Quackgrass (Agropyron repens (L.) Beauv.) was controlled with applications 1 to 8 months prior to plowing and planting of from 1 to 4 lb/A 2,3,5-trichloro-4-pyridinol (pyriclor). Corn (Zea mays L., hybrid W530) planted on pyriclor-treated plots grew normally and yielded as well as on plots given the standard preplow treatment of 2 lb/A of 2-chloro-4-ethylamino-6-isopropylamino-5-triazine (atrazine). Oats (Avena sativa L., var. Portage) was injured by soil residues of pyriclor from 2-lb/A applications made 20 months previously. Alfalfa (Medicago sativa L., var. Vernal) was somewhat more tolerant of pyriclor than was oats.

The effects of residues of 16 herbicides used to control downy brome (Bromus tectorum L.) were studied in the greenhouse. Crested wheatgrass (Agropyron desertorum (Fisch. ex Link) Schult.) was planted in soils collected from field plots sprayed 1 to 4 years previously. At the rates used, some residues were lethal to crested wheatgrass seedlings, some caused severe malformation and/or herbage yield reduction, while others had no adverse effects.

The influence of 2,6-dichlorobenzonitrile (dichlobenil) on yield, size, and pigmentation of cranberries (Vaccinium macrocarpon Ait., var. Early Black) was studied. Data on the effect of fall and spring applications were collected over a 2-year test period and comparisons made. Yield increased and berry size decreased after 1 year from both fall and spring treatments. The slight increases in yield were attributed to good weed control and not to any direct effect of dichlobenil. Treatments of cranberries for 2 successive years (fall and spring) caused slight reductions in yield and berry size. Berries treated for 2 successive years with dichlobenil were analyzed for anthocyanin development. All applications considerably enhanced pigmentation, spring treatments having the greatest effect in this respect. Anthocyanin development increased with increase in the concentration of dichlobenil applied.

Injections with 4-amino-3,5,6-trichloropicolinic acid (picloram), 2-methoxy-3,6-dichlorobenzoic acid (dicamba), and butoxyethanol ester of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) satisfactorily killed the tops of scarlet oak (Quercus coccinea L.) and white oak (Quercus alba L.) when applied in March or June. Triethylamine salt of 2,4,5-T adequately killed the tops of the oaks in June but not in March. Picloram was the most lethal herbicide used on red maple (Acer rubrum L.), and sprouting was controlled more effectively on all species with picloram than with the other herbicides.

Foliar applications of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) at 0.05 to 1.0 lb/A caused characteristic injury symptoms on cucumber (Cucumis sativus L.) plants. Analytical methods were evaluated and found suitable in detecting atrazine in cucumber leaves sprayed at a low rate of 0.005 lb/A. For analytical detection, tissue samples should be taken as soon as necrotic symptoms appear, 4 to 7 days after suspected drift, and frozen immediately.

Red beets (Beta vulgaris L., var. Detroit Dark Red) converted the herbicide 5-amino 4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) to N-2-chloro-4-phenyl-3-(2H)-pyridazinone glucosamine. Isolation was accomplished by water, benzene, and alcohol extraction of foliage followed by purification through molecular sieve columns. Identification was established by infrared spectroscopy, and thin layer and gas liquid chromatography.

Fifteen herbicidal treatments were evaluated for weed control effectiveness in peanut (Arachis hypogaea L.) culture at three locations in the peanut production area of eastern North Carolina during 1964 and 1965. Delayed preemergence treatments of 4,6-dinitro-o-sec-butylphenol (DNBP) alone and in combination with O-(2,4-dichlorophenyl) O-methyl isopropylphosphoroamidothioate (DMPA) were superior to conventional herbicidal and non-herbicidal control methods as were single and multiple incorporated treatments of S-propyl dipropylthiocarbamate (vernolate). A single postplant vernolate treatment incorporated 1 in deep provided weed control superior to that obtained for single preplant vernolate treatments incorporated 1 in or 3 in deep. Increased weed control and increased peanut safety were obtained from 2.5 lb/A of vernolate by incorporating treatments at 0, 7, and 14 days after planting rather than by using a single application. This multiple treatment was the optimum one evaluated and provided 53 days of control and required 10 hr/A of hoeing time.

