Hoary alyssum (Berteroa incana (L.) D.C.) was selectively controlled in alfalfa (Medicago sativa L.) by 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) at 2 lb/A, 3-tert-butyl-5-bromo-6-methyluracil (hereinafter referred to as DuPont 733) at ½ and 1 lb/A, 2,4-dichlorophenoxybutyric acid (2,4-DB) at ½ and 1 lb/A, and by 3-tert-butyl-5-chloro-6-methyluracil (terbacil) at ½ and 1 lb/A. Alfalfa yields were not reduced with consecutive applications for 3 years with the exception that simazine at 2 lb/A caused a significant reduction in first harvest hay yields in the first 2 years. Herbicide applications were made as soon as possible after the last forage harvest in early fall. Treatment at that time destroys the existing photosynthetic area and should reduce the accumulation of carbohydrate reserves in the roots, thereby inhibiting the development of cold hardiness by hoary alyssum plants.

Pyrazon (5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone) was absorbed by the roots of both common lambsquarters (Chenopodium album L.) and sugar beets (Beta vulgaris L.) and translocated in an acropetal direction to all parts of the plant. Common lambsquarters plants accumulated greater amounts of 3H-pyrazon per gram of tissue than did sugar beet plants and this was especially true of leaf tissues. Translocation into the leaves of both species occurred equally into mature and developing leaves. Neither basipetal nor acropetal translocation of pyrazon occurred following leaf applications of 3H-pyrazon. Pyrazon accumulated in the leaves of common lambsquarters, but it was metabolized when absorbed into sugar beets. Roots, petioles, and leaf blades of beets rapidly metabolized pyrazon while only roots metabolized pyrazon in common lambsquarters. Selectivity of pyrazon appeared to be associated with the rate of metabolic breakdown occurring in the leaf. Accumulations occurred in the susceptible common lambsquarters plant while metabolism kept pace with uptake in the leaves of the tolerant sugar beet plant.

Dodder (Cuscuta spp.) seedlings were killed when exposed to isopropyl m-chlorocarbanilate (chlorpropham) vapors in an enclosed system or in the open atmosphere in the greenhouse or field. No seedlings wrapped on the host when they were exposed for 16 hr or more in an enclosed system. Alfalfa (Medicago sativa L.) foliage restricted air movement near the treated soil and favored accumulation of vapors that killed emerged and emerging seedlings.

The volatilization of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) from a Miller clay and commercial sand was determined by analysis of air samples above the soils. The method requires no extraction of soil or traps and is sensitive to approximately 8 ppm of trifluralin in air. The loss of trifluralin was influenced more by soil moisture than by soil type. Data indicated that trifluralin vapors in air are photolytically degraded. Similar studies were conducted with 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin), but volatilization was so slow that detectable concentrations of this herbicide did not occur.

Several herbicides were applied to drainage ditchbanks in sugarcane (Saccharum officinarum L.) to control johnsongrass (Sorghum halepense (L.) Pers.) from rhizomes and seed. Five post-emergence applications of monosodium methanearsonate (MSMA) at 3.6 lb/A or 2,2-dichloropropionic acid (dalapon) at 7.4 lb/A controlled rhizome johnsongrass as effectively as 600 lb/A of sodium chlorate, the standard treatment. Johnsongrass seedlings infested ditchbanks 1 year after applying sodium chlorate. But preemergence treatments with mixtures of (2,3,6-trichlorophenyl)acetic acid (fenac), 5-bromo-3-sec-butyl-6-methyluracil (bromacil), or trichloroacetic acid (TCA) with MSMA, or postemergence applications of MSMA, dalapon, and sodium chlorate controlled these seedlings. Bermudagrass (Cynodon dactylon (L.) Pers.) rapidly vegetated ditchbanks treated with MSMA, but other herbicide treatments suppressed vegetation with desirable species to the point where erosion could become a problem.

