Removal of [2-14C] 2,4-D [(2,4-dichlorophenoxy)-acetic acid] from water was pronounced with Scenedesmus quadricauda (Turp.) Breb. and most effective uptake occurred at pH 4.7. Three other algae were relatively ineffective in removal of 2,4-D. Increasing Scenedesmus cell density increased 2,4-D removal, but the amount absorbed was not a linear function of cell density. Similarly, with a range of herbicide concentrations (0.01 to 1.0 ppmw) the amount removed was greatest at the highest concentration; however, a higher percentage of chemical was removed at lower concentrations. An equilibrium of 14C removal from water and 14C released to the water was reached by 4 hr. More herbicide was removed from water by Scenedesmus in darkness than in light and low temperature (2 C) reduced uptake slightly. Relatively high 2,4-D concentrations were required to reduce growth in any of the four algae and Scenedesmus was most sensitive. Scenedesmus metabolized [ring−14C] in 24 hr to several products which were found in suspension fluid and cells. Quantitatively, 3-OH-2,4-D [3-hydroxy-2,4-dichlorophenoxy)acetic acid] was the major metabolite, comprising 26% of the radioactivity extracted from cells compared to 15% from suspension fluid. A smaller amount of 5-OH-2,4-D [(5-hydroxy-2,4-dichlorophenoxy)acetic acid] was isolated from the suspension fluid and none from the cells.

Benefin accumulated rapidly in the roots of tobacco (Nicotiana tabacum L. ‘Kentucky 14′) seedlings incubated in nutrient solution containing 14C-labeled benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) and remained in the roots unaltered. Very low levels of radioactivity were detected in the shoots. Diphenamid (N,N-dimethyl-2,2-diphenylacetamide) accumulated in the shoots of treated plants throughout the treatment period but remained at low levels in the roots. Diphenamid was extensively metabolized in the shoots but only to a slight extent in the roots. The carbon-14 of pebulate (S-propyl butylethylthiocarbamate) accumulated in moderate amounts in both the roots and shoots of the tobacco seedlings, but attempts to recover pebulate failed.

An organic muck and a montmorillonite clay were incorporated into the surface 7.6 cm of a structureless sandy soil at rates ranging from 26,880 to 89,600 kg/ha. Prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] and fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] were surface-applied and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) were incorporated at two rates each in 1968, 1969, and 1970. Organic matter greatly reduced the biological activity of all three herbicides. Montmorillonite clay greatly reduced the activity of prometryne, slightly decreased the activity of fluometuron, and had no significant effect on trifluralin activity in all but the first year of the study. Both soil additives increased the cation exchange capacity of the soil. Muck decreased soil pH while montmorillonite increased it.

The absorption, translocation, and metabolism of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H) one] by soybean (Glycine max Merr. ‘Lee 68′) and hemp sesbania (Sesbania exaltata L.) grown in nutrient solution and in soil treated with 14C-metribuzin were investigated. Absorption studies indicated there were no significant differences in the amount of 14 C-metribuzin absorbed from treated nutrient solution by soybean (tolerant) and hemp sesbania (susceptible). When these species were grown in 14C-metribuzin treated soil, hemp sesbania absorbed appreciably more herbicide than did soybean. 14 C-metribuzin and (or) its 14C-metabolites were translocated from the roots to the shoots of both species. Radioactivity was rapidly translocated and accumulated in all the leaves of hemp sesbania, but it tended to accumulate to the greatest extent in the roots and lower leaves of soybean. Translocation differences between the two species were apparent in plants grown either in soil or nutrient solution treated with 14C-metribuzin. However, differences were greatest in plants grown in treated soil. Preliminary metabolic studies indicated that a higher rate of metribuzin degradation occurred in soybean than in hemp sesbania. The major 14 C-metabolite appeared to be the relatively nonphytotoxic deaminated diketo derivative [6-tert-butyl-1,2,4,-triazine-3-5(2H,4H)dione]. Thus, differences in the absorption, translocation, and metabolism of metribuzin all appeared to contribute to the differential susceptibility of soybean and hemp sesbania to metribuzin.

Seeds of common cocklebur (Xanthium pensylvanicum Wallr.), jimsonweed (Datura stramonium L.), ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.], giant ragweed (Ambrosia trifida L.), yellow foxtail [Setaria lutescens (Weigel) Hubb.], and velvetleaf (Abutilon theophrasti Medic.) were buried in the soil at depths down to 15.2 cm in November 1966. Seeds of jimsonweed, ivyleaf morningglory, giant ragweed, yellow foxtail, velvetleaf, common ragweed (Ambrosia artemisiifolia L.), and Pennsylvania smartweed (Polygonum pensylvanicum L.) were buried 2.5 and 10.2 cm below the surface in October 1968. Seeds were exhumed for periodic laboratory analyses of dormancy changes. All species except ivyleaf morningglory and common cocklebur germinated better in light than in darkness after at least one winter of burial in the soil. Seeds decayed faster at 2.5 cm below the soil surface than at 10.2 cm, but some viable seeds of all species were recovered from both depths after 3 years. The development or maintenance of hard seeds was considered the principle mechanism for seed survival for 3 years in these species.

