Rates of dissipation, control of troublesome aquatic weeds, and toxicity to fish by the disodium and dipotassium salts of 7-oxabicyclo(2,2,1)-heptane-2,3-dicarboxylic acid (endothall) in farm reservoirs and in growth pools were studied from 1964 to 1967. In 4 out of 14 reservoir applications, initial concentrations of 0.3 to 1.4 ppm dissipated to near the limit of detection in 8 to 20 days. In the other 10, the dissipation ranged from 23 to an increase of 160% in 12 days. The average dissipation was 71%. In growth pools, initial concentrations of 0.5 to 4.0 ppm of endothal dissipated to 0.26 to 2.5 ppm in 12 days.

The effects of 3,5-dibromo-4-hydroxybenzaldehyde O-(2,4-dinitrophenyl)oxime (hereinafter referred to as C-9122), 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil), 3,5-dibromo-4-hydroxybenzaldoxime (hereinafter referred to as bromoxime), and 2,4-dinitrophenol (hereinafter referred to as DNP) on phosphorylation and electron transport were measured in mitochondria isolated from white potato tubers (Solarium tuberosum L.) and in chloroplasts from spinach leaves (Spinacia oleracea L.). Mitochondrial oxygen utilization was monitored polarographically. All four chemicals stimulated ADP-limited oxygen utilization, inhibited non-ADP-limited oxygen uptake, and relieved oligomycin-inhibited oxygen uptake. C-9122 produced responses at lower molar concentrations than did bromoxynil, bromoxime, and DNP. The I50 value for inhibition of state 3 respiration by C-9122 was 2.7 × 10−6 M.

In chloroplasts, C-9122, bromoxime, and DNP inhibited photoreduction and coupled photophosphorylation with water as the electron donor, and with ferricyanide and NADP as electron acceptors. Cyclic photophosphorylation, with phenazine methosulfate as the electron mediator under an argon gas phase, also was inhibited. With ascorbate-2,6-dichlorophenolindophenol (hereinafter referred to as DPIP) as the electron donor, phosphorylation coupled to NADP reduction was inhibited, but not the reduction of NADP. C-9122 was the strongest inhibitor, and bromoxime was the weakest inhibitor of the several reactions. The I50 value for inhibition of the coupled ferricyanide reduction was 4.6 × 10−6 M for C-9122. C-9122 appeared to act in two different ways by (a) inhibiting electron transport at or near photosystem II and the oxygen evolution pathway, and (b) interfering with energy transfer and the generation of ATP. Bromoxynil inhibited photoreduction and photophosphorylation reactions in which water served as the electron donor; but it was a very poor inhibitor of both cyclic photophosphorylation, and photophosphorylation coupled to NADP reduction with ascorbate-DPIP serving as the electron donor. Because of the pivotal role of ATP in cellular metabolism, it is conceivable that interference with ATP generation could be a major (but not necessarily the only) mechanism through which the herbicidal activity of C-9122 is expressed.

Trifluralin a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) applied at 1.12 kg/ha inhibited lateral root development on field-grown pecan (Carya illinoensis (Wang.) K. Koch) seedlings. In a greenhouse study, inhibition of lateral roots, club-shaped radicles, and restricted penetration of tap roots resulted when pecans were planted in soil treated with 1.0 ppm trifluralin. When pecans were planted above soil treated with trifluralin, normal root development occurred only in the soil which had not been treated. Lateral roots were inhibited in the trifluralin-treated soil. Pecan nuts from trifluralin plots were smaller than those collected from controls, but other factors of quality were statistically equal or superior to nuts harvested in plots which had been treated with 2-chloro-4,6-bis-(ethylamino)-s-triazine (simazine) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). The smaller nut size was attributed to lateral root inhibition by trifluralin early during nut development.

Simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), and a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) were evaluated for weed control in pecan (Carya illinoensis (Wang.) K. Koch) orchard establishment. Maximum weed control and tree growth occurred in plots treated with diuron and simazine applied at 3.0 and 4.0 lb/A, respectively. During the second year, phytotoxic symptoms were observed in plots which had received superimposed annual treatments of diuron at 3.0 lb/A, but none appeared in simazine or trifluralin plots.

