Effects of the inhibitors DNP (2,4-dinitrophenol) and oligomycin, and the substituted dinitroaniline herbicides, trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], and oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) on mitochondrial tractions isolated from soybean (Glycine max L. ‘Lee’) hypocotyls were examined. Oryzalin and nitralin uncoupled succinate oxidation at the ADP-limited state 4, as did DNP. Trifluralin caused no effect on the second state 4, but inhibited oxidative phosphorylation in a manner similar to the effect of the energy-transfer inhibitor oligomycin. Studies of the interaction of these inhibitors indicate that the sites of action for these herbicides may be different.

Field studies were conducted to evaluate the effectiveness of one, two, and three annual applications of atrazine [2-chloro-4-(ethylamino) −6-(isopropylamino)-s-triazine], 2,4-D [(2,4-dichlorophenoxy) acetic acid], dicamba (3,6-dichloro-o-anisic acid), and a three way mix of dicamba, mecoprop [2-[(4-chloro-o-tolyl) oxy]propionic acid], and 2,4-D at a ratio of 7:5:20 at different stages of development for the control of Canada thistle [Cirsium arvense (L.) Scop.]. Two consecutive annual applications in all atrazine treatments achieved the same level of control as cultivation every 5 weeks. In the year of the last treatment, Canada thistle was controlled with two or more consecutive annual applications of the hormone-type herbicides (2,4-D, dicamba, and the three way mix); however, in the year following the last treatment, regrowth occurred.

In greenhouse studies, glyphosate [N-(phosphonomethyl)glycine] at 1.0 and 3.0 kg/ha and paraquat (1,1′-dimethyl-4,4-bipyridinium ion) at 0.6 kg/ha were applied to exposed seeds of six grasses and two legume species on continuously wet soil. Glyphosate reduced germination of both legumes and three grasses and reduced seedling growth of all species. Paraquat was toxic only to the grasses. Glyphosate mainly affected germination and growth of legumes when applied directly to their seeds. Reductions also were measured, however, when untreated legume seeds were transferred to glyphosate-treated soil.

A 6-yr project comparing four cash grain–farming systems relevant to the mid-Atlantic region of the United States was conducted from 1993 to 1999. A wide range of parameters was sampled including soil health, nutrient and agrichemical movement, economic viability, and insect and weed communities. The systems and their approaches to weed management were: continuous no-till corn without (System A1) or with (System A2) rye cover crop and preplanned herbicides based on expected weed infestations; System B was a 2-yr corn–soybean rotation with conventionally tilled corn and no-tillage soybean, with preplanned herbicides based on expected weed infestations; System C was a 2-yr rotation with no-till corn, conventionally tilled wheat, and no-till double-cropped soybean, using postemergence (POST) herbicides on the basis of field scouting; and System D was a 3-yr rotation of corn-soybean-winter wheat with rye and hairy vetch cover crops, using cultivation and reduced rates of POST herbicides based on field scouting. Spring weed assessment in 1999 was similar for species evenness (Shannon's E) and diversity (Shannon's H′) indices. Weed density was lowest in System C because wheat in this system received a spring herbicide application. In the final fall assessment, Shannon's H′ was greater in System D than System C. Common lambsquarters, eastern black nightshade, and jimsonweed were more abundant in System D than Systems A1, A2, and C. Fall 1999 assessment also indicated Canada thistle was more prevalent in Systems A1 and A2 than the other three systems. During the 6-yr period, densities of jimsonweed, eastern black nightshade, morningglory species, crabgrass, and fall panicum dramatically increased in a particular system for 1 to 2 yr, then declined to levels similar to other systems. Overall, weed communities were quite stable and effective weed management did not result in dramatic changes in the weed community, regardless of the approach to cropping systems or weed management.

Disk harrowing, spring tooth harrowing, and bed conditioning, alone or followed by bedding the rows, were evaluated in field studies to determine their efficacy to soil incorporate trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) plus metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5 (4H)-one] in soybeans [Glycine max (L.) Merr.]. Effects of the time interval between herbicide application and soybean planting were also evaluated. Effective weed control and adequate crop selectivity were obtained from all incorporation methods except those followed by bedding. Bedding occasionally reduced weed control and soybean stands as compared to incorporation without bedding. Excessive crop injury resulted from the application of a band of the herbicide mixture as a subsurface layer. The herbicide mixture was applied up to 6 weeks before soybean planting without adversely affecting crop or weed selectivity when incorporated with the spring tooth harrow without bedding.

Several herbicides and herbicide combinations were investigated for desiccation, defoliation, and killing of tropical vegetation near Mayaguez, Puerto Rico. Hydroxydimethylarsine oxide (cacodylic acid) was one of the more effective defoliants on guava (Psidium guajava L.) within 2 weeks after treatment. However, several herbicide combinations including contact: growth-regulator types were more effective 1 month after spraying. Six months after treatment, herbicides containing (2,4-dichlorophenoxy)-acetic acid (2,4-D), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), or 4-amino-3,5,6-trichloropicolinic acid (picloram) were superior to contact herbicides in controlling regrowth. In a mixed tropical forest, most rapid desiccation and defoliation of vegetation was produced by 6,7-dihydrodipyrido (1,2-a:2′,1′c) pyrazinediium salt (diquat) within 2 weeks after treatment. At 1 month after treatment and longer, the 1:1 mixture of the butyl ester of 2,4-D:2,4,5-T and a 2:2:1 mixture of the isooctyl esters of 2,4-D:2,4,5-T:picloram were superior to other herbicides.

