There is no published information on the impact of volunteer barley on wheat yield loss or on the economics of controlling barley with a herbicide. With the registration of imazamox-resistant wheat, it is now possible to control volunteer barley in wheat. Thus, the likelihood of growing wheat in rotation with barley may increase. Field experiments were conducted in 2003 and 2004 at Beaverlodge, Lacombe, and Edmonton, AB, Canada, and Saskatoon, SK, Canada, to determine the impact of volunteer barley on yield of imazamox-resistant spring wheat seeded at relatively low (100 kg ha−1) and high (175 kg ha−1) rates. Barley was seeded at different densities to simulate volunteer barley infestations. Regression analysis indicated that wheat-plant density influenced the effects of volunteer barley interference on wheat yield loss, economic threshold values, and volunteer barley fecundity among locations and years. Economic thresholds varied from as few volunteer barley plants as 3 m−2 at Beaverlodge in 2003 and 2004 to 48 m−2 at Lacombe in 2003. In most cases, wheat yield loss and volunteer barley fecundity were lower and economic thresholds were higher when wheat was seeded at the higher rate. For example, averaged over both years at Beaverlodge initial slope values (percentage of wheat yield loss at low barley density) were 4.5 and 1.7%, and economic threshold values of volunteer barley plants were 3 m−2 and 8 m−2 at low and high wheat seeding rates, respectively. Results indicate that volunteer barley can be highly competitive in wheat, but yield losses and wheat seed contamination due to volunteer barley can be alleviated by seeding wheat at a relatively high rate.

Sixteen soybean [Glycine max (L.) Merr.] cultivars were evaluated for their response to the rice herbicide propanil (3′,4′,-dichloropropionanilide) applied at two growth stages. Application of 3.4 kg/ha resulted in more injury than 0.6 kg/ha. Application at the stage of growth when three nodes on the main stem had completely unrolled leaves (V3) resulted in more injury than when eight nodes had completely unrolled leaves (V8). As determined by seed yield when treated at 3.4 kg/ha propanil at the V3 stage of growth, ‘Pickett 71′, ‘McNair 600′, ‘Tracy’, and ‘Bragg’ were the most tolerant; ‘Hutton’, ‘Hampton 266A’, ‘Bossier’, ‘Ts 74-34′, ‘Semmes', and ‘Forrest’ were moderately sensitive and Dowling’, ‘Davis', ‘Mack’, ‘Dare’, ‘Ranson’, and ‘McNair 800’ were the most sensitive to propanil injury.

Switchgrass is a potential feedstock for cellulosic bioenergy production. Weed competition from annual grass during the establishment year can reduce switchgrass establishment and resulting productivity, but the relationship between early season grass densities and outcomes of competition are not well understood. We measured how a range of giant and yellow foxtail densities in the establishment year influenced switchgrass establishment and resulting productivity in the first production year (second year of the growing season). In two of the three site–yr more than four foxtail plants m−2 reduced switchgrass plant densities below documented thresholds of establishment success. A lesser effect of foxtails in the third site–year suggested that higher switchgrass emergence rates reduced foxtail competitive ability during establishment. Effects on yield were consistent over the three site–yr. The yield (10.96 Mg ha−1 ± 0.77) decreased rapidly as foxtail density increased. One foxtail plant m−2 reduced switchgrass yield in the first production year by 25%, and yield loss was 90% or greater at densities > 50 foxtail plants m−2. Although switchgrass can establish in the presence of foxtail competition, these weed species should be controlled to maximize yields in the first production year.

Field studies were conducted to determine the effect of green foxtail density and location on the yield of potato under dryland conditions. Total and marketable tuber yields were reduced by green foxtail densities of less than 75 plants m-2. Marketable yields were affected more by increasing green foxtail density than were total yields. Increasing weed density reduced both the number and size (tuber weight) of marketable tubers but not the specific gravity or the sucrose content of the tubers at harvest. Green foxtail growing between crop rows was as competitive with potato as plants growing within the row. The effect of weed competition on total and marketable tuber yields was more pronounced in drought years than years with normal precipitation.

Field studies indicated thiazopyr at 220 g ha−1 injured soybeans planted in no-till, and 340 g ha−1 injured soybean in 1 of 2 yr planted into tilled soil. Thiazopyr half-lives in three field studies ranged from 12 to 14 d, indicating minimal potential for carryover injury to sensitive rotational crops. Thiazopyr dissipation under controlled conditions was slower than under field conditions. Half-lives at 15 and 30 C were 133 and 43 d, respectively. This indicates that microbial degradation is an important mechanism in thiazopyr dissipation, but that other loss mechanisms also play a role. A method using methanol extraction of moist soil samples followed by gas chromatography using a nitrogen-phosphorous detector had > 90% recovery of thiazopyr.

