Purposefully introduced plants that have become weeds cost the United States millions of dollars annually by reducing yields of crops and livestock, clogging navigable and recreational waterways, reducing productivity and value of grazing lands, poisoning humans and livestock, and increasing weed control costs. Research is in progress to develop methods of intercepting foreign plants that might be toxic to livestock if introduced on western ranges and pastures. Methods of intercepting include identifying poisonous plants from seed inventories, chemical analysis, chemotaxonomic investigations of biochemical relationships between related taxa, and feeding suspected plants to laboratory and domestic animals.

Research was conducted on the leachability and dissipation of sodium azide applied to soil as a solution or as granules with various coatings. The sodium azide leached readily from all formulations, leaving sections of the soil profile with insufficient concentrations to stimulate germination of dormant wild oat (Avena fatua L.) seed. Sodium azide-impregnated clay granules coated with 5% (w/w) polyethylene glycol increased germination of wild oat seed two-fold over uncoated granules at a rate of 5.6 kg sodium azide/ha in field experiments. The polyethylene glycol coating reduced the rate of sodium azide dissipation from the soil in growth chamber experiments. Formulation of sodium azide has potential for increasing wild oat germination stimulation under field conditions.

Loss in activity of foliar-applied methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} occurred under low soil moisture conditions. A loss in control of yellow foxtail [Setaria lutescens (Weigel) Hubb.], wild oats (Avena fatua L.), little-seed canarygrass (Phalaris minor Retz.), and barnyardgrass [Echinochloa crus-galli (L.) Beauv.], was observed under greenhouse and growth chamber conditions. When soil was maintained at 2 to 3% above wilting point as compared to near field capacity, herbicide activity was decreased by 15 to 50%. High soil moisture (at or above 67% of field capacity) for at least 2 to 4 days following treatment was needed to achieve maximum effectiveness of the herbicide. Daily furrow irrigations for a period of 10 days following treatment of barnyardgrass in the field resulted in highest activity as compared to that under single irrigation regimes within the 10-day period. The effect of low soil moisture was minimized by increased rates of herbicide application. Hoe-29152 {methyl-2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoate} showed similar losses in activity associated with low soil moisture. No consistent changes in uptake or translocation of 14C-labeled diclofop could be detected in association with altered soil moisture status.

Spring establishment of tall fescue (Festuca arundinacea Schreb. ‘Kentucky 31’) is preferred over fall for turfs in Nebraska. Siduron [1-(2-methylcyclohexyl)-3-phenylurea] is commonly used for weed control in spring-seeded tall fescue. Siduron application rates of 6.8, 13.6, 27.2, and 40.8 kg/ha were compared with an untreated control in this study. All siduron applications reduced stand development. The 6.8 kg/ha rate nearly doubled the number of days for seedling emergence. Abnormal seedlings increased with increasing application rates and percent germination decreased with increasing rates. Tiller number declined at rates of 13.6 kg/ha and above. Plants treated with 6.8 kg/ha were 1.3 cm shorter than those growing in the untreated control. Plant and root dry matter production decreased with increasing application rates. Root weight was reduced more than plant weight. Degree of wilting and drought injury increased at 13.6 kg/ha. Water use declined with increased siduron application rates. The amount of water lost before wilting occurred also declined as siduron application rates increased. High temperature injury on seedlings was reduced with increasing rates of siduron. Reduction in high temperature injury was significantly correlated (r = 0.98) to reduced plant tissue moisture.

Detached leaves of Drummond's goldenweed [Isocoma drummondii (T. & G.) Greene] absorbed the potassium salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid] from aqueous solutions more slowly than did sunflower (Helianthus annuus L.), and both species absorbed less of the potassium salt of picloram (4-amino-3,5,6-trichloropicolinic acid) than 2,4-D. However, there was no difference in absorption of the herbicides by Drummond's goldenweed leaves after 6 h of exposure to solutions containing 0.5% (v/v) surfactant. Attached Drummond's goldenweed leaves absorbed about 50% of available 2,4-D (diethylamine) and 25% of available picloram (potassium salt) within 5 days after spraying in the field during July or November. Herbicide accumulation in Drummond's goldenweed taproots after spray applications was generally slow, regardless of season, but translocation to taproots was substantially greater after application in November than after treatment in March or July. Accumulation of picloram in taproots was faster and more extensive than accumulation of 2,4-D. However, based on mortality at 6 months after treatment, both herbicides were translocated in quantities adequate for control. The greater effectiveness of picloram, despite its low foliar uptake, than 2,4-D is attributed to its greater mobility and root uptake in Drummond's goldenweed after broadcast sprays.