A recirculating sprayer was developed for applying herbicides in row crops to weeds taller than the crop. Herbicide solutions are applied through solid stream nozzles above and at right angles to the rows, so that a trap collects herbicide spray not deposited on weeds. Trapped solution is returned to the original spray tank by gravity flow. Good to excellent control of pigweed (Amaranthus spp.), cocklebur (Xanthium spp.), and sesbania (Sesbania spp.) was obtained with (2,4-dichlorophenoxy)acetic acid (2,4-D) while monosodium methanearsonate (MSMA) effectively controlled johnsongrass (Sorghum halepense (L.) Pers.). The better treatments increased the harvested yields of soybeans (Glycine max (L.) Merr., var. Lee) 6 to 8 bu/A when weed infestations were severe at time of treatment. Use of the sprayer permits treatment with herbicides normally considered too toxic to crops, and reduces costs through recovery of most of the herbicide solution that is not intercepted by weeds.

Seeds of Pennsylvania smartweed (Polygonum pennsylvanicum L.), quackgrass (Agropyron repens L. Beauv.), yellow foxtail (Setaria lutescens L. Beauv.), and wild mustard (Brassica kaber (DC) L. C. Wheeler) were studied to determine if histochemical differences existed in seeds of dormant and non-dormant weed species. The hulls (seedcoat) of yellow foxtail and seedcoats of wild mustard and quackgrass had distinct inhibitory effects on germination. Endosperm tissue in wild mustard and Pennsylvania smartweed also inhibited embryo growth in these species. Results obtained from specific staining techniques on seed sections 10μ thick for identification and determination of distribution of proteins, lipids, carbohydrates, and lignin in dormant and germinating seeds suggested that possible mechanisms of seed dormancy are: (a) lower protein content in seed tissues of wild mustard; (b) higher lignification in hull of foxtail and endosperm of Pennsylvania smartweed; (c) lower sterol content in embryo of wild mustard and Pennsylvania smartweed; (d) high cellulose content in hull of foxtail and endosperm of Pennsylvania smartweed. Excised embryos from dormant seeds of Pennsylvania smartweed showed a measurable amount of growth in White's standard agarnutrient. Germinating embryos of wild mustard and quackgrass were larger than those in dormant seeds; therefore, immaturity of embryos might contribute to dormancy in these species.

Nine field trials were carried out during 1968 and 1969 to study selective weed control in sugarbeets (Beta vulgaris L.) by preemergence and postemergence applications. The trials were conducted at various regions of Israel, under a wide range of climatic and edaphic conditions. Among the preemergence treatments, the herbicide 1-methyl-3-(2-benzothiazolyl)-urea (hereinafter referred to as benzthiazuron) gave adequate weed control and selectivity to sugarbeets. However, when heavy infestation with grasses was present, an addition of isopropyl carbanilate (propham) was needed to increase the spectrum of weed control. A preemergence application of 1-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon) on each side of the drill-row of sugarbeets together with an over-band application of benzthiazuron or 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) improved weed control. Among postemergence treatments, a mixture of pyrazon and propham gave excellent broad-spectrum weed control. Applying this combination in an emulsion with a non-phytotoxic oil considerably improved weed control.

Seeds of honey mesquite (Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell) were germinated and grown in aqueous solutions of the sodium salt of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) or the potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram). Elongation of germinating seedling hypocotyls and roots was progressively inhibited by increasing concn of each herbicide up to about 1 or 2 mg/L the first 2 days. After 5 and 10 days, progressively more inhibition occurred at 5 to 10 mg/L of 2,4,5-T and 1 to 2 mg/L of picloram. Four-month-old honey mesquite seedlings were treated with foliar sprays of the 2-ethylhexyl ester of 2,4,5-T or the potassium salt of picloram. Both herbicides caused curling of the stem tip, death of the growing point, cracking below the leaf, and increased numbers of lateral roots. Both herbicides caused phellem cells to enlarge radially, inner cortext and phloem parenchyma to proliferate, and xylem vessels to lignify without enlarging. Starch granules disappeared from treated plants within 8 days and re-occurred in treated plants only 53 days after spraying. Picloram was slightly more toxic to honey mesquite seedlings than 2,4,5-T.

