Under greenhouse conditions, vaporization of oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] formulations (2 EC, 25 WP, 1G) was studied on cabbage (Brassica oleracea L. var. capitata L. F. alba DC. ‘Market Prize’), tomato (Lycopersicon esculentum Mill. ‘Campbell 37’), cucumber (Cucumis sativus L. ‘Straight 8’), and lettuce (Lactuca sativa L. ‘Salad Bowl’). The emulsifiable concentrate and granular formulations caused vapor injury to plants exposed under glass bell jars. Vapor injury to all species increased when exposure times were increased from 8 to 72 h. Lettuce was the most susceptible test species. Exposure temperatures of 18 and 29 C did not alter the amount of vapor injury apparent on tomato foliage. Oxyfluorfen vapor injury did not reduce dry weight of any test species.

Solutions containing 24 or 120 g ae/L of amine or salt formulations of glyphosate [N-(phosphonomethyl) glycine], triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, and picloram (4-amino-3,5,6-trichloropicolinic acid) were applied to small shrubs with a carpeted roller. Glyphosate reduced the live canopy cover of false broomweed (Ericameria austrotexana M.C. Johnston) by 83 to 87% at one site but only by 37 to 58% at another location. The lower concentration of picloram reduced false broomweed cover by at least 92%, and the higher concentration completely controlled the weed at both study sites. Effectiveness of triclopyr was usually intermediate between glyphosate and picloram. Removing a scraper designed to abrade stems prior to herbicide deposition reduced the effectiveness of picloram but not other herbicides. The herbicides reduced canopy cover of common goldenweed [Isocoma coronopifolia (Gray) Greene ♯3 IOCCO] by 92 to 100%. Common goldenweed was also controlled by 2,4-D [(2,4-dichlorophenoxy)acetic acid] amine applied with the carpeted roller. In glasshouse experiments, 1.2 to 60 g ae/L of 2,4-D amine reduced live canopy dry weight of common goldenweed by 73 to 88% at 5 months after application with a carpeted roller.

The loss of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] from metal planchets was decreased by an increase in the amount applied and linseed oil (LO) additive. LO reduced volatility to a greater extent than did other additives. Vapor loss from plant leaves was influenced by plant species, plant leaf maturity, soil moisture, concentration of atrazine applied, volume of oil additive, type of additive, and duration of exposure. Generally, atrazine uptake by plants was inversely related to volatility. Uptake and translocation of 14C-atrazine label was increased more by oil additives than surfactant (SURF) compared to no additive. LO increased 14C-label translocation more in yellow foxtail [Setaria glauca lutescens (Weigel) Hubb.], green foxtail [Setaria viridis (L.) Beauv.], and barnyardgrass [Echinchloa crus-galli (L.) Beauv.] than in corn (Zea mays L.).

Field studies were conducted to determine the effect of crop species, tillage, and rye mulch on sicklepod growth. Competition from soybean and sunflower reduced sicklepod biomass by 19 and 77%, respectively. Sicklepod height was reduced by rye mulch. Rye root residue caused 49% reduction in sicklepod biomass, while whole plant rye mulch reduced weed growth an additional 12%. Crop competition reduced sicklepod shoot biomass to a greater extent when rye residue was present. Crop seed yield was 32% lower in tilled plots compared with no-tillage due to more weed competition in the tilled plots. In the presence of rye root residue, soybean yield showed a two-fold increase over no mulch or whole plant rye mulch. Sunflower yield increased by 30% in the presence of rye residue compared with no mulch.

A greenhouse study was conducted to determine the effectiveness of adjuvants on postemergence large crabgrass control with dithiopyr. Using barriers to isolate foliage or soil, the primary site of dithiopyr uptake was found to be via foliage. Laboratory and greenhouse studies elucidated the factors involved in enhancement of crabgrass control by dithiopyr with nine superior adjuvants. Two adjuvants increased dithiopyr absorption by 3.7 to 4.3% over the herbicide alone. However, none of the adjuvants increased dithiopyr translocation out of the treated leaf. Treatment of a single large crabgrass leaf indicated that enhancement of dithiopyr activity by adjuvants involved an effect on translocation, on spray retention, and on the external movement of the spray solution to the apical meristem, with the relative importance of any 1 factor depending on the particular adjuvant used. Because of the large losses of dithiopyr during absorption/translocation studies, a separate volatilization experiment determined that 70% of the applied dithiopyr volatilized within 24 h at 24 C. Dithiopyr absorption decreased and volatilization increased with each 10 C increase in temperature. Nonrecoverable dithiopyr ranged from 46 to 55% at 5 C to 92 to 95% at 35 C. Volatility losses of this magnitude may mitigate adjuvant enhancement of postemergence grass activity of dithiopyr.

