In a 2-year study, five densities of kochia (Kochia scoparia (L.) Schrad.) competed with sugarbeets (Beta vulgaris L.) for the entire growing season. The yield of sugarbeet roots and pounds of sucrose per acre decreased as the intensity of competition from kochia plants increased. One kochia plant per 25 ft of row reduced the average yield of roots by 2.6 T/A and sucrose by 960 lb/A. A density of one kochia plant, or more, per 2 ft of row in the first year, or one kochia plant per 1 ft of row in the second year, significantly reduced the sucrose content of the roots. Individual kochia plants significantly reduced the weight of sugarbeet tops and roots within a radius of 31 inches from the center of the sugarbeet row.

Prior to germination, seed of some plant species either adsorb or absorb some herbicides applied to the soil. Equations were developed describing the concentration of the herbicide expected in the seed both when diffusion of the herbicide in the soil is the limiting factor and when diffusion of the herbicide within the seed is the limiting factor. Expected concentrations of the herbicide in the seed were presented for combinations of three seed radii (seed were assumed to be spheres) five diffusion times, and five diffusion coefficients. The calculated concentrations of the herbicide in the seed in ppm increased as seed size or radii decreased. This theoretical result was consistent with experimental data and potentially explains why some large-seeded plant species are difficult to control with the use of herbicides. The equation developed for a perfect “sink” predicted within experimental error the concentration of isopropyl m-chlorocarbanilate (chlorpropham) absorbed by soybean (Glycine max (L.) Merr.) seed from aqueous solutions of chlorpropham.

Seedlings of corn (Zea mays L., var. GT-112 RfRf and GT-112, resistant and susceptible, respectively) to 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) were grown 48 hr in sterile Hoagland's solution containing 14C-ethyl-labeled atrazine. More incorporation of the 14C-ethyl side-chain into free amino acids was found in the roots and shoots of GT-112 RfRf than GT-112, based on radioactivity. More radioactivity was found in roots of susceptible plants than in resistant plants; however, the trend was reversed in the shoots.

Bean plants (Phaseolus vulgaris L. var. Black Valentine) pretreated with gibberellic acid (hereinafter referred to as GA) absorb and accumulate considerably more N-1-naphthylphthalamic acid (naptalam) than untreated plants. All concentrations of GA from 2.9 × 10−6 to 8.6 × 10−4M were effective; peak influence occurred at 6 × 10−4M. Plants pretreated with this concentration took up 58% more naptalam than untreated plants. When the different parts of the plant were analyzed for naptalam separately, the leaf area (on a per g dry weight basis) was influenced most by GA pretreatment. The leaf area of bean plants pretreated with 2.9 × 10−4M contained 212% more naptalam than the leaf area of untreated plants. The leaf area also included all stem and petiole tissue above and including the first true leaves.

Detached live oak (Quercus virginiana Mill.) leaves were immersed in aqueous solutions of 4-amino-3,5,6-trichloropicolinic acid (picloram) or (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) for periods up to 4 hr. Herbicide concentration ranged from 10−3 to 10−6M; solutions were adjusted to either pH 4, 6, 7, or 8. Absorption of picloram in the presence of equimolar concentrations of 2,4,5-T exceeded that noted for picloram alone. The presence of picloram in the treating solutions had no effect on absorption of 2,4,5-T. This technique allows evaluation of absorption and penetration characteristics of mixtures of herbicides, solvents, and adjuvants.

Studies were conducted on the growth and development of 55 morphologically distinct vegetative types of johnsongrass (Sorghum halepense (L.) Pers.) collected throughout the United States and from several foreign countries. Observations were made also on the growth of sorghum almum (Sorghum almum Parodi) from three foreign countries. Mature leaf-blades of the different johnsongrass ecotypes varied in length from 31 to 59 cm and in width from 1.7 to 3.4 cm. Plant height and culm density varied 2 to 4-fold for the different ecotypes. Floret production varied from 87 to 352 sessile spikelets for representative panicles of the different ecotypes. The number and arrangement of branchlets within panicles also varied as did the size of various spikelet components. Sorghum almum produced much taller plants than did johnsongrass although culm density and lateral growth were less than that of johnsongrass.

