The concept of controlled release of herbicides has created in some workers expectations beyond possibility. In this theoretical paper, we examine the results to be expected based on a simplistic model. The purpose of the development is that it serve as a guide to experimentation and as a stimulant to such experimentation by revealing the possible advantages which may occur.

Crystallization of methyl m-hydroxycarbanilate m-methyl-carbanilate (phenmedipham) occurred from aqueous emulsions of the commercial formulation when dilutions exceeded one part of the formulation to 30 parts water. Dilutions greater than 1 to 30 accelerated crystallization and increased the quantity of phenmedipham that crystallized out. Mechanical agitation increased the rate of crystallization during the first 12 hr after initial mixing. Low water temperature increased the rate of crystallization and total amount of phenmedipham that crystallized out. Phenmedipham crystallization was not altered by water hardness or pH over the range 4.0 to 8.0. Simulated refilling of a partially empty spray tank before adding formulated phenmedipham produced considerable crystallization, whereas adding formulated phenmedipham before adding water minimized crystallization. The solvent used in the commercial formulation to dissolve phenmedipham is partially soluble in water. The partitioning of this solvent into the aqueous phase of the emulsion explains crystallization of phenmedipham.

Metabolism of the herbicide 2-(α-naphthoxy)-N,N-diethyl propionamide (R-7465) by tomato plants (Lycopersicon esculentum Mill. ‘Mechanical Harvester’) was investigated. Ring-labeled R-7465-14C was taken up rapidly by the roots and distributed throughout the leaves within 8 hr. R-7465 was converted primarily into water soluble metabolites. The principal metabolite was identified as a hexose conjugate of 2-(α-naphthoxy-4-hydroxy)-N,N-diethyl propionamide. This metabolite represented 47% of the soluble radioactivity in the plant. A different hexose conjugate of 2-(α-naphthoxy-4-hydroxy)-N,N-diethyl propionamide together with a hexose conjugate of 2-(α-naphthoxy-4-hydroxy)-N-ethyl propionamide accounted for another 22% of the radioactivity. Nonmetabolized R-7465 was found to represent only 5% of the total soluble radioactivity. Other identified metabolites included 2-(α-napthoxy)-N-ethyl propionamide, 2-(α-naphthoxy-5-hydroxy)-N,N-diethyl propionamide, and 1,4-naphthoquinone. None of these metabolites individually represented more than 3% of the soluble radioactivity in the plants. Ring hydroxylation and N-dealkylation appeared to be the initial steps in detoxification of R-7465 followed by conjugation with sugars.

Exposure of pea plants (Pisum sativum L. ‘Little Marvel’) to vapors of S-(2,3-dichloroallyl)diisopropylthiocarbamate (diallate) increased the subsequent foliar uptake of 14C-labeled herbicides. Increased amounts of 14C-activity were found in the tissues of diallate-treated plants as compared to the controls when herbicides were applied to the leaves as aqueous solutions or embedded in agar blocks. The herbicides were (2,4-dichlorophenoxy)acetic acid-1-14C (2,4-D), uniformly ring-14C 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine),trichloroacetic acid-2-14C (TCA), and ethylene-14C 6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinediium ion (diquat). The increased movement of herbicides into diallate-treated peas was primarily attributed to a reduction of epicuticular lipids on leaves of the treated plants.

Varying concentrations of benzyladenine (BA), indoleacetic acid (IAA), gibberellic acid (GA), abscisic acid (ABA), and 2-chloroethylphosphonic acid (ethephon) were used to induce sprouting of dormant purple nutsedge (Cyperus rotundus L.) tubers. BA at 50 to 300 ppm stimulated sprouting. The continuous presence of BA during the sprouting period was necessary to give significant sprout stimulation. Neither IAA at 1, 10, or 100 ppm; GA at 10, 100, or 1000 ppm; nor ethephon at 10, 100, or 1000 ppm had stimulatory effects on sprouting. ABA counteracted the stimulatory effects of BA when tubers were treated with ABA following BA treatment. Sprouting was markedly greater at 33 C day, 25 C night than at 24 C day, 17 C night. Growth of plants originating from tubers pretreated with 100 ppm BA did not differ significantly from the controls. Sustained BA applications at 100 and 200 ppm produced numerous plants with tuft-type growth habit, delayed flowering, and reduced the number of inflorescences. Numerous short, diageotropic rhizomes were produced.

