The effect of quackgrass [Agropyron repens (L.) Beauv.] rhizome length and foliage height on glyphosate [N-(phosphonomethyl)glycine] translocation was determined on the basis of bud kill and 14 C-accumulation in quackgrass rhizomes. Foliar glyphosate treatments of 0.28 kg/ha resulted in significantly reduced quackgrass rhizome bud survival, and rates of 0.56, 0.84, and 1.12 kg/ha gave nearly complete bud kill. Rhizome buds on glyphosate-treated quackgrass plants with 20 to 90 nodes had a higher survival rate than rhizome buds on plants with 10 nodes. Quackgrass bud kill was greatest when glyphosate was applied to taller foliage. When all rhizome buds were not killed, those closest to the mother shoot survived glyphosate treatments. The 14C accumulation following applications of 14C-glyphosate was greatest in nodes near the rhizome tip and least in nodes near the mother shoot. This suggests that greater bud kill near the rhizome tip was due to larger accumulation of glyphosate in this part of the rhizome.

The adsorption, desorption, and mobility of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] in eight Ontario soils were investigated. The distribution coefficients varied from 0.56 for the least adsorptive Fox sandy loam soil to 31.67 for the most highly adsorptive Leamington muck soil. Most of the adsorbed metribuzin was desorbed from the mineral soils after six aqueous extractions, however substantial amounts of the herbicide remained adsorbed on the muck soils after 10 aqueous extractions. The herbicide was relatively mobile in mineral soils but was immobile in the muck soils. Mobility was inversely correlated with the amount of soil organic matter. Bioassay studies indicated that phytotoxicity of metribuzin also decreased with increasing organic matter content of the soil. Persistence of metribuzin was dependent on microbial degradation. In a field study with Guelph loam, the half-life of metribuzin was approximately 3 months.

Seedlings of fifteen different cultivars of tomato (Lycopersicon esculentum Mill.) varied greatly in tolerance to metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H) one] applied at a concentration of 0.5 mg/L in quartz sand nutrient culture during the three-true-leaf stage. Tolerance increased with seedling age, but acceptable tolerance was observed about 6 days earlier in the tolerant ‘Fireball’ compared to the susceptible ‘Heinz 1706′. Root uptake and acropetal translocation of metribuzin-carbonyl-14 C was similar in 2-week-old seedlings of susceptible Heinz 1706 and tolerant Fireball seedlings. Differential tolerance was related to the rate of detoxification by metabolism within the tomato leaves, which was approximatley two-fold greater in the tolerant Fireball seedlings.

Single and repeat applications of herbicides or herbicide combinations were made over-the-top of young cotton (Gossypium hirsutum L.). DMSA (disodium methanearsonate) and MSMA (monodosium methanearsonate) applied 4 or 8 weeks after emergence had less effect on cotton yield, boll components, and fiber properties than did applications made 12 weeks after emergence. Most single, over-the-top applications of DSMA, fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], or DSMA with fluometuron 4 weeks after emergence did not affect cotton yield, boll components, or fiber properties. One or two applications of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] or prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] alone, or with DSMA, reduced cotton yields. Applications of 1.1 and 2.2 kg/ha of fluometuron over-the-top of cotton 2 to 8 weeks after emergence did not affect cotton yields, boll components, or fiber properties.

The area influenced by individual herbicide granules was determined by rating control of weeds planted in fixed patterns around granules. The area of foxtail millet [Setaria italica (L.) Beauv.] controlled by alachlor [2-chloro-2′,6′diethyl-N-(methoxymethyl) acetanilide] was larger than the area of velvetleaf (Abutilon theophrasti Medic.) controlled by atrazine [2-chloro-4(ethylamino)-6-(isopropylamino)-s-triazine]. Control was most consistent when granules and seeds were near the same depth and was most variable when granules were on the soil surface. Control of foxtail millet with alachlor increased with increasing soil moisture, with decreasing granule depth, and with increasing seed depth. At low soil moisture, control of velvetleaf with surface-applied atrazine was better with simulated rain than with subirrigation. When soil moisture was high and atrazine granules were placed 1-cm deep, control was better with subirrigation. The area-of-influence, or the control (y) as function of distance (x) from granule, was described by y = 10e-A(x-B)2. The radius-of-control (ROC), defined as the radius of the circular area around a granule within which weeds are effectively controlled, was estimated from this relationship.

