Chlorimuron antagonized the activity of quizalofop on broadleaf signalgrass when applied in greenhouse studies as a postemergence tank mix. In vitro leaf disc assays utilizing 14C-acetate or 14C-pyruvate as substrates were conducted to ascertain the effect of clorimuron and quizalofop on fatty acid biosynthesis and to determine if antagonism between the two herbicides occurs at the biochemical sites of action. Incorporation of 14C-acetate in control treatments was linear with time to 120 min. Acetate incorporation in the presence of quizalofop (1.1 μM) was also linear but was inhibited 30 min after initialization of the reaction. The concentration of quizalofop that inhibited 14C-acetate incorporation 50% (I50) was 0.54 μM. Chlorimuron, up to 155 μM, had no effect on 14C-acetate incorporation. A mixture of quizalofop (1.1 μM) and chlorimuron (4.8 μM) inhibited 14C-acetate incorporation similar to that of quizalofop alone at 1.1 μM. Quizalofop I50 for incorporation of 14C-pyruvate was 1.1 μM, and clorimuron at 4.8 μM decreased incorporation 15%. Excess unlabeled pyruvate (5 μM) had no effect on either 14C-acetate or 14C-pyruvate incorporation in the presence of both herbicides. It is believed that antagonism of quizalofop by clorimuron is not due to an excess pool of pyruvate resulting from inhibition of acetolactate synthase by chlorimuron.

A laboratory bioassay was conducted to determine the differential tolerance of cole crops to clomazone as measured by extractable total chlorophyll and carotenoids. Clomazone concentrations causing 50% inhibition (I50) in the biosynthesis of total chlorophyll in broccoli, cauliflower, and green and red cabbage cotyledons were 16, 11, 3, and 11 μM, respectively, while I50 values for carotenoid levels were 20, 10, 4, and 8 μM clomazone, respectively. Therefore, broccoli was the most tolerant to clomazone based upon extractable chlorophyll and carotenoid concentrations. Further laboratory studies were performed to investigate the basis for differential clomazone tolerance in 3-wk-old cole crop seedlings. No differences in total root uptake of 14C-clomazone were observed between these crops after 24 h. There were no differences in rate of metabolism of 14C-clomazone to methanol-soluble metabolites in roots of these crops. Percentage of polar metabolites in roots remained fairly constant over time. There were also no differences between crops in percentage of methanol-soluble 14C-clomazone metabolites formed in shoots between 24 and 96 h. In all crops, levels of 14C-clomazone decreased in a similar manner over time in methanolic extracts of roots and shoots while nonextractable 14C levels increased, indicating a conversion of clomazone to insoluble, nonextractable forms. Differential uptake, translocation, and metabolism do not appear to account for clomazone selectivity differences between cole crop seedlings.

Ammonium fertilizers, petroleum oil concentrate, and nonionic surfactant were evaluated as postemergence spray additives to improve giant foxtail and volunteer corn control by 28 g ai ha−1 of the ethyl ester of quizalofop or 56 g ha−1 sethoxydim. Additions of 0.25% by vol nonionic surfactant or 2.5% petroleum oil concentrate improved grass control, but additions of 10% urea ammonium nitrate (28-0-0), 10% ammonium polyphosphate (10-34-0), or 0.1M ammonium sulfate (21-0-0-24S) did not consistently affect grass control. In laboratory studies with corn, greatest 14C absorption from leaf-applied 14C-quizalofop (8 h after treatment) was found with additions of petroleum oil concentrate (80% absorbed) or nonionic surfactant (18% absorbed), while less absorption was observed with treatments containing either no additive, urea ammonium nitrate, ammonium polyphosphate, or ammonium sulfate (8 to 13% absorbed). Surface tension and droplet size of spray solutions were affected primarily by additions of nonionic surfactant, petroleum oil concentrate, and the formulated herbicides. Solution density, solute potential, pH, and buffering capacity were primarily affected by fertilizer additions.

Although drought-stressing green foxtail before and up to 1 d after herbicide application did not reduce control with fluazifop-P in growth chamber trials, extending the drought stress for 2 to 4 d after herbicide application reduced control of green foxtail with fluazifop-P by 40 and 57%, respectively. Absorption and translocation of 14C-fluazifop-P 1, 4, and 10 d after herbicide application were similar between nonstressed and drought-stressed plants. Drought-stressed green foxtail converted slightly more of the parent acid of fluazifop-P to polar conjugates 4 d after herbicide application than did nonstressed plants, but these differences in metabolism were probably not adequate to explain large differences in efficacy.

