The influence of soil pH (4.3 to 7.5) on the phytotoxicity of herbicides incorporated into high organic soils was studied. Phytotoxicity increased as the soil pH increased and reached a maximum at pH 6.5 for the weak aromatic acids 3,6-dichloro-o-anisic acid (dicamba) and (2,4-dichlorophenoxy)-acetic acid (2,4-D) and the weak bases 2,4-bis(isopropylamino)-6-methoxy-s-triazine (prometone) and 3-amino-s-triazole (amitrole). Conversely, phytotoxicity increased as soil pH decreased and reached a maximum at pH 4.3 for the weak aliphatic acid 2,2-dichloropropionic acid (dalapon), the cationic herbicides 6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinediium ion (diquat) and 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat), and a nonionic herbicide S-propyl dipropylthiocarbamate (vernolate). Soil pH levels between 4.3 and 7.5 had no effect on the phytotoxicity of (a) the weak aromatic acids 3-amino-2,5-dichlorobenzoic acid (chloramben) and 4-amino-3,5,6-trichloropicolinic acid (picloram); and (b) the nonionic herbicides 2,6-dichlorobenzonitrile (dichlobenil), 5-bromo-3-isopropyl-6-methyluracil (isocil), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), and 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin). A change of one pH unit decreased the phytotoxicity of 2,4-D, dicamba, dalapon, prometone, amitrole, paraquat, and vernolate by a factor of two to four depending on the particular herbicide and the pH values considered.

Field experiments were conducted during 1968 to 1970 to determine the influence of time of herbicide application on control of kudzu [Pueraria lobata (Willd.) Ohwi]. Picloram (4-amino-3,5,6-trichloropicolinic acid) effectively controlled kudzu when applications were made as early as May 22 and as late as October 28. Acceptable control was obtained with rates of picloram 0.34 kg/ha or higher. In contrast, (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) was most effective when applied during the first half of summer. Essentially no control of kudzu was obtained from 2,4,5-T applied 1 week before the first killing frost.

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.

Thirteen prominent species decreased 40% or more after applications of (2,4-dichlorophenoxy)acetic acid (2,4-D) at 2.2 kg/ha. Four of the “most-susceptible” species [gumweed (Grindelia squarrosa (Pursh) Dunal), fringed sagebrush (Artemisia frigida Willd.), drummond milk vetch (Astragalus drummondii Dougl. in Hook.), and hairy goldaster (Chrysopsis villosa (Pursh) Nutt.)] are considered undesirable and two of them [bluebells (Mertensia lanceolata (Pursh) A. DC.) and evening-primrose (Oenothera coronopifolia Torr. & Gray)] desirable. The other seven species of this group are quite unimportant for cattle. Therefore, spraying mixed-grass prairie with 2,4-D improves range condition and increases forage production.

The techniques of cryostat sectioning, freeze-drying, and microradioautography were adapted to study the absorption and translocation of radio-labeled 3-(3,4-dichlorophenyl)-1,1-dimethylurea (14C-diuron) in root-treated cotton (Gossypium hirsutum L., var. Coker 201) plants. Diuron appeared to move primarily in the apoplast and to be transported acropetally and laterally in the transpiration stream. Radioactivity was observed to accumulate in striking concentrations in the lysigenous, or pigment, glands and the trichomes of the cotton plant. This accumulation is postulated to be a major factor in lowering the effective concentration of the herbicide in the leaves of cotton as compared to leaves of more susceptible plants, and thus may be a significant factor in the tolerance of cotton to diuron.

The selectivity of 2,4-dichlorophenyl p-nitrophenyl ether (nitrofen) among rape (Brassica campestris L., var. Echo) and two weed species, redroot pigweed (Amaranthus retroflexus L.) and green foxtail (Setaria viridis (L.) Beauv.), was determined quantitatively by a replicated dosage-response experiment. On an ED50 basis, green foxtail and redroot pigweed were, respectively, 5.8 and 63.3 times more susceptible than rape. Selectivity was divided into three parameters; viz., differential spray retention, differential penetration, and differential effects within the plant. Differences in retention were measured with the use of a water-soluble dye, while differences in penetration were determined with 14C-labelled nitrofen. Spray retention on green foxtail was 66% of that on the rape and 64% as much nitrofen penetrated redroot pigweed as penetrated rape. Under the conditions of these tests it was estimated that green foxtail and redroot pigweed were, respectively, 9 and 99 times more susceptible to nitrofen than was rape.

