Transplanted tomatoes (Lycopersicon esculentum Mill. ‘Springset’) kept weed free for 36 days after transplanting, or weeded from the 24th day after transplanting, gave yields equal to those that had been kept weed free throughout the growing season. Conversely, when weeds were allowed to remain in the crop for more than 24 days after transplanting, yields were progressively reduced. Therefore, the ‘critical period’ of weed interference in tomatoes was between 24 and 36 days after transplanting. The yield of tomatoes was reduced significantly when only 5% of the weeds were allowed to remain in the plots longer than 21 days after transplanting. Weed interference appeared to have little, if any, effect on tomato juice quality as measured by color, consistency, and flavor.

Metribuzin-3-14C [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] was absorbed, translocated, and metabolized by both metribuzin-tolerant ‘Essex’ and metribuzin-sensitive ‘Coker 102’ soybean cultivars [Glycine max (L.) Merr.]. After 48 h Coker 102 accumulated 40% greater metribuzin equivalents in the shoots than Essex, but Essex shoots contained only 29% as much unaltered metribuzin as Coker 102, 1.08 and 3.68 μg per g dry weight, respectively. Essex is resistant to metribuzin primarily owing to a capacity to rapidly detoxify metribuzin to DA [6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], to at least seven unidentified metabolites which remained in the aqueous fraction, and to an insoluble fraction. The unidentified metabolites in the aqueous fraction constituted the major detoxified breakdown products in both cultivars.

The rates of degradation of 14C-benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) and 14C-DCPA (dimethyl tetrachloroterephthalate) were significantly faster in thatch than in soil from a Kentucky bluegrass (Poa pratensis L.) turf. These results suggest that herbicides applied preemergence in turf will persist for shorter periods of time because of the carbon-enriched medium (thatch) and that higher rates or more frequent applications may be required to maintain concentrations at effective levels.

The persistence of picloram (4-amino-3,5,6-trichloropicolinic acid) was measured each spring over an 8-yr period following repeated annual applications at rates ranging from 0.020 to 0.070 kg/ha. Picloram residue levels were proportional to rate of application but averaged approximately 45% of the original levels when measured 12 months following application and declined to 10% 24 months after application ceased. Control of wild buckwheat (Polygonum convolvulus L.) was good with major population declines over the test period. Crop tolerance and yields were not affected at rates of 0.035 kg/ha or less.

Wheat (Triticum aestivum L. ‘Holley’) was grown for 14 days in 0.5 strength Hoagland and Arnon's complete mineral nutrient solution containing 0. 15.6, 31.25, 62.5, 125.0, or 250.0 ppbw EPTC (S-ethyl dipropylthiocarbamate). Gibberellic acid (GA) content, as measured by gas-liquid chromatography, was decreased 96.4% by 125.0 ppbw EPTC. When 0.05 μCi mevalonic acid-2-14C-(MVA-2-14C) (DBED salt) (0.15 mCi/mg MVA) was added to the nutrient solution, incorporation of MVA-2-14C into total kaurenoids was decreased 90% by 250 ppbw EPTC. Metabolism of kaurene was reduced by 250 ppbw EPTC with resultant 3-fold accumulations of kaurene.

Bermudagrass [Cynodon dactylon (L.) Pers. ‘Tifway’ and ‘Tifgreen’] were vertically mowed and treated with herbicides alone or in combination at various time intervals during each of 4 yr. All vertically mowed treatments significantly reduced accumulation of thatch, but more than 3 treatments were needed each year for consistently high quality turf. Vertical mowing treatments reduced the accumulation of thatch more than any of the herbicides. Vertical mowing in February prevented a delay in early spring growth of turf. Populations of large crabgrass [Digitaria sanguinalis (L.) Scop.] in the summer and chickweed [Stellaria media (L.) Cyrillo], henbit (Lamium amplexicaule L.), and brome grass (Bromus sp.) in the winter were increased from vertical mowing when herbicides were not applied for control. None of the herbicide treatments injured bermudagrass turf except oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] when applied in the fall.

