Thiobacillus thioparus, Azotobacter chroococcum, Rhizobium leguminosarum, Aspergillus niger, Paramecium caudatum, Colpidium sp., and a mixed culture of soil ciliates were not adversely influenced nor stimulated by the presence of dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA). Soil from plots treated 7 years at 5.0 ppm showed no accumulation of DCPA. Plate counts of actinomyces, bacteria, and molds from field and laboratory-treated soils showed no adverse effect. A mixed culture of soil algae and fungi grew significantly more in the presence of DCPA.

The selective properties of 5-amino-4-chloro-2-phenyl-3-(2H)-pyridazinone (pyrazon), a new herbicide for the control of weeds in sugar beets, were investigated. Common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and green and yellow foxtail (Setaria viridis (L.) Beauv. and S. glauca (L.) Beauv.) represented about 77% of the weeds emerging and developing with beets. The preemergence rate of 4 to 5 lb/A pyrazon satisfactorily controlled the two broadleaf weed species but was marginal in controlling foxtail. At 6 and 7½ lb/A, beet stands were reduced; however, because of the standard practice of overseeding, normal stands were possible and yields of roots and extractable sugar were unaffected. Preemergence applications of aqueous suspensions of pyrazon were more satisfactory than postemergence. The addition of miscible non-phytotoxic oils or adjuvants to aqueous mixtures greatly improved the postemergence activity of pyrazon. In spite of the occasional temporary beet injury, beets in the two to four-leaf stage seemed relatively tolerant to postemergence treatments. Control was excellent when weeds were treated in the seedling stage (i.e. between cotyledon and four true leaves).

Sixteen field tests conducted over 12 years showed that, under the soil and climatic conditions prevailing in the Peace River region of western Canada, application of maximum rates of 20 lb/A of 2, 2-dichloropropionic acid (dalapon) combined with tillage did not kill more than 95% of quackgrass (Agropyron repens (L.) Beauv.). Best treatment was to rejuvenate the quackgrass in the spring by thorough tillage, apply the dalapon when the resprouts were 4 to 6 in tall, till thoroughly again about 2 weeks later, and then till at monthly intervals until freeze-up. The type of implement used was not important, providing the quackgrass rhizomes were thoroughly shredded. With rates of dalapon at or below 20 lb/A, no residual effect occurred on cereal crops planted in the spring following the year of treatment.

Sorghum (Sorghum bicolor (L.) Moench) yields were correlated negatively with weed yields and positively with stover yields, sorghum heads per plant, and sorghum weight per 1000 seeds. Sorghum yields were not different when weeds were removed 1, 2, or 3 weeks after planting and each week thereafter, but a significant yield decrease occurred each week when weeds were not removed for 4, 5, 6, or 8 weeks. Sorghum kept weed-free the first 4 weeks after planting showed little yield loss from weeds emerging later. Weeds left after two cultivations reduced sorghum yields 38% below plots weeded weekly. As weed competition increased, sorghum grain yield, stover yield, sorghum heads per plant, seed weight per head, and weight per 1000 seeds decreased, whereas sorghum seed moisture at harvest increased.

A laboratory assay method was developed for studying pricklypear (Opuntia sp.) responses to herbicides. Herbicidal translocation from one pad to another and lateral translocation across a pad appeared to be very slight. Pads were killed when a butoxy ethanol ester, a propylene glycol butyl ether ester, or a 2-ethylhexyl ester formulation of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) was applied to only one side. Increasing temperatures from 21 to 43 C increased the rate of killing pads. Concentrations of 2,4,5-T at 8 lb aehg of solution usually killed the pad at temperatures above 21 C. Concentrations of 2,4,5-T at 4 lb aehg or less had little effect on the pads. Relative humidity level had little effect on 2,4,5-T activity, but the activity of a propylene glycol butyl ether ester of 2,4-dichlorophenoxyacetic acid (2,4-D) was more effective at the 90 to 95% level than at levels ranging from 30 to 75%. Water, diesel oil, and three diesel oil:water mixtures had little effect on 2,4,5-T toxicity. More toxic effects were shown by 2,4,5-T than 2,4-D. The propylene glycol butyl ether ester, the butoxy ether ester, and the 2-ethylhexyl ester of 2,4,5-T were equally effective on pricklypear at the same concentrations.

