Germination of field dodder (Cuscuta campestris Yunck.) was investigated in field and laboratory studies. Germination plots established to simulate field conditions showed a rapid decline in the number of seedlings emerging over a 5-yr period. Less than 10% of the seeds planted emerged. Time of germination was correlated with temperature. The dormancy of seeds buried at various depths was found to be broken by overwintering. Older seeds and those close to the surface germinated best. Scarified seeds did not germinate at 15 C nor at temperatures of 39 C or above. Maximum germination occurred at 30 and 33 C. Scarified seeds planted at various depths failed to emerge from 3.8, 4.0, or 7.6 cm in the three soil types evaluated; the majority emerged from 3 cm or less. Seeds stored outdoors, at 3 to 8 C, or −3 to 0 C declined in dormancy with time compared to seeds stored at 15 to 25 C.

Influence of time of planting and distance from the cotton row of pitted morningglory (Ipomoea lacunosa L.), prickly sida (Sida spinosa L.), and redroot pigweed (Amaranthus retroflexus L.) on yield of seed cotton (Gossypium hirsutum L. ‘Stoneville 213’) was determined on Decatur clay loam during 1975 through 1978. Weed growth was measured in 1977 and 1978. Seeds of the three weed species were planted 15, 30, or 45 cm from the cotton row at time of planting cotton or 4 weeks later. Weeds planted 4 weeks after planting cotton grew significantly less than did weeds planted at the same time as cotton. When planted with cotton, redroot pigweed produced over twice as much fresh weight as did prickly sida or pitted morningglory. The distance that weeds were planted from the cotton row did not affect weed growth in 1978, but did in 1977. The distance that weeds were planted from the cotton row did not affect their competitiveness in any year as measured by yield of cotton. However, in each year, yields of cotton were reduced to a greater extent by weeds planted with cotton than when planted 4 weeks later. In 3 of 4 yr, there were significant differences in competitiveness of each of the three weed species with cotton.

A continuous-belt herbicide wiper was developed to apply herbicides to weeds that are taller than cranberry (Vaccinium macrocarpon Ait.) plants. An endless belt with a sponge attached to the entire length of the belt moves through a reservoir containing a herbicide solution. A variable pressure wheel squeezes the excess liquid out of the sponge and returns it to the reservoir. The herbicide is deposited on the leaves of the weeds as the belt moves in a horizontal plane, perpendicular to the forward movement of the wiper. Control of Walter's sedge (Carex walteriana Bailey), woolgrass [Scirpus cyperinus (L.) Kunth] and switchgrass (Panicum virgatum L.) was obtained when glyphosate [N-(phosphonomethyl)glycine], dalapon (2,2-dichloropropionic acid), and paraquat (1, 1′-dimethyl-4,4′-bipyridinium ion) were applied using the continuous-belt wiper. No injury to cranberry plants was observed.

In Israel, an intensive modern agriculture has developed under difficult ecological constraints. The climate is characterized by two distinct seasons – a cool, rainy winter and a hot, dry summer. In winter, there are often temporary excesses of rain, causing erosion and preventing regular cultivation of fields; and in summer the soil dries out, and intensive cropping is only possible with irrigation. However, water is scarce and rationed directly by maximizing irrigation efficiency, and indirectly by controlling weeds, which compete for soil moisture.

The effect of the herbicide buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} on photosynthesis, respiration, anthocyanin formation and leaf ultrastructure of corn (Zea mays L. ‘Pioneer 3780’) was studied following pre- or postemergence applications. Total photosynthesis and dark respiration were measured with an infrared CO2 analyzer in an open air flow system 12, 18, and 24 days after preemergence treatment with 0, 0.56, 1.12, and 2.24 kg/ha of buthidazole. The 0.56 and 1.12 kg/ha preemergence treatments had no effect on total corn photosynthesis even 24 days after treatment, whereas buthidazole at 2.24 kg/ha inhibited photosynthesis as early as 12 days. Total photosynthesis and dark respiration were also measured in whole plants, 30 cm tall, before herbicide application and 4, 24, 48, and 96 h after postemergence treatment with buthidazole at 0, 0.28, 0.56, 0.84, and 1.12 kg/ha. Following postemergence treatment, buthidazole inhibited total corn photosynthesis at any rate examined as early as 4 h after treatment. Neither pre- or postemergence buthidazole applications influenced respiration with the exception of a transitory increase caused by 0.56 kg/ha 12 days after preemergence treatment and by 0.84 and 1.12 kg/ha 4 h after postemergence treatment. Transmission electron micrographs revealed that buthidazole applied postemergence at 0.28 and 1.12 kg/ha reduced or prevented the accumulation of starch in bundle sheath chloroplasts as early as 24 h after treatment. Ultrastructural disruptions in some mesophyll chloroplasts of treated corn plants were also evident. Preemergence application of buthidazole at rates of 0.28, 0.42, 0.56, and 1.12 kg/ha inhibited anthocyanin formation indicating an alteration in corn metabolism.