Field evaluations for control of grass species were conducted with metriflufen, the methyl ester of {2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoic acid}, applied as preemergence and postemergence treatments. The preemergence application of 0.28 kg/ha gave 84 to 100% control of all species except grain sorghum [Sorghum bicolor (L.) Moench], johnsongrass [Sorghum halepense (L.) Pers.], red rice (Oryza sativa L.), and green foxtail [Setaria viridis (L.) Beauv.]. These species required 0.84 kg/ha for at least 95% control. At the three-leaf stage, all species except cheat (Bromus secalinus L.) and red rice were highly susceptible to the herbicide at 0.56 and 0.84 kg/ha. At the six-leaf stage, 0.56 kg/ha of metriflufen gave 96% control of Texas panicum (Panicum texanum Buckl.) and goosegrass [Eleusine indica (L.) Gaertn.], but 0.84 kg/ha was necessary for 92% control of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and 85% control of large crabgrass [Digitaria sanguinalis (L.) Scop.]. Except for cheat, metriflufen gave less than 55% control if applied when grasses were heading. Little postemergence control was evident for red rice.

The distribution of sicklepod (Cassia obtusifolia L.) and coffee senna (Cassia occidentalis L.) in the United States is similar and both species are increasing as problems within their range. Sicklepod is a problem in 11 southern states and increasing in 12 while coffee senna is a problem in 7 states and increasing in 8 states. Both species germinated over a wide range of temperature. Germination characteristics were similar in the range of 15 to 36 C. Germination of coffee senna was drastically reduced at 39 C by Rhizopus sp. Seedling growth was similar for both species and was maximum from 30 to 36 C. Both species have a hard seedcoat. Abrasion for 5, 10, or 15 s, puncturing with a needle, and sulfuric acid were all effective in initiating germination. Both species emerged from a soil depth of 12.5 cm; however, emergence of sicklepod was more rapid than coffee senna with 63% of the sicklepod seedlings emerging from 2.5 cm after only 3 days.

In closed vapor exposure chambers, foliar injury on tobacco (Nicotiana tabacum L. ‘Speight G-28’) seedlings was caused by vapors arising from soils in which technical grade benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) or its commercially-formulated emulsifiable concentrate had been incorporated. The emulsifier alone did not cause injury. Dosages of the herbicide ranged from 0.84 to 6.72 kg/ha or 13.1 to 104.8 ppmw in the concentration in soils, and the lowest dosage was sufficient to induce the foliar injury. Leaves which developed during the exposure were markedly shortened, narrowed, and thickened, distorted in shape, and had an extremely poor lamina expansion and abnormal venation pattern. Severity of the foliar injury increased as the herbicide dosage and soil moisture increased, and as the soil organic matter content decreased. Leaves which were partially expanded before the exposure were affected much less. When exposed to vapors of 14C-benefin, plant seedlings readily absorbed radioactive materials by its entire foliage including the stem tip with a few tiny developing leaves. More than half of the 14C absorbed and adsorbed during a 3-day exposure was recovered by CHCl3 wash of leaves and appeared to be retained by the wax and cutin layers, and also by lipoidal secretion substances of the numerous trichomes on the leaf surface. There was a small fraction of unabsorbed or loosely retained 14C material on the surface of the leaves and stem tip, which was removed by water. That not recovered from H2O and CHCl3 washes appeared to be distributed in the internal tissues. Little acropetal translocation appeared to occur from the expanded leaves toward the stem tip. There was no translocation of 14C-benefin into roots of plants where only a single leaf was exposed to the radioactive vapors.

Absorption and translocation of the growth regulator 14C-chlorflurenol (methyl-2-chloro-9-hydroxyfluorene-9-carboxylate) and of the herbicide 14C-dicamba (3,6-dichloro-o-anisic acid) were studied in Canada thistle [Cirsium arvense (L.) Scop.]. Also investigated was how foliar treatments with chlorflurenol affected leaf uptake and distribution of dicamba by Canada thistle. Plants were grown in aerated nutrient solution. 14C-chlorflurenol showed strong acropetal and weak basipetal movement. Thirty-two percent of the foliar applied 14C-dicamba was absorbed and most of the radioactivity tended to accumulate in the young growing leaves. Only 0.6% of the applied radioactivity moved to the roots. Leaf absorption and basipetal translocation of 14C-dicamba were increased two- and ten-fold, respectively, by the simultaneous addition of chlorflurenol at 0.6 kg/ha. Root bud activity was increased when 4-week-old Canada thistle plants were foliarly treated with chlorflurenol at 0.6 kg/ha. Field work demonstrated that Canada thistle control could be enhanced by chlorflurenol addition to dicamba.