The effects on leucine uptake and its incorporation into protein by cucumber (Cucumis sativus L. ‘Ashley’) cotyledon tissue following treatments with 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) were determined. Prometryne decreased 14C-leucine uptake both in the light and in the dark. Prometryne decreased leucine incorporation into protein only when the discs were also exposed to over 4 hr of light. Percent of absorbed leucine incorporated into protein was increased by a 4 hr exposure in the light to 10−4M prometryne following a 24-hr dark exposure to this same concentration. Similar exposure to 10~5M prometryne had no effect. Percent of leucine incorporated into protein was decreased by 10-5M prometryne following a 24 hr exposure to this same concentration in the light. However, under these conditions 10−4M prometryne had no effect. It is speculated that the increased percentage of leucine incorporated into protein may be related to increased availability of the absorbed leucine for use in protein synthesis rather than an effect of the herbicide on the rate of protein synthesis

Grain sorghum (Sorghum bicolor (L.) Moench ‘RS 671’) was grown during 1969 and 1970 in competition with two other members of the same species, wild cane and Kansas Orange forage sorghum, transplanted at various densities along grain sorghum rows. All densities of wild cane and Kansas Orange significantly reduced both grain and fodder yields of grain sorghum. Grain yield was highly and positively correlated with leaf area, culm length, culms per plant, panicles per culm, seeds per panicle, and amount of light received at the grain sorghum canopy; and grain yield was negatively correlated with plant factors that benefited wild cane and Kansas Orange. Grain yield did not correlate with either plants per hectare or seed weight. Panicle size was most important in determining grain yield. Kansas Orange reduced grain yields more than did wild cane in 1969. During 1970, with less favorable rainfall, grain sorghum responded similarly to both transplanted weed types.

Species of green algae seldom grew as well in two-species cultures with other green algae, or with blue-green algae, as when cultured alone. Several species of algae apparently excreted one or more substances into the medium which inhibited the growth of the second species. Inhibition of growth of green algae was particularly great in two-species cultures with the blue-green algae, Oscillatoria rubescens Decandolle, Anabaena flos-aquae (Lyngbye) Breb., Microcystis aeruginosa Kutz., and Coccochloris peniocystis (Kutz.) Dr. and Daily. Green algae also failed to grow at normal rates in media prepared from filtrates of water from ponds which contained blooms of blue-green algae. Inhibitory substances are apparently an important factor in the development and persistence of relatively unialgal blooms of various species.

Soybean [Glycine max (L.) Merr.] seedlings grown in the greenhouse in a Wisner loam soil showed a greater reduction in plant growth from an application of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) if fertilized with 224 kg/ha of P2O5. This interaction was not observed in tolerant corn (Zea mays L.) seedlings in any of the four soils studied. The injury in sand culture of high levels of atrazine to soybean, corn, pea (Pisum sativum L.), and sorghum (Sorghum vulgare L.) seedlings increased when high levels of P (phosphorus) were present. The high level of P did not increase atrazine uptake, and in corn atrazine did not increase 32P uptake. Plants receiving the atrazine-phosphate combination exhibited a higher rate of respiration providing a possible basis for the observed interaction. The high rate of P application slightly reduced atrazine metabolism by corn and pea but not by soybean and sorghum.

Hairy galinsoga [Galinsoga ciliata (Raf.) Blake] and smallflower galinsoga [G. parviflora Cav.] are widespread weeds in New York State. Freshly harvested achenes (seed) are not dormant and germinate in the field from early May until frost. Rate of germination but not final total percentage was stimulated by alternating temperature, with the fastest rate being at 30 C day and 20 C night and with a 16-hr photoperiod and 11,000 lux of light. Some seed in each seed-lot required light for germination. Both species were day-neutral with respect to flowering. Smallflower galinsoga produced its first flower after node seven and hairy galinsoga after node six on the main axis 6 to 8 weeks after germination. Decreasing light intensity 83% decreased fresh weight.

