The chlorophyll levels and growth of oat (Avena sativa L. ‘Elgin’) seedlings were drastically reduced after foliar application of diclofop-methyl {methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate}. The leaves were chlorotic and necrotic with the newly emerging leaves being most affected. Plants treated with 2,4-D [(2,4-dichlorophenoxy)acetic acid] were similar to the controls. When 2,4-D was applied to intact plants in combination with diclofop-methyl the toxicity symptoms produced by diclofop-methyl were reduced. Diclofop-methyl disrupted membrane integrity and inhibited chlorophyll formation in excised leaf segments. Addition of 2,4-D with diclofop-methyl did not change the effects produced by diclofop-methyl alone in excised leaf segments.

Studies were conducted to determine the effect of soil moisture, seedling age, and exposure of plant parts on control of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] with diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, formulated as the methyl ester. In a Warden silt loam, moisture content of 10% or more was needed for satisfactory diclofop control of slow-growing barnyardgrass under cool, early-season conditions. Soil moisture was less critical when temperatures were higher and barnyardgrass was growing rapidly. Roots and emerging shoots both absorbed diclofop from the soil, but both plant parts were inhibited more when diclofop was applied to the roots than to the shoots. Barnyardgrass was injured from diclofop applied postemergence to either roots or shoots separately, but phytotoxicity was greatest when the whole plant was exposed. When the soil was treated, control increased with increasing amounts of post-treatment overhead irrigation. Two-leaf and four-leaf barnyardgrass plants were equally susceptible to diclofop applied postemergence, but resistance increased with age in plants with more than four leaves.

The interaction between diclofop-methyl {2-[4-(2,4-dichlorophenoxy)phenoxy] methyl propanoate} and 2,4-D [(2,4-dichlorophenoxy)acetic acid] was evaluated. Foliar applications of the two herbicides in a tank mixture were antagonistic with respect to wild oat (Avena fatua L.) control. Application of mixtures of the two herbicides to wild oat roots resulted in an additive herbicidal effect. The acid form of 2,4-D was determined to be the component of the 2,4-D formulation that reduced the toxicity of foliar-applied diclofop-methyl to wild oat. Analysis of diclofop-methyl solutions with and without added 2,4-D revealed no degradation products of dichlofop-methyl, nor any evidence of complexing between diclofop-methyl and 2,4-D. Addition of 2,4-D to the diclofop-methyl spray solution did not affect diclofop-methyl spray retention by, or penetration into, wild oat leaves. Movement of radioactivity to roots and to shoot apices following application of 14C-diclofop-methyl to wild oat leaves was reduced by addition of 2,4-D to the treatment solution. Deesterification of diclofop-methyl was inhibited by 2,4-D. The accumulation of diclofop-methyl in these wild oat leaves resulted in membrane damage and leaf necrosis. Symplastic movement of the des-methyl acid, diclofop, to sensitive meristematic areas was reduced. As insufficient toxicant reached meristematic areas to permanently interrupt meristematic activity, the wild oat plants were able to outgrow the contact damage to their leaves.

Combinations of MSMA (Monosodium methanearsonate) with either methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] or metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] were applied at various rates for postemergence control of fully developed goosegrass [Eleusine indica (L.) Gaertn.], a major weed grass in bermudagrass [Cynodon dactylon (L.) Pers.] turf. Two applications of MSMA at 2.24 kg/ha applied in combination with either methazole or metribuzin at 0.14 kg/ha controlled 96 to 98% of the goosegrass and it was as effective as methazole (1.12 kg/ha) or metribuzin (0.56 kg/ha) applied alone. Two applications of methazole (1.12 kg/ha) or metribuzin (0.56 kg/ha) had lower quality ratings (28 and 39, respectively) on bermudagrass putting green at 2 weeks after treatment than combinations of MSMA (2.24 kg/ha) with either methazole (0.14 kg/ha) or metribuzin (0.14 kg/ha) (54 and 59, respectively). The initial injury from combination treatments was not severe and turf recovered within 3 to 4 weeks.