The effect of picloram (4-amino-3,5,6-trichloropicolinic acid) on regeneration of detached leaves of Echeveria elegans Bgr. was studied. Picloram stimulated callus production at all concentrations. Low concentrations of 1 to 15 ppmw picloram did not affect shoot organogenesis and the same, however, stimulated rhizogenesis. Inhibition of both root- and shoot-organogenesis was noticeable at concentrations below 20 ppmw and above. Roots increased in number at all picloram concentrations below 40 ppmw, the maximum number being at concentration of 15 to 20 ppmw of the herbicide. Observations indicated that root elongation was considerably suppressed. Picloram-induced callus contained mature parenchyma cells devoid of contents and considerable amount of tissue disruption was noticed. Irregular vascular differentiation and obliteration of tissues particularly in the region of tracheary elements, were obvious. Although normal apical organization was lacking in root primordia and in arrested short roots, these elongated normally into mature roots when they were transferred to water, thus indicating that apical meristems were not severely affected by picloram.

Analysis of entire barley (Hordeum vulgare ‘Moravian’) seedlings exposed to triallate [S-(2,3,3-trichloroallyl)-diisopropylthiocarbamate] vapor for 5 days after a 5-day germination period resulted in a linear rate of accumulation of triallate, while wild oat (Avena fatua L.) seedlings accumulated triallate for 1/2 to 2 days after exposure with no net accumulation thereafter. Similar accumulation patterns were shown for a similar exposure period when barley and wild oat were seeded 1.3 cm below a triallate-treated soil layer in the greenhouse. More triallate accumulated in wild oat and barley when they were planted in a triallate-treated soil layer than below. Since barley accumulated greater amounts of triallate without injury than wild oat, differential uptake of triallate was not the reason for selectivity.

The occurrence, abundance, and nature of weed communities were reviewed in relation to man's manipulation of the natural environment. Manipulations of the environment necessary for agricultural production have favored secondary successional species. That many of these seral species have opportunistic genotypes has led to the development of weeds. Weeds conform to the concepts of ecologic succession, but agricultural ecosystems are very dynamic with sudden and recurrent changes. The acceleration of successional patterns has provided environments conducive to the selection of competitive genotypes among numerous weeds. Specialized breeding systems provide rapid responses to changing conditions. Weeds increase the diversity of agricultural ecosystems by utilizing environmental potential concentrated for crop production. Weeds have been the shadow of history in that they have mirrored man's activities. The introduction of weed species to new environments may be one of the greatest manipulations of the natural environment, the total consequences of which will be determined in the future.

Effects of glyphosate [N-(phosphonomethyl)glycine] and paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) on turfgrass seed germination were evaluated in the greenhouse. Glyphosate caused little effect on germination of Kentucky bluegrass (Poa pratensis L.), red fescue (Festuca rubra L.), and tall fescue (F. arundinacea Schreb.) when applied to the soil immediately before seeding or when applied directly over the seed on the soil surface. Paraquat sprayed directly over the seed on the soil surface prevented germination of most of the seeds of the three grass species. Covering seeds on the soil surface with clippings from grass turf sprayed with paraquat greatly reduced germination. About half of those that germinated either died later or were severely chlorotic. Covering seeds on the surface of the soil with clippings from turf that had been sprayed with glyphosate did not significantly reduce the number of seedlings established.