Single over-the-top and directed applications of dicamba (3,6-dichloro-o-anisic acid) were made to cotton (Gossypium hirsutum L. ‘Deltapine 16′). Dicamba applied over-the-top of cotton caused foliage malformation for about 6 weeks. Dicamba (32 g/ha) applied to cotton foliage 3 to 15 weeks after emergence reduced average cotton yields. Applications of 16 to 64 g/ha of dicamba over-the-top of cotton before bloom had less effect on cotton foliage, yield, boll components, and fiber properties than application at bloom. Directed applications of dicamba to the soil or to the base of cotton and soil caused foliage malformation but did not affect cotton yield, boll components, and fiber properties.

The influence of soil organic matter on the initial and residual phytotoxicity of thirteen s-triazine herbicides was investigated in greenhouse experiments using three Horotiu sandy loam soils with organic matter levels of 9.8, 15.5, and 20.6%. The amount of herbicide required to reduce the growth of oats (Avena sativa L. ‘Mapua’) by 50% (GR50) when compared with the control was determined for each herbicide and each organic matter level. Results showed that the GR50 values for all herbicides were highly and positively correlated with the soil organic matter. In general, the phytotoxicity of compounds of high water solubility was less influenced by soil organic matter than those having low water solubility. The chloro-triazines persisted longer in soil than did the methoxy- or methylthio-triazines. Simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] were the most persistent of the chloro-triazines.

An indigenous, host-specific, pathogenic fungus that parasitizes winged waterprimrose [Jussiaea decurrens (Walt.) DC.] is endemic in the rice growing region of Arkansas. The fungus was isolated and identified as Colletotrichum gloeosporioides (Penz.) Sacc. f. sp. jussiaeae (CGJ). It is highly specific for parasitism of winged waterprimrose and not parasitic on creeping waterprimrose (J. repens L. var. glabrescens Ktze.), rice (Oryza sativa L.), soybeans [Glycine max (L.) Merr.], cotton (Gossypium hirsutum L.), or 4 other crops and 13 other weeds. The fungus was physiologically distinct from C. gloeosporioides (Penz.) Sacc. f. sp. aeschynomene (CGA), an endemic anthracnose pathogen of northern jointvetch [Aeschynomene virginica (L.) B.S.P.], as indicated by cross inoculations of both weeds. Culture in the laboratory and inoculation of winged waterprimrose in greenhouse, growth chamber and field experiments indicated that the pathogen was stable, specific, and virulent in a wide range of environments. The pathogen yielded large quantities of spores in liquid culture. It is suitable for control of winged waterprimrose. Winged waterprimrose and northern jointvetch were controlled in greenhouse and field tests by application of spore mixtures of CGJ and CGA at concentrations of 1 to 2 million spores/ml of each fungus in 94 L/ha of water; the fungi did not damage rice or nontarget crops.

Roots or shoots of oats (Avena sativa L. ‘Dal’) and peas (Pisum sativum L. ‘Early Perfection’) were exposed to vapors of 14C-labeled benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralin [N-(2-chloroethyl)-2,6 dinitro-N-propyl-4-(trifluoromethyl)aniline], oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). All of the dinitroaniline herbicides except oryzalin were absorbed by roots and shoots of germinating oats and peas. Some root-shoot translocation of the herbicides was observed in peas, but no shoot-root transport could be detected in either peas or oats. In peas, 14C from root-absorbed benefin, fluchloralin, profluralin and trifluralin was detected in shoots, and 14C from benefin and trifluralin was detected in cotyledons. In general, vapor absorption was correlated with rates of herbicide volatilization.

