Bioassay and chemical analyses of residual α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) from greenhouse and field experiments indicated that the persistence of this herbicide is increased by deep incorporation as compared to shallow incorporation or surface application. Laboratory studies using a charcoal vapor trap indicated that trifluralin volatilization decreased with increasing depth of incorporation. Volatilization appears to be an important mode of trifluralin dissipation from the soil.

A formulation containing 2-chloroethanephosphonic acid, its ethyl ester and anhydride (hereafter referred to as 66-329), caused defoliation and, subsequently, growth of inactive basal buds of honey mesquite [Prosopis juliflora var. glandulosa (Torr.) Cockerell]. With huisache [Acacia farnesiana (L.) Willd.], the same treatments increased the number of branches and leaves per node; however, apical buds often were killed. Application of 66-329 to mesquite increased the release of ethylene to levels in the experimental system which were physiologically active. Bud release by 66-329 appeared to be mediated by ethylene. Treatments that induce growth of basal and lateral buds of woody plants may allow the killing of more plants by subsequent herbicide application.

Ioxynil (4-hydroxy-3,5-diiodobenzonitrile) and 2-(2,4-dichlorophenoxy)propionic acid (dichlorprop) appeared effective for control of fumitory (Fumaria officinalis L.) of the 10 herbicides tested in 1963. In 1964 and 1965, both herbicides were further tested under field conditions, but fumitory control results were erratic. Fumitory plants which had been treated with dichlorprop, although not killed, did not produce seed. Experiments under controlled environmental conditions showed that susceptibility of fumitory to ioxynil and dichlorprop was affected by temperature and humidity. High temperature and humidity were necessary for both herbicides to completely kill the plants although dichlorprop injured fumitory under all the environments. Fumitory was more susceptible to dichlorprop applied at the early stages of growth and more susceptible to ioxynil applied at the later stages.

We studied germination of seeds of 44 morphologically distinct, vegetative ecotypes of johnsongrass (Sorghum halepense (L.) Pers.). Seeds of most ecotypes were highly dormant. Without low temperature pretreatment, best germination occurred with continuous fluorescent light, a KNO3 substratum, and an alternating 20 to 35 C temperature regime. Pretreatment of the seeds for 2 weeks at 10 C, followed by a temperature shift to 40 C for 2 hr was effective in breaking seed dormancy. Germination of each of 12 ecotypes, from harvests in each of 2 years, was markedly similar. Interpretation of the evidence suggests that seed dormancy is largely imposed by the relative degree of mechanical restriction afforded by the seed coat.

Some effects of ammonium thiocyanate (hereinafter referred to as NH4SCN) on the starch and reducing sugar content, amylase activity, photosynthetic O2 release, Hill reaction, and glycine-14C incorporation into amino acids, organic acids, and sugar fractions in excised leaf and cotyledonary tissue of cotton (Gossypium hirsutum L., var. Acala 44) were determined. The starch content of leaf tissue floated on Hoaglands nutrient solution containing 2000 ppm NH4SCN decreased at 1 and 2 days treatment. The amylase activity of excised cotyledons was increased by 2000 and 5000 ppm NH4SCN and the reducing sugar of the same tissue was decreased. Photosynthesis of small leaf disks, as measured by O2 exchange, was decreased and respiration was increased by 2000 ppm NH4SCN. Photosynthesis in isolated chloroplasts, as measured by the reduction of 2,6-dichlorophenolin dophenol in the Hill reaction, also was inhibited by NH4SCN at concentrations above 2000 ppm. Ammonium thiocyanate at 2000 ppm inhibited the conversion of glycine to sugars but had no effect on conversion of glycine to organic acids in leaf tissue.

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.

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.

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.

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.

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.

Flax (Linum usitatissimum L., var. Bolley) was susceptible very early, when less than 2 inches tall, 1965 only, and during flowering, to 3,6-dichloro-o-anisic acid (dicamba) as determined from 9 consecutive weekly applications in the field in 1965 and 1966. Dicamba decreased flaxseed yield, percent oil and iodine number of the oil, seed size, seed germination, and plant height, and increased the days to maturity by application at either one or both of the susceptible stages of flax.

Field experiments were conducted for 2 years at Urbana, Illinois, to evaluate the response of soybeans (Glycine max (L.) Merr., var. Harosoy 63) to soil and foliar applications of 3,6-dichloro-o-anisic acid (dicamba), 4-amino-3,5,6-trichloropicolinic acid (picloram), and (2,4-dichlorophenoxy)acetic acid (2,4-D). Soil incorporated applications of 2,4-D or dicamba at rates up to 8 oz/A or 4 oz/A, respectively, just before planting soybeans did not reduce soybean yields significantly. Picloram, applied under the same conditions, reduced soybean yield almost 40% at ½ oz/A. Picloram at rates from ½ to 2 oz/A caused slight to moderate leaf malformation on soybeans planted the following year but did not reduce yield. Foliar applications of 2,4-D up to 2 oz/A on soybeans had little effect on yield when applied at the prebloom stage and only slightly reduced yield when applied during flowering. Dicamba and picloram injured soybeans at the prebloom stage considerably more than did 2,4-D. Dicamba and picloram severely restricted soybean development, and reduced yield markedly when applied during flowering; ½ oz/A of dicamba or ⅛ oz/A of picloram reduced soybean yield about 50%.