Subirrigated pot-plant systems were developed for greenhouse simulations of field methods being tested for herbicidal control of saltcedar (Tamarix pentandra Pall.). The methods included: over-the-top spraying; soil injection; soil layering, with whole plants transplanted onto the herbicide layer; and soil layering by severing the roots and concomitantly injecting herbicide. Existing foliar application techniques were improved for greenhouse testing of herbicides and results from preliminary tests were apparently similar to literature reports of limited efficacy in the field. Preliminary results from these greenhouse techniques showed that root zone applications, either by soil layering or soil injection, were very effective; stem or foliar applications were less effective.

Postemergence herbicide treatments that were most effective for controlling horsenettle (Solarium carolinense L.) were glyphosate [N-(phosphonomethyl)glycine], dicamba (3,6-dichloro-o-anisic acid), silvex [2-(2,4,5-trichlorophenoxy)-propionic acid], and picloram (4-amino-3,5,6-trichloropicolinic acid). All exhibited good to excellent long term control of the horsenettle plant when applied annually for at least 2 yr. Picloram and glyphosate both provided better control of horsenettle when applied at a postbloom or fruiting stage of growth. Dicamba and picloram also were very effective in controlling horsenettle when used as a subsurface layer (SSL) treatment. However, all of these treatments caused visual injury to peanuts (Arachis hypogaea L.). Applications of 2,4-DB [4-(2,4-dichorophenoxy)butyric acid] were effective in causing an 80 to 90% fruiting inhibition of horsenettle plants when applied at a prebloom stage of growth, with no damage to the peanuts. Applications of several dinitroaniline herbicides as SSL treatments exhibited some control of horsenettle with little crop injury. Postemergence treatments which effectively controlled seedling horsenettle plants grown in the greenhouse were glyphosate and dinoseb (2-sec-butyl-4,6-dinitrophenol).

The metabolism of Sandoz 6706 [4-chloro-5-(dimethylamino)-2-α,α,α-trifluoro-m-tolyl-3(2H)-pyridazinone] in soybean [Glycine max (L.) Merr. ‘Kent’] and in sicklepod (Cassia obtusifolia L.) was examined at 1, 2, 4, and 8 days after herbicide application to explain the relative susceptibility of soybean and sicklepod to the herbicide. The 14C-labeled Sandoz 6706 was applied via the plant roots in a liquid culture medium. The primary pathway of metabolism in both plant species involved N-demethylation to norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone and the desmethyl Sandoz 9774 [5-amino-4-chloro-2-(α,α,α-trifluoro-m-tolyl-3(2H)-pyridazinone]. Soybean was more efficient in the N-demethylation of the herbicide to less toxic metabolites than was sicklepod. A second transformation pathway which resulted in the formation of polar products was present in the roots of both species.

The degree of control of purple nutsedge (Cyperus rotundus L.) provided by Bactra verutana Zeller, a native moth, was evaluated for various stress conditions. Two, three, or four weekly infestations each with three larvae per live shoot, reduced purple nutsedge dry weight an average 77% compared with an average 55% for one infestation. Eight weekly infestations reduced plant dry weight 98%. Neither caging of the larvae on the plants nor osmotic stress with NaCl to −8 bars influenced larval efficacy, but nitrogen deficiency did reduce the effect of the larvae about 75%. Purple nutsedge had no effect on the dry weight of cucumber (Cucumis sativus L., ‘Straight Eight’) after 1 month, whether larvae were or were not present. Purple nutsedge did reduce the plant dry weight of okra (Abelmoschus esculentus (L.) Moench, ‘Clemson Spineless’) 64%, but repeated (eight) weekly infestations of larvae gave a plant weight of okra equal to that of okra grown without purple nutsedge. Purple nutsedge reduced the bulb and root dry weight of onion (Allium cepa L., ‘Big Valley’) 37%, but repeated weekly infestations of larvae gave onion growth equal to that of onion grown without purple nutsedge.