The concept of interaction arises in the context of continuous functions. Verbally, it is the action of one independent variable on the action of another, and vice versa, on a dependent variable. Quantitatively, it is the second partial derivative of a function with respect to two independent variables. Misconceptions have arisen from attempts to understand action and interaction in discrete terms. The algebraic expressions for the actions of diuron and phorate on the fresh weight of oats and their interaction were determined from the regression polynomial and plotted in three-dimensional graphs. Three other mutually incompatible methods of assessing interaction, namely, the Colby (with its modification, regression estimate), the two-parameter, and the topographical methods were evaluated.

More than 90% of the world's rice is produced in Asia. It is grown under diverse cultural methods ranging from well-drained upland conditions to wetland conditions where the soil is continuously submerged. The major system of establishing rice in Asia is transplanting. One of the major reasons for transplanting is weed control. In this system, the rice plant has a competitive advantage over the weeds from the start, and sometimes it is able to maintain this advantage throughout crop growth.

The effects of chloracetamides on protein synthesis were studied both in vivo and in vitro. Four chloracetamide herbicides, alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], CDAA (N–N-diallyl-2-chloroacetamide), and propachlor (2-chloro-N-isopropylacetanilide) were tested for inhibition of [3H]-leucine incorporation into protein. Incorporation of 3H-leucine into trichloroacetic acid (TCA)-insoluble protein was inhibited in oat (Avena sativa L. ‘Victory’) seedlings grown in sand culture and treated 12 h at 1 × 10−4M with these chloracetamides. The herbicides were also tested in a cell-free protein synthesizing system containing polyribosomes purified from oat root cytoplasm. These herbicides had no effect on the rates of polypeptide elongation nor on the synthesis of specific polypeptides when herbicides (1 × 10−4M) were added directly to the system. Polypeptide formation was inhibited 89% when 1 × 10−4M cycloheximide was added during translation. Cytoplasmic polyribosomes were isolated from oat roots treated 12 h with 1 × 10−4M herbicide. Translation rates and products were not altered when these polyribosomes were added to the in vitro system. Protein synthesis is inhibited when tested in an in vivo system; however, the inhibition does not occur during the translation of mRNA into protein.

Field studies and laboratory analyses were conducted to examine factors affecting degradation of 14C-atrazine [2-chloro-4-(ethylamine)-6-(isopropylamino)-s-triazine] under field conditions. The effects of these factors on weed control under no-tillage and conventional tillage systems were also examined. The amount of radioactivity which was unextractable in 90% methanol increased with time following treatment with 14C-atrazine. The rate of formation of unextractable 14C compounds was greater under no-tillage and increased with decreasing pH. After 14 to 18 days, a greater amount of extractable atrazine was present in areas receiving lime. The degradation of atrazine occurred more rapidly when surface pH was less than 5.0 compared with a pH greater than 6.5. The effect of lime on the amount of parent atrazine present in the soil was directly correlated to its effect on soil pH. Extractable atrazine in the soil 45 days after treatment was significantly correlated with weed control with the greatest effect under no-tillage.

Four greenhouse experiments were conducted to study the effects of plant residues and extracts of yellow nutsedge (Cyperus esculentus L.) plant residues on the growth of corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.]. At equal concentrations, tuber residues reduced the dry weight of corn and soybeans more than foliage residues. As the concentration increased, growth decreased, affecting soybeans more than corn. Soybean growth was significantly reduced by the addition of tuber extracts. At a constant residue concentration, increasing the percentage of sand in the soil mixture reduced the growth of corn and soybeans. Growth inhibition was greatest when tuber residues were in contact with the corn or soybean seed. We conclude that extracts and residues of yellow nutsedge have an allelopathic effect on corn and soybeans under greenhouse conditions.

Two 1-yr field studies were conducted to evaluate preemergence and preplant incorporated treatments of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], EPTC (S-ethyl dipropylthiocarbamate), fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] for the control of yellow nutsedge (Cyperus esculentus L.). Preemergence applications of metolachlor at 2.24, 3.36, and 4.48 kg/ha gave the best control with no significant differences observed among rates of metolachlor. Depth of herbicide incorporation did not result in any significant increase in control. Preplant incorporation of metolachlor at all rates, or fluridone at 0.56 and 0.84 kg/ha provided seasonal control of yellow nutsedge. Translocation of 14C-metolachlor applied to the root or shoot of yellow nutsedge was primarily acropetal with some limited basipetal movement. Application of 14C-metolachlor to the root or shoot of purple nutsedge (Cyperus rotundus L.) resulted in mostly acropetal translocation with little movement of 14C from the treatment site.

