The differential tolerance of prickly sida (Sida spinosa L.) and cotton (Gossypium hirsutum L.) to methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione]was studied under greenhouse conditions. Methazole at dosages up to 8.96 kg/ha did not affect emergence of either species. Applications via nutrient solution, as well as preemergence and postemergence (over-the-top) treatments were phytotoxic to both species, becoming more pronounced with increasing concentration and time. However, a margin of selectivity between species occurred at dosages from 0.56 to 3.36 kg/ha preemergence. Directed sprays of methazole were not injurious to cotton. Selectivity would be influenced by plant size and method of application as well as biochemical differences between species.

Unmodified, cyanoethylated, and crosslinked corn starches were reacted with 2,4-dichlorophenoxyacetyl chloride in pyridine to produce the corresponding 2,4-D [(2,4-dichlorophenoxy)acetic acid]esters of high acyl content. Hydrolysis studies at pH 6 and 8 at ambient temperature showed that these insoluble compositions liberated varying amounts of 2,4-D and soluble 2,4-D esters by ester link and glucoside bond cleavage, respectively, at rates that indicate their possible use as controlled-release herbicides.

A nonphytotoxic paraffinic oil at 2.5, 5, and 10% (v/v) or a blended alkylaryl sulfonate surfactant at 0.5, 1, and 2% (v/v) did not enhance the activity of propanil (3′,4′-dichloropropionanilide) at 1.7, 3.4, and 6.7 kg/ha applied as a foliage spray in aqueous systems on barnyardgrass [Echinochloa crus-galli (L.) Beauv.] or rice (Oryza sativa L. ‘Starbonnet’). Time and rate of applying propanil affected control of barnyardgrass. Barnyardgrass control and rice yield were best with treatments of 3.4 or 6.7 kg/ha of propanil to four-leaf grass plants. Propanil at 6.7 kg/ha controlled tillering and jointing barnyardgrass well enough to increase grain yields over those of untreated rice.

Competitiveness of three high-yielding, lodging-resistant rice (Oryza sativa L.) cultivars with barnyardgrass [Echinochloa crus-galli (L.) Beauv.] was compared during 3 years at Stuttgart, Arkansas. ‘Starbonnet,’ ‘Nova 66,’ and ‘Bluebelle,’ which matured in 145, 135, and 125 days, respectively, competed with barnyardgrass for periods ranging from 10 days after crop emergence to all season. ‘Starbonnet’ was the most competitive and ‘Bluebelle’ was the least. Barnyardgrass competition for 10 or 20 days did not reduce grain yields of any cultivar. Weed competition for 40 days or longer reduced yields of ‘Nova 66’ and ‘Bluebelle,’ and competition for 60 days or longer lowered yields of ‘Starbonnet.’ As the period for maturity increased, each cultivar competed more effectively with barnyardgrass.

A Shubata soil was modified by the addition of organic matter or montmorillonite clay. Three annual applications of fluometuron [1,1-dimethyl-3-(α,α,α-trifluro-m-tolyl)urea], prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine], and trifluralin (α,α,α-trifluro-2,6-dinitro-N,N-dipropyl-p-toluidine) were made and soil samples analyzed at the end of the third year. Less than 0.05 ppm prometryne was found in the subsoils. Prometryne present (by chemical analysis) in the surface soils ranged from 2% (of that originally applied) in the soil without additives to 20% in the soils modified with organic matter and clay. Approximately 12% of the prometryne present in the soil modified with organic matter and 32% of that in the soil modified with clay was detectable by bioassay. Trifluralin concentration (by chemical analysis) ranged from 2% in the soil without additives and soil modified with clay to 11% in the soil modified with organic matter. Approximately 100% of the trifluralin in soil without additives and soil modified with clay was detectable by bioassay while only 15% of that present in soil modified with organic matter was biologically detectable. Fluometuron was presented in the soils in amounts ranging from 0.6 to 1.9% of that applied. Prometryne and fluometuron greatly decreased the large crabgrass [Digitaria sanguinalis (L.) Scop.] population and increased the population of yellow nutsedge (Cyperus esculentus L.) and crowfootgrass [Dactyloctenium aegyptium (L.) Richter]. Trifluralin greatly decreased large crabgrass and crowfootgrass populations, but the plots became completely infested with yellow nutsedge. Horseweed [Conyza canadensis (L.) Cronq.] became the overall dominant species the first year after the field was taken out of production. Yellow nutsedge, bermudagrass [Cynodon dactylon (L.) Pers.], and other grasses were also prevalent.

EPTC (S-ethyl dipropylthiocarbamate) was applied to sand traps to evaluate weed control and the prevention of bermudagrass (Cynodon dactylon (L.) Pers.) encroachment. EPTC applied at 6.7 kg/ha in each of two applications at 6 to 7-week intervals, controlled an average of 88% common bermudagrass and 99% large crabgrass [Digitaria sanguinalis (L.) Scop.]. Although EPTC prevented bermudagrass from spreading into sand traps, the treatments did not cause permanent injury when applied directly to several bermudagrass varieties.