The selectivity of 4-chloro-2-oxobenzothiazolin-3-ylacetic acid (benazolin) in wild mustard [Brassica kaber (DC.) L. C. Wheeler var. pinnatifida (Stokes) L. C. Wheeler], turnip rape (Brassica campestris L. ‘Echo’), and rape (Brassica napus L. ‘Target’) was studied. On an ED50 basis wild mustard was 19 and 32 times more susceptible to foliar-applied benazolin than was turnip rape and rape, respectively. The addition of surfactant increased the toxicity of benazolin to the Brassica species. Benazolin was less selective when applied via roots. Selectivity was further studied on the bases of differential spray retention and foliar penetration. Rape retained less spray than did wild mustard and turnip rape. The inclusion of surfactants in formulations increased spray retention by rape. Less 14C-benazolin penetrated leaves of the rape species as compared to wild mustard. Surfactant enhanced penetration of 14C-benazolin into leaves of the three species. Leaf surface features which resulted in high spray retention and rapid penetration of benazolin partly explained the susceptibility of wild mustard. The variation in tolerance between the two rape species was attributed to differential spray retention.

The fate of 4-chloro-2-oxobenzothiazolin-3-ylacetic acid (benazolin) in wild mustard [Brassica kaber (DC.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler], turnip rape (Brassica campestris L. ‘Echo’), and rape (Brassica napus L. ‘Target’) was investigated with the aid of 14C-benazolin. The label was more mobile in wild mustard than the rape species following leaf treatment and accumulated in young leaves, stem, and stem apex. The label was also found in foliage after root treatment. In both cases, the translocated label was primarily that of 14C-benazolin, implying phloem and xylem transport. The susceptibility of wild mustard and tolerance of the rape species to foliar-applied benazolin can be partly explained by different rates of transport to susceptible meristematic sites. Root exudation of the label following leaf treatment was greater in wild mustard than in the rape species and was not correlated with selectivity. Labeled benazolin was rapidly metabolized by the Brassica species to four derivatives which appear to be less toxic than benazolin. Specific differences in metabolism were not sufficient to explain selectivity. Negligible amounts of 14CO2 were released by the three species following treatment with 14C-benazolin.

Mucilage was detectable on the seeds of 8% of 233 plant species collected in Nevada and adjacent California. Mucilaginous species were restricted to the Cruciferae, Euphorbiaceae, Labiatae, Onograceae, and Plantaginaceae. Many of the species with mucilaginous seed coats are weeds. Mucilage may influence seed dispersal and greatly influences moisture relations during germination.

Bromacil (5-bromo-3-sec-butyl-6-methyluracil) was much more effective in killing post oak (Quercus stellata Wangenh.) and blackjack oak (Q. marilandica Muenchh.) trees than 4-amino-3,5,6-trichloropicolinic acid (picloram) when applied to soil at 5.6 and 11.2 kg/ha in spots, bands, or by broadcasting. When applied at 5.6 kg/ha in bands or broadcast, picloram effected better crown reduction than bromacil on mockernut hickory (Carya tomentosa Nutt). Differences between rates and methods of applying bromacil were small. While bromacil was superior on the prevalent overstory species, post oak and blackjack oak, picloram excelled on the most numerous understory plants.

Chloroplasts, isolated from fresh spinach (Spinacia oleracea L.) were treated with four concentrations of each 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) or 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) to determine the influence of these herbicides on the free fatty acid content in isolated chloroplasts. The treated chloroplast solutions were sampled at 0, 5, 15, 30, 60, and 120 min following treatment. Results indicated that most herbicide treatments increased free fatty acid content in isolated chloroplasts when compared with the zero concentration treatments. The increased fatty acid content was similar for most concentrations of simazine and atrazine. Results of individual fatty acid analyses indicated that the increase in total fatty acids was a result of increases in concentration of unsaturated rather than saturated fatty acids.

In pot culture experiments in the greenhouse, rice [Oryza sativa L. ‘Nova 66’], red rice [O. sativa L.], barnyardgrass [Echinochola crus-galli (L.) Beauv.], broadleaf signal-grass [Brachiaria platyphylla (Griseb.) Nash], northern jointvetch [Aeschynomene virginica (L.) B.S.P.], and hemp sesbania [Sesbania exaltata (Raf.) Cory] were seeded 1.3, 2.5, 5.1, and 10.2 cm deep in Crowley silt loam which was held at field capacity (24% moisture), saturation (34% moisture), or submerged 1.3 or 5.1 cm. At field capacity and saturation all species seeded 1.3, 2.5, and 5.1 cm deep emerged and grew well; seeding the plants 10.2 cm deep reduced emergence and growth. Submergence of the soil controlled all weeds effectively but reduced emergence and growth of dry-seeded rice.