Herbicidal residues in water and soil were determined after treating eight ponds with six herbicides. Relatively high concentrations of 2,6-dichlorobenzonitrile (dichlobenil), 2,3,6-trichlorophenylacetic acid (fenac), and 2,4-dichlorophenoxyacetic acid (2,4-D) were present in the upper 1-in of the hydrosoil following treatments with granular formulations of these herbicides. Fenac and dichlobenil residues persisted in both water and soil for periods exceeding 160 days. Low concentrations of 2,4-D were found in water for 24 days and in the soil for 55 days following treatment. The mono-N,N-dimethylcocoamine salt of 7-oxabicyclo(2.2.1)heptane-2,3-dicarboxylic acid (amine salt of endothall), 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat), and 6,7-dihydrodipyrido(1,2-a:2’,1′-c)-pyrazidiinium salt (diquat) were relatively less persistent in water and were no longer found after 24, 8, and 4 days, respectively. However, paraquat and diquat were held by the hydrosoils and persisted in high concentrations for more than 85 and 160 days, respectively. In ponds with dense weed infestations, a large fraction of the herbicide may be held by the plants for some time.

A soil column system for determination of relative movement of herbicides in soils is described. A data presentation system which expresses the results for each herbicide in a given soil as a single number is proposed. Comparisons of mobilities of new herbicides with those known for other older, better understood herbicides should make it possible to predict the behavior of new herbicides in the field. The aromatic acid herbicides were most mobile, and the insoluble toluidines least mobile. Results for 28 herbicides are presented.

Treatments made at 2-week intervals on guava (Psidium guajava L.) with a 1:1 ratio of butoxyethanol esters of 2,4-dichlorophenoxyacetic acid:2,4,5-trichlorophenoxyacetic acid (2,4-D:2,4,5-T) have shown it to be more susceptible when treatments are made during the wet season than during the dry season. Greater susceptibility is related to a plant condition characterized by many new leaves but little or no terminal twig elongation. A similar pattern of defoliation response is caused by 2-methoxy-3,6-dichlorobenzoic acid (dicamba) and 2,3,6-trichloropicolinic acid (picloram) as by 2,4-D:2,4,5-T, but the period of maximum susceptibility based on defoliation percentages 1 year after treatment occurred later in the season.

A field study was made on the competitive effect of quackgrass (Agropyron repens (L.) Beauv.) on corn for the nutrients N, P, and K during 1962 and 1963. Quackgrass competition drastically reduced corn height and yield and delayed maturity. High levels of fertilization did not overcome the effects of quackgrass competition. The annual uptake by quackgrass during the growing seasons of 1962 and 1963 was 105, 15 and 60 lb/A of N, P, and K, respectively. Quackgrass shoots harvested at maturity in mid-July had taken up 55, 45, and 68% of the total N, P, and K, respectively, that was removed throughout the season by quackgrass shoots plus rhizomes. It appeared that the early season uptake of N and K by quackgrass may have contributed to, but was not solely responsible for, the reduction in corn height and yield and delayed maturity noted later in the season.

The effect of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) on the growth of cotton seedlings was studied under greenhouse conditions as influenced by dosage, 0.25, 0.5, 0.75, and 1.0 lb/A, and depth of soil-incorporation, 0 to 6 in in 0.5-in increments; the cotton seed were planted 1.5 in deep and watering was by subirrigation.

Trifluralin caused stunting in height of cotton seedlings and prevention of lateral root growth. The dosage of the chemical influenced the degree and persistence of stunting more than did depth of incorporation. Marked stunting occurred at 1 lb/A at all depths of incorporation and persisted for the duration of the experiments, about 1 month; slight to moderate stunting occurred at 0.75 lb/A or less but was of short duration, 1 to 2 weeks. Lateral root growth was affected more by depth of incorporation than by dosage; though the growth of the taproot was essentially unaffected, the growth of lateral roots was completely prevented by even the lowest dosage applied, 0.25 lb/A, incorporated to the greatest depth, 6 in. Root growth was prevented only along that portion of the taproot growing in treated soil; when trifluralin was incorporated above the seed, root development was unaffected. Stunting occurred independently of the effect on root growth.

