Results from both growth chamber and field experiments indicate that root absorption of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) applied postemergence to small broadleaf weeds is not a requisite for their control. Though broadleaf weeds absorb toxic quantities of atrazine from wet soil, they can be killed by foliar absorption alone because all of their meristems are exposed to a foliar spray. They are particularly sensitive when foliar penetration is enhanced by high relative humidity and wet foliage.

The release of 3-amino-2,5-dichlorobenzoic acid (amiben), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), isopropyl m-chlorocarbanilate (chlorpropham), S-ethyl dipropylthiocarbamate (EPTC), and 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) from excised soybean (Glycine max (L) Merr., var. Chippewa) roots following uptake of the herbicides from solutions for 1 hr was studied. Rates of release of herbicides into water were rapid with at least 30% of that taken up being released during the first 30 min. Herbicide X time and herbicide X concentration interactions were highly significant. In most instances, slow release continued for 4 hr, which was the duration of the experiment. Use of herbicide or nutrient solutions as release solutions did not significantly change the amounts of herbicides released. It was concluded that herbicide molecules released after 1 hr uptake were those that had diffused out from free space rather than those released from uptake or adsorptive sites.

The fate of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) in greenhouse-grown juvenile corn (Zea mays L., var. N. J. 9), soybean (Glycine max (L.) Merr., var. Kent), and crabgrass (Digitaria sanguinalis (L.) Scop.) was investigated. Linuron entered the plants from nutrient solution with the water absorbed. A small but measurable amount of the herbicide was found in the tissue as 3-(3,4-dichlorophenyl)-1-methoxyurea and as 3,4-dichloroaniline. A materials balance between linuron uptake and acetone extractable linuron plus metabolites found could not be achieved. Evidence is presented for the presence of “bound” linuron which accounted for from 15 to 25% of the herbicide absorbed.

Apical dominance, as maintained by above-ground foliage or individual rhizome apexes, is very marked in johnsongrass. (Sorghum halepense [L.] Pers.). Axillary bud development in single-node segments excised from individual rhizome pieces was least at the proximal end with increasing activity toward the distal end (apex end). Within serially excised, multi-node sections, axillary bud development was least at the proximal end and greatest at the distal end, and there was an overall increase in bud activity from proximal to distal ends of the rhizome pieces. This was true irrespective of whether the multi-node sections were cultured vertically (with buds oriented above the nodes) or were inverted (with buds oriented below the nodes). Lateral rhizomes exerted a dominating influence on the development of axillary buds from their parent rhizomes, as did the apical meristems of the parent rhizomes.

Seeds of honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.] planted immediately after extraction from mature seed pods germinated 84% and after burial overwinter germinated 97%. Seedling emergence was limited to depths of less than 4 inches. Seedling roots developed adventitious buds capable of producing new shoots about 5 weeks after emergence. Preemergence and early postemergence treatments with 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) gave 100% control of seedlings in greenhouse experiments. Heavy natural infestations of honeyvine milkweed in corn (Zea mays L.) were controlled 95% with 2,4-(dichlorophenoxy)acetic acid (2,4-D) at 0.5 lb/A when treatments were made before the weed started climbing on corn stalks. Later treatments required higher rates of 2,4-D, the use of 2,4,5-(trichlorophenoxy)acetic acid (2,4,5-T), or the combination of 2,4-D plus 2,4,5-T for adequate control.

A split-stem technique was devised for the rapid evaluation of herbicide effect on root growth and herbicide translocation. Four rows of adventitious root initials were prominent on the stem of red kidney bean [Phaseolus vulgaris L.] seedlings. They were excised at the soil level above the vascular plate. Excised stems were longitudinally split for a distance of 75 to 90 mm leaving two rows of root initials on each stem portion. Split-stem halves were immersed in herbicide-nutrient and nutrient solutions, respectively, contained in paired 25 by 150-mm test tubes. Subsequent plant growth and development of treated plants reflected effects of the herbicide on root growth. Herbicide translocation often was indicated by abnormalities of growth of plant tissues remote from the herbicide solution.

We constructed an injector-planter which simultaneously plants seed and injects herbicides. It effectively placed volatile herbicides under the soil surface in precise spatial relationship to crop seed. Rolling coulters, placed in front of the herbicide delivery system, enabled the unit to cut through trash better than previously-described equipment and, therefore, perform effectively under a wider range of soil conditions.

Endosperm dry weight, protein, and fat losses accompanied rapid radicle growth of velvetleaf (Abutilon theophrasti Medic.) between 12 and 36 hr of germination at 31 C. Cotyledonary reserves were mobilized after 36 hr. Isocitrate lyase activity sedimented with a particulate fraction in varying degrees, but maximal activity developed at times coincident with fat mobilization. Respiration of excised endosperms reached maximal rates shortly after radicle emergence. The actions of hydrogen cyanide, carbon monoxide, and 2,4-dinitrolphenol indicated that respiration of endosperms excised from imbibed and germinated seed was due to cytochrome oxidase activity, and was coupled to phosphorylation.

