Seeds of common yarrow (Achillea millefolium L.) germinated 99% with alternating temperatures of 15 and 25 C with concurrent dark and light periods. Germination was significantly higher when temperature was alternated, compared with a constant 15 or 25 C. Alternating light (8 h) and darkness (16 h) with either alternating or constant temperature significantly increased germination when compared with germination in the dark. After 9 yr, seed germinated over 41% under optimum conditions. Dicamba (3,6-dichloro-o-anisic acid) at 2.2 kg/ha reduced common yarrow infestations 90 to 95% in 3 of 4 yr, and 3,6-dichloropicolinic acid3,4 (designated D-290 in this paper) at 0.6 to 2.2 kg/ha controlled yarrow 90 to 100%. Yields on plots treated with D-290 at 0.6 kg/ha were significantly higher than those on plots treated with all rates of dicamba. Dicamba caused injury to grass and reduced its yield. Triclopyr [(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid at 3.4 kg/ha was not effective on yarrow.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)-acetanilide] mixed with plaster-of-paris in concentrations of 0.5, 1, 2, and 4% (w/w) was cast into tablets of three sizes. The controlled release of the herbicide was tested by the following methods: (a) in the laboratory with eduction by soaking tablets in water, (b) in the greenhouse with azalea (Rhododendron obtuseum Planch. ‘Richardii’) stock in container, and (c) in the lathe house with azalea stock in containers. In the laboratory experiment, the quantity of herbicide educed from tablets of equivalent volumes, weights, and concentrations were similar regardless of surface area of the three tablet sizes. Successively decreasing quantitites of alachlor were educed with each of the first 10 soakings. Following these soakings, the quantity of alachlor educed per soaking stabilized for the next 30 soakings. In both greenhouse and lathe house experiments, azalea plants treated with as much as 45 kg/ha alachlor formulated in tablet(s) were not damaged. In the best greenhouse treatments, two small tablets per container, effective weed control was obtained for up to 7.5 months from a single application of alachlor at rates of 11, 22, and 45 kg/ha.

Surfactants were evaluated in the greenhouse for their ability to enhance glyphosate [N-(phosphonomethyl) glycine] toxicity to common milkweed (Asclepias syriaca L.) and hemp dogbane (Apocynum cannabinum L.). Ethoxylated amines were among the most effective groups of surfactants. Nonionic ether and ester ethoxylates combined with a dimethyl amine or a quaternary ammonium salt were more effective than any of these surfactants alone. Effectiveness of ethoxylated amine surfactants was altered by pH changes. Cat-ionic surfactants tended to be more effective than nonionic surfactants. With exceptions, surfactants were more effective with increased ethoxylation. Amine surfactant effectiveness increased with increasing concentrations up to 0.3% (w/v). Surfactant effectiveness on a molar basis was more closely related to the ethylene oxide content of the surfactant than was effectiveness on a percentage basis. Contact angle was not related to surfactant effectiveness at high or low surfactant concentrations. Ethoxylated stearyl ether and amine surfactants gave optimum effectiveness at hydrophile-lipophile balance (HLB) values of 15 to 16 and 19 to 20, respectively. Surfactants with a low HLB were usually less effective. Effectiveness of surfactant combinations was quite variable and difficult to predict. Therefore, the indiscriminate addition of surfactants to glyphosate spray mixtures which already contain a surfactant should be avoided.

Field studies were conducted over a 3-yr period to evaluate weed control systems for soybeans [Glycine max (L.) Merr.] grown in 18- and 76-cm rows. Combinations of herbicides satisfactorily controlled a broad spectrum of annual grass and broadleaf weeds in soybeans grown in 76-cm rows with cultivation and in 18-cm rows without cultivation. Where a single herbicide treatment was used to control only annual grasses, the 76-cm rows (which were cultivated once) yielded from essentially the same as 18-cm rows up to almost 50% more than the 18-cm rows, which received no cultivation, depending on the year and broadleaf weed infestation. However, where herbicide combinations were used to effectively control all weeds, soybeans in 18-cm rows averaged up to 9% higher yields than those in the 76-cm rows.

An application of urea to the soil of potted tomato plants (Lycopersicon esculentum Mill. ‘John Baer’) increased the translocation of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] to the shoots of the plants. The rate of uptake of atrazine was more closely related to the rate of transpiration than it was to the rate of stump exudation or root pressure. The presence of urea did not change the metabolism of atrazine by the plants. Over the range of xylem flows from 12 ml/24 h in detopped roots (root pressure) to 211 ml/24 h in intact plants (transpiration) the concentration of atrazine in the xylem stream was approximately the same suggesting that the uptake mechanism tends to maintain a constant concentration of atrazine in the xylem stream.

The substituted 2,6-dinitroanilines were first reported as herbicides in 1960. At the present time, there are 14 2,6-dinitroaniline herbicides in various stages of product development. Literature on absorption, translocation, and mode of action of the dinitroaniline herbicides refers almost entirely to trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline]. These herbicides do not directly inhibit the germination of seed. Inhibition of lateral root development is the most characteristic growth response. Swelling of the root tip is a universally recognized morphological effect caused by these compounds. The cells in this region are multinucleate, indicating that the mitotic process has been disrupted. Examination of these cells shows an increase in the percentage of cells in arrested metaphase due to the disruption of spindle microtubules. Inference is made that the dinitroaniline herbicides affect chromosomes in a manner similar to colchicine, but research with pig brain (Sus scrofa) microtubules has shown that effects of the herbicide on microtubular protein is different.