A sprinkler system was developed that applied water to quadrant-shaped plots with a uniformity coefficient greater than 90% for any 2-m zone between 3 and 9 m from sprinklers that were located at the vertex of the quadrant. With this sprinkler system, many variables that affect the performance and behavior of herbicides applied in irrigation water can be studied. When applied through this sprinkler system in 1.4 cm of water, alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 3.3 kg/ha, EPTC (S-ethyl dipropylthiocarbamate) at 3.3 kg/ha, EPTC + trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 3.3 + 0.6 kg/ha, and EPTC + oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) at 3.3 + 0.8 kg/ha controlled barnyardgrass [Echinochloa crus-galli (L.) Beauv.], common lambsquarters (Chenopodium album L.), and hairy nightshade (Solanum sarachoides Sendt.) selectively in beans (Phaseolus vulgaris L. ‘Pinto 114’).

The first WSSA international session was organized by the society's International Affairs Committee with approval of the Board of Directors. The committee's objective was to present a broad view of weed research in the world. To do this, we invited participants who were presently, or who had been, on the staff of one of the international agricultural research centers. We also invited Dr. M. Horowitz, the WSSA Honorary Member for 1979, to present information on his work in Israel.

Fall panicum (Panicum dichotomiflorum Michx.) seed were found to be dormant at harvest. This dormancy was overcome by an after-ripening period of 17 to 22 weeks, alternating germination temperatures (10 C for 16 h and 30 C for 8 h), stratification, and mechanical or chemical scarification. Soaking seed in gibberellic acid (GA3) or thiourea for 1 day, or washing seed in running tap water for up to 96 h before seed were placed in a germinator, had no effect on dormancy. In the greenhouse, fall panicum emergence was greatest (82%) when seed were placed on the growth media surface. The maximum number of seedlings (39%) emerged in the field when seed were placed 1.3 cm below the soil surface, although some emerged from as deep as 5.1 cm.

Mulching the soil with polyethylene sheets before sowing during the hot season, increased the soil temperatures, which resulted in the control of soil-borne pathogens and weeds. This method was tested in a field heavily infested with Egyptian broomrape (Orobanche aegyptiaca L.). Soil was irrigated and mulched for 36 days during August–September 1977, prior to sowing carrot (Daucus carota L. ‘Nantes Tip Top’) seeds. Mulching increased soil temperatures by 8 to 12 C, up to 56 C in the top 5 cm. In the non-mulched plots the carrot plants became stunted due to heavy parasitization with broomrape and they were completely destroyed by the end of the season. In contrast, broomrape and other weeds were controlled in the mulched plots and the carrot plants grew normally. This effect was less pronounced in the border rows of the mulched plots. Mulching also greatly reduced the infestation of other weeds. Egyptian broomrape was also controlled in two other field experiments with carrots and eggplants (Solanum melongena L. ‘Black oval’). As compared with fumigation, this new method of control is economical, simple, nonhazardous, and does not employ toxic materials.

Mathematical growth analysis techniques were used to evaluate the effects of CO2 concentrations of 350, 600, and 1000 ppm (v/v) on growth and biomass partitioning in corn (Zea mays L. ‘Dekalb XL 395’), itchgrass (Rottboellia exaltata L. f.), soybean [Glycine max (L.) Merr. ‘Tracy’], and velvetleaf (Abutilon theophrasti Medic). Controlled environment chambers with day/night temperatures of 28/22 C and photosynthetic photon flux densities (PPFD) of 650 μE (microeinsteins) m-2 s-1 were used. Dry matter production in the two C3 species (soybean and velvetleaf) was increased significantly by raising the CO2 concentration above 350 ppm. In corn (a C4 species), dry matter production was least at 1000 ppm CO2 and did not differ between the 350 and 600 ppm treatments. In itchgrass (also C4), dry matter production was greatest at 600 ppm CO2 and did not differ between the 350 and 1000 ppm treatments. Increasing the CO2 concentration increased the rate of dry matter production per unit leaf area (net assimilation rate or NAR) in soybean and velvetleaf but either decreased or did not alter NAR in corn and itchgrass. At 45 days after planting, the weed/crop ratios for total dry matter production for velvetleaf/corn and itchgrass/corn were significantly greater at both 600 and 1000 ppm than at 350 ppm CO2. The weed/crop ratio for itchgrass/soybean was less at 1000 ppm than at 350 or 600 ppm CO2. Compared to the value at 350 ppm, the weed/crop ratio for velvetleaf/soybean was greater at 600 ppm and less at 1000 ppm CO2. We conclude that atmospheric CO2 enrichment probably will make weeds with the C3 photosynthetic pathway more competitive with crops having the C4 pathway. Weeds with the C4 pathway may become less competitive with crops having the C3 pathway.