Soil incorporation and site of uptake of preemergence herbicides was investigated under greenhouse conditions using green foxtail (Setaria viridis (L.) Beauv.) and the herbicides 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-N-isopropylacetanilide (hereinafter referred to as CP31393), 3-amino-2,5-dichlorobenzoic acid (amiben), 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), ethyl N,N-dipropylthiolcarbamate (EPTC), and α,α,α-trifluroro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin). As depth of incorporation of most herbicides was increased, control of green foxtail decreased, indicating a dilution effect. Subsurface application of herbicides at a 2-in depth generally was less than half as effective as surface application or shallow incorporation.

With three different moisture conditions, shallow incorporation of trifluralin to depth of 1 in was beneficial at all moisture levels. Shallow incorporation of atrazine and EPTC improved effectiveness under conditions analagous to furrow irrigation but not under conditions simulating moderate or high rainfall immediately after application. Shallow incorporation of the ammonium salt of amiben increased effectiveness significantly under high moisture but decreased effectiveness under low moisture. Effectiveness of linuron was reduced by incorporation under moderate and high moisture. Shallow incorporation did not significantly affect results with CP31393 under any moisture condition.

For the six herbicides tested, the expression of lethal action on tops of green foxtail was evident when herbicide was placed in the shoot zone but not when placed in the root zone during the 2-week period after seeding.

Wet tropical forests have a high diversity of woody species which cause problems in sampling and analysis of data regarding herbicidal effectiveness. Three simplified sampling procedures were tested to determine their reliability in providing an estimate of whole-plot defoliation from broadcast applications. A procedure using a 50-tree sample including all species will provide the most reliable data.

Postemergence application of isopropyl N-(3-chlorophenyl) carbamate (CIPC) killed small seedlings or redroot pigweed (Amaranthus retroflexus L.), large crabgrass (Digitaria sanguinalis L.), and pale smartweed (Polygonum lapathifolium L.). However, the apparent mode of action in redroot pigweed and large crabgrass was different from that in pale smartweed. The first two species showed injury symptoms 1 to 2 days after spraying, while the effect of the herbicide on pale smartweed was slow and no growth inhibition was observed until about 2 weeks after application. Injury symptoms of smartweed were different from those of the other two species. Tolerance of redroot pigweed and large crabgrass to CIPC increased rapidly with age.

Studies on respiration, C14O2 fixation, and chlorophyll content showed that the fast action in redroot pigweed and large crabgrass was accompanied by a reduction in photosynthesis, decrease in chlorophyll content, and increase in respiration. In pale smartweed, where slow action of CIPC took place, there was no change in carbon dioxide fixation, chlorophyll content, or oxygen uptake until about 2 weeks after spraying, when symptoms of this type of action were first observed.

Three experiments were conducted over a period of 2 years on native grasslands in an attempt to suppress or control the resident vegetation to permit the establishment of alfalfa. Spring applications of 1,1′-dimethyl-4,4’ bipyridilium salt (paraquat) at 1 lb/A were effective in suppressing the existing grasses and forbs, thereby enhancing alfalfa establishment; however, woody perennials were not effectively controlled. Application of a mixture of 2,4-dichlorophenoxyacetic acid(butyl ester of 2,4-D) and 2,4,5-trichlorophenoxyacetic acid (iso-octyl ester of 2,4,5-T) (2:1 ratio) at 1½ lb/A prior to paraquat treatments and alfalfa seeding also was ineffective in controlling woody perennials. Alfalfa could not be successfully established when seeded 6 days after the application of phenoxy herbicides. Fall applications of paraquat at rates up to 1.5 lb/A were not effective in suppressing the resident vegetation; thus, alfalfa seeded in the following spring failed to establish an adequate stand.