The effects of herbicides on in vivo nitrate and nitrite reduction were determined by vacuum infiltrating sections of barley (Hordeum vulgare L.) or bean (Phaseolus vulgaris L.) leaves with solutions containing nitrate and herbicides. Herbicides causing a reduction of nitrite accumulation in the dark were considered to have inhibitory effects upon nitrate reduction and those causing an accumulation of nitrite in the light were considered to inhibit nitrite reduction. Only dinoseb (2-sec-butyl-4,6-dinitrophenol) and potassium azide significantly reduced nitrate reduction in both barley and bean. All of the herbicides which inhibit photosynthesis inhibited nitrite reduction but had no significant effect on nitrate reduction in barley and bean. Nitrite reduction in an atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] resistant pigweed (Amaranthus retroflexus L.) biotype was not affected by any triazine tested. However, these triazines significantly inhibited nitrite reduction in barley, bean, and the susceptible pigweed biotype. The results suggest that the in vivo nitrate reductase technique may be a useful technique for identifying chemicals which inhibit the flow of electrons to ferredoxin, thereby inhibiting nitrite reduction in light.

The relative susceptibility of ‘Alaska’ and ‘Perfection’ cultivars of peas (Pisum sativum L.) to trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) was studied in excised roots, and in greenhouse and field plantings. Elongation of excised Alaska and Perfection pea roots was reduced 32 and 25%, respectively, by 4 mg/L dosages of trifluralin in aseptic culture, and 25 and 10% by 1.68 kg/ha dosages in greenhouse-grown plants. Seedling emergence in the greenhouse and field was reduced or delayed in both cultivars by 1.68 kg/ha trifluralin. Yields of field-grown Alaska and Perfection peas were reduced by trifluralin dosages equal to and exceeding 0.84 and 1.68 kg/ha, respectively, when there was a June water deficit (8 cm). Yields were not reduced in either cultivar when June rainfall was near normal (10.9 cm).

When the insecticide fonofos (O-ethyl-S-phenylethylphosphonodithioate) was added to a nutrient solution containing 14C-terbacil (3-tert-butyl-5-chloro-6-methyluracil), movement of total radioactivity into leaves of peppermint (Mentha piperita L. cv. ‘Todd's Mitchum’) during a 3-day treatment period approximately doubled. In addition, a higher percentage of this total radioactivity was identified as intact terbacil. Total radioactivity in the leaves was not significantly increased when terbacil was added to 14C-fonofos in nutrient solution. Studies also were conducted to measure the effect of fonofos upon the rate of terbacil metabolism in peppermint. Peppermint plants were treated for 3 days with nutrient solution containing 14C-terbacil alone or 14C-terbacil plus fonofos. The percentage of total radioactivity which remained as intact terbacil at the end of the treatment period was five times as high in plants treated with the combination as in those treated with terbacil alone. The relative rate of degradation during the succeeding 11 days was approximately the same in plants subjected to the two treatments. These results could account for damage to peppermint from closely timed applications of fonofos and terbacil in the field.

The 14C-labeled herbicide, Sandoz 6706 [4-chloro-5-(dimethyl-amino)-2-α,α,α-trifluoro-m-tolyl-3(2H)-pyridazinone], was applied to soybean [Glycine max (L.) Merr. ‘Kent’] and sicklepod (Cassia obtusifolia L.) to evaluate differential species response in uptake and translocation. Liquid scintillation spectrometry and radioautographs indicated that in both species 6706 uptake was proportional to its concentration in the cultural solution and to transpiration, provided transpiration and the uptake mechanism were not limited. Translocation of the herbicide from roots to foliage followed the apoplastic route in both plants. A higher concentration of the herbicide accumulated in the upper leaves and apical meristem in sicklpod than in soybean.

The effects of ethephon (2,chloroethyl-phosphonic acid), ancymidol [α-cyclopropyl-α-(4-methoxyphenyl)-4-pyrimidinemethanol], DPX1840 [3,3a-dihydro-2-(p-methoxyphenyl)-8H-pyrazolo(5,1-a)isoindol-8-one], Uni-P293 (2,3-dihydro-5-6-diphenyl-1,4-oxathiin), and morphactins and their interaction with GA (gibberellic acid) on the translocation of 2,4,5-T (2,4,5-trichlorophenoxacetic acid) in bean (Phaseolus vulgaris L. ‘Stringless Green-Pod’) seedlings were determined. The growth retardants and GA were either applied as foliar treatments or injected at the cotyledonary node with 2,4,5-T. Foliar pretreatment of bean seedlings with ethephon and ancymidol 2 days before 2,4,5-T treatment inhibited 2,4,5-T translocation to young shoots but did not affect basipetal translocation greatly. These effects were reversed by foliar application of GA 1 day before 2,4,5-T injection. Foliar pretreatment of bean seedlings with DPX 1840 2 days before 2,4,5-T treatment increased 2,4,5-T translocation to young shoots and inhibited basipetal translocation. The effects of DPX1840 were not reversed by GA treatment. When ancymidol, DPX 1840, and morphactins were injected into the stem tissue with 2,4,5-T the acropetal translocation of 2,4,5-T increased and basipetal translocation was decreased by DPX1840 and morphactins. These effects were not reversed by the simultaneous GA injection. Uni-P293 had little effect on 2,4,5-T translocation. Growth retardants other than Uni-P293 appear to inhibit basipetal 2,4,5-T translocation directly. Ethephon and ancymidol may have secondary effects on 2,4,5-T translocation that can be reversed by GA treatment.

