Of 15 pesticides evaluated in a screening test with respect to their effects on growth and nitrogen assimilation of the Azolla mexicana (Presl) – Anabaena azollae (Strasburger) symbiosis, the bipyridilium and phenolic herbicides at 0.1 ppmw were the most detrimental, causing up to a 75% reduction in nitrogen fixation and nitrate reduction with little or no effect on growth. Chloramben [3-amino-2,5-dichlorobenzoic acid] at 1.0 ppmw, and dicamba [3,6-dichloro-o-anisic acid], and benomyl [methyl-1-(butylcarbamoyl)-2-benzimidazolyl carbamate] at 10.0 ppmw caused an 84 to 99% reduction in nitrogen fixation without affecting nitrate reduction or growth. Simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 10.0 ppmw stimulated nitrate reduction 20 fold, causing a 99% reduction in nitrogen fixation. Growth and nitrogen assimilation were reduced at similar concentrations between 0.1 and 10 ppmw for each of the other benzoic, triazine, dinitroanaline, and urea herbicides tested. Naptalam [N-1-naphthylphthalamic acid] was the only pesticide tested that had no effect on growth or nitrogen assimilation at 10.0 ppmw.

Infestations of common milkweed (Asclepias syriaca L.), in descending order of incidence in Nebraska, occurred on areas occupied by soybean [Glycine max (L.) Merr.], oats (Avena sativa L.), sorghum [Sorghum bicolor (L.) Moench.], railroad rights-of-way, fallow land, roadsides, corn (Zea mays L.), winter wheat (Triticum aestivum L.), pasture, and alfalfa (Medicago sativa L.). Average crop yield reductions, within common milkweed communities of 11100 to 45 200 plants/ha, ranged from 2 to 10% for corn, 4 to 29% for sorghum, and 12 to 19% for soybeans. Reductions in crop yields tended to increase with increasing common milkweed populations. Germination percentage of common milkweed and sorghum were not significantly affected by growing medium conductivities below 7 and 13 mmho/cm2, respectively. Growth media at pH 2 significantly reduced germination percentage, hypocotyl length, and radicle length of both common milkweed and sorghum as compared with pH 4 to 10. Undiluted aqueous extracts of common milkweed shoot and root material significantly reduced germination percentage, hypocotyl length, and radicle length of sorghum.

A computer-based data collection system is described. It captures all the qualitative and quantitative data necessary to print an abstract from a weed-control experiment. The output is in the form of a research report that contains many abstracts. Users of the system are weed workers in western Canada who wish to contribute to the annual edition of the Research Report of the Expert Committee on Weeds (Western Canada). Each year, users fill out a set of forms and send them to a central location where the data are entered into a computer. In 1976, 60% of the research report was successfully computer-printed. The computer system captured a higher percentage of weed-control information than was present in the old system with narrative reports. A survey of weed workers indicated that the type of information entered in the report was satisfactory.

Experiments were conducted to determine the influence of the dimethylamine salt of MCPA {[(4-chloro-o-tolyl)oxy] acetic acid} pretreatment, darkness from 1 day prior to treatment until harvest, and exogenous sucrose on diclofop {2-[4-(2,4-dichlorophenoxy)phenoxyl] propanoic acid} glucose, and sucrose uptake and translocation by wild oat (Avena fatua L.). Uptake of 14C-diclofop label by wild oat foliage was not influenced by MCPA pretreatment, constant dark treatment, or the addition of exogenous sucrose. Total 14C-diclofop and 14C-glucose label uptake and translocation were similar whether 5 cm of the treated leaf tip were placed in distilled water or 1% (w/v) sucrose. Downward translocation of 14C-diclofop, 14C-sucrose, and 14C-glucose label in the phloem of wild oat was reduced similarly by MCPA, constant dark treatments, or a combination of the two. Upward translocation of 14C-diclofop label was greater and exudation of 14C-diclofop label into the ‘tip’ solution was less than that of 14C-sucrose or 14C-glucose label, regardless of MCPA or constant dark treatments. Downward translocation of 14C-diclofop label was reduced as much by MCPA topically applied to the wild oat leaf 1 cm above, 1 cm below, or with the diclofop as with the MCPA broadcast pretreatment.