Plant heights and seed yields of oats (Avena sativa L.), corn (Zea mays L.), and soybeans (Glycine max (L.) Merr.) were lower where these crops followed a heavy infestation of quackgrass (Agropyron repens (L.) Beauv.) than when they followed oats or fallow land. Application of ammonium nitrate (280 kg/ha) only partially corrected the adverse effect on yield of a previous quackgrass infestation. The effect of quackgrass persisted through the second growing season as measured by height and yield of wheat (Triticum aestivum L.) and compared with wheat after oats, corn, soybeans, or fallow, but the effect of nitrogen applied the first year only did not persist through the second year.

In the presence of relatively high but non-toxic levels of phosphate, the suppression of corn (Zea mays L.) or squash (Cucurbita maxima Duchesne) seedling growth in the dark by 3-amino-2,5-dichlorobenzoic acid (amiben) or 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) was enhanced. This effect was not due to increased uptake of either herbicide in the presence of the phosphate by roots of corn, squash, soybeans (Glycine max (L.) Merr.), or redroot pigweed (Amaranthus retroflexus L.). A proportional decrease in herbicide uptake with increasing herbicide concentration was most evident for amiben and atrazine uptake by the roots of soybean plants grown in the light.

We surveyed soils that produce rice (Oryza Sativa L.) at the University of Arkansas Rice Branch Experiment Station at Stuttgart, Arkansas, to determine whether residues of 3, 3′,4,4′-tetrachloroazobenzene (hereinafter referred to as TCAB) accumulated with repeated applications of 3′,4′-dichloropropionanilide (propanil). We sampled Crowley silt loam with known histories of propanil application to determine the effect of depth, rate, and time on TCAB formation. Propanil and TCAB were measured by electron capture gas chromatography. Low concentrations of TCAB (<0.2 ppm) generally were detected in the surface 0 to 10.1-cm layer of soil receiving applications of propanil at rates of 6.7 kg/ha. Concentration and occurrence of TCAB decreased with increasing time and depth in soil.

A variable-dosage sprayer system with a toroidal mixing chamber was constructed and used successfully in evaluation of equipment and herbicides for 2 years at the U. S. Cotton Research Station, Shafter, California. The primary advantage of this system compared to other systems is that the dilution rate is the same as predicted by theory over a wide range of conditions. Therefore, the rate of dilution can be calculated for different combinations of nozzles, or metering orifices, pressures, and spray rates without the need for direct calibration. Since the inside of the chamber is visible, some application errors are avoided and others detected that are not known with other systems. The system should be adaptable to a wide range of plot sizes and half-dosage distances by changing the volume of the toroid, the limiting factor being the availability of proper size propellers and motor.

Versatile mist chambers, framed with aluminum and glass and having access from top and sides, permit culture of an extensive number of, and different types of, vegetative plant organs as well as seeds and plant pathogens. Pneumatic atomizing nozzles are staggered to permit division of the chamber, and the spray emitted can be regulated from each nozzle. The amount of water vapor emitted is regulated by changing the air pressure or siphon height. Gauge-monitored pressure regulators and solenoid valves control the air and spray system. Timing devices can be used to inject water vapor at desired intervals. Air passing through a condensation tube is recycled past cone heaters, providing temperature from ambient to 90 F, and a duct and baffle system provides uniformity of temperature throughout. A combination recorder and controller maintains the desired temperature.

We compared various rates of 2,3,6-trichlorobenzoic acid (2,3,6-TBA), 3,6-dichloro-o-anisic acid (dicamba), and 4-amino-3,5,6-trichloropicolinic acid (picloram), and various methods of application on persimmon (Diospyros virginiana L.). Single rates of 2,3,6-trichlorophenylacetic acid (fenac) and (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) also were included. In one experiment, 8 lb/A of dicamba injected into the soil killed significantly more persimmon than the same rate applied to the soil in 4-inch bands. Otherwise, with given herbicides at comparable rates, defoliation and mortality of persimmon were similar with all methods of soil application. Foliage applications of dicamba or picloram at relatively low rates caused defoliation and mortality of persimmon equal to soil applications of dicamba or picloram at high rates. Dicamba was more effective than equal rates of 2,3,6-TBA for killing persimmon. Picloram at 2 lb/A and dicamba at 4 lb/A, as foliage applications, defoliated and killed persimmon to nearly the same extent. Fenac was relatively ineffective for killing persimmon. Soil treatments with picloram and dicamba killed 22 to 30% more persimmon when applied in summer than when applied in spring. Spring and summer foliage applications of dicamba and 2,3,6-TBA caused similar defoliation and mortality of persimmon, but mortality of persimmon was somewhat higher with spring than with summer foliage applications of picloram. Summer basal treatment with 2,4,5-T killed more persimmon than spring basal treatment.

