Ragweed Parthenium (Parthenium hysterophorus L. # PTNHY) was found to exhibit autotoxicity. The active principle(s) were isolated from two parts of the plant using polar system. Principle(s) from the inflorescence were more effective than from the leaves. Leachates derived from the plant decreased percent cell survival and chlorophyll content. Leachates from leaves were more toxic to ragweed parthenium when applied to the foliage than when applied through the roots. The polar allelochemicals were highly effective in preventing rooting and sprouting of stem cutting and in reducing the regeneration potential of mature ragweed parthenium plants.

Formulated and technical grade HOE-39866 [ammonium-(3-amino-3-carboxypropyl) methylphosphinate] at concentrations of 10–1, 10–2, and 10–3M were applied to leaf blade tissues of nonreproductive adult redroot pigweed (Amaranthus retroflexus L. # AMARE) and fall panicum (Panicum dichotomiflorum Michx. # PANDI). Tissues were sampled at regular intervals after treatment and prepared for light microscopic examination. The major response of both species involved rupture and contortion of the interveinal mesophyll cells with concomitant disorganization of the bundle sheath cells. Rapid epidermal collapse occurred in redroot pigweed but not in fall panicum. The absence of adjuvants resulted in nonuniform symptom expression as herbicide droplets accumulated in depressions and along leaf margins. No other adjuvant-specific effect was observed. Herbicide concentration did not alter the final response but the time-to-expression increased as concentration decreased.

Common ragweed [Ambrosia artemisiifolia L. # AMBEL (2n=36)] and giant ragweed [A. trifida L. # AMBTR (2n=24)] are two abundant annuals that are widespread throughout northeastern North America. They are also the main cause of hay fever in Eastern Canada. The formation of a hybrid between the two species has been reported only once and just one type of hybrid was recovered; namely, common ragweed × giant ragweed. In order to create additional suitable material for future studies of the biochemical features characterizing the allergenic pollen, the production of reciprocal hybrids between common and giant ragweed was attempted. A number of hybrid plants derived from crosses of the type common ragweed × giant ragweed were easily obtained; the reciprocal crosses, however, failed to produce viable plants. In this last case, evidence of postzygotic barriers of interspecific incompatibility were shown by the presence of underdeveloped embryos contained in the few seeds recovered. Embryo culture techniques, therefore, were used in order to bypass such barriers. By this method fifteen plants of hybrid constitution survived to maturity.

The effects of treatment with twelve metabolites of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl) benzenamine] on the gross morphology and ultrastructure of trifluralin-susceptible (S) and -resistant (R) biotypes of goosegrass [Eleusine indica (L.) Gaertner. # ELEIN] root meristems were examined. Unlike trifluralin, ten of the twelve metabolites including the major metabolites of trifluralin caused no root tip swelling even at water-saturated concentrations. Two of the minor metabolites, 3-methoxy-2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine (TR-36M) and N-(2,6-dinitro-4-(trifluoromethyl)phenyl)-N-propylpropanamide (TR-40), caused root swelling when applied as a saturated solution. The most effective metabolite, TR-36M, caused root swelling at 10 μM or greater concentrations. Because trifluralin caused swelling of the root tips even at a 0.01 μM concentration, trifluralin is 1000-fold more effective than the most herbicidally active metabolite. Both herbicidally active metabolites are also much less effective than trifluralin at increasing the mitotic index. Structural studies indicate that the two herbicidally active metabolites arrest mitosis at prometaphase due to the loss of spindle microtubules, similar to trifluralin. Cortical microtubules are also affected by the highest concentrations of these two metabolites. A resistant biotype, in which mitosis is unaffected by trifluralin, was unaffected by any of the trifluralin metabolites.

Plants of dormant and nondormant wild oat (Avena fatua L. # AVEFA) lines were grown under temperatures of 15, 20, and 25 C. A number of physiological and morphological characters in the plants and seed of both lines were influenced by temperature. Duration of dormancy in the progeny seed increased in both lines that had experienced low temperatures (15 C) during development, and decreased in seed of both lines that had experienced high temperatures (25 C) during development. High, compared to low, temperatures of development decreased plant height, vegetative and seed development time, seed numbers per plant, seed dry weight, and seed water content.