Effects of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) rate and placement in soil on growth and anatomy of soybeans (Glycine max (L.) Merr.) were studied in greenhouses. In 7-week-old plants, trifluralin caused pronounced changes in number and organization of palisade cells in leaves. In fourth internodes, xylem elements of treated plants were less organized and walls of pericycle fibers were extremely thick compared to those of untreated plants. There was starch accumulation in nodules and in xylem elements of the upper root, and binucleate and trinucleate cells were present in tips of tap and lateral roots of treated plants. The effects were more pronounced as rate of trifluralin was increased from 0.36 to 0.74 and to 1.1 kg/ha and when trifluralin was incorporated into the 5 to 15-cm depth rather than the top 5 cm of soil. However, occlusions of xylem vessels in lateral and tap roots were most pronounced at 0.74 kg/ha. Plant topgrowth was reduced more when trifluralin was incorporated into the bottom 10 cm of soil, but root growth inhibition was not affected by trifluralin placement. Trifluralin reduced nodulation of soybeans and seemed to inhibit utilization of cotyledonary reserves and redistribution of organic and mineral constituents of unifoliolate leaves.

Dimethyl tetrachloroterephthalate (DCPA) more severely inhibited growth of roots than shoots of corn (Zea mays L., var. WF9 X B37) and sorghum (Sorghum bicolor (L.) Moench., var. RS 610). Although roots of corn and sorghum were about equally susceptible to DCPA, corn shoots were much more tolerant than sorghum shoots when separately exposed. 14C-DCPA was absorbed by both shoot and root zones of corn and sorghum; however, only limited movement to other plant parts occurred. In contrast to the grass species, cucumber (Cucumis sativus L., var. Wis. SMR-15) roots were tolerant to DCPA. Hypocotyl length was reduced only when the shoot zone was exposed. 14C-DCPA absorbed by the shoot zone moved mainly acropetally. Root-absorbed 14C-DCPA tended to be accumulated there with only limited movement upward. Uptake by the hypocotyl of cucumber and movement of 14C-DCPA to foliage after emergence occurred readily, and pretreatment with unlabeled DCPA before emergence enhanced uptake.

Diphenamid (N,N-dimethyl-2,2-diphenylacetamide) severely inhibited adventitious roots in the shoot zone of sorghum (Sorghum bicolor (L.) Moench., var. RS 610) and corn (Zea mays L., var. WF9 X B37) without decreasing foliage growth. Using diphenamid to inhibit shoot zone roots, the presence of adventitious roots was shown to increase foliage injury to corn, sorghum, or both when exposed to 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron), 2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine (ametryne), or 3-tert-butyl-5-chloro-6-methyluracil (terbacil) in the shoot zone. Inhibition of adventitious roots was associated with a decrease in uptake of 14C-diuron and 14C-ametryne in both corn and sorghum. Inhibition of the adventitious roots did not alter the response of corn or sorghum, as measured by top growth, when treated with dimethyl tetrachloroterephthalate (DCPA), isopropyl-m-chlorocarbanilate (chlorpropham), S-ethyl dipropylthiocarbamate (EPTC), and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin). The meristematic region of the sorghum shoot before emergence was more sensitive than other regions of the shoot to DCPA and chlorpropham. Injury from other application sites depended upon uptake from the treated area and movement to the meristematic region, where both herbicides appear to be acting.

Cycloate (S-ethyl N-ethylthiocyclohexanecarbamate) at 3 lb/A, 2-chloro-N-isopropylacetanilide (propachlor) at 4 lb/A, and 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) at 4 lb/A were applied by 10 different procedures to moist and dry soil in 2 years. When cycloate was incorporated 3 inches deep in either moist or dry soil, it consistently controlled barnyardgrass (Echinochloa crusgalli (L.) Beauv.) and certain broadleaf weeds and caused only temporary injury to the sugarbeets (Beta vulgaris L.). No method of applying pyrazon and propachlor consistently controlled weeds selectively in sugarbeets. Activity of all herbicides was increased by some means of soil incorporation. Activity was frequently extreme when any of the herbicides was applied as a subsurface layer 1 or 2 inches deep; and sugarbeets, as well as weeds, were killed.