Burning and 2,4-D [(2,4-dichlorophenoxy)acetic acid] were used on the early stages of beaked hazel (Corylus cornuta Marsh.) understory to prevent development of a dense, continuous understory. At this early stage beaked hazel understories consisted of seedlings, small clones, and large clones. The application of 1.12 kg/ha of 2,4-D in July and August killed 84 to 100% of the seedlings and small clones, 86 to 98% percent of the large clones; while the application of 0.56 kg/ha of 2,4-D in June, July, or August caused 77 to 98% mortality of seedlings and small clones, but only 57 to 83% of large clones. Effects of burning were much more variable and generally mortality was less than with 2,4-D. One or two burns killed 23 to 100% of seedlings and small clones, and an average of only 13% (range 0 to 93%) of large clones.

Redroot pigweed (Amaranthus retroflexus L.) and robust foxtail [Setaria viridis (L.) Beauv. var. robusta-alba Schreiber or Setaria viridis var. robusta-purpurea Schreiber] were investigated to measure the accumulation of nonstructural carbohydrates throughout two separate growing seasons. Pigweed tended to accumulate more total nonstructural carbohydrates (TNC) than foxtail, particularly in the roots. In both weeds, peak levels of TNC in leaves, stems, and roots occurred during early flowering. The primary nonstructural carbohydrate in the leaves of both weeds was starch. Reducing sugars were the predominant nonstructural carbohydrate in the stems. Starch accumulated more in the leaves of the upper third of the plant and reducing sugars occurred in the greatest quantity in the middle strata of the stem. Accumulation levels of TNC in the plant organs suggested that the stem was a major sink during the vegetative growth phases of both pigweed and foxtail.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 3.4 kg/ha, EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloroacetamide) at 4.5 + 0.4 and 9.0 + 0.8 kg/ha, vernolate (S-propyl dipropylthiocarbamate) + R-25788 at 4.5 + 0.4 and 9.0 + 0.8 kg/ha, metolachlor [2-chloro N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 1.7 and 3.4 kg/ha, and metolachlor + procyazine {2-[[4-chloro-6-(cyclopropylamino)1,3,5-triazine-2-yl] amino]-2-methylpropanenitrile} at 1.3 + 1.3 kg/ha were preplant incorporated. These herbicides controlled 95% or more of the barnyardgrass [Echinochloa crus-galli (L.) Beauv.], common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), Powell amaranth (A. powellii S. Wats.), and yellow foxtail [Setaria lutescens (Weigel) Hubb.] without injuring sweetcorn (Zea mays L. ‘Golden Jubilee’) or reducing corn yields or quality. Similar results were obtained with preplant incorporated applications of butylate (S-ethyldiisobutylthiocarbamate) + R-25788 at 4.5 + 0.2 kg/ha followed by a postemergence application of the amine salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 0.6 kg/ha. Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] at 0.3 and 0.6 kg/ha and metribuzin + alachlor at 0.6 + 2.2 kg/ha applied preplant and incorporated reduced corn stands, primary ear production, and corn yields significantly. None of the herbicides significantly affected total sugars, reducing sugars, soluble solids, moisture content, or succulence of the corn.

EPTC (S-ethyl dipropylthiocarbamate), benefin (N-butyl-N-ethyl-α α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], butralin[4-(1,1-dimethylethyl)-N-(1-methylpropyl)2,6-dinitrobenzenamine], diclofopmethyl {methyl 2-[4-(2,4-dichlorophenoxy)phenoxy]-propanoate} and 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] were evaluated in the greenhouse for effects on growth, nodulation, and NH3 production of alfalfa (Medicago sativa L.) and medium red clover (Trifolium pratense L.). Some reduction in nodulation occurred from some rates of the herbicides, but reduction in nodulation was usually associated with reduced plant growth caused by herbicidal injury.

Yellow nutsedge (Cyperus esculentus L.) produced an average of 1227 and 6685 flowers per inflorescence from eight California fields sampled during 1974, 1975, and 1976. Up to 17% of the flowers produced seeds and up to 78% of the seed germinated. There was a linear relationship between seed weight and germination percentage. Purple nutsedge (C. rotundus L.) averaged between 186 and 1354 flowers per inflorescence from three California fields sampled in 1974 and 1976. Only 43 purple nutsedge seed were collected and none germinated. Yellow nutsedge produced viable seed about 2 weeks after anthesis. A day/night temperature of 38/32 C was best for seed germination, especially when accompanied by a light period. Yellow nutsedge has potential to reproduce by seed, but probability of purple nutsedge reproducing by seed is low.