A somewhat modified version of Lambert's quantitative treatment of the influence of soil-moisture content on herbicidal activity has been applied to 4-amino-3,5,6-trichloropicolinic acid (picloram) behavior in soil. The bioactivity of picloram decreased as the soil-moisture content was increased. This was due to the effect of varying soil-moisture levels on the concentration of picloram in the soil-water phase.

The preemergence herbicidal activities of 10 4-(methylsulfonyl)-2,6-dinitro-N,N-variously substituted anilines were determined on four plant species at four equimolar concentrations in nutrient solution. Several analogs were as active or slightly more active than 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline [nitralin]. Most amino groups on these compounds were of a mixed nature. Preemergence toxicity decreased when the N-substituents contained more than six carbons or less than five.

Seven herbicides were applied for selective weed control on three different seedling stands of five cool-season grasses. The herbicides were evaluated for their influence on weed control, grass establishment, and first crop grass seed production. These experiments indicate that 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) was outstanding in selective control of broadleaf weeds in seedling grass stands. Two other herbicides, 3,6-dichloro-o-anisic acid (dicamba) and 6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinediium ion (diquat) were valuable under most conditions. The remaining herbicides—(2,4-dichlorophenoxy)acetic acid (2,4-D), 2-sec-butyl-4,6-dinitrophenol (dinoseb), 2,3,6-trichlorobenzoic acid (2,3,6-TBA), and 1-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon)—were satisfactory for selective weed control under some conditions, but their effects were not uniform for the different species and plantings.

Growth and percentage survival was measured for slash pine (Pinus elliottii Engelm.), shortleaf pine (P. echinata Mill.), Virginia pine (P. virginiana Mill.), and loblolly pine (P. taeda L.) seedlings treated with: (a) 0.07 to 4.48 kg/ha 2,6-dichlorobenzonitrile (dichlobenil), (b) 0.28 to 8.96 kg/ha 1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea (fluometuron), or (c) 1.12 to 8.96 kg/ha S-propyl butylethylthiocarbamate (pebulate). Herbicide toxicity to pine seedlings was in order of dichlobenil > fluometuron > pebulate. Acceptance of mild growth reduction would permit pebulate utilization in seed bed nurseries.

Purple nutsedge (Cyperus rotundus L.) develops as a series of shoots connected by bulbs, rhizomes, and tubers. The leaves contain parallel, collateral vascular bundles with the majority of the photosynthetic cells concentrated in the sheathing girdle around each bundle. The upper leaf surface consists of a single layer of large epidermal cells covered by a thick cuticle. Stomates occur only in the lower surface. The vascular bundles vary from collateral to amphivasal as they pass from the leaves through the bulb into the rhizomes and tubers. Newly developing rhizomes and tubers appear white and fleshy with a parenchymatous epidermis and cortex. Mature rhizomes appear brown and wiry with a deteriorated outer cortex and a lignified inner cortext and endodermis. Tubers and bulbs form similarly at the rhizome apices with each accumulating starch. The interconnecting vascular system appears to remain intact throughout the growing season.

Field studies of seasonal sprouting of wild garlic (Allium vineale L.) bulbs showed that all the soft offset, aerial, and central bulbs sprouted, but only 20 to 34% of the hardshell bulbs sprouted after a short after-ripening period. Each fall, a percentage of the remaining hardshell bulbs sprouted, but after 4 years 16% of the hardshell bulbs were still dormant. Embryonic shoots of all bulb types sprouted when excised following the after-ripening period. In addition to a short after-ripening period, hardshell bulbs had a prolonged dormancy due to some mechanism which resides in, or was controlled by, the tissue surrounding the embryonic shoot.