The mode of action of two experimental pyridinyloxyphenoxy propionate herbicides, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoic acid} and CGA-82725 {2-propynyl-2-[4-[(3,5-dichloro-2-pyridinyl)oxy] phenoxy] propanoic acid} was studied. Oat (Avena sativa L.) roots showed a rate-dependent sensitivity to both herbicides. Consequently, a series of assays was performed to study cell division, cell cycle dynamics, and nucleic acid and protein synthesis in oat root tips in order to characterize growth inhibition. Both herbicides inhibited cell division, apparently by inhibiting protein synthesis in the G2 stage of interphase. Supporting evidence for this assumption comes from the following observations: a) There was almost complete absence of leucine incorporation within 1 h of exposure to 2.7 × 10−4 M of either herbicide; b) the number of 3H-labeled dividing cells was reduced to about 20% of the control within 4 h, and essentially to zero within 8 h, after exposure to 2.7 × 10−4 M of herbicide; c) the number of unlabeled cells was reduced to less than 10% of the control within 8 h of exposure to 2.7 × 10−4 M of herbicide; d) during this 8-h period, the number of 3H-labeled cells in interphase which had been exposed to herbicide greatly exceeded the control; e) thymidine incorporation into DNA was inhibited but was not proportional to reduction in cell division; f) uridine incorporation was enhanced during the first 8 h of exposure before a reduction was evident at 12 h; and g) an oat coleoptile elongation bioassay showed that cell enlargement was not inhibited at herbicide concentrations less than 2.7 × 10−4 M.

Combinations of antagonistic herbicides can be helpful in the search for seed-applied chemical safeners to protect crop plants from herbicide injury. If a particular herbicide combination is selectively antagonistic so that the crop is not injured but weed control efficacy is not reduced, it should be possible to develop a new, more selective formulation of the herbicide which includes the antagonist or antidote. A promising new approach involves the use of early pretreatments of crop plants with subtoxic levels of a particular herbicide to increase crop tolerance to later, higher rates of that herbicide. When there are different mechanisms for herbicide detoxification in different plant species, it should also be possible to develop selective herbicide synergists that would provide equal efficacy at lower rates with greater crop tolerance. As our knowledge of herbicide metabolism and mode of action develops, it will be increasingly possible to use other chemicals to selectively synergize or safen herbicides to solve problems in important crop-weed situations.

Seeds of false cleavers (Galium spurium L.) grown in mid-May germinated 12 to 14 days after planting in central Alberta. The plants flowered from early July to late August and developed fruits from mid-July to early September. Plants from the late-June sowing date developed fruits until early October unless early fall frost killed the plants. Plants from seeds sown after mid-July remained in a vegetative state until late September and did not flower. Seedlings that emerged in August and September survived a mild prairie winter and resumed growth the following spring. Under greenhouse conditions, plant height ranged from 77 to 113 cm and the number of branches at first node ranged from 6 to 14, as plant density decreased from 16 to 1 plant/pot. Shoot dry weight decreased by 50% as plant population doubled, 46 days after emergence. The number of seeds produced/plant decreased from 3500 to 175 as plant density increased from 1 to 16 plants/pot. In growth chamber studies, plant growth was greatest at 20 compared to 16 or 24C.

Polyacrylamide electrophoresis and spectroscopic methods were used to characterize biotypes A and B itchgrass [Rottboellia exaltata L.f. # ROOEX] and their F2 progeny. Electrophoretic analyses of F2 progeny showed that differences between these two biotypes are multiallelic. Spectrophotometric data indicated differences between the photosynthetic apparatus of the two biotypes. These differences may reflect different abilities to adapt to varying light conditions and infer that these biotypes promote survival of the species by increasing the number of environmental nitches that R. exaltata can occupy.

Plants produced by yellow nutsedge (Cyperus esculentus L. # CYPES) tubers planted in a field at the U.S. Cotton Research Station, Shafter, CA, at monthly intervals were harvested 2, 4, or 8 weeks after planting or at the end of a full season that varied from 12 to 37 weeks. In the 2 yr of the study, 1982 and 1983, tubers were slow to sprout in March and April, taking up to 8 weeks. From June through October about 60% of the plants emerged within 2 weeks of the planting date. Parent plants produced daughter plants by the 4-week harvest except for March, April, and October 1982, and March 1983 planting periods. All planting periods had daughter plants by the 8-week harvest. In 1982, plants of the June full-season planting had significantly more daughter plants than plants of other full-season treatments even though the June full season was 12 weeks shorter than the March full season. In 1983, the number of daughter plants produced by plants for the full-season harvest was equal for all monthly plantings regardless of the length of the full season. In 1982, for the May through September plantings, more tubers were produced by plants at the 8-week harvest than the number of tubers originally planted. In 1983, only plants of the June and August plantings produced more tubers by the 8-week harvest than had been planted. In both years, plants that grew for a full season produced more tubers than the number planted, up to 200-fold more.