I would start with a text from Bacon's New Atlantis that reads: “Men ought to know that in the theatre of human life it is only for gods and angels to be spectators.” We are at a stage of societal evolution where we must be part of the action. And action there is today – by politicians, by regulatory agencies, by industry, by scientists, by educators, and by the general public. Our basic challenge is to become a meaningful part of the action mechanism. And we are not alone among scientists trying to find our way in a very concerned and a very confused world. Science itself is suspect today.

First of all I would like to bring greetings from the Canada Weed Committee (CWC). Under one name or another this Committee has met every year since 1929 when it was organized by a handful of workers to coordinate their tests with sodium chlorate, sodium arsenite, sulphuric acid, etc. The CWC still meets as a working planning committee to review current work, up-date recommendations and coordinate testing for the forthcoming year.

Autotrophic growth, photosynthesis, and respiration of Chlorella sorokiniana Shihira and Krauss were inhibited by the cupric ion, but photosynthesis was more sensitive than respiration. The percent inhibition was determined by the ratio of cells to cupric ions present. Photosynthesis and respiration were inhibited within 2 and 5 min, respectively, after adding 1.0 mM cupric ions. Chlorella cells which had been incubated for a short time in concentrations of the cupric ion that completely inhibited photosynthesis were not able to grow when cultured in a fresh medium without cupric ions, indicating high concentrations of the ion may have destroyed the photosynthetic apparatus and deprived the cells of their ability for autotrophic growth. Dark preincubation of the cells, as well as high bicarbonate concentrations in the assay medium, decreased inhibition. Treatment with cupric ions reduced the cellular chlorophyll and sulfhydryl content, but anaerobiosis, a condition that increased toxicity, had little effect on the sulfhydryl content. Electron transport in photosystems I and II in intact Chlorella cells was inhibited, but the specific sites of inhibition in the photosynthetic electron transport chain could not be determined using intact cells.

Waterhyacinth [Eichornia crassipes (Mart.) Solms.] was partially controlled with 10.6 nm laser radiation. Radiation levels of < 1 J/cm2 for individually irradiated plants and 69 J/cm2 for group-irradiated plants significantly inhibited growth. Photosynthesis in treated plant-leaf tissue was inhibited about 50% by an exposure level of 4 J/cm2. 14C-labeled compounds fixed by plant-leaf tissue following laser treatment were found to be normally distributed.

An organic muck and a montmorillonite clay were incorporated into the surface 7.6 cm of a structureless sandy soil at rates ranging from 26,880 to 89,600 kg/ha. Prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] and fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] were surface-applied and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) were incorporated at two rates each in 1968, 1969, and 1970. Organic matter greatly reduced the biological activity of all three herbicides. Montmorillonite clay greatly reduced the activity of prometryne, slightly decreased the activity of fluometuron, and had no significant effect on trifluralin activity in all but the first year of the study. Both soil additives increased the cation exchange capacity of the soil. Muck decreased soil pH while montmorillonite increased it.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H) one] injured and reduced growth of tomato (Lycopersicon esculentum Mill.) but did not inhibit germination or emergence of several other species. In cucumber (Cucumis sativus L.), metribuzin did not have a specific site of uptake, being equally toxic when placed in the root, shoot, or seed zone. Tomato was more susceptible to metribuzin when the plants were grown under high humidity, high temperature, maintained under low light intensities before spraying, had their leaves rubbed with glass wool, or had a surfactant in the spray solution. The increased toxicity under low light was not overcome by exogenous sucrose. About 4% of the available metribuzin was absorbed by tomato leaves or roots and was translocated in the xylem. Tomato plants 13 cm in height were less susceptible to metribuzin injury than 8-cm high plants.

Weed Science is a relatively young but challenging and dynamic discipline. It includes all aspects of combating weeds and reducing their undesirable effects on mankind–directly or indirectly. The need for effective weed control is not new; it has prevailed since the primitive beginning of crop culture. It has evolved into a strong discipline, however, only since World War II, stimulated by a pressing need for more economic weed control. In response to this need, numerous advances have been made that help to produce higher crop yields at lower cost. Herbicides have become common, intensive research and educational programs have been established, and Weed Science has taken its rightful place as a respected discipline in the academic and industrial communities.

The configuration of the growth pattern for Chrysothamnus viscidiflorus (Hook.) Nutt. was determined from vegetative bud burst to flowering. Important portions of the pattern are: restrictive growth during early spring, accelerated growth in late spring when the optimum susceptibility to herbicides occurs, and a leveling off of growth before flowering. Seedlings and young plants have a more rapid and greater annual stem elongation than mature or senescent plants. Elongation during the accelerated growth period can be predicted from early spring growth with moderate precision when soil moisture and temperatures are not limiting. Populations growing on sites of higher or lower elevations or of pronounced aspect will have growth patterns moderately varying from the modal populations. The greatest factor influencing the growth pattern on years with adequate soil moisture was competition from other species and the combination of competition and age of the rabbitbrush plants.

