Tolerance of corn (Zea mays L. ‘B’), cotton (Gossypium hirsutum L. ‘coker 413’), soybean (Glycine max Merr. ‘Hardee’), turnip (Brassica rapa L. ‘Tendergreen’), sorghum (Sorghum bicolor (L.) Moench. ‘Georgia 615’), purple nutsedge (Cyperus rotundus L.), yellow nutsedge (C. esculentus L.), and johnsongrass (Sorghum halepense (L.) Pers.) to 2,6-dichlorobenzonitrile (dichlobenil) at 0, 0.14, 0.28, 0.56, 1.12, and 2.24 kg/ha in four Georgia soils was determined. Equivalent rates of dichlobenil generally were more toxic in Davidson clay loam which had the highest clay content. Crop tolerance was corn > sorghum > cotton > turnip. Purple and yellow nutsedge tolerance to dichlobenil was intermediate to that of the crops tested. Johnsongrass response was equivalent to that shown by sorghum.

There were no apparent herbicide-insecticide or herbicide-fungicide interactions when two pesticides were used on peanuts (Arachis hypogaea L.) in the greenhouse. In field studies, O,O-diethyl s-(2-(ethylthio)-ethyl)-phosphorodithioate (disulfoton), O,O-diethyl s-((ethylthio)-methyl)-phosphorodithioate (phorate), 1,2-dibromo-3-chloropropane (dibromochloropropane), and pentachloronitrobenzene (PCNB) had little influence on phytotoxicity of the herbicides 3-amino-2,5-dichlorobenzoic acid (chloramben) and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) to peanuts. There was no phytotoxic effect or yield reduction as a result of application of chloramben or trifluralin combined with the use of fungicide-treated seed in the field. However, in the greenhouse, top growth of the fungicide-treated checks was greater than that of the herbicide-fungicide seed treatments. Dibromochloropropane nematocide alone was injurious to peanut seedlings grown in the greenhouse, but the application of a herbicide did not increase the injury.

Alfalfa (Medicago sativa L.) was killed or severely injured by parasitism from dodder (Cuscuta campestris Yunck. and C. indecora Choisy) when seeded August 1 or earlier in soil containing dodder seed. Alfalfa seeded August 15 or September 2 escaped injury from dodder, and became well-established before winter. Isopropyl m-chlorocarbanilate (chlorpropham) applied at 6 lb/A the following April controlled dodder effectively and did not injure alfalfa. A preemergence application of dimethyl tetrachloroterephthalate (DCPA) at 10 lb/A, followed by sprinkler irrigation, controlled 98 to 100% of the dodder at each of six dates of seeding in each of 2 years. DCPA often injured alfalfa seedlings severely, but most of them recovered and grew satisfactorily.

The movement and adsorption of soil-applied 14C-labeled 2,4-bis(isopropylamino)-6-(methylthio-s-triazine (prometryne) and 1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea (fluometuron) in the presence of 0.01 and 0.5 N CaCl2 were studied. The soils were Ca++-saturated Eufaula loamy fine sand and Norge loam. In equilibrium adsorption studies, fluometuron adsorption was decreased and prometryne adsorption was increased by increasing the CaCl2 concentration from 0.01 to 0.5 N. The mobility of prometryne in the two water-saturated soils was decreased by an increase in CaCl2 concentration. Fluometuron mobility was unchanged by the two CaCl2 concentrations in Eufaula, but was greater in Norge at the higher CaCl2 concentration. The adsorption of each herbicide in the flowing system was less than that predicted by the distribution coefficient. Differences in CaCl2 concentration do not appear to influence the mobility of the two herbicides sufficiently at the soil-water flow rate used in this study to require changes in current field application practices.

Vapor losses of 2,6-dichlorobenzonitrile (dichlobenil) were studied under controlled laboratory conditions by trapping vapors directly in a magnesia silica absorbant. Vapor losses increased with increasing temperature. Herbicide loss from a spray formulation in 3 hr amounted to 10% at 30 C and 18% at 40 C. Volatility increased as the soil moisture level increased from air dryness to field capacity. However, as the moisture level was increased to saturation, vapor losses remained similar to losses at field capacity. Volatility from a granular formulation was reduced when compared to the spray application. Volatility decreased as the cation exchange capacity of the soils increased.

