Rhinocyllus conicus Froel. (Col.: Curculionidae) larvae feeding within the capitula of Carduus thistles may reduce production of viable seeds. Each R. conicus larva destroyed 9.7 developing musk thistle (Carduus nutans L.) seeds. An average musk thistle capitulum, 29.2 mm diameter, produced 15.3 viable achenes per millimeter of diameter for an average of 447 viable seeds. Surveys of 23 release sites in Virginia revealed that thistles at 12 had sustained a population of weevils. Weevil eggs at six sites have increased in abundance, and establishment appears assured. Colonization of R. conicus was enhanced by spring or early summer releases; larger stocks of insects were required for late summer releases. The weevils exhibited better synchronization with musk thistle than with plumeless thistle (Carduus acanthoides L.); and best success has been achieved where extensive, persistent stands of musk thistle were available.

A soil sampler was constructed to collect soil cores in plastic tubes to a depth of 30 cm. This method of sampling prevents loss of soil, minimizes soil contamination, and permits proportional sectioning of the soil core into desirable segments for bioassay or chemical analysis.

DPX 1840 [3,3a-dihydro-2-(p-methoxyphenyl)-8H-pyrazolo-(5,1-a)isoindol-8-one] modified xylem development in honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] by causing the formation of an essentially fiberless wood. More than 90% of the axial cells on the xylem side of the vascular cambium differentiated as parenchyma. These cells contained large quantities of starch and were similar in structure to the sapwood parenchyma of untreated seedlings. DPX 1840 treatment also brought about the release of basal stem buds and may be potentially useful in woody brush control.

Five 2,5-dimethyl-1-pyrrolidinecarboxanilides were effective inhibitors of the Hill reaction. However, only the cis isomers were active; the trans isomers were totally inactive. Experiments were conducted using 14C-5328 (cis-2,5-dimethyl-1-pyrrolidinecarboxanilide). A correlation existed between resistance of various plants to 5328 and their ability to metabolize it to water soluble metabolites. Velvetleaf (Abutilon theophrasti Medic.) and proso millet (Panicum miliaceum L.) seedlings were very susceptible to 5328 and were unable to metabolize it. Tall morningglory [Ipomoea purpurea (L.) Roth] seedlings were highly tolerant to 5328 and converted it completely to its metabolites. Corn (Zea mays L. ‘DeKalb variety XL-45′) seedlings which were slightly susceptible to 5328 injury were able to metabolize up to 90% of the parent compound. Corn foliage uptake of 14C-5328 applied to the soil surface occurred through the adventitious roots.

A method is described in which tissue excised from cotyledons of 10-day-old pumpkin (Cucurbita pepo L. ‘Alabama Gold’) seedlings is floated in the light on a phosphate-based medium suspected of containing a photosynthesis inhibitor. The discs sink in a few hours if photosynthesis is inhibited; otherwise they continue to float. The method is capable of detecting a 0.002 to 0.02 ppm concentration of the herbicide prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine]. The method could be used both for screening chemicals for potential herbicide use and for monitoring water for pollution by photosynthesis inhibitors.

The translocation of 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and 2,4-D [(2,4-dichlorophenoxy) acetic acid] in bean (Phaseolus vulgaris L. ‘Stringless Greenpod’) seedlings was studied. 14C-labeled herbicides in amounts of 0.75 to μg were injected into the center of the stem at the cotyledonary node with a 1-μL syringe pipette. The effects of time and duration of treatment, herbicide concentration, and herbicide interaction on acropetal and basipetal translocation subsequent to treatment were determined. There was considerable basipetal as well as acropetal translocation of herbicide from the site of injection. Acropetal translocation of 2,4,5-T to primary leaves was very rapid until 2 hr after treatment, and during the following hours of treatment the 14C disappeared from the primary leaves. Acropetal translocation of 2,4,5-T to the young shoots was slow but continuous up to 6 hr after treatment, did not decrease during the latter hours of treatment, and was enhanced by high 2,4,5-T treatment levels. Translocation of 2,4,5-T to the nutrient solution continued for at least 72 hr after treatment while the roots accumulated maximum amounts in 6 to 12 hr. High treatment levels of 2,4,5-T enhanced the translocation of 2,4-D in the young shoots. However, 2,4-D did not promote the translocation of 2,4,5-T. Considerable variation occurred in the total translocation of 2,4,5-T when treatments were made at various times during the day. Translocation rates to the nutrient solution were at a maximum at about 12 A.M. and 12 P.M. each day regardless of the time of application of the 2,4,5-T.