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.

The following species of arthropods were exported from California to the U.S.S.R. for the biological control of ragweed (Ambrosia spp.): Tarachidia candefacta Hübner (Lepidoptera: Noctuidae); Coleophora sp. near annulatella Braun (Lepidoptera: Coleophoridae); and Eriophyes boycei Keifer (Acarina: Eriophyidae). Tarachidia candefacta represents the first insect species intentionally introduced from North America into Europe and established for biological weed control.

Foliar spray retention, absorption and translocation, and the dissipation of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] and 2,4-D [(2,4-dichlorophenoxy)acetic acid] were examined to determine their importance as selectivity factors in the response of two 2,4-DB-tolerant legumes, alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.), and two susceptible broadleaf weeds, redroot pigweed (Amaranthus retroflexus L.) and common cocklebur (Xanthium pensylvanicum Wallr.). The legumes were as effective as the broadleaf weeds in metabolizing (beta-oxidizing) 2,4-DB to 2,4-D. The relatively greater tolerance of the legumes than of the broadleaf weeds to 2,4-DB arose from a combination of poorer spray retention, less effective absorption and translocation, and a more rapid degradation of the 2,4-D arising from the beta-oxidation of 2,4-DB.

Primary root elongation of prickly sida (Sida spinosa L.) at pH 5.5 was similar to that at pH 6.5 while sicklepod (Cassia obtusifolia L.) was reduced to 62% and tall morningglory [Ipomoea purpurea (L.) Roth] to 87% of that at pH 6.5. At pH 5.1, root elongation of prickly sida was reduced to 77% of that at pH 5.5. Some elongation was observed in the pH range of 5.1 to 6.5 for all species. Maximum primary root growth of tall morningglory, sicklepod, and prickly sida occurred at approximately 32° which was similar to that for cotton (Gossypium hirsutum L. ‘Empire’). Temperature as high as 39° did not significantly reduce root elongation of sicklepod. Tall morningglory root growth was reduced approximately 50% by 0.2 ppm of trifluralin (α,α,α-trifluro-2,6-dinitro-N,N-dipropyl-p-toluidine). In contrast, sicklepod and prickly sida root growth was reduced only slightly by 1 ppm of trifluralin.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H) one] injured and reduced growth of tomato (Lycopersicon esculentum Mill.) but did not inhibit germination or emergence of several other species. In cucumber (Cucumis sativus L.), metribuzin did not have a specific site of uptake, being equally toxic when placed in the root, shoot, or seed zone. Tomato was more susceptible to metribuzin when the plants were grown under high humidity, high temperature, maintained under low light intensities before spraying, had their leaves rubbed with glass wool, or had a surfactant in the spray solution. The increased toxicity under low light was not overcome by exogenous sucrose. About 4% of the available metribuzin was absorbed by tomato leaves or roots and was translocated in the xylem. Tomato plants 13 cm in height were less susceptible to metribuzin injury than 8-cm high plants.

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.

Weed Science is a relatively young but challenging and dynamic discipline. It includes all aspects of combating weeds and reducing their undesirable effects on mankind–directly or indirectly. The need for effective weed control is not new; it has prevailed since the primitive beginning of crop culture. It has evolved into a strong discipline, however, only since World War II, stimulated by a pressing need for more economic weed control. In response to this need, numerous advances have been made that help to produce higher crop yields at lower cost. Herbicides have become common, intensive research and educational programs have been established, and Weed Science has taken its rightful place as a respected discipline in the academic and industrial communities.

The effect of soil pH on the disappearance of 14C ring-labeled atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], hydroxyatrazine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine], and prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] were studied over a 5-month period in a Bladen silt loam soil under greenhouse conditions. Employment of an integrated system allowed simultaneous monitoring of degradation, volatilization, respiration, plant uptake, and leaching processes. A resulting balance-sheet indicated that a range of 87 to 99% of the 14C added could be accounted for after 5 months. Degradation was found to be the primary mode of dissipation. The pattern of atrazine degradation was characteristic of nonbiological processes, while prometryne degradation was probably by microbial action. Hydroxyatrazine was the major metabolite from the atrazine treatments while prometryne yielded an unknown and hydroxypropazine [2-hydroxy-4,6-bis(isopropylamino)-s-triazine]. Ex-tractable atrazine after 5 months amounted to 35% of the initial amount added in the pH 7.5 soil and 11% in the pH 5.5 soil, while prometryne occurred as 10% in the pH 7.5 soil and 42% in the pH 5.5 soil. Plant uptake and leaching occurred to a greater extent in the more alkaline soil with each chemical, but these pathways along with volatilization and respiration were minor contributors toward the disappearance of these herbicides.