The effects of 22 herbicides on oxidative phosphorylation in mitochondria from cabbage (Brassica oleracea var. capitata L.) have been studied. Carbamates, phenoxyacids, 3,5-dimethyltetrahydro-l,3,5,2H-thiadiazine-2-thione (DMTT), N-1-napthylphthalamic acid (NPA), 2,3,6-trichlorobenzoic acid (2,3,6-TBA), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), and 2-chloro-2-N,N-diallylacetamide (CDAA) inhibited phosphorylation to a greater extent than oxygen uptake in cabbage mitochondria. The compounds 1,2-dihydropyridazine-3,6-dione (MH), 2,2-dichloropropionic acid (dalapon), 2,2,3-trichloropropionic acid (hereinafter referred to as 2,2,3-TPA), sodium chlorate, and 3-amino-l,2,4-triazole (amitrole) at concentrations as high as 1 × 10–2 M did not have a large effect on oxidative phosphorylation in cabbage mitochondria. Respiration which was stimulated by 2,4-dinitrophenol (DNP) or adenosine diphosphate (ADP) was inhibited by 2,4-dichlorophenoxyacetic acid (2,4-D). Although 2,4-D did not affect Mg++-stimulated adenosine triphosphatase (ATPase), it inhibited an oleate-stimulated ATPase activity and the ATP-32Pi exchange reaction in cabbage mitochondria. The results suggest that 2,4-D may inhibit respiration in cabbage mitochondria by an effect on a reaction involved in coupling phosphorylation with electron transport.

Smooth bromegrass (Bromus inermis Leyss.) treated in the fall tended to be more damaged than that treated in the spring, regardless of herbicide. Nitrogen fertilizer reduced the loss in yield resulting from herbicides but was least effective with 1 lb/A of 4-amino-3,4,6-trichloropicolinic acid (picloram). Laboratory studies showed that roots of smooth bromegrass were the primary site of picloram uptake. Root uptake explained the severe damage in curred from applications of picloram made in the fall. The order of increasing phytotoxicity of herbicides to smooth bromegrass studied in these experiments was 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2,4-dichlorophenoxyacetic acid (2,4-D)<2-methoxy-3,6-dichlorobenzoic acid (dicamba) < picloram.

As determined by bioassay of segmented soil columns, a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), N-butyl-N-ethyl-a,a,a-trifluoro-2,6-dinitro-p-toluidine (benefin), and 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) varied in their leachability in a clay loam soil, even though their water solubility is the same. Nitralin was by far the more easily leached, benefin was least leached, and trifluralin slightly more so than benefin. Four A-in or more of water readily leached nitralin deep enough into the soil in amounts great enough to adversely affect the root growth of sensitive crop plants. Trifluralin and benefin were leached into the soil in relatively minute amounts, and these amounts were not great enough to affect root growth of sensitive crop plants when at least 0.5-in of untreated soil separated the seed from the layer of soil in which the herbicides had been mixed. The apparent breakdown product of nitralin present in moist soil was leached as readily as nitralin.

The herbicides 2,6-dichlorobenzonitrile (dichlobenil), 7-oxabicyclo-(2.2.1)heptane-2,3-dicarboxylic acid (endothall), and 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) were examined for their influence on the activity and synthesis of proteolytic enzyme(s) in the cotyledons of squash (Cucurbita maxima Duchesne) seedlings. None of these herbicides affected the activity per se of the isolated proteolytic enzyme(s). The presence of the herbicides in the culture solution during germination caused different effects on the development of the proteolytic activity in the cotyledons for each of the three herbicides. Dichlobenil reduced the development of the activity in both the excised cotyledons and the cotyledons of intact embryos. This inhibition was overcome in part by the addition of benzyladenine to the culture solution. The inhibition of hormone synthesis or export by the embryonic axis caused by dichlobenil could explain the observed results. Endothall inhibited the development of the proteolytic activity in the cotyledons of the intact embryo treatment but had little effect on the excised cotyledons. Benzyladenine did not reverse this inhibition. The effect of endothall resembled the inhibition caused by actinomycin D, possibly indicating that endothall interfered with ribonucleic acid metabolism. Bromoxynil inhibited the proteolytic enzyme(s) development in the cotyledons of intact embryos but not in the excised cotyledons. This inhibition was partly overcome by benzyladenine. These results suggest that bromoxynil not only interferes with the hormonal control mechanism but also proteinase synthesis.