Ten warm-season and seven cool-season weed species were grown in the glasshouse on Hartsells fine sandy loam taken from field plots that had been in long-term fertility studies. The soil pH was 5.9 and phosphorus (P) levels ranged from 8 to 95 kg/ha and the potassium (K) levels from 40 to 213 kg/ha. Growth response to P and K levels was measured by dry herbage yield. Redroot pigweed (Amaranthus retroflexus L.), jimsonweed (Datura stramonium L.), and Florida beggarweed [Desmodium tortuosum (Sw.) DC] were the most responsive warm-season weed species to P, whereas chickweed [Stellaria media (L.) Cyrillo] was the most responsive cool-season weed to P. Extreme P deficiency symptoms were evident on species giving a high response to P. P-deficient plants were severely stunted and exhibited a characteristic reddish-purple color. Showy crotalaria (Crotalaria spectabilis Roth), tall morningglory [Ipomoea purpurea (L.) Roth], sicklepod (Cassia obtusifolia L.), Carolina geranium (Geranium carolinianum L.), and coffee senna (Cassia occidentalis L.) were the most tolerant to low soil P. Redroot pigweed, jimsonweed, and Florida beggarweed were the most responsive warm-season weeds to K. Wild mustard [Brassica kaber (DC.) L.C. Wheeler var. Pinnatifida (Stokes) L.C. Wheeler] and annual bluegrass (Poa annua L.) were the most responsive cool-season weeds to K. Potassium deficiency symptoms were characterized primarily by severe stunting. Buckhorn plantain (Plantago lanceolata L.), Carolina geranium, and curly dock (Rumex crispus L.) were the most tolerant cool-season weeds to low soil K. Generally, weeds were more sensitive to low soil-test P than K.

Three preemergence and four postemergence herbicides were compared for control of prickly sida (Sida spinosa L.) in soybeans (Glycine max Merrill) and for level of phytotoxicity to soybeans. As a preemergence herbicide, chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxyl-1-methylurea] provided better control of prickly sida than did linuron [3-(3,4-dichlorophenyl)-1-methoxyl-1-methylurea] which was more consistently effective than was naptalam (N-1-naphthylphthalamic acid) plus dinoseb (2-sec-butyl-4,6-dinitrophenol). Chlorbromuron applied as a preemergence treatment caused slight crop injury. In most cases preemergence treatments followed by cultivation were effective in providing season-long control. The descending order of effectiveness for prickly sida control by the postemergence herbicides was: chlorbromuron metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] > prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] > dinoseb. Prometryne as a postemergence treatment following a preemergence herbicide increased prickly sida control more consistently than dinoseb used as the postemergence treatment. However, prometryne caused more crop injury than did dinoseb.

Comparison of soybean yields from the weedy and weed free checks show that prickly sida caused only 9 to 14% yield losses in soybeans.

Fall panicum (Panicum dichotomiflorum Michx.) and witchgrass (Panicum capillare L.) emerged in naturally infested fields as early as April 30 and May 14, respectively. The shortest period between seeding and emergence was during the warmest period of the growing season. The number of days from emergence to heading decreased progressively for later seedings. After emergence witchgrass formed seedheads about 7 days earlier than fall panicum. Fall panicum emerging in the middle of July and witchgrass seedlings emerging July 25 produced mature seeds in the fall, shaded or not. Plant height, tiller number, and yield of both grasses were highest for plants emerging in May and June. Decreased light intensity delayed seed emergence, heading, and maturity of both grasses. Plant height, yields, number of tillers, and number of panicles also were decreased by shading. Fall panicum was a coarser plant than witchgrass and produced more tillers and panicles than witchgrass. Fall panicum and witchgrass seedlings emerging between June 23 and July 7 produced the most vigorous fast growing plants.

A clean-up procedure for soil and plant samples utilizing a non-ionic exchange resin column followed by treatment with lead acetate was developed for determining microgram quantities of hexaflurate (potassium hexafluoroarsenate) spectrophotometrically. The method is sensitive to 0.45 ppm with a standard deviation of 0.09 ppm with a recovery of better than 85%. Samples high in organic matter require this treatment to remove interfering substances. Soil samples containing little or no organic matter could be analyzed by using either the lead acetate treatment or the non-ionic exchange resin column. Soil and plant samples analyzed 5 to 7 yr following treatment of south Texas soils for pricklypear (Opuntia spp.) control were found to contain trace quantities of hexaflurate. Downward movement of hexaflurate is either very slow or plants continually assimilate the ion and redeposit it on the soil surface through decomposition of plant parts. The tri- and pent-oxide forms of arsenic did not interfere with analysis of the hexaflurate ion using the clean-up procedure.