The competitive effects of pale smartweed (Polygonum lapathifolium L.) were studied on cabbage (Brassica oleracea L. ‘K-Y’) which was transplanted into rice (Oryza sativa L.) fields either 3 to 12 days before or 5 days after rice was harvested. Competitive effects were determined at weekly intervals from the time beds were formed around the cabbage at 5 days after rice harvest. Where cabbage was transplanted before rice harvest, at a time before pale smartweed germination, cabbage yields were reduced when weeds were allowed to grow for more than 4 weeks from the time the beds were formed. Where cabbage was transplanted at 5 days after the rice was harvested at a time when parts of pale smartweed had emerged, cabbage yields were reduced when weeds were allowed to grow for only 2 or more weeks after the beds were formed. Also, where weeds were removed at the beginning but allowed to grow at a later date, yield was reduced when cabbage was not kept weed-free for a minimum of 4 weeks.

Several herbicides were applied in January, February, and March with a comparison of the intervals of treatment of 2 and 4 weeks after the initial treatment each month for postemergence control of winter annual weeds in bermudagrass [Cynodon dactylon (L.) Pers.] turf. Glyphosphate [N-(phosphonomethyl)glycine] treatments applied at 2-week intervals with the initial treatment made in January or February controlled a higher percentage of annual bluegrass (Poa annua L.) than when applied in March. Hop clover (Trifolium agrarium L.) control was also higher when glyphosate was initially applied in January or February than when applied in March regardless of time interval between first and second treatment. Combination treatments of (a) 2,4-D [(2,4-dichlorophenoxy)acetic acid] + dicamba (3,6-dichloro-o-anisic acid) and (b) 2,4-D + mecoprop {2-[(4-chloro-o-tolyl)oxy] propionic acid} + dicamba applied at 2-week intervals with the initial treatment made in January or February controlled more corn speedwell (Veronica arvensis L.) and hop clover than when applied in March. Highest henbit (Lamium amplexicaule L.) control was obtained from the combination 2,4-D treatments made at 4-week intervals when initial treatment was made in February and March. Weed control was not influenced by dates and interval of repeated treatments with either paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) or atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] treatments. Germination and regrowth of weeds were greater in plots treated with glyphosate and paraquat initially in January or February than other herbicide-treated plots. Weeds were not reestablished in any of the atrazine-treated plots. Paraquat and combinations of 2,4-D + dicamba or 2,4-D + mecoprop + dicamba injured bermudagrass when applied initially in January and February even though they were applied to turf that appeared dormant. All herbicides injured bermudagrass more when applied to semi-dormant turf in March than to dormant turf in January or February. Atrazine affected bermudagrass less than any of the other herbicides tested when initial treatment was applied in March to semi-dormant turf.

The growth regulator, glyphosine [N,N-bis(phosphonomethyl)glycine], and other possible metabolites of glyphosine and glyphosate [N-(phosphonomethyl)glycine] [glycine, sarcosine, and aminomethylphosphonic acid (AMPA)] were tested individually (0.5 mM) or as a mixture (each at 0.5 mM) for their effects on growth, extractable phenylalanine ammonia-lyase (PAL) activity, hydroxyphenolic-compound production, chlorophyll and anthocyanin contents, and on soluble-protein levels in soybean [Glycine max (L.) Merr. ‘Hill’] seedlings. Most chemical treatments caused some inhibition of growth either on fresh weight accumulation or on root elongation in the light and dark over 72 h. Glyphosine was generally the most inhibitory and caused the greatest inhibition on axis dry-weight accumulation. Glyphosine significantly increased extractable PAL activity in axes of light- and dark-grown soybeans to a lesser extent than did glyphosate. AMPA had some inhibitory effects on extractable PAL activity whereas other compounds had little influence on the enzyme. These compounds had little effect on total soluble protein in axes or on soluble protein in PAL preparations from 12 to 72 h in light-or dark-grown seedlings. No in vitro effect of the chemicals on PAL activity was found at concentrations up to 0.5 mM. Hydroxyphenolic compound levels increased within 24 to 72 h (per gram fresh weight basis) in light- or dark-grown soybean axes treated with glyphosine, AMPA, or a metabolite mixture (AMPA, sarcosine, and glycine). Anthocyanin content was decreased by glyphosate and to a lesser extent by glyphosine, but was increased by AMPA and the mixture. Glyphosate significantly increased the chlorophyll a/b ratio and decreased total chlorophyll, but glyphosine decreased the chlorophyll content to a lesser degree.

