Common purslane (Portulaca oleracea L.) seeds, produced by the same plants, had different degrees of dormancy. The dormancy variations were caused neither by low seed viability nor by location on the plant where seeds were produced. Seed water content and seed age at time of collection contributed to, but were not solely responsible for, the dormancy variations. Immature, brown seeds of high water content were less dormant than the more mature, black seeds of low water content. The immature seeds germinated better in the dark than did the more mature seeds. A puncture in the seed, over the radicle, broke purslane dormancy. Dormancy was not caused by blockage of water imbibition by seeds. Purslane dormancy developed during later stages of seed maturation on the mother plant.

This invitational paper on the α-chloroacetamides is the first of a series of historical reports on each of the major classes of chemistry that have been developed for herbicides.

Growth room and field studies indicated that coating the seeds of oats (Avena sativa L.) with NA (1,8-naphthalic anhydride) at rates of 0.5 to 1% by seed weight significantly reduced the phytotoxicity of barban (4-chloro-2-butynyl m-chlorocarbanilate) applied to the foliage at rates up to 1.2 kg/ha. Complete protection was obtained when barban was applied at 0.4 kg/ha, the highest rate recommended for the control of wild oats (Avena fatua L.) in cereal crops. Treatment of oat seeds with this antidote did not reduce the herbicidal effect of barban on wild oats grown in the same soil. Thus, coating oat seeds with the antidote may allow the use of barban for the selective control of wild oats in oat crops. NA seed treatment also slightly reduced oat injury from diallate [S-(2,3-dichloroallyl)diisopropylthiocarbamate] and triallate [S-(2,3,3-trichloroallyl)diisopropylthiocarbamate].

Field and greenhouse studies were conducted on S-21634 (1-methyl-4-phenylpyridinium chloride) for control of purple nutsedge (Cyperus rotundus L.) and tolerance of several turfgrass varieties and species. Purple nutsedge was controlled during the initial year of treatment with single applications of 3.4 and 5.6 kg/ha rates. All turfgrasses were injured following treatments, however, all except centipedegrass [Eremochloa ophiuroides (Munro) Hack.] had recovered in 7 to 8 weeks. In general, the injury to centipedegrass was higher and the turf density was lower in the treated plots at the final ratings. None of the treatments applied as a single S-21634 application affected root growth of bermudagrass (Cynodon sp.), ‘Emerald zoysia’ (Zoysia japonica x Z. teniuflolia), centipedegrass, St. Augustine grass [Stenotaphrum secundatum (Walt.) Kuntze], or tall fescue (Festuca arundinacea Schreb, ‘Ky 31′).

Three poisonous varieties of timber milkvetch (Astragalus miser Dougl. ex Hook.) were grown under different temperature regimes in growth chambers. Miserotoxin, the poisonous chemical in timber milkvetch, was in greater concentration in plants grown at higher day temperatures (32 C) than at 24 C. In the field, nitrogen fertilizers did not affect miserotoxin synthesis in any variety, but significantly increased plant nitrogen in two varieties. Excluding light from Yellowstone milkvetch [var. hylophilus (Rydb.) Barneby] for 2 weeks significantly lowered miserotoxin concentration. Miserotoxin level in timber milkvetch was reduced when photosynthesis (a) was blocked by subjecting plants to prolonged darkness; (b) was disrupted by treating plants with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] or silvex [2-(2,4,5-trichlorophenoxy)propionic acid]; (c) was reduced by lowered day temperature; (d) was terminated by senescence and bleaching.

Cacodylic acid (hydroxydimethylarsine oxide) and MSMA (monosodium methanearsonate) gave slightly-visible inhibition of bacterial growth in pure culture at 1000 mg/L arsenic and moderate inhibition at 10,000 mg/L arsenic. There were no effects at 100 mg/L arsenic. Carbon dioxide evolution from three kinds of forest floor declined with increasing concentrations of MSMA and cacodylic acid. Increasing concentrations of MSMA caused an increase in carbon dioxide evolution from soil but cacodylic acid had no effect. Concentrations less than 10 mg/kg arsenic forest floor including L, F, and H horizons, or soil had no pronounced effect on organic matter decomposition.

In a 3-year study propanil (3′,4′-dichloropropionanilide) at 6.7 or 9.0 kg/ha was applied postemergence as single or split applications to rice (Oryza sativa L. ‘Starbonnet’ and ‘Nova 66′) 15 to 75 days after crop emergence. The effect on crop injury, maturity, grain yield, and seed and milling quality was measured on rice grown in weed-free plots. Residues of DCA (3,4-dichloroaniline) in grain and straw from treated rice plants and of propanil and TCAB (3,3′,4,4′-tetrachloroazobenzene) in treated soil were determined. Propanil applied at all times and rates in 1968 and 1970 or applied at all rates at 15 to 55 days after crop emergence in 1969 did not reduce grain yields, but 6.7 kg/ha applied 65 and 75 days after crop emergence in 1969 injured rice plants vegetatively and reduced grain yields. Plant maturity, seed viability and milling quality of grain were not affected. Residues of DCA in grain and straw were highest from treatments applied 65 and 75 days after crop emergence; rice straw contained more DCA than did grain.

