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.

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.

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 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 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.

The preemergence herbicide N, N-dimethyl-2, 2-diphenylacetamide (diphenamid) alone and in combination with the contact herbicides 1,1′-dimethyl-4, 4′-bipyridinium salt (paraquat) and 3, 4-dichloropropionanilide (propanil) was studied over three years. Application at planting and crop emergence (delayed preemergence) were compared. Weed control and crop tolerance were equally effective at either stage in tomatoes. Delayed preemergence applications of contact materials alone were erratic as herbicides but were more effective in peppers than in tomatoes. At emergence, combinations were more effective. Selectivity of propanil lessened when the cotyledons of tomato expanded fully.

Watering with 1 surface cm or more following spray treatment with dicamba (2-methoxy-3,6-dichlorobenzoic acid) and picloram (4-amino-3,5,6-trichloropicolinic acid) markedly increased inhibition of shoot growth from rhizome sections of quackgrass (Agropyron repens (L.) Beauv.) and bromegrass (Bromus inermis Leyss). Shoots were most sensitive to the herbicides at early stages of development. Bromegrass and quackgrass were about equally susceptible to the two herbicides. Uptake through roots or rhizomes was more effective than foliar uptake. Kentucky bluegrass in established sod was not injured by dosages of the two herbicides that killed or controlled quackgrass. Young stands of Kentucky bluegrass were more sensitive.

P32 was injected into the soil at specific locations to allow determination of the phosphorus uptake pattern of Phaseolus vulgaris (snap bean), Amaranthus retroflexus (pigweed), and Setaria viridis (green foxtail). All species absorbed phosphorus primarily from the top 6 inches of soil. Bean absorbed phosphorus from a zone of relatively small volume. Pigweed roots showed the greatest amount of lateral spread and foxtail roots the deepest soil penetration.

One, two, three, or four plants of each of the above-mentioned species were grown 6 inches from a test bean plant to evaluate the effects of associated plants on the phosphorus uptake of the test bean. The effects observed were quite different for the three species studied.

A 4-year study was made at Huntley, Montana. When the seed coats were ruptured, 100% germination of sago pondweed (Potomogeton pectinatus L.) seeds occurred. Tubers grow in soil to a depth of 18 inches. Formation of tubers was greatest in August. Single plants of sago pondweed, grown from a tuber and a seed, in 6 months developed over 36,000 tubers and 63,000 seeds, respectively. Tubers survived winter temperatures well when buried in the soil. When dipped in paraffin tubers survived up to four years in storage.

On three soils, 3-amino-2,5-dichlorobenzoic acid (amiben) at 1.5 and 15 ppmw did not inhibit the nitrifying microflora, but 150 and 1500 ppmw significantly reduced the nitrate nitrogen produced by the soil microflora. No breakdown of amiben in liquid media was detected during 70 days. Amiben had a net minus charge in solution, and traveled at about the same rate on paper strips in electrophoresis as the dye brilliant blue. The organic matter content of soil was the property most closely associated with adsorption of 14C-labeled amiben. Only kaolinite, of four clays studied, adsorbed amiben significantly. There was no volatilization of amiben from stainless steel planchets stored at temperatures of 15, 25 or 35 C and relative humidities of 0, 33, 66, or 100 per cent.

The atomization of jet streams from circular orifices, 279, 483, and 1016 microns in diameter, was measured under operating pressures less than 5 psi. The jet streams disintegrated into uniform large drops approximately twice the diameter of the jet orifice, and small drops making up less than 1% of the liquid volume from the small jet. About 80% of the spray from a jet discharging horizontally was deposited in a band 2 inches wide. The distribution pattern of horizontal jet streams positioned on a 2 inch spacing was improved by angling the jet streams 10–15° from the direction of travel.

Exposures of trifluralin, α. α, α-trifluoro-2,6-dinitro-N, N-dipropyl-p-toluidine, coated on glass and soil surfaces were made to sunlight and to artificial light from a mercury-vapor source having a wavelength range of 300–700 millimicrons. Ultraviolet absorption spectra of irradiated samples exhibited progressive change with time and intensity of exposure. Exposures on a glass surface to sunlight for four to six hours resulted in a decrease in the plant growth inhibitory activity of trifluralin. Exposures on soil surtaces also indicated that photodegradation occurs, but at a much reduced rate.

Giant foxtail (Setaria faberii Herrm.) was seeded the day the crop was planted and 3, 6, 9, and 12 weeks later. Foxtail that began growing with the crop and was left to maturity reduced corn yields 13% and soybean yields 27%. Foxtail seeded 3 weeks or later after the crop was planted did not cause yield reductions in corn or soybeans. Although not competitive, foxtail seeded 3 weeks after corn was planted produced 500 pounds of dry matter per acre, and all seedings in corn produced seed. Soybeans produced more shade than corn, and foxtail from the 3-week or later seedings in soybeans produced little or no dry matter or seed.