A bioassay for photosynthetic and respiratory inhibitors was devised. The chlorophyll production of Chlorella pyrenoidosa Sorokin, high temperature strain 7-11-05, served as the basis of the bioassay which required 18 to 36 hr to complete. The sensitivity to nine photosynthetic and two respiratory inhibitors ranged from 0.013 to 0.4 ppm. The bioassay was successfully employed to assay leachates from soil columns and to monitor a field residue of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine).

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.

Dimethyl tetrachloroterephthalate (DCPA) caused swelling of a localized region of the hypocotyls of cucumber (Cucumis sativus L., var. Wis. SMR-15), tomato (Lycopersicon esculentum Mill., var. Heinz 1370), and jimsonweed (Datura stramonium L.). DCPA caused stem swelling in jimsonweed by affecting dividing and/or differentiating cells in the vascular cambium. As swelling proceeded, xylem tissue was increased over the controls and xylem cells were disorganized and no longer continuous. Swelling was induced at the site of DCPA application, and was reduced when DCPA concentration per unit of stem was lowered, even though the same amount per plant was applied. Uptake of 14C-DCPA from the treated stem region was slow, but the treated area had the highest specific activity.

Several chemicals were evaluated for their potential use in selectively killing cocklebur (Xanthium pensylvanicum Wallr.) seed in cocklebur-cottonseed (Gossypium hirsutum L.) mixtures. Reduction in cocklebur embryo viability from 64 to 100%, without injury to cottonseed, resulted from soaking seed in: (a) 20% ethyl or methyl acetate and 80% water for 3 to 15 min; (b) 35% methanol, 15% glacial acetic acid, and 50% water for 3 to 15 min; or (c) 50% methanol or ethanol, 20% glacial acetic acid, and 30% water for 15 to 30 sec. Evaluations of injury were based on tetrazolium tests, standard germination, germination in soil, and seedling dry weight.

Nitrofen (2,4-dichlorophenyl p-nitrophenyl ether) injured meristematic tissues and reduced germination and growth of cabbage (Brassica oleracea var. capitata L.) in the dark. Cabbage was more susceptible to nitrofen when the plants were grown under a low water potential or when they were maintained in the dark after spraying. This toxicity was overcome by exogenous sucrose and light was not required for nitrofen activity. Nitrofen promoted membrane permeability of red beet (Beta vulgaris L.) root sections and this was enhanced by dimethylsulfoxide (DMSO). Sucrose or Carbowax 1500 prevented this increase in permeability. Nitrofen inhibited non-cyclic photophosphorylation and electron transport in isolated spinach (Spinacia oleracea L.) chloroplasts and increased oxygen uptake of cabbage leaf sections. These effects appeared dependent upon permeability. Nitrofen induced stomatal closure, decreased transpiration, and increased leaf temperature. The leaf sustains thermal injury under high temperatures or high light intensities.

The herbicide 4-amino-3,5,6-trichloropicolinic acid (picloram) was applied to several bermudagrasses (Cynodon spp.). Most of the grasses were susceptible to picloram; however, some were resistant and recovered within 16 months from the initial treatment. There were no detectable metabolites of 14C picloram in bermudagrass (C. dactylon (L.) Pers. ‘U-3’) or common Kentucky bluegrass (Poa pratensis L.). Also, there were no abnormal changes in cells of swollen nodes of picloram-treated bermudagrass that could explain the selective herbicidal injury of picloram on bermudagrass.

Comparative phytotoxicity of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) and 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) on several plant species indicated trifluralin was more toxic than nitralin to the shoots while nitralin was more toxic than trifluralin to the roots. An E0 concentration, defined as that concentration required to prevent seedling emergence, was established for trifluralin on nearly all species assayed. Nitralin did not prevent emergence of any species. Trifluralin was more toxic than nitralin to the shoots of sorghum (Sorghum bicolor (L.) Moench, var. RS-610) and cucumber (Cucumis sativus L., var. Wis. SMR-15 and Pioneer) via shoot exposure. Nitralin was more toxic than trifluralin to the roots via root exposure. A comparison of the phytotoxicity through vapor activity showed trifluralin was much more toxic than nitralin.