Nineteen granular herbicides were applied at two rates to garden chrysanthemums (Chrysanthemum morifolium Ram.) in plantings at St. Paul and Morris, Minnesota. The soil at St. Paul was classified as silt loam and at Morris, as clay loam. All herbicides were applied to freshly cultivated plots which then were irrigated. The compound a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) at 8 lb/A gave excellent weed control at both locations; trifluralin at 4 lb/A gave 99% and 97% weed control at St. Paul and Morris, respectively; 3-amino-2,5-dichlorobenzoic acid (amiben) at 6 lb/A gave 99% control at Morris and 76% control at St. Paul; 2,6-dichlorobenzonitrile (dichlobenil) at 3 lb/A gave 93% control at St. Paul and 88% at Morris. Application of 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne) at 8 lb/A gave excellent weed control at both locations but caused serious injury to the chrysanthemums.

An experiment to investigate tillage practices for producing safflower (Carthamus tinctorius L.) and controlling weeds was conducted from 1963 to 1965. Three tillage intensities designated excessive, moderate, and minimum, depending on the number and kind of tillage operations performed prior to planting, were used. Three different tillage tools used as the primary implement in preparing the seedbed were sweep machine, oneway, and moldboard plow.

Excessive, moderate, and minimum tillage plots averaged 342, 374, and 413 lb/A of safflower and 72, 73, and 63 lb/A of weeds, respectively. The sweep machine plots produced the highest safflower yields and lowest weed yields at all intensities with the oneway and moldboard plow about the same. Yields produced from the best treatments in the experiment (minimum tillage with the sweep machine and seeding with the shoe drill) averaged approximately 300 lb/A more than commercial fields and weed control was effective.

The proteolytic activity of the cotyledons of squash (Cucurbita maxima Duchesne) increases several fold during germination. The different herbicides varied widely in their ability to inhibit this increase. An attempt was made to correlate this inhibition with inhibition of growth. A direct correlation was evident only when the inhibition of proteolytic activity was severe or very slight to nonexistent.

Six herbicides were applied at 3, 9, and 27 lb/A to the soil in forests of three types in Puerto Rico. The forests differed in soil type, amount and pattern of rainfall, and species composition. Defoliation occurred slowly, but the correlation between percentage defoliation and plants killed was significant at the 1% level of probability. Some defoliation was evident 1 month after treatment and increased slowly during the next 6 to 8 months. The most effective herbicide was 4-amino-3,5,6-trichloropicolinic acid (picloram). Generally, 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 2-methoxy-4,6-bis(isopropylamino)-s-triazine (prometone), and 5-bromo-3-sec-butyl-6-methyluracil (bromacil) were less effective than picloram. Both 2,3,6-trichlorophenylacetic acid (fenac) and 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron) were ineffective. Defoliation was greatest and more plants were killed in the driest site.

One year after treatment, fenac was the most persistent herbicide in the soil. Herbicides were found to a 36 to 48-in depth within 3 months after application.

Herbaceous and woody seedlings were present at all sites within 18 months after herbicide application. There was no definite relationship between herbicidal treatment and secondary succession, except that the number and frequency of successional species were greater on plots having the highest percentage of defoliation.

The loss of 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and 4-amino-3,5,6-trichloropicolinic acid (picloram) in runoff water was determined with a gas chromatograph and bioassays. When determined 24 hr after application, losses of dicamba and picloram were greater from sod plots than from fallow plots while 2,4,5-T losses were about equal. Four months after application, losses of all herbicides averaged less than 1% of that lost 24 hr after application. The amount of picloram lost in a simulated rainfall of 0.5 inch varied with rate, but the percentage lost was the same. The slope of the plot and movement over untreated soil influenced the percentage of picloram lost. The maximum loss obtained for any herbicide was 5.5% and the average approximately 3%.