A portable electric sprayer is described which can be used for greenhouse and small field experiments. It has the flexibility of larger conventional sprayers and precision of laboratory sprayers. The unit is compact, lightweight, and easy to construct.

The phytotoxicity of soil-applied terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine] to wheat (Triticum aestivum Vill.) was significantly affected by soil moisture and soil temperature. Distribution coefficients (Kd) provided a better indication of the phytotoxicity of terbutryn to wheat than any single measured parameter contributing to herbicide adsorption by the soil. Soil temperatures and soil moisture levels suitable for good plant growth tended to enhance the phytotoxicity of terbutryn. No phytotoxic levels of terbutryn to wheat were detected in Teller sandy loam after 20 weeks of incubation at above 10C and 14% soil moisture by weight. However, phytotoxicity to wheat was observed in air-dry terbutryntreated soil after an incubation period of 20 weeks, regardless of incubation temperature. Significant quantities of terbutryn may remain in the field under dry soil conditions.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] (0, 0.56, 1.12, 1.68 kg/ha) applied the soybean (Glycine max (L.) Merr.) cultivars ‘Bragg,’ ‘Hampton,’ ‘Bienville,’ ‘Coker 318,’ ‘Coker 102,’ and ‘Hardee’ induced significant changes in total fatty acid concentration of soybean oil. Minor changes in soybean oil quality were induced by metribuzin but percent protein was not influenced.

MSMA (monosodium methanearsonate) and DSMA (disodium methanearsonate) were applied to seedling orchardgrass (Dactylis glomerata L.) – alfalfa (Medicago sativa L. ‘WL-304′) and reed canarygrass (Phalaris arundinacea L. ‘Ioreed’)-birdsfoot trefoil (Lotus corniculatus L. ‘Dawn’) mixtures before grasses were beyond the three-leaf stage. MSMA and DSMA controlled foxtails (Setaria spp.), large crabgrass [Digitaria sanguinalis (L.) Scop.] and fall panicum (Panicum dichotomiflorum Michx.), but were not effective on barnyardgrass [Echinochloa crus-galli (L.) Beauv.]. The addition of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] or bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) to MSMA or DSMA increased broadleaf weed control over that obtained with MSMA or DSMA alone. The forage mixtures tolerated 2 to 3 kg/ha of MSMA or DSMA and increased in yield when weeds were controlled. Elemental arsenic found in the forage increased in forage as the rates of MSMA or DSMA increased. Eighty-six to 96% less arsenic was found in early-than in late-treated forage.

UHF energies (45 to 730 j/cm2, 2450 MHz) were applied to irrigated and non-irrigated soils in the field just before planting of cantaloupe (Cucumis melo L., var. reticulatus Naudin) and onion (Allium cepa L.) to study the influence of UHF energy on plant growth. London rocket (Sisymbrium irio L.) and sunflower (Helianthus annuus L.) were controlled with 180 j/cm2 of UHF energy applied after seed had imbibed water from soil. These species and ridgeseed spurge (Euphorbia glyptosperma Engelm.), redroot pigweed (Amaranthus retroflexus L.), common purslane (Portulaca oleracea L.), and Japanese millet [Echinochloa frumentacea (Roxb.) Link.] were controlled with 360 j/cm2 (0.0048 kmph) regardless of seed or soil moisture. London rocket and sunflower were not controlled by several soil-incorporated herbicides. UHF energy had no deleterious effects on the growth of cantaloupe or onion and tended to increase the yields above those of the hand-weeded vegetables. Phytotoxic UHF radiation penetrated 7.5 and 10 cm in irrigated and non-irrigated soil, respectively, at 360 j/cm2. Soil temperature after UHF treatment increased with increasing UHF energy levels and decreasing soil moisture and depth.

The management of Eurasian watermilfoil, an inimical aquatic weed in the Tennessee Valley, involves the use of water level management and herbicidal treatment with 2,4-D [(2,4-dichlorophenoxy)acetic acid]. The possible use of other chemicals to make 2,4-D more effective was tested by measuring growth of Eurasian watermilfoil under laboratory conditions with combinations of sublethal levels of 2,4-D and partially inhibitory concentrations of AlCl3, NH4Cl, Na2AsO2, BaCl2, Na2B4O7, CuSO4, HgCl2, Pb(NO3)2, NaCl, and ZnSO4. At the levels tested, BaCl2, Pb(NO3)2, and ZnSO4 were only additive in effect with 2,4-D. Other compounds produced synergism at some concentrations and mutual antagonism at other levels. The greatest synergism was obtained by using HgCl2, AlCl3, and NaCl at 0.2 μM, 10.0 μM, and 200.00 mM respectively.