Rates of loss of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], and pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] from soil surfaces were evaluated in a series of field sampling studies. Herbicides were sprayed onto soil enclosed in rings with nylon mesh bottoms, exposed to field conditions, and analyzed periodically by gas chromatography. The herbicides were lost rapidly in the first 3 to 5 days from Bosket silt loam and Sharkey clay, although the initial rate of loss was less rapid in the clay. Trifluralin and fluchloralin were lost more rapidly than pendimethalin. Half-life values for the first 3 to 5 days for trifluralin, fluchloralin, and pendimethalin, respectively, were 2, 1.5, and 4 days on silt loam and 2, 4, and 6 days on clay. Rates of loss were much lower for the remainder of the 7- or 12-day sampling periods. Rainfall on the first day of the sampling period resulted in increased initial loss of all herbicides. Shading from direct sunlight greatly reduced the loss of fluchloralin and pendimethalin as compared to exposure to full sunlight, although trifluralin loss remained fairly rapid under shaded conditions. Simulated rainfall on the first day resulted in significantly increased dissipation of fluchloralin and pendimethalin.

A field experiment involving seven cultural practices was begun in 1974 in an area heavily infested with velvetleaf (Abutilon theophrasti Medic.) seed. Our objective was to determine the time required to eradicate velvetleaf seed from the soil. This paper reports the results of the first 4 yr of a long-term study. A cultural practice is repeated on the same plot year after year. Since the experiment was begun, no velvetleaf plants have been allowed to produce seed in any plots. The number of viable velvetleaf seeds is monitored by yearly soil sampling. In 1978, after 4 yr of a fallow treatment involving intensive tillage (two plowings per yr plus monthly tillage throughout the growing season), only 10% of the original seed population remained. However, that 10% was 1,300 viable seeds per m2 (to a depth of 23 cm). Four other practices that involved tillage gave generally similar results. Under undisturbed, continuous alfalfa, 56% of the original seed population remained after 4 yr, and under undisturbed, continuous chemical fallow, 37% remained. The results thus far demonstrate the extreme difficulty of eradicating velvetleaf seeds from the soil, and generally agree with reports in the literature, which primarily include studies conducted under more artificial conditions than we used. Our results also suggest that, in soil, velvetleaf seeds that have become water permeable (nonhard) may later again become water impermeable (hard).

The susceptibility of 2- and 4-month-old perennial ryegrass (Lolium perenne L.), orchardgrass (Dactylis glomerata L.), Kentucky bluegrass (Poa pratensis L.), red fescue (Festuca rubra L.) and highland bentgrass (Agrostis tenuis Sibth.) to glyphosate [N-(phosphonomethyl)glycine] was studied in the greenhouse. All 2-month-old grasses were killed by 0.28 kg/ha and higher rates of glyphosate. At 0.14 kg/ha, red fescue was moderately resistant, and bluegrass, orchardgrass, and perennial ryegrass were moderately susceptible. Bent-grass was very susceptible. When 4-month-old grasses were treated, bluegrass was as tolerant to 0.28 kg/ha of glyphosate as was red fescue. At this same rate, orchardgrass and perennial ryegrass were moderately susceptible, whereas bentgrass remained the most susceptible. Dosages lower than 0.28 kg/ha had little effect; whereas higher doages injured all five species. 14C-glyphosate was absorbed and translocated via both apoplast and symplast in 1-month-old red fescue, orchardgrass and perennial ryegrass seedlings. Comparatively, less radioactivity was transported to the untreated areas in red fescue than in orchardgrass and perennial ryegrass. Thus, the differential tolerances of these species to low rates of glyphosate may be explained, in part, by differential translocation of glyphosate.

Methazole [2-(3,4-dichlorophenyl)-4-methyl-l,2,4-oxadiazolidine-3,5-dione], metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], and combinations of MSMA (monosodium methanearsonate) with either methazole or metribuzin were applied to bare ground at 0, 1, 2, and 4 weeks before planting with bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’] as sprigs, stolons, and seed. In most instances, the growth of newly planted bermudagrass was as good or better from combination of MSMA (2.2 kg/ha) with either methazole or metribuzin at 0.1 kg/ha than with methazole or metribuzin applied alone at higher rates. MSMA + methazole can be applied safely on day of planting with sprigs and seed, but a 1-week interval between treatment and planting was needed with stolons in 1 of 2 yr. The MSMA + metribuzin combination can also be applied safely to sprigged bermudagrass on day of planting, but a 1-week interval was needed between treatment and planting with stolons and a 2-week interval between treatment and planting with seed to insure minimum bermudagrass injury.