Postemergence applications of MSMA (monosodium methanearsonate) for weed control in spring wheat (Triticum aestivum L.) were evaluated in the field, greenhouse, and controlled environmental chamber. MSMA controlled weeds better when applied to wheat at the four- to five-leaf stage than when applied at the two- to three-leaf stage. MSMA, tank mixed with barban (4-chloro-2-butynyl-m-chlorocarbanilate) or diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, controlled wild oat (Avena fatua L.), green foxtail, [Setaria viridis (L.) Beauv.] and broadleaf weeds better than did MSMA applied alone. Wild oat control with tank-mix applications of MSMA and difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) was variable. Weed control with MSMA was enhanced by 30 C air temperatures, 90% relative humidity, and adequate soil moisture. A simulated rainfall of 0.5 mm within 0.5 h or 4 mm with 4 hr after application reduced wild oat control with MSMA.

Field trials were conducted in 1986 and 1987 to determine the effects of moisture on herbicidal activity of cinmethylin applied preemergence at 0.0, 0.3, 0.6, and 0.9 kg ai ha to both dry and moist sandy loam soil. Herbicide application was followed by varying amounts of irrigation. Weed species included velvetleaf, prickly sida, green foxtail, and barnyardgrass. When cinmethylin was applied to a moist soil or when 2.5 cm of irrigation was applied 5 days after cinmethylin application to a dry soil, overall weed control was reduced. Optimum weed control resulted from cinmethylin application to dry soil followed either by a 2.5-cm irrigation within 8 h or a 7.6-cm irrigation within 36 h.

Yellow nutsedge (Cyperus esculentus L.) tuber maturity was studied to determine its influence on accumulation of 14C from urea and NAA (naphthaleneacetic acid). Radioactive carbon from the above sources accumulated in tubers in decreasing amounts as tubers became more mature when the plants to which they were attached were treated. Tubers that were young at treatment accumulated the highest concentration of radioactivity and parent tubers (most mature) accumulated the least 14C. Tubers that were classified as mature, but not parents, accumulated insignificant amounts of radioactive carbon.

Glyphosate applied at rates of 0, 0.3, 0.6, 1.1, 2.2, 3.4, 4.5, 6.7, 9.0, and 13.4 kg ai ha−1 was evaluated for the control of greenhouse-grown Erythroxylum novogranatense var. novogranatense and E. coca var. coca plants. Glyphosate reduced live weight of both species, 6 wk after treatment, at rates as low as 0.6 kg ha−1, but was more effective in reducing live weight and regrowth on E. novogranatense than E. coca. Glyphosate at 1.1 kg ha−1 killed 100% of E. novogranatense plants 5 mo after treatment. Glyphosate rates of 2.2 kg ha−1 and higher reduced regrowth of E. coca plants 65 to 100%, independent of leaf age at time of spraying. Control of regrowth persisted for over 17 mo after treatment, with 37% of E. coca plants dying at rates of 13.4 kg ha−1 between 6 mo and 1 yr after treatment. Glyphosate, applied up to 6.7 kg ha−1, had no significant effect on regrowth of E. coca when plants were defoliated 24 h before treatment. Glyphosate at 2.2 kg ha−1 effectively killed E. novogranatense plants and reduced leaf production of E. coca plants.

The precise delivery of small quantities of herbicide solutions to leaf surfaces is difficult to achieve, yet most absorption research has this requirement. An atomizer for delivering microliter quantities of herbicide solutions has been designed, constructed, and tested. The function of the atomizer is to quantitatively apply low-volume (1-to 10-μl) solutions of herbicides, especially radioactive herbicides, to plant surfaces. The appearance of droplets from the atomizer and a flat-fan nozzle were similar and both yielded deposits that were much smaller than a 1-μl droplet applied by syringe. There was no splatter loss of herbicide when applied with the atomizer, and the bio-activity of the herbicide was equal to that applied as a single droplet. The atomizer yielded drops similar to those from a flat-fan nozzle and should produce absorption results more representative of those found under field conditions.