Soybean [Glycine max (L.) Merr. ‘Tracy′] and two associated weeds, sicklepod (Cassia obtusifolia L.) and showy crotalaria (Crotalaria spectabilis Roth), were grown in controlled-environment chambers with day/night temperatures of 29/23 C, photosynthetic photon flux density (PPFD) of 600 μE·m−2·s-1, CO2 concentrations of 350 or 675 ppm, and one-eighth or one-half strength Hoagland's nutrient solution applied three times daily. Leaf areas and dry weights of plant parts were determined at 1, 3, and 5 weeks. Stomatal resistances, transpiration rates, leaf water potentials, and leaf chlorophyll contents were measured, and net assimilation rates (NAR) and leaf area durations (LAD) were calculated. In all species, growth in 675 ppm CO2 enhanced dry-matter production through increases in both NAR and LAD. The increased dry-matter production with one-half strength compared to one-eighth strength Hoagland's solution was, however, caused by increased LAD. Stomatal conductances and transpiration rates decreased in 675 ppm CO2, but were not affected by nutrient level. High CO2 concentration or low nutrient level generally decreased leaf chlorophyll content per unit area. Growth enhancement by high CO2 was greater in one-half strength than in one-eighth strength Hoagland's solution.

Flowering dates, seed production, and disease and insect susceptibility of seven Ipomoea spp. and smallflower morningglory [Jacquemontia tamnifolia (L.) Griseb.] were determined under field conditions in 1973 and 1974. Seed produced per plant were as follows: ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.], 6000; entireleaf morningglory [I. hederacea (L.) Jacq. var. integriuscula Gray], 5000; pitted morningglory [I. lacunosa L.], 10000; wild tall morningglory [I. purpurea (L.) Roth.], 26000; commercial tall morningglory [I. purpurea (L.) Roth ‘Crimson Rambler′], 15 000; cypressvine morningglory (I. quamoclit L.), 9000; cotton morningglory [I. trichocarpa Ell. var. torreyana (Gray) Shinners], 9000; palmleaf morningglory (I. wrightii Gray), 7000; and smallflower morningglory, 11000. Seed weights were about 29, 26, 22, 21, 19, 13, 19, 37, and 5 mg/seed, respectively. Pitted morningglory appeared to have a qualitative short day-length requirement for flower initiation and the other species appeared less day-length sensitive. Ivyleaf morningglory and entireleaf morningglory were highly susceptible to orange rust [Coleosporium ipomoeae (Schw.) Burrill] and white rust [Albugo ipomoea panduratae (Schw.) Swingle], but the other Ipomoea species were only slightly susceptible and smallflower morningglory was resistant. Cotton bollworms (Heliothis zea Boddie) and cabbage loopers (Trichoplusia ni Hubner) fed preferentially on ivyleaf morningglory and entireleaf morningglory.

Analysis of reciprocal F1, F2, F3, and backcross progeny from crosses between atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]-resistant and several susceptible genotypes of Brassica campestris L. indicated that triazine resistance was inherited cytoplasmically from the female parent. A partially dominant chlorotic cotyledon was used as a genetic marker to confirm true hybrids in the reciprocal F1 progenies. Phytotoxicity of atrazine was correlated with loss of the Hill reaction.

Little barley (Hordeum pusillum Nutt.) seeds germinated readily without pregermination chilling on substrates moistened with either water or 0.2% aqueous KNO3. Little barley seeds were physiologically mature and viable as early as 11 days after flowering. Pregermination chilling induced dormancy in mature seeds moistened with water, but not those moistened with 0.2% KNO3. Mature seeds frequently germinated better at alternating temperatures from 20C (16 h) to 30C (8 h) than at constant 20C. Germination of seeds after 1 week in a thermogradient table varied from 1% at 34C to 77% at 21C. Seeds were able to germinate over an extended period in the fall and spring. Forage and seed production were highest from the first fall planting date and decreased with later plantings. Plants emerging from seeds planted in March and April did not produce seed.