A method for isolating roots of a growing plant was devised. The technique allows treatment of an isolated portion of the root system without disturbance or injury to the untreated root mass. A specially designed planter-box was used to induce natural separation of the root system in 3 to 4 weeks. Weeping willow (Salix babylonica L.) seedlings were used to test the performance of dichlobenil (2,6-dichlorobenzonitrile), paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), sodium hydroxide (NaOH), and copper sulfate (CuSO4 • 5H2O) in reducing the viability of treated roots. A tetrazolium chloride assay was used to determine the difference in viability of the treated roots. Copper sulfate and paraquat-treated plants produced symptoms of systemic injury.

The loss of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] from metal planchets was decreased by an increase in the amount applied and linseed oil (LO) additive. LO reduced volatility to a greater extent than did other additives. Vapor loss from plant leaves was influenced by plant species, plant leaf maturity, soil moisture, concentration of atrazine applied, volume of oil additive, type of additive, and duration of exposure. Generally, atrazine uptake by plants was inversely related to volatility. Uptake and translocation of 14C-atrazine label was increased more by oil additives than surfactant (SURF) compared to no additive. LO increased 14C-label translocation more in yellow foxtail [Setaria glauca lutescens (Weigel) Hubb.], green foxtail [Setaria viridis (L.) Beauv.], and barnyardgrass [Echinchloa crus-galli (L.) Beauv.] than in corn (Zea mays L.).

Weed competition in soybeans [Glycine max (L.) Merr. ‘Clark 63′] with planted stands of velvetleaf (Abutilon theophrasti Medic.), prickly sida (Sida spinosa L.), and Venice mallow (Hibiscus trionum L.) is reported. Weeds were planted 0, 10, 20, 30, and 40 days after soybeans and competed until soybeans matured. Soybean seed yields were reduced 720, 250, and 230 kg/ha by velvetleaf, Venice mallow, and prickly sida, respectively. Weeds that emerged with soybeans reduced yields 1,010 kg/ha. Weeds planted 10 days later reduced yields 480 kg/ha, but weeds planted 20 to 40 days after soybeans did not significantly reduced yield. Soybean yields were reduced regardless of weed placement in or between soybean rows. Weed competition reduced numbers of soybean pods per plant more than other soybean-yield components.

The distribution of simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] in whole plants and the effect of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] on isolated leaf cells and chloroplasts of two biotypes of common groundsel (Senecio vulgaris L.) were studied. Both biotypes accumulated 14C at the leaf margins 60 hr after exposure of roots to 14C-simazine. No difference in herbicide distribution between the two biotypes was observed. Atrazine (10 μM) inhibited photosynthesis, RNA synthesis, and lipid synthesis in isolated susceptible (S) cells but not resistant (R) cells. Lipid synthesis in S cells but not R cells was enhanced by exposure to 1 and 0.1 μM atrazine for 1 hr. Photochemical activity of R chloroplasts was not inhibited by atrazine but S chloroplasts were severely inhibited.

Seeds of wild safflower (Carthamus oxyacantha Bieb.) collected from the Bajgah area, Iran, in 2 successive years were subjected to stratification and scarification treatments and their germination percentage and subsequent seedling growth (length) were measured at room temperature (23 ± 2 C). Maximum germination and seedling length occurred in the seeds stratified in moist sand at 4 C for 2 weeks. The response of the freshly-harvested seed to scarification was linear while that for 1-yr-old seed was quadratic. Both scarification and stratification independently increased germination but germination never reached the viability level of the seed.

Betacyanin efflux from “aged” red beet (Beta vulgaris L.) root tissue, measured spectrophotometrically, was increased as temperature and EPTC (S-ethyl dipropylthiocarbamate) concentration increased. Acetate-2-14C (∗Ac) incorporation into the total fatty acid content was inhibited by EPTC. EPTC inhibited the incorporation of ∗Ac into the dienoic fatty acids and NA (1,8-naphthalic anhydride) reversed the EPTC induced inhibition of the incorporation of ∗Ac into dienoic fatty acids.