Immediately following postemergence application, similar quantities of metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] were retained on the foliage of downy brome (Bromus tectorum L. # BROTE) and winter wheat (Triticum aestivum L.). Three days following treatment, more metribuzin was present on the surface of the foliage of downy brome than of winter wheat and similar quantities of metribuzin had been absorbed into the interior of the foliage of both species. Fourteen days after treatment, metribuzin had disappeared from the surfaces of the foliage of both species but more metribuzin was present in the interior of the foliage of downy brome than of winter wheat. Results from petri dish studies in the field suggested that the amount of unaltered metribuzin available for absorption by leaves was influenced primarily by volatilization and secondarily by photodecomposition. In addition, small quantities of rainfall may have washed metribuzin from leaf surfaces. In 1984, yield of winter wheat was greater in metribuzin-treated plots than in nontreated check plots.

Several crop and weed species were field grown to maturity and their residues incorporated with soil to determine the effects of the plant residues on the growth of subsequent plantings in a spring-fall planting sequence in 1980 to 83. Growth of Palmer amaranth (Amaranthus palmeri S. Wats. # AMAPA) was studied in 1984 and 1985, and the effects of soil-incorporated Palmer amaranth on the growth of cabbage (Brassica oleracea var. Capitata L.) and carrot (Daucus carota L. var. sativa) seedlings were studied in 1985. Under warm, moist, saline soil conditions and intense sunlight following the spring plantings of the 1980 to 83 study, soil-incorporated residues of Palmer amaranth inhibited the growth of carrot 49% and onion (Allium cepa L.) 68%. Johnsongrass (Sorghum halepense L. Pers. # SORHA) residues inhibited the growth of onion 67%, and in one of two years inhibited the growth of cabbage 26% and common sunflower (Helianthus annuus L. #HELAN) 10%. In 1984 and 1985, Palmer amaranth grown at population densities of 300 plants/m2 attained heights of nearly 2 m and biomass of 2 to 3 kg/m2 within 10 weeks after planting. Phytotoxicity with these biomasses persisted 11 weeks in cabbage and carrot plantings. In 1985, phytotoxicity was dissipated 16 weeks after soil incorporation of the weed.

Genetic engineering is a powerful new technology that makes possible rapid development of herbicide tolerances in superior crop varieties. Use of the technology will have a major impact on future agricultural practices and the agrichemical industry. Possible risks as well as significant likely benefits – to agricultural users, corporate suppliers, and the environment – are discussed. Increased product lifetimes, decreased costs, and increased usefulness of broad-spectrum, high-potency, environmentally safe herbicides and herbicide combinations are predicted.

Germination and longevity of weedy and three domestic okra [Abelmoschus esculentus (L.) Moench. # ABMES] cultivars were investigated. Hard seed coats are the major reason for okra seed dormancy. Hard seeds of weedy okra, induced to germinate by scarification of seed coats, produced plants yielding 94 to 99% hard seeds. Of these, 40% remained hard but viable after overwintering in the soil at 5 cm deep. Nonhard seeds of weedy okra produced plants that yielded 95 to 99% hard seeds, but only 20% remained hard after overwintering in the soil at 5 cm deep. The ‘White Velvet’ cultivar of okra produced a few hard seeds, but none survived longer than 3 months in the soil. The other domestic cultivars, ‘Dwarf Green Long Pod’ and ‘Clemson Spineless', produced no hard seeds. None of these seeds survived over winter in the soil. Some seeds of White Velvet became slightly harder during dry storage based on time in concentrated H2SO4 necessary to induce 80% germination. Although the hard-seed trait existed in the population of this domestic cultivar, it is unlikely that the seeds would overwinter. Seeds that overwinter in a dry condition may be the exception. Because a high percentage of hard seeds overwinter and germinate the following spring, weedy okra has the potential to become a persistent problem.

Field experiments were conducted to determine whether aerial and subterranean stem sections taken from Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] plants in four stages of development (spring-vegetative, bud, postbloom, and fall-vegetative) could survive and produce infestations the following year. Partially buried aerial stem sections from all stages of development had greater survival 28 days after planting than completely buried aerial stem sections. Few completely buried aerial stem sections survived. Partially or completely buried subterranean stem sections from Canada thistle at the postbloom stage had the highest survival rate. Few partially or completely buried subterranean stem sections from the other three growth stages survived. Surviving stem sections from spring-vegetative, bud, and postbloom stages of Canada thistle produced adventitious roots that overwintered and produced new infestations the following spring. Surviving stem sections from Canada thistle at the fall-vegetative stage did not develop an adequate root system for winter survival.

