Herbicides applied April 30, May 10, or October 14 gave best control of musk thistle (Carduus nutans L.). The most effective herbicide at all dates and rates was 4-amino-3,5,6-trichloropicolinic acid (picloram). Two lb/A of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) also was effective at all spring dates. Two lb/A of 2,4-dichlorophenoxyacetic acid (2,4-D) resulted in excellent control of musk thistle when applied May 10 or October 14.

More musk thistle seedlings became established in nongrazed, cool season grass pastures than in nongrazed, mixed warm season grass pastures. Greater germination was attributed to the reserve moisture and accumulation of litter which served as an excellent germination medium. However, only one musk thistle plant remained in the nongrazed pastures 1 year after seeding. The remainder of the seedlings and young rosettes found in the protected areas in 1965 had succumbed to the heavy competition by 1966.

A poisonous pasture weed, western whorled milkweed [Asclepias subverticillata (Gray) Vail] is capable of spreading in a few years from scattered clumps, highly variable in number of stems, to an almost solid, uniform stand. The most effective herbicide evaluated for its control was 4-amino-3,5,6-trichloropicolinic acid (picloram). Use of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) gave only fair control. The herbicides 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4–5-trichlorophenoxyacetic acid (2,4,5-T), 2-(2,4,5-trichlorophenoxy)propionic acid (silvex), and 3-amino-l, 2,4-triazole (amitrole) were ineffective. The addition of amitrole did not enhance the effectiveness of dicamba or picloram for control of this species.

Seedlings of wheat (Triticum aestivum L.), corn (Zea mays L.), and sorghum (Sorghum vulgare Pers.) were exposed to 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) in solution culture. Following prolonged treatment, the tolerant species, corn and sorghum, accumulated leaf concentrations of unaltered atrazine which were comparable to those found in the sensitive species at the point of acute toxicity. In the sensitive species, wheat, there did not seem to be a critical leaf concentration of atrazine which was necessary to bring about acute toxicity. The leaf concentration in wheat could be raised by increasing the concentration of atrazine in the nutrient solution or by lowering the temperature at which the plants were grown. The loss of chlorophyll in sensitive species was closely related to and preceded acute toxicity symptoms.

Considerable differences in rate of root elongation were observed. Species studied in order of decreasing rate root elongation were cocklebur (Xanthium pensylvanicum Wallr.), palmer amaranth (Amaranthus palmeri S. Wats.), barnyardgrass (Echinochloa crusgalli (L.) Beauv.), buffalobur (Solanum rostratum Dunal), kochia (Kochia scoparia (L.) Schrad.), crabgrass (Digitaria sanguinalis (L.) Scop.), sorghum (Sorghum vulgare L., var. RS 610), Russian thistle (Salsola kali L., var. tenuifolia Tausch), and tumblegrass (Schedonnardus paniculatus (Nutt.) Trel.). In 15 days, cocklebur and tumblegrass roots grew 33 and 11 in, respectively. With all species, the rate of root elongation always exceeded the rate of height increase. There was poor correlation between rate of root elongation and weed height, top weight, and root weight.

Conflicting reports on the dissipation of ie isopropyl N-phenylcarbamate (IPC) and isopropyl N-(3-chlorophenyl) carbamate (CIPC) prompted the present investigation on the dissipation and biological activity of these two herbicides. The dissipation patterns of IPC and CIPC were similar. Under the field and laboratory conditions described, more than 90% of both herbicides was gone in 4 weeks. CIPC was biologically more active than IPC on all plants tested, and both herbicides were nearly 10 times more toxic to buckwheat (Fagopyrum esculentum Moench.) in quartz sand as in a silt loam soil. Although both herbicides were present in equal amounts throughout their dissipation, CIPC appears to persist longer in field applications, as it is more toxic to most plants than IPC.

