Radioactive sodium salt of 2,2–dichloropropionic acid (dalapon) was applied to the leaves or to the roots of sugar beets, a species tolerant of the herbicide, and yellow foxtail (Setaria glauca), a susceptible species. Autoradiographs indicated that dalapon entered through the leaves and roots, and moved throughout all portions of both species within 48 hours. Accumulation of dalapon was greatest in the younger tissues of both species. Paper chromatographic separations of aqueous extracts of the plants indicated no metabolic derivatives of dalapon in either species.

The sodium salt of 2,2–dichloropropionic acid (dalapon) at 4 lb per acre was applied as a foliar spray to sugar beets, a species tolerant of the herbicide, and yellow foxtail (Setaria glauca), a susceptible species. Shoots of treated and untreated plants were collected during three weeks after treatment and assayed. Dalapon appeared to cause protein degradation to amino acids in the shoots of both species. Striking increases in the concentration of amides (primarily glutamine in sugar beets and asparagine in yellow foxtail) were found. The free pantothenic acid in the shoots of both species rose greatly following treatment. In sugar beets, observed recovery of treated plants was accompanied by return of the concentrations of the constituents studied to levels near those in untreated plants. Yellow foxtail did not recover after treatment and concentrations of the constituents studied generally remained at a high level compared to the untreated plants. The similarity in initial biochemical responses of the two species and the fact that sugar beets recovered may indicate that some mechanism capable of inactivating dalapon was operating in sugar beets.

The toxicity indices to cotton of 12 soil-incorporated herbicides were highly and positively correlated with soil organic matter, cation exchange capacity, exchangeable calcium, moisture equivalent, free drainage value and total exchangeable bases. The characteristics of the responses indicate that adsorption of the 12 herbicides on organic matter occurs and that this greatly affects their toxicity. For equal toxicity approximately five times more herbicide was required at 20% organic matter than at 4% regardless of the herbicide involved.

The effect of PBA, dalapon and amitrole applications on the osmotic pressure, electrical conductivity and pH of quackgrass rhizome sap and the total nitrogen and hygroscopic capacity of dried rhizomes, from May 17 through October 15, are reported. Characteristic seasonal curves were developed for all five specific factors studied. The herbicide treatments accentuated the variation in some of these factors but did not appreciably modify the seasonal curves.

Toxicity of 3,6–endoxohexahydrophthalic acid (endothal) was measured by the inhibition of growth of germinating flax roots, compared to known standards. In the field, endothal applied at 0.3 to 10.0 ppm was not detectable after an average of 2½ days, and a maximum of 4 days. In aquaria, endothal at these rates was detectable much longer than this, and much longer when the aquaria contained only water than when they also contained mud and plant debris.

The method was based on the minimum dosage of 2,4–dichlorophenoxyacetic acid (2,4–D) that would produce strapping or cupping of cotton leaves. Dilutions of an unknown were applied to cotton cotyledons. The minimum dosage required to produce strapped or cupped leaves two weeks later was approximately 0.05 μg/plant. The results of this bioassay were comparable to tracer methods, but the latter can detect smaller quantities of 2,4–D.

Effects of 2,4–dichlorophenoxyacetic acid (2,4–D), 2,4,5–trichlorophenoxyacetic acid (2,4,5–T), 2–methyl–4–chlorophenoxyacetic acid (MCPA) and 4–(2–methyl–4–chlorophenoxy)butyric acid [4–(MCPB)] on Oxalis latifolia H.B.K. were compared. 2,4,5–T killed leaves and up to 50% bulbs, 2,4–D was slightly less effective while MCPA and MCPB killed or distorted leaves but did not affect bulbs appreciably. Effectiveness of spray was increased by spraying in the evening rather than the morning and by applying nutrient solution for three weeks prior to spraying, but spray additives, sucrose, boric acid or urea gave no significant alteration. Studies with C14–labelled 2,4–D indicated accumulation in rapidly developing organs with less movement to organs of slower development.

