The movement of chemicals in the soil caused by water percolation was treated in a manner analogous to the development of materials through chromatographic columns. A “slotted tube test” was developed, which simulated a miniature field plot, utilizing a chromatographic soil column and the growth of either seeds or an indicator organism in agar as the detector. It was found that the median effective dose was higher for the more strongly sorptive soils. When correlations were made between soil compositions and the corresponding median effective doses for nonionic organic molecules, virtually all of the variations in required dosages were accounted for by percent organic matter and water content. The “active fraction” of organic matter, that fraction concerned with sorption equilibria, appeared to be of the same nature in soils of various compositions from various sources. This provided a technique for calculating the percent “active” organic matter of soil.

Toxicity to oats of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), monuron (3-(p-chlorophenyl)-1,1-dimethylurea), and fenuron (3-phenyl-1,1-dimethylurea), exposed to sunlight on soil surface for 25 days was significantly decreased even when surface soil temperatures did not exceed 120 F. Only atrazine and monuron exhibited significantly less phytotoxicity after 60 days exposure than after 25 days. Simazine phytotoxicity also was significantly reduced when held on soil in the dark for 60 days. With the exception of fenuron, there was no difference between treatments within compounds when soil temperatures reached maximums as high as 180 F. Under these conditions, phytotoxicity of the herbicides was reduced 65 to 97 percent by all exposures.

A 7-year ecological study of natural infestations of globe-podded (Cardaria pubescens) and lens-podded (C. chalapensis) hoary cresses was conducted under conditions of irrigation and dry land farming in southern Saskatchewan. Density and area measurements were compared annually in competition with grasses, forbs and shrubs in several environments. The hoary cresses are well adapted to moist situations but are not particularly vigorous in dry, semi-arid environments. Globe-podded hoary cress was better able to survive a period of drought than the lens-podded species. Native roses (Rosa spp.), western snowberry (Symphoricarpos occidentalis) and Russian knapweed (Centaurea repens) were the most effective competitors of the hoary cresses. Alfalfa and to a lesser degree, bromegrass were also effective. As these infestations of hoary cress are situated upstream from the Saskatchewan River Irrigation Project, they constitute a serious threat to many acres of irrigable farmland. Control by cultural means is shown to be feasible.

Combinations of row spacings, tillage, and herbicides were evaluated on Clark soybeans grown on Mexico silt loam. Weeds were not always completely controlled with 3-amino-2,5-dichlorobenzoic acid (amiben) or sodium pentachlorophenate (PCP). When herbicides were used, soybeans in 20- and 24-inch rows usually needed no more than one cultivation, while those in 32- and 40-inch rows usually needed at least one and sometimes two cultivations for good weed control and high soybean yields. Soybeans in narrow rows always equalled and sometimes produced higher yields than those in wide rows. The soybean canopy covered the ground more rapidly in narrow rows than in wide rows so that when herbicides suppressed early weed growth, less weeds were produced in narrow rows than in wide rows. In some situations, cultivations increased soybean yields when few or no weeds were present.

Differences in the competitive effects of three major species of foxtail on soybeans were due primarily to differences in the mature plant yields of the species. Giant foxtail (Setaria Faberi) grew more vigorously and caused greater soybean yield reductions than did either yellow foxtail (Setaria lutescens) or green foxtail (Setaria viridis). The competitive effects of velvetleaf (Abutilon theophrasti) per cwt. of mature weeds were approximately double those of yellow and green foxtail, but produced about the same yield reduction.

The various descriptive names used in the literature for each bulb type of wild garlic are reviewed and a suggested standard system of bulb nomenclature is presented. The life cycle of the species is briefly reviewed, with emphasis on cycles between plant and bulb types. The morphology, anatomy, ontogeny and physiology of the common bulb types are compared.

Early spring or late fall treatments of 2,6-dichlorobenzonitrile (dichlobenil) were effective for the control of several annual and perennial sedges, grasses, and broadleaf weeds in cranberry bogs. Isopropyl N-(3-chlorophenyl) carbamate (CIPC) 2,4-dichlorophenoxyacetic acid 2,4-D and 2-chloro-4,6-bis (ethylamino)-s-triazine (simazine) as spring applications were less effective than dichlobenil for the wide spectrum of weeds encountered. Single spring applications of as much as 4 lb/A of dichlobenil, 6 lb/A of 2,4-D, 24 lb/A of CIPC, and 2 lb/A of simazine were tolerated by the cranberry vines. Dichlobenil at 4 and 6 lb/A caused reductions in upright growth and fruit size. Keeping quality of mature fruit was not adversely affected by herbicidal rates of any of the materials.