Peanuts [Arachis hypogaea (L.) ‘Florunner’], infested with sicklepod (Cassia obtusifolia L.) and Florida beggarweed [Desmodium tortuosum (Sw.) DC.] were grown in 20.3-, 40.6-, and 81.2-cm rows on Dothan sandy loam at Headland, Alabama, and on Greenville sandy clay loam at Plains, Georgia. In-row seeding rates were equal, regardless of row width. Peanuts were maintained free of sicklepod and Florida beggarweed for 0, 2, and 5 weeks after emergence or throughout the season. In either the absence or presence of weeds, peanut yields generally increased with decreasing row width. Quality of peanuts was not adversely affected; in fact, desirable attributes such as percent sound mature kernels (SMK's) were sometimes increased as the row width decreased. Weed growth with close rows was much less than with standard 81.2-cm rows. Although yields of peanuts were lower with increasing time of weed competition, the influence of row spacing on competitiveness of the peanut canopy remained relatively constant on both soil types. Generally, weeds from either seeded or natural stands produced equivalent competitive results.

A 4-yr field test was initiated in 1975 to determine susceptibility of a natural infestation of six morningglory species to herbicides which can be applied to the soil and foliage in soybeans [Glycine max (L.) Merr.]. The species studied were pitted morningglory (Ipomoea lacunosa L.), entireleaf morningglory [Ipomoea hederacea (L.) Jacq. var. integriuscula], ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.], purple moonflower [Ipomoea muricata (L.) Jacq.], palmleaf morningglory [Ipomoea wrightii (Gray)], and small flower morningglory [Jacquemontia tamnifolia (L.) Griseb.]. Control with herbicides applied preplant incorporated and preemergence was dependent on morningglory species and on rainfall to allow plant uptake of the herbicide. Herbicides applied to the soil were not as effective as those applied postemergence. Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] gave the best and longest lasting preemergence control, averaging 79% control for all species. Preemergence control with metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] was dependent on species, with 84% control of small flower morningglory and only 26% for ivyleaf and 18% for entireleaf morningglory. At V2 (one trifoliolate) and V5 stages of soybean growth, acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} at 0.56 kg/ha applied over-the-top and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] at 0.28 kg/ha applied post-directed gave 90 and 92% control of all species, respectively. Most effective were repeated post-directed applications at V5 and V7 stages of soybean growth. Metribuzin + 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] (99%), linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] + 2,4-DB (98%), 2,4-DB (95%), and paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) + 2,4-DB (93%) provided excellent control regardless of the morningglory species.

Two formulations of triallate [S-(2, 3, 3-trichloroallyl)diisopropylthiocarbamate] were evaluated for their effectiveness in controlling wild oat (Avena fatua L.) in spring wheat (Triticum aestivum L.) in 12 field experiments conducted between 1967 and 1978. Control of wild oat was greater with fall applications of triallate granules than liquid or with spring applications of either liquid or granules. Further-more, 1.1 kg/ha of triallate granules applied in the fall controlled wild oat as well as did 1.7 kg/ha of liquid triallate applied in the fall. Wild oat control with triallate was usually better when soil incorporated than when surface applied regardless of formulation or time of application. Triallate granules controlled wild oat similarly on either plowed ground or wheat stubble; whereas, liquid triallate controlled wild oat better on plowed ground than wheat stubble. A delay of 8 h in triallate incorporation did not reduce wild oat control with either formulation; however, a delay of 24 h reduced wild oat control with the liquid formulation.

Enzymatically isolated American pondweed (Potamogeton nodosus Poir.) epidermal tissues were exposed to 14C-labeled dichlobenil (2,6-dichlorobenzonitrile), diquat (6,7-dihydrodipyrido[1,2-α: 2′, 1′-c] pyrazinediium ion), silvex [2-(2,4,5-trichlorophenoxy) propionic acid] or 2,4-D [(2,4-dichlorophenoxy)acetic acid] at concentrations of 5 × 10−4, 5 × 10−5, and 5 × 10−610M, and the amount of herbicide crossing the tissue layer was measured. Rates of herbicide movement were compared to those found when copper sulfate pentahydrate was added as a potential synergist at concentrations of 5 × 10−5 M (12.5 ppm), 5 × 10−6 M (1.25 ppm), and 5 × 10−7 M (0.125 ppm). Copper sulfate at 5 × 10−6 M increased the rate of movement of all herbicides. However, diquat and dichlobenil exhibited the most enhanced movement in the presence of copper sulfate. Without copper sulfate, 0.1 nmoles of 5 × 10−6 M 14C diquat penetrated the tissue within 24 h, compared to 1.3 nmoles following the addition of 5 × 10−7 M of copper sulfate.