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 I50 values obtained with preemergence applications of 2-sec-butyl-4,6-dinitrophenol (dinoseb) for shoot and root growth in soil, or root growth in a bioassay were determined for 68 plant varieties representing 66 species. The I50 values in soil indicate a difference of more than 240 fold between the most sensitive species, shepherdspurse (Capsella bursa-pastoris (L.) Medic.) and the most tolerant species, peanut (Arachis hypogaea L.). The correlations among the I50 values for shoot and root growth in soil and the root bioassay were significant. The I50 values between susceptibility of plants to soil-applied dinoseb and their seed size are correlated significantly. Large-seeded plant species and larger seeds within varieties, in general, were more tolerant to dinoseb than small-seeded species and smaller seeds within a given variety. However, there appeared to be other factors involved in susceptibility. For example, there were differences in response among families; the Leguminosae were the most tolerant, while the Solanaceae and Cruciferae were particularly susceptible.

Dicamba (3,6-dichloro-o-anisic acid) and 2,3,6-trichlorobenzoic acid (2,3,6-TBA) applied in lanolin pastes to leaves or roots of host plants growing in soil were translocated acropetally and affected witchweed (Striga lutea Lour.) plants parasitizing roots of host plants. Emerged witchweed plants exhibited characteristic epinastic responses while emergence of other witchweed plants was delayed. Broadcast foliar treatments of dicamba and 2,3,6-TBA to corn (Zea mays L.) applied before witchweed emergence generally reduced the intensity of the infestation and delayed emergence. However, injury to corn, expressed as failure of kernel development and grain yield decreases, sometimes occurred. Injury was greater when herbicide application was delayed until corn was in the early tassel stage. Dicamba was more effective than 2,3,6-TBA for witchweed control. However, no treatment gave season-long control of witchweed. Yearly variations in corn injury precluded a selection of optimum treatment dates and rates for control of witchweed by this technique.

The technique of microradioautography was used to study the absorption and translocation of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) by cotton (Gossypium hirsutum L., var. Coker 201) and soybean (Glycine max (L.) Merr., var. Lee). Radioactivity from 14C-trifluralin was retained primarily on the surfaces of the roots of cotton and soybean. This was apparently due to a tenacious adsorption or binding of the radioactivity to the epidermis and cuticle. Entrance of radioactivity into the roots of these species was greatly facilitated by breaks in the epidermis, such as might occur from seedling diseases or mechanical damage. Within the roots, radioactivity was noted in the walls of the xylem vessels and cortical cells. Little movement out of the soybean roots was observed, but limited movement of radioactivity into the leaves of cotton, apparently via the metaxylem, was noted. Radioactivity accumulated in the protoxylem of the cotton stem where many elements appeared to be plugged. Results of this study indicate that care should be used in interpreting data from studies where loss of radioactivity from nutrient media is used as a criterion of herbicide absorption, and where gross radio autography is used as an indicator of herbicide translocation.

The influence of mineral nutrition on the parasite-host relationship of witchweed (Striga lutea Lour.) and sorghum (Sorghum vulgare Pers. ‘Texas Bighead’) was investigated in greenhouse and growth chamber studies. Sorghum was grown in Eustis loamy sand, either infested or not infested with witchweed, and treated with one of three levels of mineral nutrients. Witchweed reduced host-shoot yields by about 70% at the low nutrient levels and by about 45% at the highest nutrient level. Witchweed produced seed at all nutrient levels, whereas the host produced seed at the highest level only. Increased nutrition also increased witchweed yields. Regardless of nutrient level, an early attack by witchweed was more destructive to the host than a late attack. Growth of witchweed in soil also was studied after the parasite was detached from the host or the host shoot was removed. When only the host shoot was removed, (a) witchweed growth was inhibited; (b) feeding of sucrose to witchweed did not restore parasite growth; (c) mineral nutrients were toxic to the parasite; and (d) high relative humidity around witchweed protected it from the nutrient toxicity. High relative humidity enhanced survival of the detached parasite but markedly inhibited growth of witchweed in the intact parasite-host relationship.