Germination responses of redroot pigweed (Amaranthus retroflexus L.) seeds to temperature, water potential, atmospheric ethylene and carbon dioxide concentrations, light, and nitrate ion were examined individually. Seeds kept in dry storage at −20 C and tested within 2 yr of harvest germinated at 35 C (12 to 25%) or 39.5 C (40 to 65%), but only 0 to 2% at 30 C and below. Germination at 35 C was prevented by water potentials below −4 bars. When seeds were kept in dry storage at 24 to 28 C, afterripening became evident within 2 months. After storage at this temperature for 4 yr, seeds showed 38% germination at 14 C, 40% at 35 C and −8 bars water potential, and over 90% under more favorable conditions. Ethylene (1 to 100 ppmv) or continuous light enhanced germination at 30 C regardless of degrees of afterripening, although the ethylene effect was most dramatic in nonafterripened seeds. Ethylene at 100 ppmv caused 40% germination in these seeds, compared to 1% for controls. Neither carbon dioxide (0.001 to 4.5% v/v) nor dissolved potassium nitrate (0.02 to 0.2% w/v) influenced germination. These results are discussed in relation to environmental factors influencing field emergence of redroot pigweed.

Scanning electron micrographs that depict the surface and internal structure of several starch-encapsulated granular formulations of EPTC (S-ethyl dipropylthiocarbamate) and butylate (S-ethyl diisobutylthiocarbamate) relate well with herbicidal release rates previously reported. Fast-release formulations appear to have a porous surface with little distinctive internal structure. Diffusion would be expected to be more rapid as fewer diffusion barriers are present. Slow-release formulations have a smooth, hard surface with irregular surface pores and a honeycombed internal structure. The slower release characteristics are associated with stronger oxidants used for crosslinking xanthate in the entrapment of herbicides. The scanning electron microscope would be an excellent quality control technique in the preparation of starch-encapsulated herbicides.

Seed germination responses to temperature and osmotic stress were determined for smallflower morningglory [Jacquemontia tamnifolia (L.) Griseb.] and seven species of Ipomoea. Cypressvine (I. quamoclit L.), willowleaf (I. wrightii Gray) and smallflower morningglory germinated and seedlings developed more slowly than the other morningglories at 16 C. Maximum germination of ivyleaf [I. hederacea (L.), Jacq. var. hederacea], entireleaf [I. hederacea (L.) Jacq. var. integriuscula Gray], pitted (I. lacunosa L.), tall [I. purpurea (L.) Roth], cotton (I. trichocarpa Ell.), and smallflower morningglories occurred in 24 h at 20 C. Cypressvine and willowleaf morningglories reached maximum germination in 24 h at 24 C. Optimal root-hypocotyl development occurred at 24 C for pitted, tall, and willowleaf morningglories, while all other species required a temperature of 28 C for maximal root-hypocotyl development in 4 days. Increasing osmotic pressure decreased or delayed germination of all morningglory species. Species tolerance to osmotic stress during germination could be ranked, most to least tolerant, as follows: ivyleaf=entireleaf>pitted=cotton>tall = willowleaf>cypressvine=smallflower. Maximum germination was delayed approximately 24 h for each 2 bar increment increase in osmotic pressure.

The International Institute of Tropical Agriculture (IITA) is one of the agricultural institutes financed through the Consultative Group on International Agricultural Research (CGIAR) sponsored by FAO, UNDP (United Nations Development Program), and the World Bank. One of IITA's mandates is to conduct research on farming systems in the humid and subhumid tropical zones to identify viable alternatives to shifting cultivation capable of maintaining productivity of food crops under continuous cultivation (14). The research efforts of the institute are organized into four programs. The three commodity-oriented research programs—the Cereals Improvement, the Grain Legume Improvement, and the Root and Tuber Improvement programs – provide improved planting materials that the scientists in the fourth program – the Farming Systems Program – use to develop land use systems capable of sustaining soil productivity as land and economic pressures accelerate the transition from shifting to continuous cultivation (13).

Various chemical and cultural treatments were evaluated for smutgrass [Sporobolus poiretii (R.&S.) Hitchc], control and their effects on pangolagrass (Digitaria decumbens Stent.) and bahiagrass (Paspalum notatum Flügge). Herbicide treatments were dalapon (2,2-dichloropropionic acid) at 1.7, 3.3, and 5.0 kg/ha with Sunoco HE spraying oil at 0, 9.4, 19.0 and 37.0 L/ha. Five weeks after herbicide treatment plots were clipped (clipped vs. nonclipped) and fertilized (0 vs. 112 kg/ha N). Increasing dalapon from 1.7 to 5.0 kg/ha increased smutgrass control and decreased the number of smutgrass plants/plot. Pangolagrass ground cover generally increased with fertilization, as the rate of dalapon increased up to 3.9 kg/ha. Bahiagrass ground cover decreased with rates of dalapon above 1.7 kg/ha. Increasing the rate of oil increased bahiagrass ground cover after 90 days. Nitrogen applied 5 weeks after dalapon treatment and semi-annually for 5 yr generally decreased ground cover of smutgrass and bahiagrass, but increased pangolagrass. Clipping treated smutgrass plants increased pangolagrass and bahiagrass ground cover while decreasing the ground cover of smutgrass.