Studies in outdoor, circular pools have shown that one shoot tip of hydrilla (Hydrilla verticillata Royle) produced as much plant dry weight during a 16-week period as 16 tips planted under the same conditions. Dry weight of plants 16 weeks after planting was as high as 1,561 times that of the shoot tips planted. Tubers were present within 8 weeks after planting the tips; higher numbers of these vegetative propagules were associated with the higher number of tips planted. Plants under a photoperiod of 11.5 h or less produced more tubers than those exposed to 12 h or more of light.

Pronamide [3,5-dichloro-(N-1, 1-dimethyl-2-propynyl) benzamide] phytotoxicity was compared in 10 Wisconsin soils and the relationship of activity to soil physical and chemical properties appraised. Twelve soil properties were measured and correlated with pronamide I50 (50% fresh weight inhibition) values using oats (Avena sativa L. ‘Portal’) as the indicator plant in bioassays conducted under greenhouse conditions. Organic matter was the soil variable most inversely correlated with pronamide phytotoxicity. Cation exchange capacity, field moisture capacity, and Mg content were also inversely correlated with pronamide phytotoxicity, but probably reflect changes in soil organic matter levels. Clay content did not significantly affect pronamide phytotoxicity.

Yellow nutsedge (Cyperus esculentus L.) develops as a series of shoots, bulbs, and tubers connected by rhizomes. The leaves contain parallel, collateral vascular bundles with the majority of the chlorophyll-containing cells concentrated in two sheathing girdles around each bundle. The upper leaf surface consists of a single layer of large epidermal cells covered by a thick cuticle. Stomates occur primarily in the lower surface. The vascular bundles are collateral in the leaves and amphivasal in the rhizome, changing their anatomical arrangement as they pass through the basal bulb. Newly developing rhizomes and tubers are white and fleshy with a parenchymatous epidermis and cortex. Mature rhizomes are brown and wiry with a deteriorated outer cortex and a lignified inner cortex and endodermis. Tubers and bulbs form similarly at the rhizome apices with the tubers accumulating starch. The rhizome vascular system remains intact throughout the growing season.

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.

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).

In tropical and subtemperate regions of the world, farmers plant vegetables and other crops in a vast array of cropping systems that often involve more than one crop being grown on the same parcel of land in a year. Weed communities within each cropping system shift depending on physical and climatic factors and the specific crop and weed management practices employed. Modern weed management strategies involve combinations of crop production practices and specific weed control technologies intended to reduce weed competition, thereby shifting the competitive balance in favor of the crop. Weed research and, training efforts, therefore, must focus on the entire cropping system with emphasis on year-round and multi-year management of weed communities.

The overall objective of research at ICRISAT (International Crops Research Institute for the Semi-Arid Tropics) is to develop effective, economically feasible, improved weed-management systems for major crops and cropping systems of the Semi-Arid Tropics (SAT). Initially, emphasis has been on surveys, ecological studies, weed management in crops, and herbicide screening. The aim was to identify possible cultural, mechanical, biological, and chemical inputs, and to determine their relative feasibility for small farmers. Systems research has involved manipulation of cropping systems to obtain better weed management and identification of the most effective techniques. Herbicide-related studies are designed to increase productivity rather than reduce the cost of hand weeding. Research on individual crops has been aimed at determining the extent of crop-weed competition in major crops. In collaboration with economists, operations research in farmers' fields was initiated to observe the success of farmers' weed-control methods. The primary program emphasis will be the evaluation of weed-management principles that may have wide applicability throughout the SAT. This paper outlines the approaches to weed-management research at ICRISAT and gives a conceptual framework of future research needs.

Latin America is a region of contrasts including mountains and valleys, deserts and jungles, forests and prairies, prosperous and poor, modern and traditional, small farms and huge ones, malnourished and well-fed, machines and manpower, herbicides and machetes. Any country from Mexico to Chile would provide examples of these contrasts. The countries share a common heritage of language, culture, religion, and education. Each is unique in its present developmental stage and future plans (6).