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.

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.

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.

Dalapon (2,2-dichloropropionic acid) was applied at 3.3 kg/ha during late May or early June to a well-established grass sward consisting of smutgrass [Sporobolus poiretii (R.&S.) Hitchc], pangolagrass (Digitaria decumbens Stent.), and bahiagrass (Paspalum notatum Flugge. ‘Pensacola’). Two cultural treatments, mowing or roller chopping, and two fertilizer treatments, 0 or N-P-K at 112-25-93 kg/ha were superimposed on the dalapon treatments at four different time intervals in a split plot design. Chopping or mowing 2 weeks after the dalapon treatment resulted in the highest bahiagrass ground cover and smutgrass control with a minimum amount of bare soil. Chopping tended to favor pangolagrass recovery, and mowing favored bahiagrass recovery. Fertilizer application increased pangolagrass ground cover 90-days after treatment, and smutgrass control after 1 yr. Fertilizer application 6 weeks after dalapon treatment generally increased pangolagrass ground cover and smutgrass control. Pangolagrass responded to fertilizer regardless of chopping or mowing. Mowing controlled more smutgrass than did chopping on the non-fertilized plots.

A charcoal barrier was used to determine the importance of root, shoot, and seed exposure on the activity of nine acetanilide herbicides to peas (Pisum sativum L.) grown in a greenhouse. Greater reduction of plant weight occurred from root exposure than from shoot exposure. For all herbicides, the average reduction in shoot and root weight from shoot exposure was 7 and 20%, respectively; and root exposure reduced shoot and root weight 15 and 40%, respectively. The average reduction in shoot and root weight from exposing all plant parts to herbicides was 47 and 69%, respectively. Seed exposure had no influence on plant weight. This response indicates that pea roots are the primary site of activity for many acetanilide herbicides, and provides support to previous findings that showed rainfall was necessary to leach acetanilide herbicides down to the root zone of processing peas for maximum reduction of shelled pea yield. Field studies, conducted over a 2-yr period, were designed to evaluate annual weed control and pea injury from preemergence and early postemergence applications of seven acetanilide herbicides. Shelled pea yield was not reduced by any treatment. All treatments provided good to excellent grass control and fair to good broadleaf weed control.

Studies were undertaken to evaluate the phytotoxicity to yellow nutsedge (Cyperus esculentus L.), length of soil persistence, and tolerance of corn (Zea mays L.) to several acetanilide herbicides. The herbicides involved were alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide]. diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl)glycine], H-26910 [N-(chloroacetyl)-N-(2-ethyl-6-methylphenyl)glycine-1-methylethyl ester], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], Ortho 19790 [1-(chloroacetyl)-2,2-dimethyl-3-oxa-1-azaspiro-[4, 5]-decane], and Vel 5052 [2-chloro-N-(2,6-dimethylphenyl)-N-(1,3-dioxolan-2-ylmethyl)acetamide]. Most of these herbicides were equally active on yellow nutsedge in solution culture; only metolachlor and Vel 5052 were significantly more active than H-26910. Metolachlor and alachlor were the most toxic to yellow nutsedge in greenhouse and field experiments. Metolachlor persisted the longest of the herbicides in the field after spring applications. The tolerances of corn differed little among the herbicides at expected use rates.

Effects of various herbicides on growth of ectotropic mycorrhizal fungi were determined over a 3-week period on modified Melin-Norcrans agar amended with the herbicides at rates of 0, 1, 3, 5, 10, 40, 80, 100, and 500 μg active ingredients/ml. Considerable variation in effect was observed among the herbicides for certain fungi and among the fungi for certain herbicides. All of the test fungi grew in the presence of each of the test herbicides at a rate of 80 μg/ml, and some growth was observed at the 500 μdg/ml rate in a majority of the herbicide-fungus combinations. Significant decreases (P = 0.05) in growth were observed for specific herbicide-fungus combinations at herbicide rates of 1 and 3 μg/ml; however, 50% or greater decreases in fungal colony areas were observed in only 12 of 112 of the combinations at such low rates. The herbicides, in decreasing order of activity against the fungi, were: diphenylethers > dinitroanilines > s-triazines > substituted amides > perfluidone [1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide]. With few exceptions, the herbicide concentrations necessary to affect fungal growth significantly were considerably higher than would be expected to occur in soil treated with the test herbicides at recommended application rates.

Canopy cover of false broomweed (Ericameria austrotexana M.C. Johnston) on the Rio Grande Plains of Texas was initially reduced by 96% by glyphosate [N-(phosphonomethyl)glycine] applied at 2.2 kg/ha in the spring. Acceptable control of this shrub with glyphosate lasted at least 4 yr. Glyphosate severely reduced basal cover of perennial grasses during the year of treatment, but grasses completely recovered within 2 yr after treatment. Standing forage crop increased by an average of 83%, compared to untreated areas, and livestock carrying capacity increased from 1 animal unit (AU)/13 ha to 1 AU/7 ha. Picloram (4-amino-3,5,6-trichloropicolinic acid), paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), and paraquat plus atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] applied in the spring were less effective than glyphosate. Canopy reductions of false broomweed 6 months after applications of 2.2 kg/ha of picloram, paraquat, or paraquat plus atrazine were equivalent to that from 1.1 kg/ha of glyphosate, and control with these herbicides was usually restricted to the season of application. Dicamba (3,6-dichloro-o-anisic acid), 2,4-D-[(2,4-dichlorophenoxy)acetic acid], atrazine, and 2,4-D plus atrazine were not effective when applied in the spring or fall. Time required for recovery of false broomweed canopy apparently varied with amounts of rainfall received after herbicide application.

In field and greenhouse experiments, liquid or granular formulations of EPTC (S-ethyl dipropylthiocarbamate) applied by hand directly in the row with seed of alfalfa (Medicago sativa L. ‘Vernal’), controlled grass seedlings in bands, usually 5 to 8 cm wide, without injuring alfalfa significantly. Grass was similarly controlled selectively when a mixture of alfalfa seed and clay granules, similar in size to alfalfa seed and containing 10% EPTC, was seeded mechanically.

Picloram (4-amino-3,5,6-trichloropicolinic acid) injected directly into a small, central-Arizona stream was lost by normal stream flow actions, such as the mixing of fast- and slow-moving water, and the interchange of surface and subsurface water in gravel and sand beds along the stream. Picloram was injected at a concentration of 6.26 ppmw; the maximum amount detected was 2.362 ppmw at 0.4 km downstream, 0.943 ppmw at 0.8 km, 0.316 ppmw at 1.6 km, 0.014 ppmw at 3.2 km, 0.001 ppmw at 6.4 km, and none further downstream. Picloram was detected near the limits of detection (0.001 to 0.004 ppmw) 2 days after injection at the 0.4-, 0.8-, and 1.6-km sites. In photodegradation tests, sunlight decomposed 57% of the picloram in containers after 8.8 h of exposure.