Golf putting greens were sprayed with N-(2-mercaptoethyl) benzenesulfonamide S-(O,O-diisopropyl phosphorodithioate) (bensulide). Creeping bentgrass (Agrostis palustris Huds.) and annual bluegrass (Poa annua L.) were observed for injury. Preemergence and postemergence treatments of 5-bromo-3-sec-butyl-6-methyluracil (bromacil), 5-chloro-3-tert-butyl-6-methyluracil (terbacil), and 5-bromo-3-tert-butyl-6-methyluracil (hereinafter referred to as DP 733) were applied to a prepared seedbed planted with Kentucky bluegrasses (Poa pratensis L., var. Merion and var. Newport) and annual bluegrass.

Thirty lb/A of bensulide produced leaf discoloration and root length reduction of established annual bluegrass plants without injuring creeping bentgrass. Terbacil at 0.2 lb/A and bromacil at 0.4 lb/A gave highly selective control of annual bluegrass in Merion and Newport Kentucky bluegrasses when applied preemergence to the three grasses. Postemergence applications of these compounds produced moderate selective control of annual bluegrass.

Greenhouse and field studies showed that α,α,α,-trifluro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) gave better control of wild cane [Sorghum bicolor (L.) Moench] when incorporated in the soil above rather than below the wild cane seed. Of four herbicides studied in field experiments, trifluralin gave the best control of wild cane in soybeans (Glycine max L., var. Clark) followed by S-propyl dipropylthiocarbamate (vernolate). Herbicides were more effective than cultivation in controlling wild cane, but neither alone was adequate. A combination of cultivation plus herbicides markedly increased soybean yields on wild cane infested areas. These results show that an economical crop of soybeans can be produced on wild cane infested land.

Preliminary field experiments with 3,4-dichloropropionanilide (propanil) indicated that methods of application had little effect on the activity of this herbicide. Growth of tomato (Lycopersicum esculentum Mill.) plants was reduced for about 7 days. Susceptible plants were killed in 3 to 7 days. Propanil inhibited the growth of tomato radicles and the auxin-induced growth of Avena coleoptiles. Propanil destroyed the permeability of red beet (Beta vulgaris L.) membranes and also destroyed chloroplast membranes in vitro. Oxygen uptake by isolated mitochondria and treated leaf tissues, and phosphate esterification in mitochondria were severely inhibited by propanil. Photosynthesis was completely inhibited within 20 min after treatment but began to return to normal in resistant plants (tomato) after 6 hr.

S-ethyl hexahydro-1 H-azepine-l-carbothioate-C14 (molinate-C14) applied to the leaves of barnyardgrass [Echinochloa crusgalli (L.) Beauv.] and rice (Oryza sativa L.) was predominantly translocated acropetally. Root-applied molinate-C14 was translocated readily throughout the plant. Excised organs of barnyardgrass absorbed more molinate-C14 than did corresponding organs of rice. With surface application, injury by 5 or 10 ppm molinate to rice planted at depths of 0, 0.5, 1.0, or 1.5 in decreased with increasing depth of planting, but injury increased in incorporated treatments with increasing depth of planting. Barnyardgrass was markedly suppressed at all depths of planting. Inhibition of elongation of barnyardgrass by molinate was overcome by an equimolar concentration of gibberellic acid. Molinate reduced the level of soluble RNA in barnyardgrass coleoptiles.

Eight technically pure herbicides were evaluated for their relative phytotoxicity to hydroponically grown seedlings of red maple (Acer rubrum L.) and white ash (Fraxinus americana L.). Six of the herbicides (acids) were prepared as the triethylamine salts to provide formulation uniformity. With four compounds, equi-mole dosages per plant produced different toxic responses depending upon whether the herbicide was applied to the shoot or root. The 2,4,5-trichlorinated phenoxyaliphatic acids 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 2(2,4,5-trichlorophenoxy) propionic acid (2,4,5-TP), and 4(2,4,5-trichlorophenoxy) butyric acid (2,4,5-TB) were consistently more toxic on a mole basis when applied to the roots of both species than when applied to the shoots. The opposite effect was observed with ammonium sulfamate (AMS) where shoot treatments were always more toxic. Shoot and root treatments were equally effective for the compounds 2,4-dichlorophenoxyacetic acid (2,4-D), 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 3-amino-l,2,4-triazole (amitrole). Differential species susceptibilities to certain compounds were observed.