A bench-mounted sprayer-flamer for research work is described. Constant rate spraying, logarithmic-dosage spraying, and flaming can be done at variable spray pressures and 10 speeds. The sprayer-flamer facilitates accurate and rapid application of material on plants and soil in pots and flats. The logarithmic-dosage sprayer gives a 16-fold variation in spray concentration over a 3-ft distance.

The persistence of five herbicides in six soils across Nebraska can be ranked from greatest to least as follows: 5-bromo-3-isopropyl-6-methyluracil (isocil) at 5 and 25 1b/A, 2-chloro-4,6-bis-(isopropylamino)-s-triazine (propazine) at 3 and 9 1b/A, 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) at 3 and 9 1b/A, trichlorobenzyl chloride (hereinafter referred to as TCBC) at 7 and 49 1b/A, and 3-(3,4-dichlorophenyl)-1-methoxyl-1-methylurea (linuron) at 3 and 9 1b/A. Soil texture differences (sandy loam, very fine sandy loam, silt loam, and silty clay loam) had a greater influence on herbicide residue carryover than did climatic differences across Nebraska during 1962 to 1968. Soil carryover of herbicide residues was greater in coarse rather than fine-textured soils and in the drier regions of western than in eastern Nebraska. Leaching of herbicides into the soil profile was an avenue of herbicide dissipation.

More 4-amino-3,5,6-trichloropicolinic acid (picloram) was detected in soil samples by soybean (Glycine max (L.) Merr., var. Ford) bioassay when the herbicide was applied in the fall than when it was applied in the spring to several pasture types. Downward movement was greater in sandy loam than in silty clay loam. Dissipation of picloram was greatest in the upper 12 inches regardless of soil type. More picloram was detected in the 24 to 36-inch depth from plots treated 1, 2, or 3 years before sampling than in plots sampled the year of treatment. This indicated downward movement into the subsoil.

Herbicides 4-amino-3,5,6-trichloropicolinic acid (picloram) and 5-bromo-3-sec-butyl-6-methyluracil (bromacil) effectively controlled live oak (Quercus virginiana Mill.) when applied in the spring and fall in south Texas. A mixture of picloram plus (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) also was effective. Higher rates of bromacil were required than for picloram or picloram plus 2,4,5-T for effective control. Bromacil was more injurious to herbaceous vegetation. The phenoxy herbicides (2,4-dichlorophenoxy)acetic acid (2,4-D) and 2,4,5-T were ineffective.

The responses of established, spaced-planted strains of johnsongrass (Sorghum halepense (L.) Pers.) to repeated, foliar applications of herbicides were studied under irrigated desert conditions. Monosodium methanearsonate (MSMA) and disodium methanearsonate (DSMA) were the most effective herbicides. Six to 10 applications with 3 to 6 lb aihg of either herbicide (totaling 24 to 60 1b/A) killed johnsongrass in most experiments. Treatments initiated in the fall were more effective than similar treatments started in the spring. Higher rates of organic arsenicals were required to destroy topgrowth of johnsongrass in the spring and fall than during the summer. DSMA applications at 4 and 6-week intervals were more effective than applications at 8-week intervals. Six 1b/A of DSMA in 100 gpa of water applied broadcast was as effective as 400 gpa containing 6 lb aihg of DSMA applied as a spot treatment. Removing topgrowth of johnsongrass 4 or 24 hr after treatment did not reduce the effectiveness of DSMA. Combining or alternating organic arsenicals with 2,2-dichloropropionic acid (dalapon) reduced the effectiveness of the arsenicals. Susceptible strains were destroyed by five or six applications of DSMA and MSMA while 9 or 10 applications were needed to kill more resistant strains.

Field studies were conducted during 1967 and 1968 at the University of Wisconsin Experimental Farm, Arlington, Wisconsin, to determine the comparative effectiveness of combinations of row spacings and rates of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) for control of yellow foxtail (Setaria glauca (L.) Beauv.) and barnyardgrass (Echinochloa crusgalli (L.) Beauv.) in soybeans (Glycine max (L.) Merr.). Soybean yields and weed control increased as row spacing decreased. Lower rates of linuron were required for comparable weed control as row spacing decreased. Yield increases with decreasing row width were much greater in 1968 than in 1967, probably because of better rainfall during July, August, and early September in 1968. Improved weed control in the narrow rows may have been due partially to absorption by soybean leaves of light wavelengths that may be most favorable for photosynthesis and vegetative growth of some weed species.