The reduction and assimilation of nitrate ions by 14-day old tall morningglory [Ipomoea purpurea (L.) Roth] seedlings were studied by monitoring the leaf nitrate, protein, and activity of the enzyme nitrate reductase (NADH: nitrate oxidoreductase, EC 1.6.6.1). The pH's of the grinding and assay mixtures yielding maximum nitrate reductase activity were determined to be 8.8 and 7.5 to 7.7, respectively. The maximum assay time for a linear reaction rate for nitrate reductase was estimated at 10 minutes. Decay rates of the enzyme preparations indicated a half-life of 30 min. Requirements for a cofactor to support the reaction were met with the addition of NADH (1 × 10−3 M final concentration) to the assay mixture. NADPH was not effective in supporting nitrate reductase activity. Inclusion of cysteine (1 × 10−2 M) in the grinding medium was necessary to insure maximum activity of the enzyme preparations. Both light and nitrate were required for nitrate reductase activity in morningglory leaves. Nitrate accumulated in leaf tissue in proportion to the concentration of nitrate in the nutrient medium. Above 7,530 lux luminescence, enzyme activity and tissue protein were related to the light intensity and the availability of nitrate in the nutrient medium on which the plants were grown.

In greenhouse studies, atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine killed Canada thistle [Cirsium arvense (L.) Scop.] when applied as preemergence or postemergence treatments. Postemergence atrazine applications caused more rapid kill when allowed to cover the ground as well as the foliage compared to only foliar atrazine applications. In three field experiments conducted in 1967, 1968, and 1969, Canada thistle was controlled with atrazine and amitrole (3-amino-s-triazole) + NH4SCN. Control resulting from atrazine was as good or superior to amitrole + NH4SCN when both were applied to foliage prior to plowing. Control from 2.2 kg/ha of atrazine applied prior to plowing was 78% for the 3-year average. Atrazine applied preemergence at 2.2 kg/ha resulted in inferior control, whereas postemergence atrazine applications resulted in thistle control similar to treatments applied prior to plowing.

The effects of drop-size, dosage, and spray volume on the toxicity of aqueous sprays of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) were measured using sunflower (Helianthus annuus L. ‘Peredovik’). Small drops (100 μ) were more phytotoxic than large ones (350 μ), and concentrated solutions (5.5 L/ha) were more phytotoxic than dilute solutions (2.2 L/ha) at the same dosage rate.

The response of several hundred soybean [Glycine max (L.) Merr.] cultivars to postemergence application of four herbicides was evaluated in the field, greenhouse, and growth chamber in 1970, 1971, and 1972. Postemergence application of 3.4 kg/ha of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide] did not significantly reduce yields of the seven commercially important soybean cultivars evaluated. All entries in the regional breeding trials, Uniform Test I to IV, were relatively tolerant of postemergence applications of the herbicides at rates about double those required for weed control. The observed order of phytotoxicity was 3.4 kg/ha of bentazon < 3.4 kg/ha of chloroxuron [3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea] < 0.3 kg/ha of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) = 0.4 kg/ha of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid]. Of the 338 named U.S. and Canadian cultivars in the U.S. Department of Agriculture soybean germplasm collection, all but one were tolerant to a postemergence application of 3.4 kg/ha bentazon. One U.S. cultivar, ‘Hurrelbrink,’ and ten plant introductions from Japan were highly sensitive to bentazon. These 11 cultivars were also highly sensitive to bromoxynil and 2,4-DB and somewhat sensitive to chloroxuron.