Studies were conducted to characterize qualitatively and quantitatively the water-soluble carbohydrates in johnsongrass [Sorghum halepense (L.) Pers.]. Glucose, fructose, and sucrose were the only sugars detected in other than trace amounts in leaves, culms, or rhizomes. Sucrose was the major storage carbohydrate, although glucose and fructose were present throughout most of the life cycle in both leaves and rhizomes. Levels of glucose, fructose, and sucrose in rhizomes were maximum when plants began flowering and minimum at 10 to 30 days after plant emergence. Glucose, fructose, and sucrose were at a maximum in leaves within 30 days after plant emergence. Glucose was present only in trace amounts in leaves for about 10 days during initial flowering; fructose was at a maximum at that time. Sucrose in leaves occurred in greatest quantities soon after plant emergence, immediately before flowering, and after flowering. Leaf blades and sheaths contained nearly equal concentrations of carbohydrates, but stems contained greater concentrations than leaves. Basal shoots and secondary culms from nodes on primary culms contained greater concentrations of carbohydrates than leaves on primary culms. Regrowth from clipped shoots had significantly higher concentrations of glucose and sucrose than did unclipped shoots. Rhizomes of clipped plants had significantly less sucrose but more glucose than rhizomes of unclipped plants.

More force was required to induce leaf slippage in coleoptiles from corn (Zea mays L. ‘Tenn 5009′) plants grown in the presence of 25 ppmw alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] than in the controls, or in coleoptiles from plants grown in the presence of 25 ppmw alachlor in combination with 150 ppmw 1,8-naphthalic anhydride (hereafter referred to as NA). NA alone reduced the force required to induce leaf slippage below that of all treatments. Incubation for 16 hr in 10 ppmw IAA (indoleacetic acid) did not lower the force required to induce leaf slippage in coleoptiles from plants grown in the presence of 25 ppmw alachlor even though the length of the coleptiles increased 30% more than coleoptiles not receiving the IAA treatment. Percent dry matter, dry matter per 100 plants, and percent protein increased in coleoptiles from alachlor treated plants, while percent cellulose and lignin decreased. The extent of variation in these parameters was lessened when NA was applied in combination with alachlor, with the exception of percent lignin which was further decreased by the combination treatment. Percent hemicellulose was not affected by alachlor, NA, or their combination.

Onion (Allium cepa L.) and bean (Phaseolus vulgaris L.) seedlings grown in soil treated with DCPA (dimethyl tetrachloroterephthalate) were less susceptible to northern root-knot nematode (Meloidogyne hapla Chitwood) infection than seedlings grown in untreated soil. DCPA treatment of nematode larvae did not alter their pathogenicity. Resistance could be correlated with altered cell structure of the root epidermis, increased root exudate as evidenced by soil adherence, reduced fibrous root development, or both.

The configuration of the growth pattern for Chrysothamnus viscidiflorus (Hook.) Nutt. was determined from vegetative bud burst to flowering. Important portions of the pattern are: restrictive growth during early spring, accelerated growth in late spring when the optimum susceptibility to herbicides occurs, and a leveling off of growth before flowering. Seedlings and young plants have a more rapid and greater annual stem elongation than mature or senescent plants. Elongation during the accelerated growth period can be predicted from early spring growth with moderate precision when soil moisture and temperatures are not limiting. Populations growing on sites of higher or lower elevations or of pronounced aspect will have growth patterns moderately varying from the modal populations. The greatest factor influencing the growth pattern on years with adequate soil moisture was competition from other species and the combination of competition and age of the rabbitbrush plants.

The effects of eight s-triazines on respiration of (Phaseolus vulgaris L. ‘Black Valentine’) bean and rat liver mitochondria and on cyclic photophosphorylation of pea (Pisum sativum L. ‘Thomas Laxton’) chloroplasts were determined. All triazines inhibited state 3 respiration and cyclic photophosphorylation. The degree of inhibition was similar in both rat liver and bean mitochondria. Prometryne [2,4-bis-(isopropylamino)-6-(methylthio)-s-triazine] was the most potent inhibitor of both respiration and cyclic photophosphorylation. Triazines with the methylthio group showed the most activity, followed by those with the methoxy and chloro substituents in that order.