Tests with 18 growth regulators and chemicals revealed that the cytokinins [zeatin, kinetin, and 6-benzylaminopurine (BAP)], ethylene, and sodium hypochlorite stimulate germination of cowpea witchweed seeds at various concentrations. Witchweed seeds preconditioned in different concentrations of sodium hypochlorite for 3 wk had germination rates of 25 to 89% after incubation in distilled water, 10−5M solution of kinetin, 50 mg L−1 of 2-chloroethylphosphonic acid, and exudates from cowpea roots. Witchweed seeds preconditioned in distilled water and subsequently incubated in distilled water did not germinate.

A laboratory bioassay showed that inhibitors of gibberellin synthesis (flurprimidol, paclobutrazol, and uniconazole) reduced plant height but did not affect physiological parameters such as photosynthesis, respiration, and chlorophyll content in two weedy submersed aquatic plants, hydrilla and Eurasian watermilfoil. Eurasian watermilfoil was sensitive to these compounds at concentrations as low as 0.75 μg L−1. Hydrilla sensitivity was in the range of 75 to 750 μg L−1. The three compounds reduced main and lateral stem lengths in hydrilla; however, at 75 μg L−1 the number of lateral stems and roots was greatly increased over untreated controls resulting in a stoloniferous growth habit. Dominant growth form of treated Eurasian watermilfoil was a single shortened stem with numerous compacted buds. Photosynthesis, respiration, and chlorophyll content were not affected in either plant at nontoxic dosages in which stem reduction was obtained. Both plants required only a 24-h exposure to maintain main stem length reduction for 6 wk after transfer to untreated medium. Our results indicate that these gibberellin synthesis inhibitors would be effective in reducing plant height in aquatic systems.

Research was conducted during 1988 and 1989 in Georgia and Florida to determine the densitydependent effects and critical periods of wild poinsettia interference with peanut. Peanut yield loss ranged from 0 to approximately 50% over the wild poinsettia density range from 0 to 32 plants 9 m−1 peanut row. Predicted peanut yield losses across 2 yr in Georgia were 0, 4, 8, 12, 15, 26, 40, and 54% for season-long wild poinsettia interference at densities of 0, 1, 2, 3, 4, 8, 16, and 32 plants 9 m−1 of row, respectively. Across 2 yr in Florida, predicted peanut yield losses were 0, 9, 14, 22, 30, 37, and 41% for wild poinsettia densities of 0, 1, 2, 4, 8, 16, and 32 plants 9 m−1 row, respectively. Peanuts had to be maintained poinsettia free for 10 wk after peanut emergence to prevent yield loss. Wild poinsettia that interfered with peanut for more than 2 wk after peanut emergence reduced peanut yield.

Different growth rates of young seedlings (genets) and plants grown from root pieces (ramets) of yellow toadflax could influence their respective competitive ability and their susceptibility to management techniques. Shoot production was similar for genets and ramets (approximately 10 shoots were produced 12 or 13 wk after transplanting or cotyledon appearance, respectively), but the rate of shoot biomass accumulation was higher for genets than for ramets. Genets consistently produced more underground shoots than ramets. Replanted underground shoots separated from their roots were able to produce new shoots and roots. Rate of elongation for roots 0.5 to 1.5 mm in diameter was higher for ramets than for genets, but their shoot production potential was the same. Root pieces from genets did not have the ability to produce daughter shoots until 3 wk after cotyledon appearance. This indicates that very young genets would be more susceptible than older genets or ramets to management control systems.

Autumn-planted sugarcane was seeded with itchgrass in early March to give 1 plant per 30.5 cm of row length (1.8 plants m−2). In three of four experiments, itchgrass was allowed to reseed and develop naturally in the second or third-yr ratoon crops. In the first-yr crop, itchgrass stands developed by May 15 and itchgrass was removed after 30, 60, or 180 d of interference. After 30 d interference, on about June 15, itchgrass biomass ranged from 200 to 2700 kg ha−1 in four experiments and reduction in sugar yield averaged 7%. After 60 d interference, on July 15, the biomass ranged from 1400 to 2900 kg ha−1 in two experiments and reduction in sugar yield averaged 17%. Itchgrass removed at harvest in November, after 180 d interference, reduced sugar yield by 19% in four experiments. Itchgrass infestations removed in the second-yr crop on May 1, June 1, and November 15 harvest reduced sugar yield in one experiment by 3, 11, and 72%, respectively, compared to a 2-yr weed-free control. Itchgrass interference reduced sugar yield primarily by reducing stalk population even though full-season interference increased sugar concentration of juice by 2 to 10%. These studies indicate that itchgrass must be removed from sugarcane well before June 15 (30 d of interference) under Louisiana growing conditions to prevent a rapid increase in itchgrass biomass and loss in sugar yield. However, sugarcane stands and yield recovered almost completely when maintained weed free in the second-yr crop following full-season itchgrass interference in the first-yr crop.