Benefin accumulated rapidly in the roots of tobacco (Nicotiana tabacum L. ‘Kentucky 14′) seedlings incubated in nutrient solution containing 14C-labeled benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) and remained in the roots unaltered. Very low levels of radioactivity were detected in the shoots. Diphenamid (N,N-dimethyl-2,2-diphenylacetamide) accumulated in the shoots of treated plants throughout the treatment period but remained at low levels in the roots. Diphenamid was extensively metabolized in the shoots but only to a slight extent in the roots. The carbon-14 of pebulate (S-propyl butylethylthiocarbamate) accumulated in moderate amounts in both the roots and shoots of the tobacco seedlings, but attempts to recover pebulate failed.

Primary root elongation of prickly sida (Sida spinosa L.) at pH 5.5 was similar to that at pH 6.5 while sicklepod (Cassia obtusifolia L.) was reduced to 62% and tall morningglory [Ipomoea purpurea (L.) Roth] to 87% of that at pH 6.5. At pH 5.1, root elongation of prickly sida was reduced to 77% of that at pH 5.5. Some elongation was observed in the pH range of 5.1 to 6.5 for all species. Maximum primary root growth of tall morningglory, sicklepod, and prickly sida occurred at approximately 32° which was similar to that for cotton (Gossypium hirsutum L. ‘Empire’). Temperature as high as 39° did not significantly reduce root elongation of sicklepod. Tall morningglory root growth was reduced approximately 50% by 0.2 ppm of trifluralin (α,α,α-trifluro-2,6-dinitro-N,N-dipropyl-p-toluidine). In contrast, sicklepod and prickly sida root growth was reduced only slightly by 1 ppm of trifluralin.

Onion (Allium cepa L.) and bean (Phaseolus vulgaris L.) seedlings grown in soil treated with DCPA (dimethyl tetrachloroterephthalate) were less susceptible to northern root-knot nematode (Meloidogyne hapla Chitwood) infection than seedlings grown in untreated soil. DCPA treatment of nematode larvae did not alter their pathogenicity. Resistance could be correlated with altered cell structure of the root epidermis, increased root exudate as evidenced by soil adherence, reduced fibrous root development, or both.

Benzyladenine (BA), kinetin, and gibberellic acid (GA) at concentrations of 6 × 10−4 and 4 × 10−3 M, respectively, were used to induce formation of basal bulbs above ground in rhizomes of purple nutsedge (Cyperus rotundus L.). BA plus GA induced a tropistic response in all of the rhizomes and only above ground bulbs were produced, while kinetin plus GA induced a tropistic response and bulbs formed above and below the soil surface. Control plants as well as those treated with GA, kinetin, or BA produced underground bulbs and rhizomes but no bulbs above ground. Height of above ground secondary bulbs induced by kinetin plus GA was significantly greater than those induced by BA plus GA. Transformation of primary rhizomes to shoots in the control plants did not differ significantly from transformation of those originating from plants of the various treatments. Height of primary plants of all treatments differed significantly from the controls.

Twelve different johnsongrass (Sorghum halepense L.) clones were selected from four different regions of the United States and were grown in the greenhouse. The johnsongrass clones grew differently depending upon the environment from which they were originally obtained, suggesting that geographical ecotypes of johnsongrass exist. The parameter of growth most closely correlated to the latitude from which the plants were obtained was the time required for floral initiation. Plants from a more northern latitude consistently flowered earlier than plants obtained from a more southern latitude. Differences in height, stem number, and the weight of rhizomes, shoots, and roots also supported the hypotheses that geographical ecotypes of johnsongrass exist. Susceptibility to dalapon (2,2-dichloropropionic acid) appeared not to be correlated to the latitude from which the plants were obtained.