In greenhouse studies, soil organic matter reduced the herbicidal activity of ethalfluralin (N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine). Fifty percent inhibition (I5.0) values for barnyardgrass [Echinochloa crus-galli (L.) Beauv.] stand, injury, and shoot fresh weight increased as the soil organic-matter level increased. No difference in ethalfluralin tolerance was found among 16 cucumber (Cucumis sativus L.) cultivars. When grouped according to market type, fresh market cultivars tended to be injured more than pickling cultivars by excess ethalfluralin. Both shoots and roots of cucumber absorbed the herbicide, but exposure of roots to ethalfluralin was more toxic than exposure of shoots. Field studies indicated that with certain edaphic and environmental conditions, cucumbers can be injured by preemergence applications of ethalfluralin. Injury was greatest in a low organic-matter soil following a heavy rain. Ethalfluralin at 1.3 kg/ha gave adequate weed control in 1 and 3% organic-matter soils, but not in a 9% organic-matter soil.

Field experiments were conducted to determine the effectiveness of the herbicide antidote R-25788 (N,N-diallyl-2,2-dichloroacetamide) in protecting corn (Zea mays L.) cultivars from EPTC (S-ethyl dipropylthiocarbamate) injury. Preplant-incorporated applications of EPTC, with and without R-25788, were made to a fine sandy loam in 1976 and a loamy sand soil in 1977. EPTC at 6.7 kg/ha was 20 to 30% more injurious to the susceptible cultivars grown in sandy, lower organic-matter soil than in fine sandy loam. R-25788 did not decrease the weed-control efficacy of EPTC. The cultivar ‘TXS114’ was highly tolerant to EPTC at 6.7 kg/ha with or without antidote protection. Most of the other EPTC-susceptible cultivars showed significant stand improvement when R-25788 was used in combination with EPTC. R-25788 did not alleviate EPTC phytotoxicity toward ‘XL55’ and ‘XL379’ cultivars. EPTC applied in combination with R-25788 showed no, or only, slight injury to all other cultivars.

Germination of jointed goatgrass (Aegilops cylindrica Host.) seed in nitrate nitrogen (NO−3-N), gibberellic acid (GA3), or distilled water was studied in the laboratory, and depth of emergence of seedlings from soil was studied in the greenhouse and laboratory. After 14 days in germination chambers in distilled water, no difference in percent germination of 1-yr-old or freshly harvested seed existed between 10, 15, or 20 C. Jointed goatgrass seed germinated at temperatures ranging from 10 to 35 C and responded to temperature more than to NO−3-N. Seedlings did not emerge from below 5 cm in greenhouse and 6 cm in laboratory studies even though germination occurred. Jointed goatgrass has the seed germination and seedling emergence characteristics to develop into a severe annual grass weed in winter wheat (Triticum aestivum L.)-producing regions, particularly where reduced-tillage practices are utilized.

Germination of prostrate spurge (Euphorbia supina Raf.) seeds collected in August, September, October, and November 1977 at Riverside, California was 53, 30, 18, and 16%, respectively. Stratification of seeds collected in August, September, and October at 5 C for 3 weeks or more increased germination to 70 to 80%. Prostrate spurge seeds germinated at constant temperatures of 20 to 40 C, with optimum temperatures of 25 to 30 C. Maximum germination occurred under alternating temperatures with a high temperature of 30 to 35 C and a low temperature of 15 to 25 C. Germination in the dark was much lower than in the light. Seedling establishment of seeds collected in August sown at 0.0- to 0.5-cm depths was 30 to 35%, but establishment from 2 cm declined to near 0%. Light intensity did not affect the number of seedlings established, but the seedlings established were larger under higher light intensities.

Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] is a preemergence herbicide used for the control of most annual grasses and many annual broadleaf weeds. Its influence on the uptake and translocation of N, P, K, Ca, Mg, Cu, Fe, and Zn by four plant species was observed. Napropamide influenced, in some cases dramatically, the uptake and movement of the essential elements, but its influence was not consistent from one type of plant to another.