The influence of 2,6-dichlorobenzonitrile (dichlobenil) on yield, size, and pigmentation of cranberries (Vaccinium macrocarpon Ait., var. Early Black) was studied. Data on the effect of fall and spring applications were collected over a 2-year test period and comparisons made. Yield increased and berry size decreased after 1 year from both fall and spring treatments. The slight increases in yield were attributed to good weed control and not to any direct effect of dichlobenil. Treatments of cranberries for 2 successive years (fall and spring) caused slight reductions in yield and berry size. Berries treated for 2 successive years with dichlobenil were analyzed for anthocyanin development. All applications considerably enhanced pigmentation, spring treatments having the greatest effect in this respect. Anthocyanin development increased with increase in the concentration of dichlobenil applied.

Red beets (Beta vulgaris L., var. Detroit Dark Red) converted the herbicide 5-amino 4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) to N-2-chloro-4-phenyl-3-(2H)-pyridazinone glucosamine. Isolation was accomplished by water, benzene, and alcohol extraction of foliage followed by purification through molecular sieve columns. Identification was established by infrared spectroscopy, and thin layer and gas liquid chromatography.

Nineteen granular herbicides were applied at two rates to garden chrysanthemums (Chrysanthemum morifolium Ram.) in plantings at St. Paul and Morris, Minnesota. The soil at St. Paul was classified as silt loam and at Morris, as clay loam. All herbicides were applied to freshly cultivated plots which then were irrigated. The compound a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) at 8 lb/A gave excellent weed control at both locations; trifluralin at 4 lb/A gave 99% and 97% weed control at St. Paul and Morris, respectively; 3-amino-2,5-dichlorobenzoic acid (amiben) at 6 lb/A gave 99% control at Morris and 76% control at St. Paul; 2,6-dichlorobenzonitrile (dichlobenil) at 3 lb/A gave 93% control at St. Paul and 88% at Morris. Application of 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne) at 8 lb/A gave excellent weed control at both locations but caused serious injury to the chrysanthemums.

Six herbicides were applied at 3, 9, and 27 lb/A to the soil in forests of three types in Puerto Rico. The forests differed in soil type, amount and pattern of rainfall, and species composition. Defoliation occurred slowly, but the correlation between percentage defoliation and plants killed was significant at the 1% level of probability. Some defoliation was evident 1 month after treatment and increased slowly during the next 6 to 8 months. The most effective herbicide was 4-amino-3,5,6-trichloropicolinic acid (picloram). Generally, 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 2-methoxy-4,6-bis(isopropylamino)-s-triazine (prometone), and 5-bromo-3-sec-butyl-6-methyluracil (bromacil) were less effective than picloram. Both 2,3,6-trichlorophenylacetic acid (fenac) and 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron) were ineffective. Defoliation was greatest and more plants were killed in the driest site.

One year after treatment, fenac was the most persistent herbicide in the soil. Herbicides were found to a 36 to 48-in depth within 3 months after application.

Herbaceous and woody seedlings were present at all sites within 18 months after herbicide application. There was no definite relationship between herbicidal treatment and secondary succession, except that the number and frequency of successional species were greater on plots having the highest percentage of defoliation.