Maximum castorbean (Ricinus communis L.) yields were obtained from combinations of chemical and mechanical treatments. The rotary hoe controlled weeds when used preemergence and during the early stages of crop growth. The flame cultivator gave preemergence weed control and was selective on weeds less than four to five inches tall after castorbeans had attained a height of 12 to 14 inches. The cultivator controlled weeds between castorbean rows, but weeds were occasionally found within the row. 2-Chloroallyl diethyldithiocarbamate gave unsatisfactory preemergence weed control. Ethyl N,N-dipropylthiolcarbamate (EPTC) gave excellent weed control, injured castorbeans at 3 lb/A, but not at 2 lb/A. N-1-naphthylpthalamic acid at 4 lb/A gave good early weed control.

The effects of various rates of 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid (endothall), isopropyl N-phenylcarbamate (IPC), and 2-methoxy-3,6-dichlorobenzoic acid (dicamba) on Bromus tectorum L. (downy brome) on four soils with surface litter and incorporated organic matter treatments were studied. Significant differences were found in reaction of downy brome seedlings to the herbicides in the four soils. The soil with the highest organic matter content generally inhibited herbicide action to the greatest extent. Straw mulch alone caused a significant decrease in growth of downy brome seedlings. Action of IPC was most inhibited by straw, and endothall the least.

The photosynthetic capacities of three species of dodder, largeseed dodder (Cuscuta indecora, Choisy), field dodder (Cuscuta campestris, Yuncker), and small-seeded dodder (Cuscuta approximata, Bab.) were studied by radioactive carbon dioxide uptake in light and darkness, and by manometric methods. Both methods showed that all three species were able to carry on a small amount of photosynthesis. The photosynthetic capacity was highest in the seedling, and decreased as the dodder became parasitic.

Combinations of 3-chloro-2-methyl-p-valerotoluidide (solan) with 1,1′-dimethyl-4,4′-dipyridylium cation (paraquat) were used postemergence in transplanted tomatoes (Lycopersicon esculentum Mill.). Addition of .05 lb/A of paraquat to 2 or 4 lb/A of solan resulted in more effective control of crabgrass (Digitaria sanguinalis (L.) Scop.) than did doubling the rate of solan. The combinations were synergistic on crabgrass but only additive or more often antagonistic on tomato plants. The herbicides dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA) and sodium 2,4-dichlorophenoxyethyl sulfate (sesone) were applied for preemergence weed control in strawberry beds. Velvetleaf (Abutilon theophrasti Medic.) was resistant to both DCPA and to sesone, but was quite susceptible to the combination. Combinations of 4,6-dinitro-o-sec-butylphenol (DNBP) with 2-methoxy-4,6-bis(ethylamino)-s-triazine (simetone) were highly synergistic on tomato plants. This synergism was more pronounced at low rates of herbicides.

Seedbed preparation was completed about October 15, just before the fall rains. Four herbicide treatments, 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat), 6,7-dihydrodipyrido(1,2-a:2’,1′-c)pyrazidiinium salt (diquat), isopropyl N-phenylcarbamate (IPC) + butoxyethanol ester of 2,4-dichlorophenoxyacetic acid (2,4-D), and 3-amino-l,2,4-triazole + ammonium thiocyanate (amitrole-T) were successfully applied before Janaury 15 for control of weeds and volunteer crop plants. Grasses for seed production were sown in March without disturbing the soil. An application of paraquat at seeding greatly increased subsequent seed yields. Little additional germination of contaminating weed grasses occurred after the grasses were planted and they became established rapidly. By the following October most species could be treated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) to control winter annual weeds. Where weeds were thus effectively controlled during the establishment period, excellent stands resulted which produced high yields of weed-free seed in the first year of seed production.

The growth and development of newly-planted red tart cherry trees on a silt loam soil were satisfactory following six annual treatments of 2.5, 5, and 10 lb/A of 2-chloro-4,6-bis (ethylamino)-s-triazine (simazine) or 2.5 lb/A of 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (diuron). Measurements of tree diameter and leaf area gave no evidence of injury. The control of annual and perennial weeds was excellent. In survey experiments, trees which received 80 lb/A of simazine in 4 years were not injured, but 160 lb/A in 4 years produced leaf injury in the fourth and fifth years.

Preemergence applications of DCPA (dimethyl 2,3,5,6-tetrachloroterephthalate) controlled germinating seedlings of largeseed dodder (Cuscuta indecora Choisy) in alfalfa, and the control continued throughout the season. Applications of DCPA were necessary prior to germination of dodder seed. Under California conditions, applications of DCPA made during early winter (December) provided early season control but not satisfactory control throughout the season as was accomplished with the March treatments. Autoradiographic studies showed only limited movement of tracer in alfalfa plants.