Adsorption of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] and fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] on a Taloka silt loam (Mollic Albaqualf) and a Roxana silt loam (Typic Udifluvent) from the 10- to 20- and 40- to 50-cm soil depths was measured. The order of adsorption of the herbicides was fluometuron = metolachlor > metribuzin. Adsorptivity of the soil from the 10- to 20-cm depth was greater than from the 40- to 50-cm depth. At 7, 15, 23, and 37C, all herbicides degraded more rapidly as temperature increased. Metribuzin was least persistent and fluometuron and metolachlor were similarly persistent. The time required for the initial herbicide concentration to decrease by 50% in the Taloka silt loam from the 10- to 20-cm depth at 23C was 2.6, 9.4, and 10.1 weeks for metribuzin, fluometuron, and metolachlor, respectively.

The absorption, translocation, and metabolism of 14C-ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] in sugarbeet (Beta vulgaris L.), common ragweed (Ambrosia artemisiifolia L.), redroot pigweed (Amaranthus retroflexus L.), and common lambsquarters (Chenopodium album L.) were studied as possible bases for selectivity of preemergence-applied ethofumesate. The sensitive redroot pigweed and common lambsquarters plants translocated more 14C-ethofumesate from nutrient culture to the leaf tissue than did the tolerant sugarbeet and common ragweed. The radioactivity was more highly concentrated in sugarbeet and common ragweed roots. The rapid metabolism of ethofumesate by sugarbeet and common ragweed, particularly that which accumulated in the leaf tissue, appeared related to tolerance.

The effects of common cocklebur (Xanthium pensylvanicum Wallr.) on soybean [Glycine max (L.) Merr. ‘Wells′] development and seed yield were investigated at Urbana, Illinois, from 1974 through 1977. Increased densities of common cocklebur reduced soybean seed yield, total dry weight, and number of pods per plant. Under full-season competition, one common cocklebur/3 m of row reduced soybean seed yield by 3 to 12%. Soybean seed yield, total dry weight, and number of pods per plant increased as the length of time from soybean emergence to common cocklebur emergence increased. Common cocklebur emerging 4 weeks after soybean emergence reduced soybean seed yield by 7%. As duration of competition with common cocklebur increased, soybean seed yield, total dry weight, and number of pods per plant decreased. The reduction in soybean seed yield was less than 10% when common cocklebur was removed 6 weeks after soybean emergence. Effects of common cocklebur competition with soybeans in Illinois were similar to those observed in the southern United States.

Differences in susceptibility of sugarbeet (Beta vulgaris L.) to preemergence application of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate], pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone], and TCA (trichloroacetic acid) were evaluated in several combination treatments. Exposure of plants to ethofumesate severely decreased epicuticular wax deposition on leaf surfaces. Separation of epicuticular wax into major components by gas-liquid chromatography indicated that ethofumesate decreased deposition of alkanes and sec-ketones, but increased the percentage of long-chain waxy esters. TCA also decreased deposition of alkane and ketone components, but not of waxy esters. Waxes were unaffected by pyrazon. Greater foliar absorption of 14C-ethofumesate, 14C-desmedipham [ethyl m-hydroxycarbanilate carbanilate (ester)], and 14C-ethofumesate + 14C-desmedipham was observed in plants that received preemergence treatments of ethofumesate plus TCA compared to pyrazon or a control.

Studies in growth chambers indicated that CGA-43089 {α-[(cyanomethoxy)imino] benzeneacetonitrile} applied at a rate of 1.25 g/kg of seed reduced the phytotoxicity of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], bensulide [o,o-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl) benzenesulfonamide], EPTC (S-ethyl dipropylthiocarbamate), UBI-S734 {2-[(1,2,5-dimethylphenyl)ethylsulfonyl] pyridine N-oxide} and MBR-18337 {N-[4-(ethylthio)-2-(trifluoromethyl)phenyl] methanesulfonamide} to grain sorghum [Sorghum bicolor (L.) Moench] during seed germination and seedling emergence. The protected sorghum tolerated metolachlor over a wider range of rates than it tolerated the other herbicides. CGA-43089 did not protect sorghum from the phytotoxicity of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Of seven other oximes tested as seed treatments, dimethylglyoxime, benzophenone oxime, pyridine-2-aldoxime, benzoin-α-oxime, and methyl thioacetohydroxamate showed promise for increasing the tolerance of grain sorghum to metolachlor. In general, higher rates of these oximes than the rate of CGA-43089 were required for equivalent protection of sorghum.