The treatments in this 3-year study consisted of 54, 12, 6, 3, 1, ½, and no foxtail plants per foot of crop row. Yield reductions for the heaviest stand of foxtail averaged 25% for corn and 28% for soybeans. For both corn and soybeans, the increase in foxtail dry matter was proportional to the decrease in the dry matter from the crop; the combined yield did not vary significantly. As stand of foxtail increased, there was a decrease in yields of grain, cobs, stalks or straw, diameter of cornstalks, ear weight, light intensity beneath the crop, soil temperatures under corn, and number of soybean pods. There was little or no significant effect on moisture content of grain, height of crop, shelling percentage of corn, oil or protein content of beans, weight of 100 beans or number of beans per pod. Increased corn lodging was associated with increasing foxtail stand in one of three years.

Wild cucumber (Sicyos angulatus) and cultivated cucumber (Cucumis sativus) were treated with carboxyl-labeled C142,4–D (2,4–D*) and 2,4,5–T (2,4,5–T*) and autoradiographs developed. The distribution pattern of 2,4–D* was achieved in 24 hours and changed little by the end of 4 or 8 days. The pattern of 2,4,5–T* translocation continued to change during an 8-day period, indicating a highly mobile compound. Metabolic studies indicated that considerably more 2,4–D* than 2,4,5–T* was absorbed by these species but 75% of the absorbed 2,4–D* was converted into two major metabolites within 24 hours. The absorbed 2,4,5–T* formed only traces of these metabolites even after 8 days. Evolution of C14O2 was approximately 10 times greater from 2,4–D*-treated plants than from 2,4,5–T*-treated plants. The greater phytotoxicity of 2,4,5–T on these species seems to be related to the inability of the plants to detoxify this compound as rapidly as 2,4–D.

Dalapon–2–C14, applied as droplets, was employed in tracer studies by autoradiography and counting. That dalapon remained non-metabolized throughout the experiment was confirmed by chromatography. Surfactants greatly enhanced (cuticular) penetration. Small amounts of herbicide were sorbed almost instantaneously (15–30 seconds). Movement away from the treated area “showed” or “appeared as” first a diffusional pattern, but soon became channelized in veinlets and larger vascular bundles. Dalapon applied off the midvein did not enter the midvein in appreciable quantities during basipetal transport. Dalapon which entered the midrib originally remained highly concentrated in this channel. During transport, some dalapon was retained or retarded by tissues through which it passed. Retention was greatest in the basal sections (intercalary meristem regions) of young grass blades. A 10-fold build-up of dalapon was demonstrated following drop application off the main vein, but not after treatment on the midrib. Results are explicable on the basis of the known anatomy of Zea and the translocation of dalapon with assimilates.

Species studied at Lincoln, Nebraska for 4 years were downy brome (Bromus tectorum L.), hairy chess (B. commutatus Schrad.), Japanese chess (B. japonicus Thunb.), and cheat (B. secalinus L.). These grasses were usually winter annuals, but also became spring annuals or biennials when sown in late March or early April.

In the greenhouse, an inductive period either of vernalization or short day lengths appeared necessary for panicle production by downy brome and hairy chess. For both species, long day lengths following the inductive period were necessary for flowering.

When a mixture of smooth bromegrass (Bromus inermis Leyss.) and 5.4 per cent of weed bromegrasses was sown in the fall, weed bromes made up 48 per cent of the total basal density and 87 per cent of the total seed yield the following summer. Panicles of weed bromes were absent or nearly so when this mixture was sown soon after April 1.

The best time for mowing hairy chess and downy brome for their control in pasture was approximately one week after the heads had emerged.

Practical control of weed bromegrasses has generally been obtained by prevention of seed production for two years. A practical program has included killing all emerged weed bromegrasses by tillage between April 1 and heading. A spring cereal or row crop, such as corn or sorghum, was then planted. The next season, timely tillage followed by the above crops, or summer fallow, has permitted return of fields to the usual alternate winter wheat and fallow sequence.

Effective control of weed bromegrasses also was accomplished by isopropyl N-phenylcarbamate (IPC), isopropyl N-(3-chlorophenyl) carbamate (CIPC), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), sodium salt of trichloracetic acid (TCA), 3,6–endoxohexahydrophthalic acid (endothal), 4,6-dinitro-o-sec-amylphenol (DNAP), and mixtures of these herbicides.

