Several methods were used to overcome herbicide phytotoxicity to upland rice (Oryza sativa L., ‘IR8′). Seed pelleting with activated carbon and band application of activated carbon slurry over the rice seed were ineffective in reducing the toxicity of chloramben (3-amino-2,5-dichlorobenzoic acid) and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] to upland rice. In contrast, a 2.5-cm layer of activated carbon and vermiculite mixture (1:1) placed over the rice seed was effective in overcoming the toxicity of these herbicides. Deep sowing (3.0 to 4.5 cm) of rice seed was adequate in protecting upland rice from herbicides which are toxic to direct seeded, flooded rice but are not toxic to transplanted rice. The degree of protection from deep sowing, however, was determined by site of uptake, herbicide adsorption by soil, leaching, and inherent toxicity of the herbicides to rice seedlings.

Lateral roots of a clone of field bindweed (Convolvulus arvensis L.) were dug each month for 12 months, cut into 6-cm long sections and grown in the dark on moist paper at 23 C to determine if regeneration varies seasonally. New shoots and roots were measured after 8, 11, and 14 days. After 14 days, 69% to 98% of the sections had produced shoots. The mean number of shoots per section was greatest in April (6.4) and least in November (2.0). The monthly mean shoot length ranged from 24 to 43 mm. Although most sections produced shoots, very few produced roots. In May, 31% of the sections grew roots, but only 2% to 16% had new root growth in the other months. For the test period, 83% of the sections produced shoots and only 10% produced roots.

When planted with narrow (53 cm) row spacing, cotton (Gossypium hirsutum L.) ‘McNair 210’ produced maximum yields with as little as 6 weeks of weed-free maintenance. With wider row spacing (79 and 106 cm), however, 10 and 14 weeks of weed-free maintenance were required for maximum yield. When weeds were allowed to grow in cotton for more than 2 to 4 weeks after planting, yield reductions occurred. This tolerance period did not differ with row widths of 53, 79, or 106 cm.

The effects of prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine], diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], fluometuron [1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea], and MSMA (monosodium methanearsonate) on Chlorella pyrenoidosa Chick ‘Strain 252′, Trichoderma viride Pers. ex Fr., and Aspergillus terreus Thom were investigated. Minimum herbicide concentrations necessary to decrease C. pyrenoidosa growth after exposure for 35 generations were 10-8M diuron, 10-7M prometryn, and 10-6M fluometuron. MSMA had no effect. C. pyrenoidosa photosynthesis was essentially stopped by a 2-hr exposure to 5 × 10-6M prometryn or diuron and by 5 × 10-5M fluometuron. Prometryn (5 × 10-5M) or diuron (5 × 10-7M) increased respiration by 70 and 44%, respectively after an 80-min treatment. Maximum fluometuron inhibition of respiration was ca 25% and MSMA had little or no effect. Herbicide concentrations of 0, 10-6, 10-5, and 10-4M were used to measure their effects on colony diameter growth, gain in mycelial dry weight, sporulation, and respiration of the two fungi. No concentration of any of the herbicides had any major effect on any of these parameters except sporulation. T. viride sporulation was increased approximately 20, 30, 35, and 50% by 10-6M concentrations of prometryn, diuron, fluometuron, and MSMA, respectively. Sporulation of A. terreus was also somewhat increased by these herbicides.

Field experiments were conducted for 2 yr on pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl)benzamide] treatments in the Piedmont region of Georgia to aid the transition of overseeded cool-season turf to warm-season turf in early spring. Pronamide applied to overseeded perennial ryegrass (Lolium perenne L. ‘Game’ and ‘Manhattan’) gradually reduced the growth of perennial ryegrass and permitted bermudagrass [Cynodon dactylon (L.) Pers. ‘Tifdwarf’] to initiate spring growth with little competition. Total turfgrass cover and turf quality ratings in pronamide treated plots were lower than ratings for untreated plots during the transition period. However, the reduction in turf quality and stand was minimal when pronamide was applied March 20 at 0.8 kg/ha. The turf quality and stand was 76 and 88% of the untreated check on April 23 and May 9, respectively, but the turf fully recovered within 2 weeks. The turf quality was higher in plots treated with pronamide on March 20 than in untreated check throughout June. The optimum date of promanide treatment in the Piedmont Region for transition of cool-season grass to warm-season grass was March 20, when compared to applications made on February 28, April 9, or April 29.