Injury to the top of plants is recognized by stunting, development of dark green color, and swelling and brittleness of the stem or hypocotyl. The major sites of uptake are the shoot of monocots and the hypocotyl or hypocotyl hook for dicots. Exposure of seedling roots to the dinitroaniline herbicides does not kill the plant, but exposure of the young shoot will result in death. Available data indicate that the dinitroaniline herbicides are either absorbed or adsorbed by the roots due to the proximity of the roots to the herbicide, but that translocation from the root to the top is minimal. When a dinitroaniline was found in the plant, the parent compound was the major product present with metabolites equal to 5% or less.

Insufficient information is available to accurately describe effects of these herbicides on plant carbohydrates, lipids, and nitrogenous compounds. The effect of trifluralin on RNA and DNA varies with the plant species, treatment time, concentration of herbicide, and plant part investigated, but differences observed do not correlate with dinitroaniline-susceptible and resistant species. Enzyme activity does not appear to be greatly inhibited by the dinitroaniline herbicides. However, the dinitroaniline herbicides interfere with photosynthesis and respiration in vivo and in vitro.

The phytotoxic action of trifluralin can be antidoted with the organophosphorus insecticides, phorate [0,0-diethyl-S-(ethylthiomethyl)-phosphorodithioate], disulfoton [0,0-diethyl-S-2-(ethylthioethyl)-phosphorodithioate], and externally applied lipids such as D-α-tocopherol. There is a strong correlation that seeds with a high lipid content are resistant to trifluralin and those with a low lipid content are susceptible. Despite all the work that has been conducted, the mode of action of the dinitroaniline herbicides is still unclear.

UHF energy (2450 MHz) was applied to seeds and seed-soil mixtures with a waveguide under controlled conditions. After treatment, seeds were germinated at 27 C to determine viability. Seeds were either killed or seedlings grew normally with no intermediate levels of inhibition typical of that produced with sub-lethal dosages of herbicides. The energy required to kill several species of dry seeds ranged from 88 to 183 J/cm2 and could be reduced 12 to 42% by a 24-hr imbibition period prior to treatment. When several seed-soil mixtures were treated, the greatest toxicity occurred in a moist muck and clay loam soil, with the least toxicity on a dry loamy sand soil. Although attenuation of activity occurred in dry soils of three types, less energy was required to kill seeds in moist soils than was required in the absence of soil. Increasing the power levels reduced the time of exposure necessary to kill barnyardgrass [Echinochloa crus-galli (L.) Beauv.] seeds. Less energy was required to kill seeds as the soil temperature was increased from −20 to +18 C.

During 1971 and 1972, 4,400 adults of Rhinocyllus conicus Froelich were introduced into southern California from Italy for the biological control of milk thistle [Silybum marianum (L.) Gaertner]. These flowerhead-infesting weevils were colonized at nine, and successfully established at five, widely separated locations. Field data on the incidence and increase of R. conicus at colonization sites are presented. Biotic mortality factors reported for R. conicus in southern California include predation of eggs by ladybird beetles (Hippodamia sp.) and of adults by snakeflies [Raphidia (Agulla) adnixa Hagen] and spiders, destruction of weevils in flower-heads consumed by cattle and rodents, and larval and pupal parasitism by pyomotid mites.

In field trials, soybeans [Glycine max (L.) Merr.] treated with trifluralin [α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine] at 0.56 and 0.84 kg/ha were protected from injury by metribuzin [4-amino-6-tert-butyl-3-(methylthio-as-triazine-5(4H)one] at 0.28 to 1.12 kg/ha. Soybean injury from metribuzin at high soil pH values was reduced by applying it in combination with trifluralin. Trifluralin also protected soybeans from injury caused by low rates of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] greenhouse studies. The trifluralin treatment reduced root development and greatly reduced 14C-atrazine and 14C-metribuzin uptake and content within the soybean plant.

The tolerance of four legume species to nitrofen (2,4-dichloro-phenyl-p-nitrophenyl ether), fluorodifen (p-nitrophenyl α,α,α-trifluoro-2-nitro-p-tolyl ether), and oxyfluorofen [2-chloro-1-(3-ethoxy-4-nitro-phenoxy)-4-(trifluoro-methyl)benzene] was investigated both pre- and postemergence in the greenhouse. Seedlings of species that emerged most rapidly seemed to be most tolerant to preemergence herbicide applications. There was no direct relationship between preemergence and postemergence tolerance. Oxyfluorfen was found to be at least 10 times as active as the other two herbicides both pre- and postemergence. Field experiments were conducted at two locations in Indiana to test the effect of method of application on the activity and selectivity of fluorodifen and oxyfluorfen on soybean [Glycine max (L.) Merr. ‘Wayne’] and greenbean (Phaseolus vulgaris L. ‘Spartan Arrow’). Crop injury and grass weed control were reduced by incorporation of the herbicides 8 cm deep in a silt loam. Method of application did not affect the activity of the herbicides on a sandy soil low in organic matter. Soybean was more tolerant than greenbean to both herbicides when applied preemergence but oxyfluorfen was far more active than fluorodifen on both crops.