Corn, cotton, peanuts, and soybeans in various rotations received six separate herbicidal treatments in a 5-year rotation from 1959 through 1963. Several of the combination treatments were highly effective in controlling witchweed (Striga spp.). Land heavily infested with witchweed required 3 to 4 years of herbicidal treatments before the competition of witchweed was eliminated and normal corn yields were produced. The most effective treatment for the control of witchweed without crop injury was postemergence applications of ½ lb/A 2,4-dichlorophenoxyacetic acid (2,4-D) as needed in continuous corn.

At the end of the 5-year study, all plots were planted to corn, Using corn yields as a criteria, there were no differences in witchweed competition in herbicide treated plots with continuous corn and herbicide treated plots in which corn was rotated with other crops.

The potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram) was applied as soil, foliar, and soil plus foliar treatments to defoliated and non-defoliated huisache (Acacia farnesiana (L.) Willd) grown in the greenhouse. Soil applications of ⅛ lb/A were more effective than foliar treatments. However, soil or foliar applications at ½ lb/A were lethal on non-defoliated plants. Defoliated plants treated with ½ lb/A showed considerable regrowth, indicating that leaves were important for absorption and movement of the herbicide into stem and root tissues. Plants treated with ¼ lb/A of picloram and defoliated after 0, 4, 10, and 24 hr indicated that 24 hr were necessary to obtain maximum herbicidal effectiveness.

Picloram content was determined in the leaves, upper stem, lower stem, and roots by gas chromatographic analysis, 3, 10, and 30 days after treatment. Most of the picloram applied to foliage was found in and on the leaves 30 days after treatment. The upper stem contained several times more picloram than the lower stem. No detectable amounts of picloram were found in the leaves and upper stem 3 and 30 days after soil treatment. The concentration of picloram in roots from soil applications was similar to foliar treatments. Absorption and movement studies showed that a period of 24 hr was required to move lethal amounts of picloram into stem and root tissues of huisache after foliar treatments.

The depth of leaching of 3(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) in a Yolo sandy clay loam soil was altered by the various types—anionic, cationic, or nonionic—of surfactants. The effects of surfactants Aliquat 204 and Aliquat 221 on the leaching of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), 1-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon), and diuron may reflect a sorption complex of the substituted urea herbicide, surfactant, and the soil. This sorption appears to be closely associated with the dilauryl portion of the surfactant molecule. Other surfactants of the Aliquat series containing lauryl, dioctyl, and distearyl substitutions had little or no effect on this sorption phenomenon.

Differences in degree of seed dormancy were shown to exist both among and within the four varieties of wild oats (Avena fatua L. spp. fatua (L.) Thell.) occurring in natural infestations throughout southwestern Alberta. Among the varieties, pilosissima was the most dormant, intermedia was more dormant than vilis, and glabrata possessed about the same dormancy as intermedia. Dormancy was overcome more rapidly under dry storage in vilis and glabrata than in intermedia and pilosissima. Seed dormancy of most collections made in 1959 differed from that of collections made at the same locations in 1962, being both higher and lower by as much as 40% in either of the varieties vilis or intermedia. In seeds from plants grown as transplants at three sites, dormancy differed within varieties, but there was no consistent pattern of difference evident among sites.

Amitrole (3-amino-1,2,4-triazole) is absorbed and actively bound to non-physiological sites in Salmonella typhimurium. Accumulation of amitrole is inhibited by purines; but the effect does not seem to explain adenine protection against growth inhibition by amitrole. Guanine, xanthine, and hypoxanthine cannot replace adenine in growth protection but do inhibit accumulation of amitrole in the bacterial cells.

Subsurface application of liquid or granular formulations of ethyl N,N-dipropylthiocarbamate (EPTC) at planting time effectively controlled annual grass weed species in new seedings of alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.). Control of annual broadleaf weeds by EPTC was incomplete. A postemergence application of 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB) in addition to the EPTC treatment resulted in excellent overall weed control. Benefits of weed control were more evident in birdsfoot trefoil than alfalfa.