Sicyos deppei G. Don (Cucurbitaceae) is an annual weed that disperses dormant seeds. The influence of scarification and light on their germination was studied in the laboratory. Scarified seeds collected in 1987, 6, 7, 8, and 9 mo postharvest, gave high germination both in white light (89 to 100%) and darkness (64 to 96%), in comparison with nonscarified seeds which germinated 7 to 20% in both conditions. Scarified seeds collected in 1989, 3 mo postharvest, germinated higher (52 to 69%) than nonscarified seeds (0 to 5%). Exposure to light did not break dormancy of nonscarified seeds. The reversal of dormancy by scarification describes them as hard seeds. Scarified seeds, 3 mo postharvest, were light indifferent, germinating even in the usually inhibitory condition of far-red light. However, a low proportion of scarified seeds, 6 and 7 mo postharvest, presented a positive photoblastic response and germinated 23 and 36%, respectively.

Growth and development of red rice (strawhull) and ‘Lemont’ and ‘Newbonnet’ rice were compared in 1987 and 1988 under noncompetitive field conditions at Stuttgart, AR. Growth and developmental differences were greater between red rice and rice than between rice cultivars. Compared to rice, red rice was taller, produced more culms m−2 and aboveground dry weight, had higher leaf area indices, and had a greater flag leaf area. Also, it had lower leaf to stem ratios late in the season, had greater crop growth rate early in the season but less late in the season, and produced a lower grain weight than rice. Compared to Newbonnet, Lemont plants were shorter at 60 d after emergence or later, produced more culms m−2, had a greater leaf area index, and produced higher grain weight than Newbonnet. Also, Lemont and Newbonnet produced comparable leaf to stem ratios, crop growth rates, and flag leaf areas.

Chloroplast DNA (cpDNA) restriction fragment length polymorphisms (RFLPs) were analyzed to assess genetic variation and relatedness among selections of North American and Eurasian leafy spurge. Leafy spurge accessions from Nebraska, Montana, Russia, Italy, and Austria were evaluated. Total DNA was extracted from young leaves and digested with the restriction endonuclease, EcoRI. CpDNA fragment patterns were determined by Southern blot analysis using mung bean cpDNA probes. Colinearity between the mung bean and leafy spurge chloroplast genomes was indicated by the observation that common fragments were hybridized by adjacent probes. Minimum estimates of chloroplast genome size for the five leafy spurge accessions, which ranged in kilobase size from 130 to 132, were within the size range of most terrestrial plants. Structural collinearity and reasonable estimates of chloroplast genome size provided evidence that the mung bean cpDNA library was suitable for characterizing leafy spurge cpDNA. Seven of the 13 mung bean probes hybridized to polymorphic leafy spurge cpDNA fragments. Based on number of polymorphisms unique to each Eurasian accession, the Austrian accession appeared to be most divergent followed by the Italian and Russian. The North American accessions seem to be most closely related to each other and to the Russian leafy spurge accession.

Shattercane interference in irrigated soybean was evaluated during 1987, 1988, and 1989 at Clay Center, NE, using ‘Rox’ forage sorghum to simulate shattercane. Soybean yield reduction did not occur if shattercane was removed by 2 wk after emergence in 1987 and 6 wk after emergence in 1988 and 1989. Shattercane interference with soybean began when shattercane height exceeded soybean height. Soybean yield was reduced up to 25% before the height differential reached 30 cm, the minimum difference required for selectively applying glyphosate with a wiper applicator. Soybean nodes per stem, pods per stem, and beans per pod decreased as duration of interference increased. A direct relationship between soybean yield loss and shattercane density fit a rectangular hyperbolic function. Yield loss per shattercane plant was highest at low shattercane densities. Soybean plant height, biomass, nodes per stem, pods per stem, pods per node, and beans per pod decreased as shattercane density increased. An interference model for estimation of soybean yield and economic loss based on shattercane density was developed.

Barnyardgrass inflorescence length ranged from less than 2 to over 20 cm. Inflorescences less than 4 cm long were a single first-order raceme, while the largest had 20 to 50 primary branch racemes. Inflorescences longer than about 12 cm and with more than about 12 racemes showed second-order branching. Air-dried structural biomass increased from less than 2 milligrams for the smallest to over 300 milligrams for the largest inflorescences. Inflorescence length and structural biomass were positively correlated (r2 = 0.95). Floret numbers increased from about 15 for smallest inflorescences to over 2000 for largest inflorescences and were positively correlated with inflorescence length (r2 = 0.94) and with inflorescence structural biomass (r2 = 0.94). Biomass of caryopses plus aborted florets had the same relationships as those for floret number. Measurement of frequency distribution of size and determination of numbers of inflorescences per plant should provide a means to predict fecundity in barnyardgrass.