The production of red triphenyl formazan (hereinafter referred to as TPF) from colorless 2,3,5-triphenyl tetrazolium chloride (hereinafter referred to as TTC) by living cells was used as a vitality indicator for examining the effects of 6,7-dihydrodipyrido[1,2-a:2′,1′-c] pyrazidiinium salt (diquat) in elodea (Elodea canadensis Michx) shoots at varying light intensities. Diquat at 10 ppmw completely killed the elodea in 6 hr at 183 ft-c and at almost the same rate at 13,000 ft-c due to light saturation near the lower level. Over 24 hr were required for this effect in the dark. Between 29 and 183 ft-c, TPF production varied inversely with the light intensity. A comparison is made with the destruction of chlorophyll by diquat.

Dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA) on the soil surface inhibited rooting at bermudagrass (Cynodon dactylon L., var 328) stolon nodes. Histological studies of these root tips showed that cell division had ceased while cell enlargement continued for some time. Cells became excessively large and irregularly shaped. In corn (Zea may L., var. Pioneer 310), radicle cell size was about the same in both instances; however, treated tissue contained six times as many dinucleate cells as untreated radicle tissue. Numerous nuclei were at metaphase stage of mitosis in treated tissue. In untreated onion (Allium cepa L., var. Yellow Globe Danvers) root tips, many nuclei were found at anaphase and telophase stage of mitosis while very few cells were dividing in treated tissue.

The phytotoxicity and the persistence of ethyl N,N-dipropylthiocarbamate (EPTC), S-propyl butylethylthiocarbamate (pebulate), ethyl N-ethyl-N-cyclohexylthiocarbamate (hereinafter referred to as R-2063), and S-2,3-dichloroallyl N,N-diisopropylthiolcarbamate (diallate) were studied in nutrient solution and in five soil types. Both in nutrient solution and in soil, EPTC was the most toxic to barnyardgrass [Echinochloa crusgalli (L) Beauv.], followed in order by pebulate, R-2063, and diallate. Herbicidal injury, as reflected by the morphological aberrations that occurred in treated plants, was much more severe than the reduction in fresh weight. Thus, toxicity studies based on plant height had greater validity than those based on weight. The initial toxicity of each herbicide was high in those soils low in organic matter and low in soils high in organic matter. The persistence of the four thiocarbamates in the soil was associated primarily with adsorptive forces and microbial degradation. In a soil with extremely large or small adsorptive capacity, there was rapid inactivation of the herbicides because of strong adsorption to the colloids or lack of adsorption with consequent loss by volatilization. Under the latter conditions, the microbial breakdown played only a secondary role. The herbicides persisted longer in soils with more moderate adsorptive capacities but were subjected to more striking degradation by microorganisms. The patterns and rates of inactivation of the four herbicides in a given soil were quite similar. A particular concentration of each herbicide stimulated growth in barnyardgrass, as reflected both in the fresh weights and in the heights of the plants. The nature of this stimulation was not determined.

In a study of the selective action of 3-(3,4-dichlorophenyl)-l-methoxy-l-methylurea (linuron), parsnip (Pastinaca saliva L., var. Harris Model) possessed a high degree of tolerance as compared to tomato (Lycopersicum esculentum Mill., var. Kokomo). Linuron was readily taken up by the roots of tomato and distributed throughout the plant, but it remained mostly in the roots of parsnip. Linuron in the leaves of parsnip was metabolized, to a great extent, while very little of the metabolite (s) was found in tomato. The herbicide caused rapid and complete inhibition of photosynthesis in tomato, and the plants never recovered. Photosynthesis in parsnip was inhibited but only temporarily. Therefore, it appears that the selectivity of linuron on these two species may be explained by the two mechanisms of differential accumulation in the foliage and metabolism of the herbicide.