (Xanthium strumarium L. ♯ XANST), and velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH), and then translocated in the xylem and phloem to meristematic regions. AC 252 214 was metabolized rapidly by soybean and velvetleaf but appeared to be metabolized slowly by cocklebur. The order of tolerance of these three species to AC 252 214 was soybeans > velvetleaf > cocklebur. This order of tolerance was directly correlated in young plants with the half-life of AC 252 214 within the tissue. Velvetleaf exhibited increased tolerance to AC 252 214 with age, which was attributed partially to greatly reduced absorption of the herbicide by older leaves and more rapid metabolism of the herbicide.

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.

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.

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.

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.

Multiple regression analysis of data from field experiments conducted in Alberta at two locations between 1972 and 1983 indicated that there was a significant relationship between yield loss of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) and relative time of emergence of wild oat (Avena fatua L. ♯ AVEFA). At a given wild oat density, percent yield loss increased the earlier wild oat emerged relative to the crops and gradually diminished the later it emerged. However, the magnitude of the yield loss for both species varied with the year. Regression equations based on data pooled over years and locations were developed to provide an estimate of yield loss of barley and wheat due to relative time of wild oat emergence and wild oat density. The information should be considered when barley and wheat losses due to wild oat are being assessed.

Experiments were conducted to evaluate effects of various densities of bermudagrass [Cynodon dactylon (L.) Pers. ♯ CYNDA] in cotton (Gossypium hirsutum L. ‘Stoneville 213’) during the initial and second seasons following grass establishment and to evaluate bermudagrass competition in three cotton row spacings. During the season of grass establishment, densities of 1 to 16 plugs/7.5 m of cotton row had minimal effects on yield. Established, perennated bermudagrass was much more competitive. During second-season competition, 1 plug/7.5 m had formed a 76% ground cover and reduced yields by 600 kg/ha (25%) or more. The highest densities reduced yields 60 to 80%. In separate experiments, a cotton row spacing of 0.5 m reduced bermudagrass ground cover compared to 1.5 m row spacing.

The general appearance of plants was similar for 14 accessions of velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH) obtained from Stoneville, MS (33° 25’ N), Rosemount, MN (44° 43’ N), and various locations in between. All accessions were equally susceptible to bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. Variation in maturity characteristics was found among the accessions in the field at Rosemount; southern accessions began seed capsule production later and continued it longer than did northern accessions. Velvetleaf accessions from Stoneville and Rosemount both produced seeds in the field at Weslaco, TX (26° 09’ N), but at Fairbanks, AK (64° 49’ N), neither accession produced seeds before being killed by frost.

The control of western juniper (Juniperus occidentalis Hook.) trees released shrub and herbaceous vegetation from dominance of the tree overstory. Revegetation of the woodland with desirable browse and forage species required weed control of both shrub and herbaceous species. The method of tree control (herbicidal, mechanical, or wood harvesting) influenced subsequent weed control-revegetation options in the understory. Physical restraints imposed by standing dead trees resulting from picloram (4-amino-3,5,6-trichloropicolinic acid) treatment limited the use of weed control and seeding equipment. Accumulation of litter interfered with the use of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] for annual grass control on both the picloram and wood harvest plots. Establishment of forage species was most successful on the mechanically cleared plots. Attempts to revegetate with browse species were largely foiled by native herbivores, and selective predation occurred on herbaceous species.

Interference of Powell amaranth (Amaranthus powellii S. Wats. ♯ AMAPO) in sugarbeet (Beta vulgaris L. ‘Mono Hy A4’) was determined in field experiments. Yield of sugarbeet roots and recoverable sucrose/ha decreased as the density of Powell amaranth increased. At densities of 6, 12, 18, and 24 Powell amaranth plants/30 m of row, root yields were reduced 8, 14, 24, and 25%, respectively, and recoverable sucrose yields were reduced 7, 13, 23, and 24%, respectively. The minimum number of Powell amaranth plants required per 30 m of row to reduce sugarbeet root yields was estimated to be nine in 1982 and 11 in 1983.

The relationship between Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn. ♯ FAGTA) plant density (x) and percent yield loss (ŷ) was expressed by the following linear regression equations for barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.), respectively; ŷ = 0.63 + 2.75 √x and ŷ = 5.04 + 3.05 √x. Tartary buckwheat causes serious yield reduction in barley and wheat. A Tartary buckwheat density at 30 plants/m2 at emergence reduced barley yield by 16% and wheat yield by 22%.