In three field experiments at the University of Arkansas Rice Branch Experiment Station, Stuttgart, S-ethyl hexahydro-1H-azepine-1-carbothioate [molinate] at 2, 3, 4, and 6 lb/A was applied into the flood water 3, 6, 11, and 17 days after emergence of rice [Oryza sativa L.] and barnyardgrass [Echinochloa crusgalli (L.) Beauv.]. Molinate at 2 or 3 lb/A applied 3, 6, 11, or 17 days after emergence of rice and barnyardgrass, when weeds ranged from the one-leaf to tillering stages, provided acceptable weed control and rice tolerated these treatments satisfactorily. A rate of 3 lb/A frequently controlled barnyardgrass better than 2 lb/A, and usually was as effective as 4 or 6 lb/A. Sometimes, rates of 4 or 6 lb/A, applied 11 or 17 days after rice emergence, injured the crop moderately to severely and reduced grain yields.

In eastern Washington Dalmatian toadflax (Linaria dalmatica (L.) Mill) produces seeds for about 3 months, beginning in early July, with over 95% produced during the first 5 weeks. A large plant will produce a half million seeds under good conditions. Seeds are sharply angular, slightly winged, and 1 to 2 mm long. Approximately 7,000 weigh 1 g. Seeds are spread by wind and browsing animals. Some seeds will germinate under laboratory conditions the same season in which produced, but germination from dry storage increases for 2 to 3 years, with a periodic low in November and a high in April. Over 90% germination is obtained with 2 to 3-year-old seeds in the laboratory. Germination in the field occurs in both spring and fall, and seedlings can emerge from a soil depth of 2 to 2.5 cm.

The herbicide, 2,6-dichlorobenzonitrile (dichlobenil), applied to the soil surface at 2 lb/A controlled dodder (Cuscuta spp.) and other weeds for 4 to 6 weeks in the field, and did not injure established alfalfa (Medicago sativa L.) significantly. Soil incorporation increased the herbicidal effect of dichlobenil on alfalfa and dodder, but alfalfa injury was increased more than dodder control. Dichlobenil was effective when applied just before sprinkler irrigation, or on moist soil after irrigating. In the greenhouse, dichlobenil vapors moved from a wettable powder formulation mixed with moist soil or from granules on the surface of moist soil, and killed dodder in adjacent untreated soil.

We compared foliage sprays of (2,4-dichlorophenoxy)acetic acid (2,4-D) and 4-amino-3,5,6-trichloropicolinic acid (picloram) for control of Macartney rose (Rosa bracteata Wendl.) applied with ground equipment and airplane. Picloram at 0.5 lb/A was more effective than 2,4-D at 2 lb/A at all dates of application on mowed roses; however, time of application was important. Picloram was most effective in late April and early May, but 2,4-D was most effective in late May and early June. Combinations of picloram and 2,4-D were effective from late April to late June. If mowing is followed by foliage treatment of 2,4-D, the interval between mowing and spraying should be at least 1 year if mowing is done in the spring. The interval between mowing and spraying was not critical when picloram was applied not later than early May. Mowing in the summer reduced the effectiveness of subsequent 2,4-D and picloram treatments applied the following year. Aerial applications of 2,4-D and picloram on undisturbed Macartney rose plants in the fall were not as effective as spring applications; however, two successive fall applications of picloram at 1 lb/A resulted in control equivalent to that obtained with a single 2 lb/A application in spring.

A relatively inexpensive, cold-temperature germination bar was constructed. The optimum temperature gradient of the bar for our low-temperature seed germination studies ranged from −4 to 11 C. An independent compressor and a chest-type deep freeze were compared for cooling sources. Alumnium foil Petri dishes were developed for use on the bar.

Phytase activity increased 2 to 3 fold in barley (Hordeum vulgare L.), 6 fold in corn (Zea mays L.), and 12 fold in squash (Cucurbita maxima Duchesne) seedlings 2 days after the initiation of germination in the dark. Most of the phytase was found in the embryo of the seed, presumably in the cotyledon(s). Gibberellic acid and benzyladenine supplied during germination exerted only limited influence on the development of phytase in these seedlings. Of the herbicides studied, only sodium arsenite exerted an influence on phytase activity per se that was of physiological significance. The presence of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 3-amino-2,5-dichlorobenzoic acid (amiben), 2-chloro-N-isopropylacetanilide (propachlor), 2,6-dichlorobenzonitrile (dichlobenil), or α,α,α-trifluoro-2,6-dinitro-N-N-dipropyl-p-toluidine (trifluralin) in the culture solution during germination partially inhibited the development of phytase activity. The herbicidal inhibition was enhanced if potassium phosphate at a non-inhibitory level also was present in the culture solution. The interaction of atrazine and amiben with phosphorus was not due to increased internal concentrations of inorganic phosphorus to a level inhibitory to the development of phytase activity.