Differences were shown to exist in photosynthetic rate, transpiration rate, and carbon dioxide leaf diffusive resistance between atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] susceptible (S) and resistant (R) plants of redroot pigweed (Amaranthus retroflexus L.). Chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea] and diruon [3-(3,4-dichlorophenyl)-1,1-dimethylurea] were the only herbicides tested that controlled both biotypes, but all of the herbicides except norea [3-(hexahydro-4,7-methanoindan-5-yl)-1,1-dimethylurea] controlled the S biotype. Although photosynthetic activity and transpiration were reduced in both biotypes by atrazine at 50 and 70 ppm, the decline was much greater in the S biotype than in the R biotype and persisted a longer time in the S biotype. Leaf CO2 diffusive resistances of the biotypes were increased by atrazine applications. Mesophyll resistance was increased to a greater extent than stomatal resistance suggesting that reduction of photosynthesis is due to a greater effect of atrazine on the mesophyll tissue than on the guard cells.

A method for isolating roots of a growing plant was devised. The technique allows treatment of an isolated portion of the root system without disturbance or injury to the untreated root mass. A specially designed planter-box was used to induce natural separation of the root system in 3 to 4 weeks. Weeping willow (Salix babylonica L.) seedlings were used to test the performance of dichlobenil (2,6-dichlorobenzonitrile), paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), sodium hydroxide (NaOH), and copper sulfate (CuSO4 • 5H2O) in reducing the viability of treated roots. A tetrazolium chloride assay was used to determine the difference in viability of the treated roots. Copper sulfate and paraquat-treated plants produced symptoms of systemic injury.

A brief history of chemical weed control in Europe from ancient Greek and Roman times to 1850 is given. The use of the various chemicals recorded is discussed and their possible efficacy commented upon.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] residue analysis of soil samples showed greater amounts of residue extractable at soil pH 6.7 than 4.6. Metribuzin leaching increased with increasing soil pH. Metribuzin disappearance from soil followed pseudo first-order kinetics. The half-life of metribuzin decreased as soil pH increased and increased at all soil pH levels as depth of sampling increased. The decreased activity and decreased rate of metribuzin dissipation at lower soil pH is apparently due to protonation and increased adsorption.

The seed weevil (Microlarinus lareynii Jacquelin duVal) and the stem weevil (M. lypriformis Wollaston) were introduced into the United States and the West Indies to control puncturevine (Tribulus terrestris L.) and Jamaica feverplant (T. cistoides L.). In 14 yr these weevils have partially controlled these weeds in most areas where weevil establishment has occurred. However, indigenous parasitoids, predators, and cold weather affect weevil densities. Presently a coldhardy strain of seed and stem weevils has become established in Nevada and promise control in colder areas.

The loss of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] from metal planchets was decreased by an increase in the amount applied and linseed oil (LO) additive. LO reduced volatility to a greater extent than did other additives. Vapor loss from plant leaves was influenced by plant species, plant leaf maturity, soil moisture, concentration of atrazine applied, volume of oil additive, type of additive, and duration of exposure. Generally, atrazine uptake by plants was inversely related to volatility. Uptake and translocation of 14C-atrazine label was increased more by oil additives than surfactant (SURF) compared to no additive. LO increased 14C-label translocation more in yellow foxtail [Setaria glauca lutescens (Weigel) Hubb.], green foxtail [Setaria viridis (L.) Beauv.], and barnyardgrass [Echinchloa crus-galli (L.) Beauv.] than in corn (Zea mays L.).

A technique of collecting contiguous soil samples was developed that showed the distribution of nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] in the soil profile. About 60 days after the herbicide was applied and incorporated with a disk harrow, the soil was sampled from two sites in 1968, five sites in 1969, and five sites in 1970. Bioassays, that utilized root lengths of grain sorghum [Sorghum bicolor (L.) Moench ‘Dekalb 57E’], indicated large variation in herbicide concentrations among adjacent or on contiguous soil samples.

Methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] were evaluated in separate experiments for postemergence control of large crabgrass [Digitaria sanguinalis (L.) Scop.] and goosegrass [Eleusine indica (L.) Gaertn.] and on tolerance of centipedegrass [Eremochloa ophiuroides (Munro) Hack.], St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’]. Methazole was also evaluated on tolerance of Kentucky bluegrass (Poa pratensis L. ‘Common’). Metribuzin applied at 0.6 kg/ha and methazole at 1.1 kg/ha as single treatments controlled 82 and 87% goosegrass, respectively. Repeated treatments were needed for similar control of large crabgrass. These treatments did not permanently injure bermudagrass or centipedegrass. St. Augustinegrass was severely injured when treated with single applications of methazole at 1.1 kg/ha or metribuzin at 0.6 kg/ha while Kentucky bluegrass was severely injured by methazole applied at any rate. Methazole caused moderate to severe injury to bermudagrass when applied at 2.2 kg/ha in each of two applications and to centipedegrass when applied at 4.4 kg/ha in each of two applications.