The bacterially produced phytotoxin 2-amino-4-(2-amino-3-hydroxypropoxy)-trans-3-butenoic acid (rhizobitoxine) was tested for herbicidal properties in comparison with 3-amino-s-triazole (amitrole) and 4-chloro-5-(dimethylamino)-2-(a,a,a,-trifluro-m-tolyl)-3(2H)-pyridazinone (metflurazone). In postemergence tests with various plant seedlings, rhizobitoxine and amitrole were approximately equal in phytotoxicity on a weight basis, and both were generally much more phytotoxic than metflurazone. Phytotoxicity of rhizobitoxine varied markedly among grass species. Sorghum (Sorghum bicolor (L.) Moench ‘Hegari’) was very sensitive to rhizobitoxine, large crabgrass (Digitaria sanguinalis (L.) Scop.) was moderately sensitive, wheat (Triticum aestivum L. ‘Thorne’) was tolerant, and Kentucky bluegrass (Poa pratensis L.) was very tolerant. In contrast, amitrole was almost as phytotoxic to bluegrass as to large crabgrass, and metflurazone had little effect on either. In a preemergence test with mustard (Brassica japonica (L.) Coss. ‘Southern Giant Curled’) rhizobitoxine was as effective as amitrole, when compared on a molar basis, in inhibiting chlorophyll synthesis and root growth and was superior in retarding overall growth and development.

Weed control and sugarbeet (Beta vulgaris L.) injury from applications of methyl m-hydroxycarbanilate m-methyl-carbanilate (phenmedipham) were influenced by additives, volume of additive, and species in both field and greenhouse experiments. Oils were more effective than the surfactant as additives to phenmedipham on green foxtail (Setaria virdis (L.) Beauv.), yellow foxtail (Setaria glauca (L.) Beauv.), redroot pigweed (Amaranthus retroflexus L.), or common lambsquarters (Chenopodium album L.). Herbicidal activity of phenmedipham on kochia (Kochia scoparia (L.) Schrad.) or wild mustard (Brassica kaber (D.C.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler) was not enhanced by any additive. Linseed oil (2.34 L/ha) enhanced the herbicidal activity of phenmedipham on green foxtail, yellow foxtail, and redroot pigweed more than petroleum (2.34 L/ha) or sunflower (Helianthus annus L.) oil (2.34 or 9.35 L/ha). However, linseed oil reduced the herbicidal activity of phenmedipham on kochia.

The absorption of 14C-labeled herbicides by soybean (Glycine max (L.) Merr. ‘Lee’) seed from aqueous solutions and treated soil was investigated. A comparison of the absorption of the various herbicides from aqueous solution showed that differences existed in the rate and amount of herbicide absorbed by the seed. Calculations showed that the concentration of herbicides at the seed coat surface varied with absorption time which indicated that the permeability of the soybean seed to these herbicides changed during the absorption process. The rate of absorption of isopropyl m-chlorocarbanilate (chlorpropham) and 2-chloro-4-(ethylamino)-6-(iso propylamino)-s-triazine (atrazine) by soybean seed in soil was rapid for the first 4 hr and then decreased steadily until the event of germination at which time the rate increased. When the amount absorbed by the soybean was compared with that predicted by the perfect sink equation, it was found that the soybean was a better sink during the first few hours than afterwards. The amount of herbicide moved to the seed in the imbibed water could not account for the total amount of chlorpropham absorbed indicating considerable contributions from diffusive transport. Only during the initial 4-hr period was uptake of atrazine greater than that moved to the seed by mass flow.

Tubers of yellow nutsedge (Cyperus esculentus L.) were buried in the field 2.5 to 30.5 cm below the surface in November 1969 and 1970 at Urbana, Illinois. In both years, shoots began to emerge the following May and continued emergence until July. Very few additional shoots emerged after July. Shoots emerged from less than 2% of the tubers buried at 2.5 cm; the maximum number of shoots emerged from tubers at the 10.2 and 20.3-cm depths. Tubers at the 2.5 and 5.1-cm depths were more susceptible to winterkill than tubers at lower levels, probably because of the differences in soil temperature at these levels during cold periods. Kinetic analysis of laboratory-determined tuber viability for periods up to 22 months revealed that the half-life was 4.4 and 5.7 months for tubers buried at 10.2 and 20.3 cm, respectively. The extrapolated minimum temperature required for initiation of tuber germination in the laboratory was 12 C. This temperature minimum could not readily be related to initial shoot emergence in the field. The temperature at which 50% of the tubers survived a cold treatment for 4 to 48 hr was −7 C.