The genus Orobanche includes chlorophyll-lacking root parasites that parasitize many dicotyledonous species and cause severe damage to vegetable and field crops worldwide. In the United States, small broomrape is a federally listed noxious weed that has been found in red clover seed production fields in Oregon. In this study, we classified the susceptibility of red clover, white clover, and crimson clover to small broomrape infection under controlled conditions. Red, white, and crimson clover seeds were sown in pots containing small broomrape–inoculated soil. Differences in susceptibility to infection were observed among clover species; red clover was severely infected, white clover was slightly infected, and crimson clover was not infected.

Winter chilling in the field removed the primary dormancy in common ragweed (Ambrosia artemisiifolia L.) seeds and allowed them to germinate in both light and darkness. A secondary dormancy was induced in the spring and seeds again failed to germinate in light or darkness. Kinetin (K) + ethephon (E) + gibberellin A4 + A7 (GA4+7) applied to the soil in December prevented secondary dormancy. The following May only 20% of the seeds at the 15-cm depth remained viable. The rest had germinated or decayed. In contrast, 89% of the untreated seeds remained viable. Application of K + E + GA4+7 on April 22 and May 2 also broke the secondary dormancy. Gibberellin A3 (GA3) was less effective than GA4+7 in preventing or breaking secondary dormancy.

The weedy annual and perennial members of Euphorbia are widespread in the United States, occurring in every state. In at least nineteen states E. esula is considered serious enough to be declared noxious by law (PMA, 1946). In other states, to date, the members of this group occupy the position of a minor nuisance, to be controlled in the general clean-up of other weeds. E. corollata is noxious in Idaho and Wyoming; E. lucida in Idaho and South Dakota.

Isopropyl N-phenylcarbamate (IPC) and isopropyl N-(3-chlorophenyl)carbamate (CIPC) were the most effective herbicides for controlling downy brome without serious injury to perennial grasses grown for seed production in eastern Washington. The disodium salt of 3,6-endoxohexahydrophthallic acid (endothal) gave good downy brome control at Spokane, but was not satisfactory for control at Hooper and Pomeroy, Washington.

The use of preplow foliar application of 2,2-dichloropropionic acid (dalapon) for two seasons, a pre-emergence soil incorporated treatment of ethyl N,N-dipropylthiolcarbamate (EPTC) for three seasons, and tillage during all 3 years was effective in the control of Johnsongrass (Sorghum halepense (L.) Pers.) while corn was being produced on the land. The use of tillage alone, dalapon plus tillage, or EPTC plus tillage resulted in neither satisfactory Johnsongrass control nor corn yield. Dalapon plus tillage reduced the rhizomatous Johnsongrass population and increased corn yield the season following preplow treatments; reinfestation occurred, however, from Johnsongrass seedlings that emerged in the row after the corn was planted. EPTC afforded early season control of seedling Johnsongrass. EPTC plus tillage did not satisfactorily control Johnsongrass or increase corn yield over tillage alone. Injury to corn planted 1 in deep was noted in the first season's treatments; however, corn planted 1½ in deep in subsequent years was not affected.

The increasing use of dalapon (sodium salt of 2,2–dichloropropionic acid) by farmers and agricultural workers has stimulated interest in its effect upon the soil microflora and soil microbiological processes. Thiegs and Holstun and Loomis concluded that dalapon is broken down by an undertermined fraction of the soil microbial population. Magee and Colmer reported that dalapon at rates higher than those used in field applications, was toxic, as measured by manometric methods, to certain species of Azotobacter. Smith, Dawson, and Wenzel reported the effects of several other herbicides on soil microorganisms under laboratory conditions.

It was shown that less sprouting of blue oak (Quercus douglasii) and California black oak (Q. kelloggii) occurred when treated stumps were (a) cut 30 cm rather than 90 cm high, (b) treated at once after cutting rather than after 7 days, (c) treated with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) amine rather than with 2,4-dichlorophenoxyacetic acid (2,4-D) amine, and (d) left uncovered rather than covered. The differences between treatments eventually disappeared because of the death of the sprouts, possibly due to the levels of herbicide used in making the treatments.

The downward movement of carboxyl C14-labeled 2,4-D and 2,4,5-T, 3-amino-1,2,4-triazole-5-C14, and C14-labeled urea in interior live oak (Q. wislizenii) stumps was studied. Rainfall, level of 2,4-D applied, and time interval all appeared to influence downward movement.