In field plots, Japanese millet [Echinochloa crus-galli (L.) Beauv. var. frumentacea (Link) W. F. Wight] competed strongly with yellow nutsedge (Cyperus esculentus L.), reducing its dry weight and the number of plants and tubers with no loss of dry weight to the millet. Because Japanese millet did not shade the nutsedge for more than half the day, the main competition was thought to be ‘root’ competition (nutrient and water) with light competition as a minor factor. The greenhouse studies verified that roots were the primary area of competition. However, light competition between the two species was stronger in the greenhouse than in field plots. Also, when confined to limited light and soil volumes with a 1-month growing period, Japanese millet was reduced in dry weight by nutsedge competition.

Laboratory experiments were conducted to determine the effect of three phenolic acids, acetone, and riboflavin on aqueous photolysis of chlorimuron and imazaquin. The phenolic acids investigated were caffeic acid (CA), ferulic acid (FA), and p-coumaric acid (PCA). Treatment solutions were contained in quartz vessels and irradiated with 300 to 400 nm UV light in a photoreactor. The extrapolated photolysis half-life of chlorimuron in pure solution was 107 h, compared to a half-life of 0.42 h for pure aqueous imazaquin. Chlorimuron in solutions containing 10 ppmw riboflavin, acetone, CA, FA, or PCA exhibited half-lives of 9, 57, 58, 67, and 146 h, respectively. Imazaquin in solutions containing 10 ppmw riboflavin, acetone, CA, FA, or PCA had half-lives of 0.70, 0.55, 0.55, 0.48, and 0.55 h, respectively. The presence of PCA in aqueous media delayed chlorimuron photolysis, whereas all other compounds, especially riboflavin, sensitized chlorimuron photolysis. In contrast, imazaquin photolysis was delayed in the presence of the test compounds, with riboflavin having the greatest effect and causing in a 68% increase in imazaquin half-life over that of imazaquin alone. Quantum yields for sensitized photolysis of chlorimuron by riboflavin and for riboflavin by imazaquin were 0.1134 and 0.0477, respectively. These results suggest that some soluble and naturally occurring organic compounds may enhance chlorimuron photolysis yet delay imazaquin photolysis in surface waters.

The herbicide 3-tert-butyl-5-chloro-6-methyluracil (terbacil) applied in an isoparaffinic oil caused, in susceptible ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.), rapid and nearly complete inhibition of photosynthesis, from which it never recovered. Photosynthesis in peppermint (Mentha peperita L.), a tolerant species, was decreased only temporarily. Terbacil was readily absorbed by leaves of both species; however, there was little or no movement out of the treated peppermint leaves. Terbacil was translocated out of the treated leaves of ivyleaf morningglory to the untreated leaves and shoot apex. It was metabolized in both species but at a higher rate in peppermint. Therefore, it appears that foliarly-applied terbacil may be bound in peppermint leaves and this, together with the higher rate of metabolism, may contribute to the tolerance of peppermint. Terbacil was readily taken up and translocated to the foliage of both species when applied to the roots. Again, it was metabolized in both plants but at a higher rate in peppermint. However, the rate of metabolism alone did not appear to be sufficient to account for peppermint tolerance to root-applied terbacil.

Seventy-three rice (Oryza sativa L.) cultivars and uniform advanced-generation dwarf lines were evaluated for their response to molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate) at concentrations of 0, 1, 2, and 4 ppmw in a 7-day laboratory screening test. These rice entries varied significantly in their response to each molinate concentration when shoot height of each entry was compared to that at the 0 ppmw level. Entries were ranked according to their molinate response at the 2 ppmw concentration and categorized as being either tolerant, intermediate or susceptible. Entries categorized as susceptible at 2 ppmw were further subdivided into highly susceptible and moderately susceptible categories based on their response to the 1 ppmw concentration. Those categorized as tolerant at the 2 ppmw concentration were likewise divided into highly tolerant and moderately tolerant categories on the basis of their response to the 4 ppmw concentration. The results of this bioassay indicates the possible existence of a genetically inherited response to molinate which might be manipulated by plant breeders to develop cultivars which have a high tolerance to molinate.