The apex of western ironweed (Vernonia baldwini Torr.) vegetative bud shoots adheres to the tunica-corpus theory. Two layers of cells with the plane of wall formation anticlinal to the main axis (tunica) lie over a body of tissue with no pattern to wall formation (corpus). The bud shoot can be divided into the promeristem, the zone of elongation, and a zone of maturation on the basis of histology. It is suggested that the promeristem may be the seat for dormancy mechanisms in western ironweed and that future investigations be concentrated on this site. There was no evidence of a structural barrier to translocation separating the rhizome and bud shoot.

The phytotoxicity of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea (fluometuron), 3-(hexahydro-4,7-,methanoindan-5-yl)-1,1-dimethylurea (norea), and 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) to cotton (Gossypium hirsutum L., var. Acala 4-42) was compared. Warburg experiments indicated that fluometuron and norea inhibited photosynthesis in isolated leaf disks to a much smaller extent than did diuron and prometryne. When the plants were grown in solution culture, diuron and prometryne were much more phytotoxic to cotton than fluometuron and norea, whereas when grown in soil, prometryne was the least phytotoxic, followed by norea, fluometuron, and diuron. Results of experiments on root vs. shoot uptake showed that all four herbicides entered the cotton seedlings through the roots, and no injury occurred to cotton when the compounds were applied to the shoot zone only. Norea and fluometuron were much more leachable than prometryne and diuron. These results indicate that depth protection in the soil, in addition to translocation and metabolism, might account partially for the tolerance of cotton to preemergence application of the tested herbicides.

Emergence of 23 medusahead (Taeniatherum asperum (Sim.) Nevski) selections from four seeding depths in two soils was investigated and compared with that of other grasses. Increased depth markedly reduced total emergence of medusahead and variability among selections. Selections of intermediate wheatgrass (Agropyron intermedium (Host) Beauv) and pubescent wheatgrass (Agropyron trichophorum (Link) Richt.) and downy brome (Bromus tectorum L.), among other grasses, greatly exceeded medusahead in emergence from all depths. Standard crested wheatgrass (Agropyron desertorum (Fisch. ex Link) Schult.) had less emergence than medusahead from all depths. The 3 and 4-inch planting depths exceeded the coleoptile length of medusahead. When medusahead emerged from these depths, the first true leaf was recurved and chlorotic.

While establishing birdsfoot trefoil (Lotus corniculatus L., var. Viking), the following weed control treatments were compared for effectiveness: (A) ethyl N,N-dipropylthiocarbamate (EPTC) impregnated on granular fertilizer and applied through the placement assembly of a grain drill during planting; (B) EPTC applied as a spray before planting and incorporated by multiple disking; (C) a combination of treatments A and B. All treatments involving EPTC controlled annual grasses. Where perennial grasses and sedges were abundant, treatment C was more effective than the others. All three methods resulted satisfactory birdsfoot trefoil establishment.

In growth chamber studies, high relative humidity and rewetting crystalline spray deposits of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) increased absorption by and phytotoxicity to giant foxtail (Setaria faberii Herrm.), but phytotoxicity was restricted to expanded (unrolled) leaves unless some atrazine was absorbed by the roots. Though phytotoxicity was increased by simulated rainfall when root absorption was prevented, an appreciable number of the plants were killed only when atrazine residues were washed into the soil. In field studies, atrazine applied to a wet soil surface was as effective as the same rate of atrazine foliarly applied. In other field experiments, atrazine applied to giant foxtail on a wet soil and followed by simulated rainfall reduced stand and dry weight, but on a dry soil and not followed by simulated rainfall, atrazine reduced dry weight less and did not reduce stand. These results are due to root absorption of atrazine from wet soil. Spray additives increased phytotoxicity.