Alfalfa (Medicago sativa L.), beans (Phaseolus vulgaris L.), corn (Zea mays L.), potatoes (Solanum tuberosum L.), spring wheat (Triticum aestivum L.), and sugarbeets (Beta vulgaris L.) were severely injured and had reduced foliage dry weights when grown in soil containing 0.10 ppmw or more terbacil (3-tert-butyl-5-chloro-6-methyluracil). Activated carbon at 150 kg/ha prevented a significant loss in weight of beans and corn in soil containing 0.10 ppmw terbacil and fully protected potatoes in soil containing 0.19 ppmw terbacil. Carbon at 300 kg/ha fully protected sugarbeets and prevented a significant weight loss in alfalfa in soil containing 0.19 ppmw terbacil. Carbon at 600 kg/ha did not protect wheat from 0.19 ppmw terbacil.

Hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] toxicity, absorption, translocation, metabolism, and effect on photosynthesis were investigated with rooted cuttings of highbush blueberry (Vaccinium corymbosum L.), rabbiteye blueberry (V. ashei Reade), and hollow goldenrod (Solidago fistulosa Miller # SOOFI). Highbush and rabbiteye blueberry plants were three times more tolerant to root applications of hexazinone than hollow goldenrod. Blueberry plants absorbed an average of 7.9% of root-applied 14C-hexazinone and hollow goldenrod absorbed an average of 10.1%. An average of 6.8% of root-absorbed hexazinone (14C-label) was translocated from the roots of blueberry to stem and leaves. Radioactivity in hollow goldenrod was distributed equally between roots and shoots. The majority of radioactivity in both species was recovered as hexazinone. Root-absorbed hexazinone caused a rapid inhibition of photosynthesis in intact hollow goldenrod leaves. Root-absorbed hexazinone was capable of inhibiting photosynthesis in intact blueberry leaves; however, this occurred only when roots were exposed to high concentrations of hexazinone.

The fungus Pleospora papaveracea is a potential biocontrol agent for opium poppy. The objective of this study was to characterize the growth and production of propagules of P. papaveracea on various substrates and determine their infectivity on opium poppy. Pleospora papaveracea was grown on agar media containing wheat bran, corn cobs, soy fiber, cottonseed meal, rice flour, cornstarch, pectin, dextrin, or molasses, all with the addition of brewer's yeast (BY). Maximum radial growth of P. papaveracea occurred on molasses, soy fiber, and wheat bran media. Pleospora papaveracea produced chlamydospores on dextrin–BY and cornstarch–BY only. Pleospora papaveracea growth in liquid media with 1% (wt/v) dextrin, cornstarch, soy fiber, or wheat bran resulted in the production of greater than 106 colony-forming units (cfu) ml−1 within 3 to 5 d of incubation. Pleospora papaveracea produced less than 105 chlamydospores ml−1 after 10 d of incubation in wheat bran–BY and soy fiber–BY liquid media compared with the production of greater than 105 chlamydospores ml−1 after 5 d of incubation in dextrin–BY or cornstarch–BY liquid media. Fewer cfu were produced by P. papaveracea in 0.25% dextrin or 0.25 and 0.50% soy fiber liquid media than with 1 or 2% substrate. Greater than 107 chlamydospores g−1 dry weight and 108 cfu g−1 dry weight of P. papaveracea were produced in dextrin–BY liquid media in a commercial bench-top fermentor. After air drying biomass for 6 d, propagules of P. papaveracea remained infective on opium poppy. Mycelia and chlamydospores of P. papaveracea grew and formed appressoria during the infection process. Air-dried biomass, when rehydrated in 0.001% Tween 20, caused necrosis within 48 h after application to detached opium poppy leaves. At least 94% of the propagules from air-dried biomass that germinated and infected detached opium poppy leaves were of mycelial origin.

A field trial was conducted in 1988 and 1989 to confirm the efficacy of naphthalic anhydride (NA) for providing full-season protection of corn from imazethapyr applied at various times and rates. NA applied as a 1% by weight dust to corn seed caused 6% injury 2 weeks after treatment (WAT) in 1989; however, plants recovered within 6 WAT and grain yield was not affected. Imazethapyr applied to corn untreated with NA resulted in greater than 30% injury for all treatments in both years except PRE in 1988. NA reduced phytotoxicity from all imazethapyr applications in 1989 and from PPI, early POST, and 4- to 5-leaf stage (mid-POST) applications in 1988. Despite the safening effect, corn injury was still observed 6 WAT in NA-treated corn for all imazethapyr applications in both years except early POST in 1988. Higher yields were produced from NA-treated than untreated corn with imazethapyr applied PPI in both years, PRE in 1989, early POST in both years, and mid-POST in 1988. Safened corn treated PPI and early POST yielded the same as the safened corn in the control in both years. Imazethapyr applied at the 8- to 10-leaf stage caused total yield loss regardless of NA treatment. Drought conditions may have caused the lower corn injury and yield loss from imazethapyr observed in 1988 compared to 1989.