Burley tobacco (Nicotiana tabacum L. ‘Kentucky 14′) was grown as a no-tillage crop in 1974 and 1975 by planting tobacco directly into an existing stand of orchardgrass (Dactylis glomerata L.) or rye (Secale cereale L.). Paraquat (1,1′-dimethyl-4,4′bipyridium ion) and glyphosate [N-(phosphonomethyl)glycine] were used to kill existing vegetation. Benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), oryzalin (3,5-dinitro-N4,N4-dipropylsulfaniiamide), metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)one], and chlorbromuron [3-(4-bromo-3-chlorophenyl), 1-methoxy-1-methylurea] were used to control annual grasses and broadleaf weeds.

Glyphosate was generally more effective than paraquat in killing existing vegetation. There was some injury to the tobacco associated with the glyphosate and paraquat treatments, but this was generally confined to those plants which came into contact with the treated herbage. Metribuzin caused severe damage to the tobacco and was discontinued after the first year. Chlorbromuron caused little injury if kept on the surface but injured the tobacco if incorporated by cultivation as in conventional tillage. Benefin and oryzalin caused little or no injury to the tobacco. All four herbicides gave adequate control of annual grasses and broadleaf weeds.

Most herbicides are applied preemergence onto bare soil or during the early stage of plant development. Therefore, the major part of the active ingredient either reaches the soil surface immediately or later with decaying plant material. The further fate of the herbicide depends largely on the physicochemical behavior of the respective compound, the amount and method of application, and a number of soil, plant, and climatic factors influencing the persistence and bio availability of organic compounds in a given soil (5, 7). Especially in the upper 2-cm soil layer, drastic changes in temperature and moisture content during a growing season have a great influence on the degradation and adsorption of herbicides in soil (10, 31).

Foliar applications of (2,4-dichlorophenoxy)acetic acid (2,4-D) to both field- and greenhouse-grown honeyvine milkweed (Ampelamus albidus (Nutt.) Britt.) caused 22% and 36% reduction in starch in roots at 2 and 3 days after treatment, respectively. No changes in soluble sugars occurred during the period, but protein had increased by 35% and 80% on the two respective dates. No increase in α-amylase was measured. Leakage of nucleotides and α-amylase from root sections began 2 days after treatment. A 20 to 30-fold increase in cellulase activity occurred in roots of treated plants starting 2 days after treatment.

Directed applications of low rates of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), disodium methanearsonate (DSMA), monosodium methanearsonate (MSMA), 1,1′-dimethyl-4,4′-bipyridinium salts (paraquat), and 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) controlled annual weeds in irrigated cotton (Gossypium hirsutum L.). Although the first applications of most herbicides caused temporary, localized foliage chlorosis or burning, cotton yields, fiber properties, and boll components were not affected. Early applications of DSMA followed by diuron selectively controlled annual weeds. When a herbicide was applied before planting, fewer postemergence applications were needed for weed control.

Resistance to propanil by a barnyardgrass (BYG) biotype has been reported, and its occurrence is becoming widespread in U.S. rice-producing regions. Interactions between propanil and the herbicides anilofos, molinate, pendimethalin, piperophos, quinclorac, and thiobencarb and the insecticide carbaryl were evaluated in laboratory studies for improved control of propanil-resistant barnyardgrass (R-BYG). Chlorophyll fluorescence measurements of BYG leaf segments were used to ascertain electron transport inhibition and to assess the synergy/antagonism of propanil (100 μM) with the various additives (50 μM). Synergistic effects on photosynthetic inhibition were found with anilofos, carbaryl, pendimethalin, and piperophos in combination with propanil. Such synergistic actions of chemicals with propanil may lead to chemical combinations useful for R-BYG control.

A hammer mill removed most of the lemmas, paleas, and pericarps from cheat florets. Typically, the cuticular layer of the testa was the only remaining intact layer, and damage to the embryos and endosperm was severe. A roller mill disrupted tissue organization of lemmas, paleas, and outer layers of the caryopses primarily at the cuts. Large gaps between the aleurone layer and testa, between testa and pericarp, and between the scutellum and endosperm were created. In the field, germination of mill-damaged florets was reduced, and florets exhibited progressive degradation the longer they were buried. Nematodes and fungi penetrated the cuticular layer of mill-damaged seed. Attaching a hammer mill or a roller mill to a grain combine to treat cheat seed before it is returned to the field could provide a novel method of cheat control.