Satisfactory selectivity of 4-chloro-2-butynyl m-chlorocarbanilate (barban) for the control of wild oats (Avena fatua L.) in spring wheat was obtained when it was applied from 4 to 14 days after emergence of wild oats. Following this period, the effectiveness and selectivity declined rapidly. Depending on the season, this period of maximum efficiency represented the following growth stages of wild oats; 1 to 3-leaf stage in 1960, 1½ to 3½-leaf stage in 1961, and 1½ to 2½-leaf stage in 1962. Injury to wheat was most pronounced during a period beginning about 15 days after crop emergence and continuing for several weeks. This pattern of wild oat control and wheat susceptibility was virtually identical over the 3-year period even though growing conditions varied considerably. This suggests that days after emergence may be at least as reliable as leaf stages as an index for the proper timing of barban treatments and would be more easily determined under practical field conditions. If leaf stages are used, then spraying should not be recommended later than 2½-leaf stage, since in some years, wild oats will have reached resistant stages. Furthermore, it may be desirable to apply barban early, perhaps even before all the plants are fully in the 2½-leaf stage. When wild oats reach the 2-leaf stage, it may be too late, at least in years of abundant moisture.

Susceptibility of a system to colonization by a weed is in part a function of environmental resource availability. Doveweed [Murdannia nudiflora (L.) Brenan] can establish in a variety of environments; however, it is found mostly in wet or low-lying areas with reduced interspecies competition. Four studies evaluated the effect of mowing height, interspecies competition, and nitrogen, light, and soil moisture availability on M. nudiflora establishment and growth. A field study evaluated the effect of mowing height on M. nudiflora establishment. In comparison with unmowed plots, mowing at 2 and 4 cm reduced spread 46% and 30%, respectively, at 9 wk after planting. Effect of mowing height and nitrogen fertilization on ‘Tifway’ bermudagrass (Cynodon dactylon Burtt-Davy×C. transvaalensis L. Pers.) and M. nudiflora interspecies competition was evaluated in a greenhouse trial. Murdannia nudiflora coverage was 62% greater in flats maintained at 2.6 cm than flats maintained at 1.3 cm. Supplemental application of 49 kg N ha−1 mo−1 increased M. nudiflora coverage 75% in comparison with 24.5 kg N ha−1 mo−1. A difference in M. nudiflora coverage could not be detected between flats receiving 0 and 24.5 kg N ha−1 mo−1, suggesting moderate nitrogen fertilization does not encourage M. nudiflora colonization. Effect of light availability on M. nudiflora growth and development was evaluated in a greenhouse study. Growth in a 30%, 50%, or 70% reduced light environment (RLE) did not affect shoot growth on a dry weight basis in comparison with plants grown under full irradiance; however, internode length was 28% longer in a 30% RLE and 39% longer in a 50% and 70% RLE. Effect of soil moisture on M. nudiflora growth and development was evaluated in a greenhouse study. Plants maintained at 50%, 75%, and 100% field capacity (FC) increased biomass>200% compared with plants maintained at 12.5% or 25% FC.

Interactions among the components of an herbicidal solution may take place (a) in the solution itself, (b) at the plant surface or within tissues to influence absorption and translocation, and (c) at the cellular site of toxic action. This broad meaning of the term interaction is employed in the present report. Similarly, the meanings of antagonism and synergism are considered as inhibition and enhancement, respectively, of the toxic action of one substance due to the influence of another, regardless of the location and nature of the interaction.

The absorption and translocation of 2,4-D (2,4-dichlorophenoxyacetic acid) has been extensively studied by numerous investigators and a number of reviews have been written (3, 7, 8). The methods used in these studies have been critically evaluated (1, 5, 8) and the general conclusion is that in the study of the absorption and translocation of biologically unstable organic compounds, such compounds should be isolated and identified.

Six herbicides, simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], propham (isopropyl carbanilate), terbacil (3-tert-butyl-5-chloro-6-methyluracil), carbetamide [D-N-ethyllactamide carbanilate (ester)], pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide], and secbumeton [N-ethyl-6-methoxy-N′(1-methylpropyl)-1,3,5-triazine-2,4-diamine] were applied annually for four years to establish forage alfalfa (Medicago sativa L. ‘Washoe’). Downy brome (Bromus tectorum L.) control ranged from 80 to 100%. The average control of broadleaf weeds was 90 to 100% with simazine, terbacil, and secbumeton, compared to 30 to 40% with propham, carbetamide, and pronamide. Only simazine and terbacil were phytotoxic to the alfalfa. Based on weed control and crop tolerance, secbumeton performed best on the coarsetextured soil in this experiment.

A 4-yr study was conducted to evaluate the response of rice (Oryza sativa L. 'Starbonnet′) to sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl-3-hydroxy-2-cyclohexen-1-one}, haloxyfop {2-[4-[13-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, and quizalofop {(±)-2-[4-(6-chloro-2-quinoxalynyloxy)phenoxy] propanoic acid}. In general, rice was more sensitive when herbicides were applied at panicle initiation than at the tillering stage of development. Quizalofop severely reduced rice yield when applied wih a surfactant. Applied at tillering, sethoxydim at 210 g ai/ha did not reduce rice height, grain yield, milling yield, or seed quality.