Among 15 different herbicides tested for eradication of Turkey oak (Quercus laevis Walt.) over a period of four years on Lakeland fine sand in Florida, only monuron, diuron, and fenuron at minimal rates of 10 lb/A were effective. One full growing season after application was required for complete kill. Phenoxy compounds gave variable top-kill but not satisfactory control. AMS, dalapon, and four formulations of benzoic acid were ineffective in these tests.

Out of 13 different grasses, Pensacola bahiagrass (Paspalum notatum Flugge) and weeping lovegrass (Eragrostis curvula Schrad.) were best adapted to these deep sandy soils. Seedbed preparation was essential to obtain a good stand of either. After establishment, the lovegrass vigorously persisted throughout the experiment; the bahia also persisted but the lack of fertilization was extremely evident. Both grasses could be established satisfactorily on soil treated two years earlier with monuron or diuron at 10 lb/A.

Rhizomes were sampled from quackgrass sod weekly during two seasons. The activity of buds on one-bud sections from mature rhizomes was used to determine periods of growth and dormancy. The rhizome buds showed a steady decrease in activity from mid-April to June 1. During June, the buds were dormant. Recovery began in late June and continued the rest of the summer. Only one-third of all rhizome material in a three-year-old sod was viable. The amount of viable mature rhizomes decreased during the season while the viable new rhizomes increased, and the total viable level remained fairly constant. This suggested a definite cycle in rhizome production and decomposition from year to year and a short life-period in the soil. The term “late-spring dormancy” is suggested for quackgrass rhizomes, based on the prevailing cool and moist weather conditions and the late-spring time of occurrence during the year. This distinguishes the type of dormancy described from “summer dormancy”.

In semi-arid areas, good control of field bindweed with 1 lb/A of 2,4–dichlorophenoxyacetic acid (2,4–D) will occur if there is at least 1.5 inches of available soil moisture when runners are 6 to 10 inches long. Under these conditions carbohydrates are high in the leaves and low in the roots. Analysis of rainfall records from Amarillo, Texas indicates that soil moisture conditions during May will be favorable for good bindweed control with 2,4–D 54% of the time.

Amiben (3–amino–2,5–dichlorobenzoic acid) was applied to the surface of various soil types in cylinders which were then leached with water. The leached soil was tested biologically for herbicide activity. Loss was most rapid from sand, followed by clay, with muck remaining phytotoxic much longer. There was only a slight increase in the toxicity of loam soil given repeated treatments with amiben. Incubation of treated soil for various periods of time indicated that microorganism breakdown is important in soils relatively high in organic matter.

Carboxyl labeled 2,4–dichlorophenoxyacetic acid (2,4–D) was applied to ironweed, a perennial composite, at various stages of growth in the field and greenhouse. During phases of rapid plant development, C14 tended to concentrate in new leaves, axillary buds, petioles and stems. As plants approached full vegetative development greater quantities were detected in rhizomes and roots and less in stems and leaves. The herbicide was translocated readily into new leaves, stems and roots of ironweed seedlings. Considerable quantities of 2,4–D–C14 absorbed by ironweed were rapidly metabolized to compounds not extracted by alcohol. Non-herbicide activity was also found in alcohol extracted fractions. C14 accumulations in field-treated ironweed were detected in roots and rhizomes 3 to 6 weeks after treatment.

Wheat, bean, and pigweed (Amaranthus retroflexus) seeds were immersed in solutions of 2,4–D (ester) and MCPA (ester) ranging from 0.001 ppm. and then germinated in petri dishes. Both products induced analogous effects but MCPA appeared to be slightly less active. Germination in pigweed was promoted by the 0.1 ppm. solutions. Growth of plumule and radicle in wheat was stimulated by lower (0.001 to 1 ppm.) concentrations and depressed by higher ones (100 and 1000 ppm.), the threshold between stimulation and depression being around 10 to 100 ppm. depending on the product and the organ affected.

The percentage of quackgrass (Agropyron repens (L.) Beauv.) rhizome buds producing shoots was greater with one-inch than with six-inch or longer rhizomes. The longer the rhizome cutting, the stronger the shoot and the greater the recovery from deep planting. Recovery of rhizomes covered with four or more inches of soil was poor. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) at 1½ and 3 lb per acre did not affect the number of shoots produced. It was more effective when applied ½ inch above rhizomes than one inch or three inches above them.

Placements which did not wet the root collar and sprouting zone gave poor kills of roots.