Under field conditions, more photoassimilate moved to roots of Canada thistle at the bolt than at the bud, flower, or postflower stages. Similarly, greater photoassimilate accumulated in roots of Canada thistle in the greenhouse at the rosette and bolt than at the flower bud stage. Growth chamber experiments indicated that environmental conditions typical of fall, and possibly early spring, favored photoassimilate movement to the root and superseded growth stage control of assimilate partitioning. Allocation of assimilate within the root was strongly influenced by growth stage, with most assimilate being utilized for growth at the rosette stage and for fructan reserves in bolt and flower bud stages.

The objectives were to compare the growth of black and eastern black nightshade and develop predictive models for their growth. Black and eastern black nightshade were planted on June 3 and 23, and July 12 in 1988 and May 28, June 17, and July 10 in 1989. Exponential models were strongly correlated with the growth of both species across all planting dates. Eastern black nightshade produced more biomass than black nightshade, although weight of berries was equivalent. Leaf area per plant 60 d after planting was five times greater for eastern black nightshade than black nightshade. Eastern black nightshade responded to self-shading by increasing specific leaf area.

Bentazon reduced paraquat phytotoxicity to Texas panicum, sicklepod, Florida beggarweed, and peanut. Bentazon applied alone had minimal effect on these species. Smallflower morningglory was more sensitive to bentazon than to paraquat; the interaction of paraquat and bentazon varied from antagonistic to synergistic depending upon the specific combination of rates. Antagonism with tank-mixed combinations was also obtained by applying bentazon prior to paraquat, but not with the reverse. Studies with 14C-labeled herbicides revealed that each herbicide inhibited foliar penetration of the other. In field studies, adding bentazon to paraquat reduced crop injury. However, except for smallflower morningglory, weed control was also reduced.

Field studies were conducted over 3 yr to investigate the effect of chemicals on field beans density and weed control. Predominant weed species were common lambsquarters, fumitory, henbit, corn poppy, prostrate knotweed, and wild mustard. All herbicide treatments except linuron injured field beans. Mean field beans survival at harvest was 78% in alachlor and 84% in alachlor containing treatments. Only 5% survived atrazine at 1.9 kg ai ha−1. Ethalfluralin, pendimethalin, simazine, terbutylazine plus terbutryn, and trifluralin treatments produced plant survival values of 56, 82, 86, 74, and 71%, respectively. Chemical control of the main weed species overshadowed the detrimental effect on field beans density, and thus most herbicide treatments except alachlor resulted in increased dry beans yield. The best overall results occurred with linuron, simazine, terbuthylazine plus terbutryn, and pendimethalin which increased dry beans yields 76, 63, 56, and 40%, respectively, over the control plots. Common lambsquarters was the dominant weed, and prostrate knotweed and corn poppy were the most difficult and the easiest species to control, respectively.

Absorption and translocation of 14C-fluroxypyr were determined for leafy spurge at various growth stages, under differing relative humidity and temperature conditions, and when applied with picloram or 2,4-D. Absorption of 14C-fluroxypyr was greater in vegetative plants (39%) than in flowering or postflowering plants (25%), while total translocated to roots averaged 2% of applied herbicide regardless of growth stage. Greater 14C-fluroxypyr absorption and translocation occurred in plants exposed to high relative humidity (>90%) compared to low humidity (<30%) for 6 h or longer following treatment. Absorption and translocation to roots was independent of temperature (18 or 24 C). Absorption and translocation declined by 50% when applied with picloram or 2,4-D. However, absorption and translocation of 14C-picloram or 14C-2,4-D were not affected by fluroxypyr. Fluroxypyr would likely be used in a leafy spurge control program only during environmental conditions adverse to control with picloram such as unseasonably warm or cold temperatures or in areas with a high water table.

Cotton (Gossypium hirsutum) response was evaluated when quinclorac was applied prior to cotton emergence (preemergence) and to cotton in the cotyledon and pin-head square stages in 1988, 1989, and 1990. Quinclorac applications at 9, 17, 35, 70, and 140 g ha−1 prior to cotton emergence had little effect on cotton growth, with only 140 g ha−1 causing stand reduction or stunting. Quinclorac application to cotton in the cotyledon stage caused more damage, and 70 g ha−1 caused crop injury. Greatest phytotoxicity was observed when quinclorac was applied to cotton at pin-head square, with all rates including 9 g ha−1 causing injury. Cotton injury consisted of leaf strapping and malformation of reproductive structures. Regression analysis revealed yield was reduced by quinclorac applications to cotton in the cotyledon or pin-head square stage. The approximate regression equation to predict cotton yields after pin-head square application of quinclorac was [yield] = [yield with no injury] − 10(quinclorac rate in g ha−1).