Pelleting rice (Oryza sativa L., ‘IR8′) seeds with activated carbon was developed as a means of overcoming herbicide phytotoxicity to direct-seeded, flooded rice. Field and greenhouse experiments showed that pregerminated rice seeds coated three times with activated carbon with 50% polyvinyl acetate as an adhesive, were adequately protected from the injurious effects of chloramben (3-amino-2,5-dichlorobenzoic acid), butachlor [N-(butoxymethyl)-2-chloro-2′,6′-diethylacetanilide] and oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one]. The performance of carbon-coated rice seeds in flooded soil, however, was dependent on time of flooding, method and rate of sowing, rate and time of herbicide application, and quality of activated carbon.

Light after treatment was found to be required for the herbicidal activity of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] following postemergence applications of both herbicides to greenbean (Phaseolus vulgaris L. ‘Spartan Arrow’). The effect of photosynthate and/or light before treatment was investigated. A 24-hr dark period prior to postemergence treatment of the bean seedlings had no effect on herbicidal activity when light followed treatment. The effect of plant pigments on the activity of both herbicides was studied using mutants of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. A white mutant of corn was much more resistant to the herbicides than a greenish-yellow mutant or the normal plant. A yellow mutant of soybean was equally as susceptible as the normal type. Studies with radiolabeled foliar applications of both herbicides showed no significant difference in translocation in the light or dark.

The dissipation of sodium azide (NaN3) from soil was significantly affected by pH, soil moisture, and relative humidity (RH). Loss was more rapid from acid than from alkaline soils. Moist soil (20 to 60% field capacity) or air dry soil in a moist environment (100% RH) lost NaN3 more rapidly than air dry soil in a dry (0% RH) environment. However, dissipation was decreased when soil moisture exceeded 60% field capacity. Degree of leaching and phytotoxicity of NaN3 was not affected by soil pH. Bioassay studies indicated that 10 ppm NaN3 in the soil significantly reduced germination and growth in plant species tested. At concentrations of NaN3 below 10 ppm, plant germination was often delayed but normal growth occurred after NaN3 dissipation.

Propham (Isopropyl carbanilate) at 10-5 M concentration does not inhibit DNA synthesis nor does it reduce the number of dividing cells. It does, however, induce a number of abnormal mitotic figures. At higher concentrations (10-3 M) propham inhibits DNA, RNA, and protein synthesis as well as stopping entry of cells into mitosis and causing those which divide to be aberrant. DNA and RNA synthesis are not inhibited for approximately 3 hr, while protein synthesis is reduced within 1 hr. The metabolic inhibitory effect of propham is reversible at least in roots treated for 8 hr. The most likely mode of action of propham is the inhibition of certain mitotic specific proteins, or possibly some kind of protein binding function as has been suggested in the literature.

Six herbicides were applied monthly from February to May for control of large crabgrass [Digitaria sanguinalis (L.) Scop.] and goosegrass [Eleusine indica (L.) Gaertn.]. Bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] applied in February or March controlled at least 70% of large crabgrass, whereas, treatments applied in April resulted in similar control at two of three locations. All herbicides failed to control large crabgrass when applied in May. Oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] and butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamide] controlled goosegrass for the full season when applied in March or April. Oxadiazon also controlled goosegrass when applied in May.

Benzoylprop ethyl [Ethyl N-benzoyl-N (3,4-dichlorophenyl)-2-amino-propionate] and WL 29761 [methyl-N-benzoyl-N-(3-chloro-4-fluorophenyl)-2-amino-propionate] were applied to wild oat (Avena fatua L.) in wheat (Triticum aestivum L. ‘Manitou’) to study the yield benefits occurring and the efficacy of the compounds on wild oat. Even though removal of the wild oat was at the later growth stages, benzoylprop ethyl and WL 29761 did produce significant yield increases at both rates tested. Efficacy on wild oat ranged from mediocre to virtually complete control. Crop tolerance was satisfactory throughout the study.

Weed competition in soybeans [Glycine max (L.) Merr. ‘Clark 63′] with planted stands of velvetleaf (Abutilon theophrasti Medic.), prickly sida (Sida spinosa L.), and Venice mallow (Hibiscus trionum L.) is reported. Weeds were planted 0, 10, 20, 30, and 40 days after soybeans and competed until soybeans matured. Soybean seed yields were reduced 720, 250, and 230 kg/ha by velvetleaf, Venice mallow, and prickly sida, respectively. Weeds that emerged with soybeans reduced yields 1,010 kg/ha. Weeds planted 10 days later reduced yields 480 kg/ha, but weeds planted 20 to 40 days after soybeans did not significantly reduced yield. Soybean yields were reduced regardless of weed placement in or between soybean rows. Weed competition reduced numbers of soybean pods per plant more than other soybean-yield components.