The substituted urea herbicides were rated according to their effectiveness as aquatic herbicides in this order: diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], monuron [3-(p-chlorophenyl)-1,1-dimethylurea], neburon [1-butyl-3-(3,4-dichlorophenyl)-1-methlyurea] and TCA(trichloroacetic acid) mixtures with them. They showed greatest potential in controlling certain aquatic plants in pre-emergence and early postemergence applications. However, relatively high concentrations were required to control filamentous algae (Cladophora, Pithophora and Spirogyra), chara (Chara), coontail (Ceratophyllum), naiad (Najas), and pondweeds (Potamogeton) for periods of time exceeding three months and up to three years. Granular formulations achieved better distribution of herbicides for control of rooted aquatic plants along the margins of lakes and ponds. Wettable powder and liquid emulsifiable concentrates were superior to granular formulations for the control of algae and emergent or floating aquatic plants.

Monuron and fenuron were less toxic to fish than were diuron and neburon. The TCA mixtures were somewhat more toxic than the simple ureas. Some species of fish were more sensitive than others and fingerlings more sensitive than adults of the same species. Fish-food organisms were reduced appreciably in plastic enclosures at herbicidal concentrations.

In nutrient solution, 2,3,6-trichlorobenzoic acid (2,3,6-TBA) was less toxic to oats than either 2-methoxy-3,6-dichlorobenzoic acid (dicamba) or 3-amino-2,5-dichlorobenzoic acid (amiben). The latter two herbicides were similar in phytotoxicity.

In soil, dicamba was the most phytotoxic in each of four soils used, while 2,3,6-TBA and amiben were similar in toxicity in all soils except the organic soil, in which amiben was less phytotoxic than 2,3,6-TBA. In the sandy soils the same amount of herbicide was required to reduce the growth of oats by 50% as was required in nutrient solution, but considerably higher amounts were required in the organic soil. This reduction in phytotoxicity was attributed to adsorption of the herbicides in an unavailable form by the organic matter of the soils, amiben being adsorbed to a greater extent than 2,3,6-TBA or dicamba. Practically no adsorption occurred on the clay colloids of the various soils.

In persistence studies, amiben was more subject to apparent microbial decomposition than 2,3,6-TBA or dicamba. Decomposition was more rapid in the organic soil than in the clay or sandy soils. In leaching studies, the three herbicides were readily washed out of columns of the various soils. Differences in movement of herbicide in these soils could be related to the rate of water movement through the soil.

Germination of dormant crabgrass seed, Digitaria ischaemum (Schreb.) Muhl. and D. sanguinalis L., was increased by treatment with the nematocides 1,2-dibromo-3-chloropropane and ethylene dibromide.

Mugwort (Artemisia vulgaris L.) was controlled by soil applications of potassium azide at 100 lb/A and equimolecular amounts of sodium azide in greenhouse studies. Rooted Artemisia plants exposed to exponential concentration ranges of these herbicides in ¼ strength Knops nutrient solution showed lethal effects at 10-3 M of either the potassium or sodium azide. Vapors of the potassium and sodium azides caused leaf injury at relatively low rates. Bioassays indicated dissipation of 100 lb/A of the azides in the soil in 6 weeks under greenhouse conditions.

The most successful herbicides for control of downy brome (Bromus tectorum L.) in grassland were: 3-amino-1,2,4-triazole (amitrole), 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine), and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine). More consistent downy brome control was obtained with atrazine than the other s-triazines. Amitrole improved postemergence control of the s-triazines in the tillering stage. Intermediate wheatgrass (Agropyron intermedium (Host.) Beauv.), crested wheatgrass (Agropyron cristatum L. Gaertn.), western wheatgrass (Agropyron smithii Rydb.), blue grama (Bouteloua gracilis (H. B. K.) Lag.), and sedge (Carex spp.) appeared to be more sensitive to most s-triazines than needle-and-thread (Stipa comata Trin. & Rupr.) and sand dropseed (Sporobolus cryptandrus Torr.). Sand dropseed was extremely tolerant.

In greenhouse studies, Johnsongrass [Sorghum halepense (L.) Pers.] seedlings were killed when the first internode passed through treated soil. Shoots from rhizomes were not killed, but lateral root development was inhibited on that stem portion in contact with treated soil. Trifluralin may control Johnsongrass seedlings, but it is not likely that it will be useful in the control of established stands.