The utility, advantages, and disadvantages of several spectrofluorometric and in vivo spectrophotometric methods in plant science are reviewed, with emphasis on their use in weed science. Examples of the use of in vivo, dual-wavelength spectrophotometry to probe the effects of herbicides on cytochrome f oxidation/reduction, the P515 chromatic shift, phytochrome synthesis, and other processes are discussed. Use of in vivo spectrophotometry to examine effects of herbicides on phytylation of chlorophyllide, protochlorophyllide photoconversion, porphyrin accumulation, and other processes that result in spectral changes is discussed and examples are provided. Spectrofluorometric methods for pigment identification and quantification and for enzyme assays are illustrated with examples. Spectrofluorometric methods used in conjunction with high-pressure liquid chromatography (HPLC) and thin-layer chromatography (TLC) are discussed.

The effect of temperatures below 0 C and plant maturity on the phytotoxicity of glyphosate [N-(phosphonomethyl)glycine] on rapidly growing alfalfa (Medicago sativa L. ‘Vernal’) and quackgrass [Agropyron repens (L.) Beauv.] plants was studied in a controlled environment. Pretreatment at −4 C partially protected alfalfa from injury by 0.8 kg/ha of glyphosate at six alfalfa maturities. This same treatment had no significant effect on glyphosate phytotoxicity to quackgrass. Pretreatment at −4 C increased translocation of glyphosate in quackgrass but reduced its translocation in alfalfa. A greater reduction in translocation occurred in the smaller alfalfa plants.

The occurrence of asymbiotic nitrogen fixing bacteria in the rhizosphere of twenty weed species has been investigated. Using the roll tube method root-rhizosphere soil samples were diluted and added to test tubes containing low N media. Tubes were flushed with nitrogen, stoppered, and rolled to form a thin film of media on the inner wall. After 7 days incubation the nitrogen fixation rates were estimated using the acetylene reduction technique. Rates ranged from 38 to 783 nmoles acetylene reduced per hour. Of twenty species tested, three showed high rhizosphere populations of asymbiotic nitrogen fixing bacteria.

Combinations of 4-amino-3,5,6-trichloropicolinic acid (picloram) and 5-bromo-3-sec-butyl-6-methyluracil (bromacil) pellets applied to the soil gave antagonistic responses on oats (Avena sativa L. ‘Clintland 64′) with either 5.6 plus 11.2 kg/ha or 11.2 plus 11.2 kg/ha of picloram plus bromacil. In nutrient culture a significant antagonistic response occurred over a 15-day period with a picloram to bromacil ratio of 30 to 1. Of the ratios evaluated, picloram appeared to interfere with the phytotoxic effect of bromacil. The uptake of 14C-bromacil alone by oats from nutrient solution was nearly double that of 14C-bromacil when combined with picloram. Thin layer chromatographic analyses revealed that 47% of the 14C activity from bromacil in the oat was intact bromacil and that 70% of the labeled activity from picloram was unaltered picloram. The loss of nutrient solution by evapotranspiration was less from containers with picloram and bromacil than from those with bromacil alone. Picloramtreated roots were shorter than untreated or bromacil-treated roots.

Spring small grains were not as competitive with barnyardgrass and witchgrass as winter wheat. Winter wheat grain yields were greater than spring barley or spring wheat in 1986, 1987, and 1988 and oat in 1986 and 1988. Barnyardgrass, stinkgrass, and witchgrass control with glyphosate plus 2,4-D plus atrazine at 0.6 plus 0.8 plus 1.7 kg ha−1 was usually less when the herbicides were applied to stubble of spring small grain versus winter wheat due to the advanced weed growth at treatment Barnyardgrass and witchgrass were more difficult to control than stinkgrass, redroot pigweed, tumble pigweed, kochia, and tumble thistle. No-till corn planted into winter wheat stubble had fewer barnyardgrass and witchgrass than corn planted into spring wheat stubble. The addition of metolachlor plus atrazine at 1.7 plus 0.6 kg ha−1 eliminated differences among small grain cultivars in weed control in corn. Corn grain yields from winter wheat plots were greater than other small grains in 1989 because of better weed control and more crop residue.