A washer was designed and tested for washing soil from weed seed buried in fabric packets and for separating weed seed from soil. The washer was constructed from inexpensive, readily available materials and was found to function efficiently.

Peanut (Arachis hypogaea L. ‘Florigiant’) seed yield was reduced 25% by a fall panicum (Panicum dichotomiflorum Michx.) density of one weed per 4.9 m of row. Greater weed densities resulted in greater yield losses. Peanut seed yield was reduced by fall panicum interference for 2 weeks or more after peanut emergence. Peanuts kept weed-free for 8 weeks after emergence failed to yield as well as those kept weed-free all season. However, control for the first 2 weeks appeared to be the most critical.

Production of native grasses following aerial application of 1.12 kg/ha of 2.4.5-T ((2,4,5-trichlorophenoxy)acetic acid), 2,4,5-T + dicamba (3,6-dichloro-o-anisic acid), or 2,4,5-T + picloram (4-amino-3,5,6-trichloropicolinic acid) (1:) to a south Texas mixed-brush (Prosopis-Acacia) community was significantly increased by all herbicide treatments the year of application, by the herbicide combinations during the second year, but only by 2,4,5-T + picloram the third year after treatment. Moisture-use efficiency based on kg/ha native grass produced/cm precipitation was greastest where the herbicide combinations were applied. Defoliation of woody plants in years of above-average rainfall resulted in favorable grass production responses regardless of herbicide(s). However, range improvement over the 3-yr of study was dependent on maintenance of herbicide effectiveness, especially control of underbrush which resulted only where 2,4,5-T + picloram were applied. Consumption of native grass was a direct function of availability in response to brush control as augmented by rainfall. Forb production was reduced by all herbicides the year of treatment and by 2,4,5-T + picloram the year following application, but was not reduced by any treatment during the third growing season.

The persistence of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)-one] in several soils from the lower alluvial floodplain of the Mississippi River was studied in the greenhouse and laboratory using bioassay and gas chromatographic methods of residue detection. Bioassay results indicated that metribuzin phytotoxicity was lost in several soil types within a few weeks of application. Longevity of phytotoxicity depended upon soil type. However soil type had little effect on the rate of metribuzin degradation measured chemically. Gas chromatographic techniques indicated that metribuzin degradation followed first-order kinetics with half-life values ranging from 17 to 28 days in six soils under greenhouse conditions. Incubation studies indicated that metribuzin was degraded more rapidly in nonautoclaved field soil and in soil enriched with glucose than in soil that had been air dry for 1 yr or had been autoclaved. Degradation was more rapid at 30 C than at 20 C. Microbiological activity apparently is important in the degradation of metribuzin in soil.

Enzymatically isolated leaf cells from cotton (Gossypium hirsutum L. ‘Stoneville’) and soybean (Glycine max (L) Merr. ‘Kino’) were used to study the effect of SAN 6706 [4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] on photosynthesis, protein, RNA, and lipid synthesis during the first 19 hr of herbicidal treatment. Cotton plants are tolerant to SAN 6706, whereas soybean plants are susceptible. SAN 6706 inhibited the incorporation of 14C-bi-carbonate, uridine, and acetate into cotton leaf cells but stimulated incorporation of leucine. Incorporation of all of these precursors into soybean cells was inhibited. Cotton and soybean cells each took up equivalent amounts of labeled SAN 6706. The incorporation activity of the cotton and soybean cells appeared to regulate the entrance of the precursors into the cells by depleting the intracellular precursor pools. It is suggested that the inhibition of RNA and lipid synthesis in cotton and soybean cells is an indirect result of inhibited photosynthesis. Isolated cotton cells were not tolerant of the herbicide.