The response of wheat (Triticum aestivum L.) and wild oat (Avena fatua L.) to barban (4-chloro-2-butynyl-m-chlorocarbanilate) was studied as influenced by plant morphology and air temperature after application. Growth of wheat and wild oat seedlings was reduced by barban at 0.3 μg and 0.6 μg applied to the first node, respectively. Barban application to the base and midpoint of the first leaf blade required a lower dose to reduce wild oat growth than wheat growth. Increased tillering occurred from barban injury to the main culm in wheat. Wheat and wild oat susceptibility to barban increased as the post-treatment temperature decreased from 32 to 10 C. Barban selectivity for wild oats in wheat was greater at 27 and 21 C than at 16 and 10 C.

Uptake of 2,4,5-T-1-14C [(2,4,5-trichlorophenoxy)-acetic acid] by immersion of honey mesquite [Prosopis juliflora (Swartz) DC var. glandulosa (Torr.) Cockerell] leaflets rapidly diminished as pH was increased from 3.5 to 9.5. Uptake diminished less rapidly as pH increased when 10-μl droplets were applied to leaflets that were kept moist. Uptake was equivalent from solutions of pH 3.5, 5.5, and 7.5; but severely reduced at pH 9.5, when leaflets were droplet treated and let dry. Uptake under dry conditions from pH 7.5 and 9.5 droplets containing 1 M NH4Cl was equivalent to uptake from pH 3.5 and 5.5 droplets lacking NH4Cl. NH4Cl had no enhancing effect on uptake at any pH when leaflets were immersed or droplet-treated and maintained moist. Low concentrations of urea had no enhancing effect on uptake at pH 9.5 by droplet-treated leaflets that were allowed to dry. Urea concentrations above 0.1 M inhibited uptake.

Growth-chamber studies were conducted to determine some effects of MSMA (monosodium methanearsonate) and DCPA (dimethyl tetrachloroterephthalate) treatments on ‘Pennstar’ and common Kentucky Bluegrass (Poa pratensis L.), grown at three different temperatures. Herbicide was applied at recommended rates at the beginning of regrowth following mowing. At sampling time, height and weight were recorded and some fresh tissue was frozen for chlorophyll analysis and the rest was oven-dried for amino acid analysis. Chlorophyll content of ‘Pennstar’ was significantly increased by MSMA. Common bluegrass grown at 18 C had significantly higher levels of free amino acids than did ‘Pennstar’ grown at the same temperature. At 27 C, asparagine and alanine were significantly higher in common bluegrass than in ‘Pennstar.’ MSMA had a more significant effect on all detected free amino acid concentrations except cysteine in ‘Pennstar’ than in common bluegrass. DCPA was more active than MSMA on common bluegrass; all amino acids were increased significantly by treatment.

Weed species or genera previously and currently targeted for biological control with phytophagous insects or phytopathogens in the United States (including Hawaii) and Canada are listed. The current status of and natural enemies involved in national, federal, state, and university biological control projects are reported.

Near isogenic strains of okra, super okra and normal leaf cotton (Gossypium hirsutum L.) were grown in rows spaced 25, 50, and 100 cm apart and were sprayed with various combinations of trifluralin (α,α,α,trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and fluometuron [1,1-dimethyl-3-(α,α,α,-trifluoro-m-tolyl)urea]. Neither row spacing nor leaf type had any effect on early season weed control. Late season control was better with normal and okra leaf types than with the super okra leaf type. Weed control was significantly better with additional postemergence application of herbicides than with only preplant and preemergence applications. Although the cotton varied in opening date with herbicide programs there was no difference in total yield.

Weeds in corn (Zea mays L.), cotton (Gossypium hirsutum L.), peanuts (Arachis hypogaea L.), and soybeans (Glycine max (L.) Merr.), grown continuously or in rotation, were controlled with either cultural or herbicidal programs designed for broad-spectrum control. The herbicidal program initially selected for each group was used each year from 1968 to 1971. Herbicides controlled more weeds than cultural practices in all cropping sequences. Weeds were almost eliminated, judging by percent ground cover at harvest time, in five of the eight cropping sequences in each of the last three years of the experiment. Although several rotations drastically reduced the number of weeds, the composition of the weed population was not altered significantly. When cultural weed control practices were used, the cropping sequence and rainfall influenced the level of weeds present at harvest time. More weeds were present at harvest in corn grown continuously and in sequence than in the other crops. In addition to three or four cultivations, we used a yearly average of 86 manhours/ha of hand-hoeing in corn and 195 manhours/ha of hand-hoeing in cotton during the first 6-week period after planting to keep these crops weedfree until the last cultivation. The cropping sequence did not affect the amount of hand-hoeing required in these crops. In general, cropping sequence did not affect crop yield.