The phytophagous insects associated with silverleaf nightshade (Solanum elaeagnifolium Cav.) were surveyed in southern California, Arizona, New Mexico, and southwestern Texas. In California, this introduced weed was largely free of deleterious insect injury. Its insect associates mostly were sap or foliage-feeding species that attack a wide range of plants, a few were species restricted to Solanaceae, and several were species economically important as crop pests. The insect fauna became increasingly complex in species diversity and plant parts attacked as the survey progressed eastward from California towards southwestern Texas and the presumed native habitats of this weed in adjacent Mexico. The feasibility of biological control of silverleaf nightshade and the value of faunistic surveys in ascertaining the indigenous or alien status of plants are good.

The germination and growth of six pigweeds (Amaranthus spp.) were studied in the germinator and greenhouse. Treatments with sulfuric acid, acetone, sodium hypochlorate, and potassium nitrate variously influenced species germination. Seedlings emerged more rapidly at 100 F than at other soil temperatures. Variation in seedling characteristics was noted. Some species were more susceptible to 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) and 2,4-bis (isopropylamino)-6-(methylthio)-s-triazine (prometryne) than others in the greenhouse. In the field little variation in susceptibility to several preplant and preemergence herbicides was found; but there were differences when postemergence herbicides were used.

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.

Repeated, foliar applications of monosodium methanearsonate (MSMA) controlled established, space-planted purple nutsedge (Cyperus rotundus L.) while three other herbicides were less effective. Four to eight applications of 5.6 to 16.8 kg/ha of MSMA in 1 year destroyed most plants. There was little difference in final control from applications made at 2, 3, or 4-week intervals or from 187 to 1496 L/ha of spray solution. Clones of purple nutsedge responded similarly to herbicide treatments.

A reduction in soybean (Glycine max (L.) Merr.) yield of 25% (1968) to 30% (1969) resulted from one smooth pigweed (Amaranthus hybridus L.) per ft in 30-inch rows. A giant foxtail (Setaria faberii Herrm.) infestation of one plant per ft in 30-inch rows reduced yield 13% in 1969. Harvesting before weeds were desiccated resulted in significant threshing and separating losses as speed was increased from 1 to 2 and 3 mph. Stubble, lodging, and stalk losses were more than double in the pigweed and foxtail plots when compared to the weed-free plots after weeds were desiccated by frost.

Application of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) to intermediate wheatgrass (Agropyron intermedium (Host) Beauv.) increased forage yields, plant protein, and nitrate over a 4-year period. Atrazine or 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) applied to a sward of red brome (Bromus rubens L.), Arabian grass (Schismus arabicus Nees.), and red-stem filaree (Erodium cicutarium (L.) L'Her.) increased dry-matter yields sixfold and also increased protein and nitrate nitrogen. Nitrate in plants treated with atrazine increased to near-toxic levels for livestock.

A belt-carried small-plot sprayer for field research work was constructed. Spray materials are prepared in 1-quart polypropylene bottles, and these are placed directly in the pressure canister of the sprayer for application. The system is charged by a CO2 pressure source and the spray applied through conventional booms.

Effects of 4-amino-3,5,6-trichloropicolinic acid (picloram) on mitochondrial volume changes and ATPase activity were studied with isolated barley (Hordeum vulgare L., var. Wong) and safflower (Carthamus tinctorius L., var. U. S. 10) mitochondria. Changes in mitochondrial volume and/or configuration of mitochondrial membranes were recorded in terms of changes in light scattering, which was expressed as absorbance. Picloram caused swelling of mitochondria previously contracted by ATP. Picloram-induced swelling was characterized by a later partial recovery of the mitochondria to a contracted state. Picloram did not affect succinate-induced contraction nor cause any additional swelling of the mitochondria in 0.3 M KCl medium. A high concentration (10−3 M) of picloram enhanced the activity of ATPase by 31%. This result was consistent with an increased rate of picloram-induced swelling in mitochondria contracted earlier by ATP. The action of picloram apparently differs from that of known mitochondrial swelling agents.

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.