Survival of foxtail grass in undisturbed sites was tested in a 4-yr study of robust white foxtail (Setaria viridis var. robusta-alba Schreiber), robust purple foxtail (Setaria viridis var. robusta-purpurea Schreiber), giant green foxtail [Setaria viridis var. major (Gaud.) Posp.], yellow foxtail [Setaria lutescens (Weigel) Hubb.], and giant foxtail (Setaria faberi Herrm.). Regardless of taxa seeded, giant foxtail dominated the stand with small amounts of yellow foxtail in the fourth year. Although the foxtail taxa stands corresponded to the taxa seeded in the first year of growth, robust white foxtail, robust purple foxtail, and giant green foxtail completely or nearly disappeared within 4 yr of having been seeded alone or with other taxa, and generally sooner when mixed with giant foxtail. Because of the rapid dominance of giant foxtail, the robust white foxtail, robust purple foxtail, and giant green foxtails are not likely to become a source of seed for infestation from fencerows to production fields.

Field studies were conducted over a 3-yr period to evaluate weed control systems for soybeans [Glycine max (L.) Merr.] grown in 18- and 76-cm rows. Combinations of herbicides satisfactorily controlled a broad spectrum of annual grass and broadleaf weeds in soybeans grown in 76-cm rows with cultivation and in 18-cm rows without cultivation. Where a single herbicide treatment was used to control only annual grasses, the 76-cm rows (which were cultivated once) yielded from essentially the same as 18-cm rows up to almost 50% more than the 18-cm rows, which received no cultivation, depending on the year and broadleaf weed infestation. However, where herbicide combinations were used to effectively control all weeds, soybeans in 18-cm rows averaged up to 9% higher yields than those in the 76-cm rows.

The substituted 2,6-dinitroanilines were first reported as herbicides in 1960. At the present time, there are 14 2,6-dinitroaniline herbicides in various stages of product development. Literature on absorption, translocation, and mode of action of the dinitroaniline herbicides refers almost entirely to trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline]. These herbicides do not directly inhibit the germination of seed. Inhibition of lateral root development is the most characteristic growth response. Swelling of the root tip is a universally recognized morphological effect caused by these compounds. The cells in this region are multinucleate, indicating that the mitotic process has been disrupted. Examination of these cells shows an increase in the percentage of cells in arrested metaphase due to the disruption of spindle microtubules. Inference is made that the dinitroaniline herbicides affect chromosomes in a manner similar to colchicine, but research with pig brain (Sus scrofa) microtubules has shown that effects of the herbicide on microtubular protein is different.

Injury to the top of plants is recognized by stunting, development of dark green color, and swelling and brittleness of the stem or hypocotyl. The major sites of uptake are the shoot of monocots and the hypocotyl or hypocotyl hook for dicots. Exposure of seedling roots to the dinitroaniline herbicides does not kill the plant, but exposure of the young shoot will result in death. Available data indicate that the dinitroaniline herbicides are either absorbed or adsorbed by the roots due to the proximity of the roots to the herbicide, but that translocation from the root to the top is minimal. When a dinitroaniline was found in the plant, the parent compound was the major product present with metabolites equal to 5% or less.

Insufficient information is available to accurately describe effects of these herbicides on plant carbohydrates, lipids, and nitrogenous compounds. The effect of trifluralin on RNA and DNA varies with the plant species, treatment time, concentration of herbicide, and plant part investigated, but differences observed do not correlate with dinitroaniline-susceptible and resistant species. Enzyme activity does not appear to be greatly inhibited by the dinitroaniline herbicides. However, the dinitroaniline herbicides interfere with photosynthesis and respiration in vivo and in vitro.

The phytotoxic action of trifluralin can be antidoted with the organophosphorus insecticides, phorate [0,0-diethyl-S-(ethylthiomethyl)-phosphorodithioate], disulfoton [0,0-diethyl-S-2-(ethylthioethyl)-phosphorodithioate], and externally applied lipids such as D-α-tocopherol. There is a strong correlation that seeds with a high lipid content are resistant to trifluralin and those with a low lipid content are susceptible. Despite all the work that has been conducted, the mode of action of the dinitroaniline herbicides is still unclear.

In field trials, soybeans [Glycine max (L.) Merr.] treated with trifluralin [α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine] at 0.56 and 0.84 kg/ha were protected from injury by metribuzin [4-amino-6-tert-butyl-3-(methylthio-as-triazine-5(4H)one] at 0.28 to 1.12 kg/ha. Soybean injury from metribuzin at high soil pH values was reduced by applying it in combination with trifluralin. Trifluralin also protected soybeans from injury caused by low rates of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] greenhouse studies. The trifluralin treatment reduced root development and greatly reduced 14C-atrazine and 14C-metribuzin uptake and content within the soybean plant.