There were usually no significant differences in weed and crop yields between plots receiving aerial and ground applications of herbicides. Where differences were found, aerial application was the more effective.

Tissue abnormalities in colonial bentgrass (Agrostis tenuis Sibth.) were observed after foliage applications at normal doses of 2,4-dichlorophenoxyacetic acid (2,4-D), 2-(2, 4, 5-trichlorophenoxy)propionic acid (silvex), or 4-(2,4-dichlorophenoxy)-butyric acid [4-(2,4-DB)]. They included proliferations of the pericycle, hypertrophic cortical cells, and massed lateral root and root hair formations. The abnormalities usually resulting from phenoxy rates of 1, 1-½, or 3 pounds active per acre were often followed by death of the bentgrass within 20 days after treatment.

Studies in New Mexico showed basal and stump applications of ester and oil-soluble amine formulations of 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) to be effective for control of saltcedar (Tamarix pentandra Pall.). Trees with trunks 2 inches or larger in diameter were harder to kill than smaller trees and retreatment was often needed. Spraying the lower 2 feet was no more effective than spraying the lower foot. Cutting the larger trees and spraying the stump increased effectiveness.

In 1:1 slurry, adsorption of 2-chloro-4,6-bis (ethylamino)-s-triazine (simazine) by acid soils from saturated solution varied from 13 to 90%. Percent of adsorption from more dilute solutions was approximately that from the saturated solution. The adsorption of simazine by 18 soils was not correlated significantly with soil pH, but was correlated significantly with percent clay and highly significantly with organic matter and titratable acidity. Simazine was considered to be adsorbed by soils by proton association. Using titratable acidity as a measure of H-soil, equilibrium constants were calculated which did not vary greatly as a result of changes in acidity up to pH 8.5, or as a result of concentration of simazine in the added solution. Leon, the most adsorptive of the tested soils, gave values for the equilibrium constant that were somewhat higher than for four other soils. Simazine penetrated more deeply into limed soil than into unlimed soil. Liming reduced the decomposition of simazine as did intermittent drying. Recovery decreased with time.

(Arbutus menziesii Pursh.) trees in the field (15–20 cm diameter) xyacetic acid (2,4-D*) and 2,4-5-trichlorophenoxyacetic acid (2,4,5-T*) in blue oak (Quercus douglasii H. & A.) seedlings occurred following application of these herbicides to cuts made through the bark into the wood of stems. Downward transport was limited. C14-labeled 3-amino-1,2,4-triazole (amitrole*), maleic hydrazide (MH*), urea*, and P32-labeled phosphate translocated extensively into the roots as well as upward into the shoots. High humidity had little effect on translocation of 2,4-D* and 2,4,5-T* into the roots, but had marked effect on translocation of amitrole*, MH*, and urea*. The addition of herbicidal amounts of unlabeled 2,4-D or 2,4,5-T reduced translocation of labeled compounds into the roots. Unlabeled 4-amino-3,5,6-trichloropicolinic acid (picloram) or 2,4-D applied to cuts prevented translocation into the roots of all but traces of MH* applied to the same cuts. Treatment of blue oak or madrone (Arbutus menziesii Pursh.) trees in the field (15–20 cm diameter) with herbicidal doses of 2,4-D or picloram largely inhibited the downward movement of P32O4 applied to the same cuts at all stages of growth; such interference was less pronounced in madrone than in blue oak.

The control of blue oak (Quercus douglasii H. & A.) was investigated by cut surface applications of water-soluble amine formulations of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP), 2-(2,4-5-trichlorophenoxy)propionic acid (silvex); ester formulations of 2,4,5-T and silvex; potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram); and ammonium sulfamate. All phenoxy herbicides were relatively effective in controlling blue oak; the least favorable results were obtained with undiluted ester forms of 2,4,5-T and silvex, and ammonium sulfamate. Picloram was more effective than the water-soluble amine salts of 2,4-D on both blue oak and madrone (Arbutus mensiesii Pursh). Relatively favorable results were obtained on madrone by single-point applications to stems with picloram. Applications to holes 1 inch deep were more effective than when applied in deeper or shallower holes. Diluting alkanolamine salts of 2,4-D with water and butoxyethanol ester of 2,4,5-T with diesel oil had a generally depressing effect on kill (except for the first dilution of the ester). Plant kill decreased as the diameters of the trees increased. Rainwater analyses did not furnish an explanation for the marked increase in growth of the grass beneath the treated trees.

Mature yellow foxtail [Setaria glauca (L.) Beauv.] infestations, growing in rows of corn, were harvested in 3 foot segments from paired 30 foot rows of corn. Basic analyses of variance were calculated so that the variances of plot sizes involving multiples of 3 feet could be determined and compared. Precision indices were calculated for harvesting various fractions of the plot area. Loss of precision did not exceed 25 percent when only 40 percent of the total area was harvested in random samples of 1-row X 3 feet, or in multiples of this basic unit. Practical implications of the findings are related to estimates of weed yields in crop-weed ecology studies and herbicide evaluation tests.