In a study of the selective action of 3-(3,4-dichlorophenyl)-l-methoxy-l-methylurea (linuron), parsnip (Pastinaca saliva L., var. Harris Model) possessed a high degree of tolerance as compared to tomato (Lycopersicum esculentum Mill., var. Kokomo). Linuron was readily taken up by the roots of tomato and distributed throughout the plant, but it remained mostly in the roots of parsnip. Linuron in the leaves of parsnip was metabolized, to a great extent, while very little of the metabolite (s) was found in tomato. The herbicide caused rapid and complete inhibition of photosynthesis in tomato, and the plants never recovered. Photosynthesis in parsnip was inhibited but only temporarily. Therefore, it appears that the selectivity of linuron on these two species may be explained by the two mechanisms of differential accumulation in the foliage and metabolism of the herbicide.

The growth of tomato (Lycopersicoti esculentum Mill., var. Heinz 1350) plants was enhanced by low concentrations of both N,N-dimethyl-2,2-diphenylacetamide (diphenamid) and the filtrate from two fungal species Trichoderma viride (Tode) Harz and Aspergillus candidus Link. High concentrations of the filtrate from these fungi inhibited the growth of tomatoes, but this was overcome by the addition of diphenamid. Diphenamid also increased the growth of these two fungi.

Large Crabgrass (Digitaria sanguinalis (L.) Scop.) and barnyardgrass (Echinochloa crusgalli (L.) Beauv.) plants were grown from seedlings to maturity under five light qualities of equal energy levels. For crabgrass, both fresh and dry weight yields of plant tops grown under red light and under cool white light were significantly greater than those under green, yellow, or blue light. Length of stem followed this same order. Effects of light quality on reproduction were not as consistent; green and blue light caused the largest numbers of seed heads to form, while yellow light delayed flowering and resulted in the least number and weight of seed heads. Somewhat similar responses to light were found with barnyardgrass plants, except that yields under yellow light were close to those under red light for this species. Blue light caused smallest plants in both kinds of weeds.

Five preplant, soil-incorporated herbicides were evaluated over a 2-year period for their effect upon the growth of representative varieties of 15 common species of spring-planted annual flowers. Of these, α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) was effective in combining freedom from plant injury with control of weeds. Only in phlox (Phlox nana compacta Nutt., var. Fireball) was growth reduced significantly over the 2-year period by this herbicide at 2 lb/A while petunia (Petunia hybrida, var. Snow Lady) was reduced in 1 of 2 years. N,N-dimethyl-2,2-diphenylacetamide (diphenamid) at 4 and 8 lb/A was effective and ethyl N,N-dipropylthiocarbamate (EPTC) at 4 lb/A was fairly effective, but both were tolerated by fewer flower species. N-(2-mercaptoethyl) benzenesulfonamide S-(O,O-diisopropyl phosphorodithioate) (bensulide) at 10 lb/A and methyl 3,4-dichlorocarbanilate (swep) at 5 lb/A were not phytotoxic to any species but were relatively ineffective in controlling the weeds present.

One year after the last of six annual applications of 3-(p-chlorophenyl)-l,l-dimethylurea (monuron) at 2.4, 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron) at 2.4 and 7.2, and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) at 1.0 and 3.0 lb/A in a furrow-irrigated vineyard on Warden silt loam, a bioassay using oats (Avena sativa L., var. Kanota) as the indicator showed that 1.6, 2.8, 10.6, 0.6, and 2.0 lb/A, respectively, remained in the surface 12 in of soil. Of the total, 62 to 89% was located in the surface 2 in and 86 to 100% was in the surface 4 in. Three years after the last of four annual applications of monuron at 7.2 lb/A, 0.8 lb/A remained in the surface 12 in.

Annual grasses were removed by l,l′-dimethyl-4,4′-bipyridinium salt (paraquat) from subclover (Trifolium subterraneum L.)-Hardinggrass (Phalaris tuberosa L., var. stenoptera (Hack.) Hitchc.) pastures with only temporary damage to these species. If sprayed at the recommended time, total forage production was unchanged and forage quality was improved. Species composition of the pasture was improved by all spraying treatments.