An accession of velvetleaf (Abutilon theophrasti Medik. # ABUTH) known to be highly tolerant of atrazine [6-chloro-N-ethyl-N-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and a normal susceptible accession were crossed reciprocally. F1 plants were intermediate in response to atrazine, but they were more like the tolerant parent than the susceptible parent. The response of F1 plants was the same for each reciprocal cross, indicating that atrazine tolerance was not cytoplasmically inherited. Response of F2 plants to atrazine was consistent with a ratio of one tolerant: two intermediate: one susceptible. These results and further evaluations of F3 plants indicated that atrazine tolerance was controlled by a single, partially dominant gene.

Studies were conducted at Grand Rapids, MN, to determine the effect of giant burreed (Sparganium eurycarpum Engelm. # SPGEU) planted at 6, 12, and 24 corms/m2 on wild rice (Zizania palustris L. ‘K2′) growth and yield. Giant burreed, a spreading perennial, had shoot densities of 21, 29, and 42/m2 at harvest for the 6, 12, and 24 corms/m2 treatments, respectively. Wild rice yield and panicle number were reduced approximately 60% when giant burreed shoot density was 40/m2 or higher when compared to the weed-free control. Giant burreed did not interfere with nutrient uptake of wild rice on a whole-plant basis, and increased N fertilizer application did not reduce losses in dry weight. Giant burreed reduced penetration of photosynthetically active radiation (PAR) from 2 to 35% in the wild rice canopy from the early tillering to the anthesis stage of wild rice development. In growth chamber studies, wild rice dry weight and panicle number were reduced by 46 and 65%, respectively, when wild rice was shaded for 12 weeks and compared to a full light treatment. Reduction of PAR penetration into the wild rice canopy appears to be the major mechanism of giant burreed interference with wild rice.

Weed seeds were germinated in incubators at constant temperatures ranging from 4 to 32 C increments. Percent germination per day was regressed against temperature with the x-intercept representing the low threshold temperature for development. Low threshold temperatures for development (low TTD's) calculated for wild proso millet (Panicum miliaceum L. # PANMI), barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG], common lambsquarters (Chenopodium album L. # CHEAL), and redroot pigweed (Amaranthus retroflexus L. # AMARE) were 6.9, 9.7, 6.0, and 10.0 C, respectively.

Artemisinin (qinghaosu), a sesquiterpenoid lactone peroxide constituent of annual wormwood (Artemisia annua L. # ARTAN) that is used as an antimalarial drug, was tested for phytotoxic properties. It inhibited germination of lettuce (Lactuca sativa L.) and annual wormwood, and growth of roots and shoots of lettuce, redroot pigweed (Amaranthus retroflexus L. # AMARE), pitted morningglory (Ipomoea lacunosa L. # IPOLA), annual wormwood, and common purslane (Portulaca oleracea L. # POROL) was inhibited at 33 μM. No effects of 33 μM artemisinin were detected on growth of velvetleaf (Abutilon theophrasti Medik. # ABUTH) and grain sorghum [Sorghum bicolor (L.) Moench.]. Chlorophyll content was not affected in lettuce, and chlorosis was not observed in any species tested. The probable biosynthetic precursors of artemisinin, arteannuin B and qinghao acid, had no effect on growth or chlorophyll content of lettuce; however, they inhibited lettuce seed germination. Artemisinin and cinmethylin {exo-1-methyl-4-(1-methylethyl)-2-[(2-methylphenyl)methoxy]-7-oxabicyclo [2.2.1] heptane} were equally effective in reducing growth of lettuce; however, cinmethylin had no effect on germination. Respiration of lettuce roots or cotyledons was not inhibited by artemisinin. Artemisinin only marginally increased the mitotic index of lettuce root tips at 33 μM. At the ultrastructural level, however, chromosomes were less condensed during mitosis in artemisinin-treated than control meristematic cells. The growth-inhibiting ability of artemisinin could not be reduced by feeding the plants with hydrolyzed protein or treatment with putrescine. Artemisinin is a selective phytotoxin that reduces growth by a mechanism other than mitotic disruption or inhibition of protein synthesis.