Effects of the inhibitors DNP (2,4-dinitrophenol) and oligomycin, and the substituted dinitroaniline herbicides, trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], and oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) on mitochondrial tractions isolated from soybean (Glycine max L. ‘Lee’) hypocotyls were examined. Oryzalin and nitralin uncoupled succinate oxidation at the ADP-limited state 4, as did DNP. Trifluralin caused no effect on the second state 4, but inhibited oxidative phosphorylation in a manner similar to the effect of the energy-transfer inhibitor oligomycin. Studies of the interaction of these inhibitors indicate that the sites of action for these herbicides may be different.

Bensulide [0,0-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] and trifluralin (α,α,α-trifluroro-2,6-dinitro-N,N-dipropyl-p-toluidine) were incorporated to a depth of 2.5 and 7.5 cm in sandy loam soil on the same plots in three annual applications to study the effect of incorporation depth on movement and persistence of the herbicides in furrow-irrigated soil. Bioassays and gas-liquid chromatographic assays indicated that, regardless of rainfall, both herbicides remained within the original soil zones of incorporation. Trifluralin persisted longer in soil as depth of incorporation was increased. Neither bensulide at 4.5 or 9.0 kg/ha nor trifluralin at 1.1 kg/ha persisted in appreciable amounts 12 months after treatment. At these rates, significant residues of bensulide and trifluralin were detected after 6 months only when tillage was restricted. Herbicide concentrations that persisted 6 months as determined in laboratory assays caused severe reduction in growth of field-grown sorghum [Sorghum bicolor (L.) Moench].

The plant hormones gibberellic acid (GA) and benzyladenine (BA) stimulated the development of dipeptidase activity in distal-half cotyledons of squash (Cucurbita maxima Duch. ‘Chicago Warted Hubbard’). The herbicides 2,4-D [(2,4-dichlorophenoxy)acetic acid], dicamba (3,6-dichloro-o-anisic acid), and naptalam (N-1-napthylphalamic acid) inhibited the development of dipeptidase activity in this tissue. Herbicide concentrations which inhibited the development of this enzyme activity about 30% were used for the herbicidehormone interaction study. The addition of GA or BA counteracted the inhibition induced by 2,4-D and naptalam. Neither hormone grossly altered the inhibition induced by dicamba; however, BA did significantly reduce the inhibition caused by dicamba.

The rates of degradation of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], the isopropyl analog [4-ammo-6-isopropyl-3-(methylthio)-as-triazin-5(4H)-one], and the cyclohexyl analog [4-amino-6-cyclohexyl-3-(methylthio)-as-triazin-5(4H)-one] in soil were determined under laboratory and field conditions. First-order kinetics best described the rate of degradation of the three herbicides. At 5 and 20°C, metribuzin and the isopropyl analog degraded more slowly than the cyclohexyl analog. At 35°C, the rates of degradation for all three herbicides were similar. The calculated half lives were approximately 329, 44, and 16 days for the three herbicides at 5, 20, and 35°C, respectively. Rates of 1.12 and 2.24 kg/ha, applied in the field, remained in the upper 5 cm of the soil profile, and the pattern of herbicide degradation followed that found in the laboratory study at 20°C.

In a 3-year field study in corn (Zea mays L.), several herbicides and combinations were studied for the control of yellow nutsedge (Cyperus esculentus L.), giant green foxtail [Setaria viridis var. major (Gaud.) Posp.], and fall panicum (Panicum dichotomiflorum Michx.). Best yellow nutsedge control (87 to 88%) resulted from applications of 4.48 kg/ha of either alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] preplant incorporated or atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] preplant incorporated plus atrazine postemergence with a phytobland oil. Between 72 to 83% control of yellow nutsedge resulted from applications of 2.24 kg/ha of alachlor, 4.48 kg/ha of butylate (S-ethyl diisobutylthiocarbamate), and combinations of atrazine plus butylate. Greater than 90% control of giant green foxtail and fall panicum resulted from butylate plus atrazine or alachlor; postemergence applications of atrazine resulted in significantly less control of fall panicum or giant green foxtail.