Soil applications of α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), O,O-diethyl S-((ethylthio)methyl)-phosphorodithioate (phorate) and their combinations did not affect cotton (Gossypium hirsutum L.) germination. Plants grown on soil treated with trifluralin were shorter than plants on soil treated with phorate. High rates of phorate reduced shoot weights. Root weights of phorate-treated plants were higher than those of trifluralin-treated plants but lower than those of the controls. In culture solution and soil, trifluralin inhibited lateral roots of cotton. In the presence of phorate, trifluralin-treated plants produced more lateral roots than plants treated with trifluralin alone. Other organophosphorus compounds, when used in combination with trifluralin, did not increase the number of lateral roots.

A cooperative study to evaluate the accuracy and precision of bioassays was carried out among investigators at several locations for 3 years. Oats (Avena sativa L., var. Cimarron) seedlings were used as indicator plants for soil-applied 2,4-bis-(isopropylamino)-6-methylthio-s-triazine [prometryne]. Assay results varied a great deal initially, and ranged from 147% below to 234% above the prometryne actually applied. The adoption of uniform conditions and procedures greatly increased the uniformity of the determinations between locations to a range of from 37% low to 0% high in prometryne applied. Chemical analyses of the soils ranged from 13% low to 20% high. Measurements of herbicidal activity included dry and fresh plant weights, plant height, visual injury ratings, and plant water use. The average concentration of prometryne in the soil as estimated with several types of measurements gave a much better measure of prometryne content than any one measurement alone. Prometryne rapidly and greatly affected the utilization of water by oats seedlings and careful measurement of water use showed potential of being a good early indicator of prometryne activity.

The compound N-(l,l-dimethylpropynyl)-3,5-dichlorobenzamide affected the development of quackgrass (Agropyron repens (L.) Beauv.) by inhibiting the growth of meristematic regions. The nodes at the apex of treated rhizomes became swollen and necrotic and exhibited increases in DNA, RNA, and protein over untreated rhizomes. These changes in the terminal nodes were accompanied by a dramatic increase in the levels of cellulase and by several disruptive changes in the meristematic, nodal, and internodal tissue of quackgrass rhizomes.

Combinations of herbicides as single or separate applications to the soil were compared in furrow-irrigated cotton (Gossypium hirsutum L.). In seven tests, preplanting applications of four herbicides, primarily effective for grass control, were combined with postemergence applications of 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron). Preplanting applications of 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) before furrowing retarded growth of cotton and sometimes reduced stands. Herbicides applied after furrowing did not appear to affect cotton development. Combinations of the four herbicides with diuron gave satisfactory control of annual weeds until harvest. In 15 tests, preplanting applications of O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl) benzenesulfonamide (bensulide) were combined with preplanting or postemergence applications of four herbicides primarily effective for control of broadleaf weeds. Preplanting applications of 3-(p-chlorophenyl)-l,l-dimethylurea (monuron) usually caused temporary chlorosis and stunting of cotton seedlings. Postemergence applications of monuron and 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) sometimes caused temporary chlorosis of cotton foliage. Combinations of herbicides controlled weeds until harvest in 14 of the 15 tests. There was no difference among the herbicide combinations in yield of cotton in 21 of the 22 tests. In the 15 tests sampled there were no differences in fiber properties and boll components among herbicide combinations.

A method is described to quantitatively record the upward force of an emerging seedling that exhibits epigeal germination. A soybean [Glycine max (L.) Merr.] seedling showed an average maximum emergence thrust of 434 g at 8 to 10 days after planting. Herbicides can be grouped into those that inhibit, have no effect, or stimulate the upward thrust exerted by an emerging soybean seedling. At the rates studied, the herbicide 4-amino-3,5,6-trichloropicolinic acid (picloram) showed the greatest inhibition and 3-amino-2,5-dichlorobenzoic acid (chloramben) the greatest stimulation of emergence force of soybean seedlings.