The metabolism of 14C-SAN-6706 [4-chloro-5-(dimethylamino)-2-(a,a,a-trifluoro-m-tolyl)-3(2H)-pyridazinone] and 14C-norflurazon [4-chloro-5-(methylamino)-2-(a,a,a-trifluoro-m-tolyl)-3(2H)-pyridazinone] were studied in cranberry plants (Vaccinium macrocarpon Ait. ‘Early Black’) for a 36-day period. Both compounds were readily translocated with progressively more label being present in the shoot portion with time. The two compounds are demethylated to the desmethyl analogue SAN-9774 (4-chloro-5-amino-2-(a,a,a-trifluoro-m-tolyl)-3(2H)-pyridazinone). Berry samples from cuttings contained no detectable radioactivity while samples from 2 year-old cranberry plants contained 20 ppb or less.

The competitive effects of common cocklebur (Xanthium pensylvanicum Wallr.) on soybeans [Glycine max (L.) Merr. ‘Lee 68′] were studied on Dundee silty clay loam soil from 1970 to 1972. Full-season competition by common cocklebur at 3,300, 6,600, 13,000, and 26,000 plants/ha reduced the 2-year average soybean seed yields 10, 28, 43, and 52%, respectively. Competition from common cocklebur at 100,000 plants/ha for 4, 6, 8, 10, 12, and 16 weeks after soybean emergence reduced soybean seed yields 10, 36, 40, 60, 80, and 80%, respectively. A reduction in soybean stand occurred after 12 or more weeks competition, and an increase in soybean plant height occurred after 10 or more weeks competition. When common cockleburs were removed during the first 4 weeks after soybean emergence, no further removal was required to obtain maximum soybean yield. Bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide] at 1.1 to 2.2 kg/ha applied over-the-top of common cockleburs and soybeans was as effective as hand removal in terminating competition provided common cocklebur plants were not flowering.

Height, true-leaf area, shoot dry weight, and survival of the seedlings of four varieties of cucumber (Cucumis sativus L.) were measured for differences occurring when treated preemergence with naptalam (N-1-naphthylphthalamic acid) alone, chloramben (3-amino-2,5-dichlorobenzoic acid) methyl ester alone, or with combinations of these two herbicides. These factors were reduced, depending upon the variety of cucumber, with each of the herbicide treatments. The only reduction associated with naptalam alone was the true-leaf area of ‘Model’ and ‘Wisconsin SMR 58.’ ‘Ohio MR 17,’ ‘Model,’ and ‘Wisconsin SMR 58’ had less reduction of all measured responses than ‘Pixie’ when treated with chloramben methyl ester alone or with combinations of naptalam and chloramben methyl ester. The herbicide variety interactions present in seedling injury under greenhouse conditions were not reflected in the yields of these varieties when grown in the field. The only significant yield reduction occurring under field conditions was with the 4.48 kg/ha rate of chloramben methyl ester in the first harvest.

Foliar abscission induced by mist blower applications of endothall [7-oxabicyclo(2,2,1)heptane-2,3-dicarboxylic acid] combined with ethephon [(2-chloroethyl)phosphonic acid] occurred within 14 days on six field-grown deciduous species. Refoliation was essentially complete after one dormant season except on pin oak (Quercus palustris Muenchh.), which exhibited shoot damage from May and June treatments. Abscission did not occur on coniferous species. Effective doses ranged from 150 to 2,400 μg/ml endothall with 4,800 μg/ml ethephon. In greenhouse experiments on white ash (Fraxinus americana L.), the most effective levels of surfactant with endothall/ethephon ranged from 0.5 to 1.3%, and a spray volume as low as one-quarter runoff gave adequate coverage.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] provided adequate preemergence weed control on direct-seeded or transplanted tomato (Lycopersicon esculentum Mill.) on Plainfield sand and Drummer silty clay loam soils. Metribuzin demonstrated selective postemergence activity in the field but in glasshouse studies tomato cultivars had a wide range of tolerance to metribuzin applied to the foliage. Tomatoes were more susceptible to injury when they were less than 10-cm tall. Metribuzin was more effective in controlling broadleaf weeds than grass weeds, but grass control was acceptable with higher rates. Ultraviolet light decomposed metribuzin and weed control was improved when metribuzin was incorporated into the soil after application. Metribuzin treatment increased fruit yields. No metribuzin activity was found in the plots by the end of the growing season.