The relation between soil moisture and the effectiveness of preemergence herbicides for control of giant foxtail (Setaria faberii Herrm.) was studied under greenhouse conditions using surface soil from Drummer silty clay loam with 25, 31, and 37% moisture. Herbicides used were 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), ethyl N,N-dipropylthiocarbamate (EPTC), 3-amino-2,5-dichlorobenzoic acid (amiben), α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), 2-chloro-N-isopropylacetanilide (propachlor), and 2-chloro-N-(methoxymethyl)-2',6'-diethyl-acetanilide (hereinafter referred to as CP 50144). The effectiveness of atrazine and EPTC was increased when soil moisture was raised from 25 to 31%, but no further increase was obtained at 37% moisture. Response to amiben increased linearly and response to trifluralin decreased linearly with increasing moisture. Increasing moisture within this range had little effect on propachlor or CP 50144.

The effects of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), N,N-dimethyl-2,2-diphenyl-acetamide (diphenamid), and N-(p-bromophenyl)-N'-methyl-N'-methoxyurea (metobromuron) upon autotrophic growth of four unicellular green algae were studied. Growth of Chlamydomonas reinhardi Dangeard was completely inhibited by 1 μg/ml metobromuron or 0.5 μg/ml atrazine and was stimulated by diphenamid. Five μg/ml metobromuron were toxic to Chlamydomonas eugametos Moewus, while atrazine and diphenamid had little effect on growth. Growth of Chlorella vulgaris Beijerinck was partially inhibited by atrazine and stimulated by diphenamid and metobromuron. At high concentrations, atrazine or metobromuron inhibited Chlorella pyrenoidosa Chick while growth was stimulated by diphenamid. The results obtained by treating with a combination of atrazine and metobromuron varied greatly with the organism. The effect of these three herbicides upon heterotrophic growth of Chlamydomonas reinhardi also was investigated. Both metobromuron and diphenamid were toxic in the dark. Atrazine had no effect upon heterotrophic growth.

Competition between wild buckwheat (Polygonum convolvulus L.) and flax (Linum usitatissimum L.) was studied in field experiments at various North Dakota locations and in a controlled environment chamber in relation to soil moisture, soil fertility, light, wild buckwheat density, flax seeding rate, and length of the competition period. In the field, flaxseed yield losses caused by competition were lowered by increasing the flax seeding rate and by early wild buckwheat removal. Fertilizer increased flaxseed yield losses at the high seeding rate and generally doubled wild buckwheat dry matter production. Flax dry matter was reduced by competition at the lower seeding rates. The field and controlled environment studies indicated that competition occurred mostly in the root zone. In the latter study, wild buckwheat was a better competitor than flax on a dry weight basis and the dry weights appeared to be related to nitrogen uptake. Wild buckwheat utilized water for growth more efficiently than flax.

Effects of sub-acute levels of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) on bluegill sunfish (Lepomis macrochirus Rafinesque) were assessed in a pond environment. Eight 0.1-A earthen ponds were each stocked with 300 bluegill fingerlings and treated once with diuron wettable powder at 0, 0.5, 1.5, and 3.0 ppmw, two ponds per treatment level. Dissolved oxygen was reduced severely in some pond waters 2 days following treatment and the low level persisted for 3 to 4 days. Gill lamellae were ruptured and hemorrhagic in 20% of the fish from the 3.0 ppmw ponds at 3 days post-treatment. Fish in a cage succumbed during this period in a 3.0 ppmw pond. No further bluegill mortality was observed in treated ponds 3 days after treatment. Hematocrit measurements of treated and control fish could not be correlated with treatment level. Best growth was exhibited by control fish and their progeny. Diuron residues were not detectable in treated pond waters after 28 days. Residues of diuron in treated-pond vegetation were detectable up to 95 days following treatment, whereas residues in mud were measured by gas chromatography 122 days after treatment. Invertebrate populations increased in all ponds with time, indicating little or no effect of the herbicide on their numbers. Good control of filamentous algae and vascular aquatic vegetation was demonstrated in the treated ponds.