When clay granules containing chlorpropham (isopropyl m-chlorocarbanilate) were applied to the surface of moist soil, the herbicide gradually moved to the atmosphere as a vapor and little entered the soil. Chlorpropham killed seedlings of field dodder (Cuascuta campestris Yunck.) and largeseed dodder (C. indecora Choisy) effectively whether it contacted them in the soil or in the air above the soil.

Dwarf spikerush [Eleocharis coloradoensis (Britt.) Gilly] is an aquatic plant that will displace waterweeds. It was studied to obtain information that will help to manage unwanted vegetation in natural aquatic situations. The morphology of seed and tubers was examined at the light- and scanning-electron microscope levels. Inflorescences were found to bear 3 to 12 florets that matured acropetally. The pericarp was made up largely of rows of annulated cells covered with a water-soluble, waxlike substance that leached away when stored in water at 4 to 6 C. The seed coat consisted of three layers. Each layer contained lipids, giving evidence that they were composed of cutin. When the seed germinated, the cotyledonary sheath emerged first, followed by the culms. Tubers formed and matured in about 30 days. The shoot apices of tubers each had two buds that were protected by five to seven overlapping membraneous leaf scales. When tubers sprouted the longest bud grew first. The second bud contained the culm meristem.

The effects of photoperiod and temperature on the translocation of triclopyr {[1(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, picloram (4-amino-3,5,6-trichloropicolinic acid) and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] were studied on tanoak [Lithocarpus densiflorus (Hook. & Arn.) Rehd.], snowbush ceanothus (Ceanothus velutinus Dougl.), bigleaf maple (Acer macrophyllum Pursh), bean (Phaseolus vulgaris L. var. ‘Red Kidney’) and barley (Hordeum vulgare L. var. CM-67). Isolation of 14C and analysis for the radioactive herbicides revealed little metabolism of the herbicides. Regardless of herbicide or plant species herbicide movement was greatest under warm temperature and long day conditions. Among the herbicides tested, 14C associated with triclopyr was the most mobile in each species. Each herbicide moved readily in the symplast but root applications of each herbicide revealed limited apoplastic mobility.

The host range of an isolate of the fungal pathogen Alternaria macrospora Zimmerman from infected spurred anoda [Anoda cristata (L.) Schlecht.] leaves was studied in the greenhouse and growth chamber. The fungus was inoculated to representative plants in the Malvaceae, Solanaceae, Leguminosae, and Gramineae families. Evidence of infection was limited to plants in the Malvaceae, with spurred anoda being the most susceptible species tested. Only negligible damage was incited on cotton (Gossypium hirsutum L. ‘Stoneville 213′) and long staple cotton (G. barbadense L. ‘Pima S–5′), hollyhock [Althaea rosea (L.) Cav.], okra (Hibiscus esculentus L. ‘Clemson spineless’), prickly sida (Sida spinosa L.), velvetleaf (Abutilon theophrasti Medic.), and Venice mallow (Hibiscus trionum L.). Disease symptoms induced in cotton by the spurred anoda isolate of A. macrospora were much less severe than those reported for other isolates of the fungus. Therefore, the spurred anoda isolate may be a specialized form of the fungus.

Twenty-eight commercial soybean [Glycine max (L.) Merr.] cultivars of maturity classes V through VIII were evaluated for differences in response to metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] 0.125 ppm w/w in hydroponic culture. Top dry weight (TDW) of treated ‘FFR 666’ soybeans equaled that of the cultivar check and five other cultivars were not significantly different (P = 5%). ‘Semmes' was most sensitive to the herbicide with TDW 40% of cultivar check. ‘Tracy’ and ‘Coker 156’ were not significantly different (P = 5%) from Semmes. The other cultivars tested were intermediate in response to metribuzin.