Demand for organic food products has consistently increased for more than 20 yr. The largest obstacle to organic soybean production in the southeastern United States is weed management. Current organic soybean production relies on mechanical weed control, including multiple postplant rotary hoe uses. Although postplant rotary hoe use is effective at the weed germination stage, its efficacy is severely compromised by delays due to weather. Preplant rotary hoeing is also a practice that has been utilized for weed control but the effectiveness of this practice to reduce the need for multiple postplant rotary hoeing for organic soybean production in the southeastern United States has not been investigated. Preplant rotary hoe treatments included a weekly rotary hoeing 4 wk before planting, 2 wk before planting, and none. Postplant rotary hoe treatments consisted of zero, one, two, three, and four postplant rotary hoe uses. Weed control was increased with preplant rotary hoeing at Plymouth in 2006 and 2007 but this effect disappeared with the first postplant rotary hoeing. Multiple postplant rotary hoe uses decreased soybean plant populations, decreased soybean canopy height, lowered soybean pod position, and decreased soybean yield. Plant mapping revealed that the percentage of total nodes and pods below 30 cm was increased by increased frequency of postplant rotary hoe use.

The chloro-substituted benzoic acid compounds discussed here were included with a number of other chemicals tested in 1955, 1956, and 1957 as soil sterilizing herbicides at Hays, Kansas. The experiments were designed to yield information on the effectiveness of various treatments for field bindweed (Convolvulus arvensis) control. Results of the bindweed control studies have been briefly summarized by Phillips (9).

Studies were conducted to determine whether photosynthesis-inhibiting herbicides atrazine or bifenox, and shade affect the number, weight, senescence, and N fixation activity of nodules on the roots of the perennial legume crownvetch. Atrazine and bifenox were applied at rates of 2.24 kg ai/ha to shaded and unshaded plots. The shade was varied during the growing season to simulate changing irradiance levels beneath a corn canopy. Atrazine and bifenox treatments reduced nodule number to 13 and 42% of the untreated control, respectively, in 1980, and 18 and 35% in 1981. Shade treatments reduced nodule number to a low of 40% of the control in 1980 and 50% in 1981. Combined effects of herbicides and shade on nodule numbers were more than additive. Nodule fresh weights were reduced an average of 37% by herbicide treatments and 39% by shade treatments. Sloughed nodule numbers decreased in the herbicide and shaded treatments, suggesting that the reduction in nodule numbers was due to fewer nodules being produced. Nodule numbers were reduced a greater percentage by herbicides and shade than was herbage dry matter production. Specific nodule activity (SNA) did not differ in nodules from the atrazine, bifenox, or shade treatments on the six sampling dates in 1980 or on two of three sampling dates in 1981.

Norflurazon adsorption and dissipation under field and laboratory conditions, and distribution within the soil profile were determined in three soils representative of cotton-growing regions of the southeastern U.S. Norflurazon adsorption was greater in soil from 0 to 8 cm in a Lexington silt loam (Tennessee) and a Beulah silt loam (Mississippi) than in a Dothan loamy sand (Georgia). Adsorption was directly related to organic matter. Norflurazon degradation under controlled conditions in soil from 0 to 8 cm from each state was not different among locations, with half-lives ranging from 63 to 167 d. Degradation at 30 C in soil from the 30- to 45- and 60- to 90-cm depths was not different among locations, and was slower at the 60- to 90-cm depth than in surface soil. Norflurazon dissipation was more rapid under field conditions than under laboratory conditions, with half-lives ranging from 7 to 79 d in the 0- to 8-cm soil horizon. Dry field conditions slowed norflurazon dissipation. Norflurazon was not detected below 15 cm in the profile in any soil, and concentrations in the 8- to 15-cm soil zone were < 36 ppbw 112 d after treatment.

In order to germinate successfully, large crabgrass [Digitaria sanguinalis (L.) Scop.] seeds require a period of after-ripening. Some changes, either physical, biochemical or both, must occur in these seeds during this after-ripening process. This paper reports the differences in the activities of several enzymes between dormant (non-after-ripened) and nondormant (after-ripened) large crabgrass seeds at various periods of hydration. The total protein content of dormant seeds does not change during imbibition but increases greatly in nondormant seeds at 48 and 76 h of hydration. Initially, nondormant seeds exhibit high alpha-amylase activity and low peroxidase and acid phosphatase activities. Alpha-amylase activity remains unchanged relatively in both dormant and nondormant seeds up to 36 h of hydration, but increases greatly in nondormant seeds at 48 and 76 h of hydration. Peroxidase activity, which is initially low in nondormant seeds, increases substantially at 48 and 76 h of soaking. Acid phosphatase activity in dormant seeds does not change following hydration but is gradually elevated in nondormant seeds with duration of soaking. Lipase activity in dormant seeds remains fairly constant upon hydration. In nondormant seeds, however, the activity gradually decreases with duration of soaking, the decrease being 3 to 4 fold at 76 h of imbibition. Except for lipase, there is a positive correlation in the activities of alpha-amylase, peroxidase, and acid phosphatases with the increase of total protein content of nondormant seeds.