Aquatic plants and physical-chemical data were collected during 1969 from 19 ponds and lakes. The fertility of these waters, as indicated by specific conductance, appeared to be a function of watershed area over the range 0 to 100 hectares. For watersheds greater than 100 hectares, differences in soil type and farming intensity were major causes of variability. Chara (Chara spp.) was found at specific conductances from 96 to 445 micromhos/sq cm (at 18 C) but was most abundant between 218 and 300. Chara also grew best in the upper half of the transparency range at Secchi disc readings varying from 2.4 to 5.8 m. Elodea (Elodea canadensis Michx.) flourished at specific conductances of 224 to 300 micromhos/sq cm and at transparencies from 2.7 to 5.8 m. Largeleaf pondweed (Potamogeton amplifolius Tuckerm.) was found only in the least fertile impoundment, whereas curlyleaf pondweed (P. crispus L.) occurred only in the most fertile impoundment. Sago pondweed (P. pectinatus L.) occurred at specific conductances of 200 to 349 micromhos/sq cm but was most prolific from 229 upward. This species also favored extensive shallow areas subject to a continuous summer flow.

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.

In greenhouse studies, magnesium-deficient tomato (Lycopersicon esculentum Mill.) plants were more susceptible to 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) than normal plants when grown under continuous light. Under a 12-hr photoperiod, magnesium-atrazine interactions were not significant. Magnesium deficiency and continuous light each caused reductions in chlorophyll content in tomatoes. A combination of these two conditions caused an additive reduction in chlorophyll content and also caused the greatest susceptibility to atrazine. The influence of magnesium on atrazine toxicity may be due to its effect on chlorophyll content rather than a direct effect on atrazine action.

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.

Added surfactant and high relative humidity enhanced penetration of 4-amino-3,5,6-trichloropicolinic acid (picloram) into leaves of Canada thistle (Cirsium arvense (L.) Scop.). Leaves and roots of Canada thistle readily absorbed picloram after which it was translocated in both phloem and xylem. Picloram tended to accumulate in young, growing leaves following both foliar and root uptake. In field-grown plants, injury symptoms appeared in young shoots as far as 1 m from treated shoots. The results are in harmony with a “source-to-sink” pattern of picloram translocation in the phloem. Leaves, but not roots, retained a substantial portion of the picloram absorbed. Following foliar application, small amounts of picloram were exuded by the roots into surrounding soil.

The Nebraska till-plant system of planting corn (Zea mays L.) moves weed seed away from the corn row. A reduction of weed seed in the row reduces the number of weeds emerging with the corn. In contrast, the conventional disking and plowing system of seedbed preparation does not remove weed seed from the row.

Field experiments were conducted to study the effectiveness of 2,2-dichloropropionic acid (dalapon) for the control of 55 morphologically distinct ecotypes of johnsongrass (Sorghum halepense (L.) Pers.) collected throughout the United States and from several foreign countries. Ecotypes varied widely in their response to dalapon whether collected from Mississippi, from 10 other states, or from eight foreign countries. Initial control of seven ecotypes with dalapon increased 8 to 35% when nitrogen fertilization was increased from 0 to 300 lb/A. Regrowth of surviving plants was more vigorous with increased nitrogen levels so increased fertility reduced final control. Comparative differences in the susceptibility of the seven selected ecotypes to monosodium methanearsonate (MSMA) were not as great as those obtained with dalapon. Varying the rate of nitrogen fertilization had less effect on johnsongrass susceptibility to MSMA than to dalapon. Dalapon controlled sorghum almum (Sorghum almum Parodi) better than johnsongrass.

When localized treatments of α,α,α-trifluoro-2,6-di-nitro-N,N-dipropyl-p-toluidine (trifluralin) and 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) were applied to the shoot zone of sorghum (Sorghum bicolor (L.) Moench, var. RS-610) and cucumber (Cucumis sativus L., var. Wis. SMR-15) before seedling emergence, the most susceptible sites were the sorghum coleoptilar node and the cucumber hypocotyl hook. The longer before emergence that the sorghum shoot was exposed to the herbicides, the greater was the injury. However, if herbicide concentration was sufficient, the growing point just above the sorghum coleoptilar node was inhibited by both herbicides when applied after seedling emergence. Maximum uptake of 14C-trifluralin and 14C-nitralin occurred through the coleoptilar node and hypocotyI hook of sorghum and cucumber, respectively. Rate of entry, uptake, and translocation of 14C-trifluralin was greater than that of 14C-nitralin in sorghum and cucumber shoots.