Field and laboratory experiments were conducted over a 3-yr period to evaluate the persistence of several dinitroaniline herbicides. Incorporation of these herbicides was delayed for 1, 3, and 7 days after application. Herbicidal activity was assessed by a sorghum bioassay, and by GLC analysis of soil samples. Herbicides least affected by a 2-day delay in incorporation were oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide, nitralin 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline, butralin 4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine, dinitramine (N4, N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralin N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline, and penoxalin N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine. Of the herbicides evaluated, trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-P-toluidine) and profluralin N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine, were the least persistent after a 1-day incorporation delay. Losses of nitralin, butralin, dinitramine, fluchloralin, penoxalin, trifluralin, profluralin, benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), and isopropalin (2,6-dinitro-N, N-dipropylcumidine) increased dramatically when incorporation was delayed 3 or more days. Persistence on the soil fur-face under field conditions was demonstrated the most by oryzalin. After incorporation, dinitramine was least persistent. The effects of temperature in UV light and dark on loss of dinitroaniline herbicides were demonstrated in the laboratory by applying the herbicide to TLC plates of soil. While herbicide losses did occur in 24 h of UV light, differences in herbicide losses were not significantly different between butralin, penoxalin, profluralin, trifluralin, isopropalin, oryzalin, nitralin, fluchloralin, and benefin. Dinitramine was most affected by the UV light. Butralin, oryzalin, nitralin, isopropalin, and dinitramine were least affected by 45 C in the dark with losses of 2 to 10% in 24 h. Profluralin, benefin, and trifluralin were found most volatile with losses of 35%, 25%, and 18%, in 24 h respectively. With increasing moisture levels, no significant increased losses were detected for butralin, nitralin, oryzalin, penoxalin, and isopropalin at the greater moisture contents. There was a moderate increase in the loss of dinitramine with increased soil moisture. AT 33% initial soil moisture, fluchloralin, benefin, and trifluralin were rapidly lost (75 to 94% in 24 h at 30 C). The trifluoro-methyl group was a common structural component where moisture affected the compound's loss. Application of the intermediate to very volatile dinitroanilines to moist soil surfaces without soil incorporation as soon as possible is not feasible unless higher rates of herbicide are applied.

The selectivity of {2-[4-(2′,4′-dichlorophenoxy) phenoxy] methyl propionate}, (hereinafter referred to as dichlofop methyl), among wheat (Triticum aestivum L. ‘Neepawa’), barley (Hordeum vulgare L. ‘Bonanza’), wild oat (Avena fatua L.), and green foxtail (Setaria viridis (L.) Beauv.) was investigated. On an ED50 basis, barley, wild oat, and green foxtail were 2, 190, and 1,090 times more sensitive, respectively, to foliar-applied dichlofop methyl at the two-leaf stage than was wheat. Selectivity decreased with increasing maturity of the plant material with the ratio of selectivity between barley and wild oat decreasing from 55 at the two-leaf stage to three at the four-leaf-plus-one-tiller stage. Greater spray retention and more rapid penetration of dichlofop methyl partially explained the susceptibility of green foxtail, but did not explain selectivity between wheat, wild oat, and barley. Root uptake of 14C-dichlofop methyl by the four species was proportional to the amount of solution absorbed during the treatment period and to the concentration of dichlofop methyl in the treatment solution but was not related to species sensitivity to this herbicide.

A method is described that provides an accurate and useful assessment of herbicide performance in small plot experiments. This method is an extension of previous rating systems and provides an assessment of the control of individual species through an estimation of the percentage that each contributes to the total broadleaf or grass weed cover on the whole plot area. It permits data collection on individual weed species but is less time-consuming than counting individual plants and it takes into account the size and vigor of individual weed plants as well as their relative abundance. Further, the system allows tabulation of data from across the entire plot rather than from small areas within the plot. The data can be readily entered into various computerized retrieval systems.

Differences in the phytotoxicity of tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimehtylurea) to nine plant species were observed on the basis of calculated GR50 values. Japanese brome (Bromus japonicus Thunb.) with a GR50 value of 0.016 ppmw was the most susceptible and corn (Zea mays L. ‘Gold Rush’) with a GR50 value of 0.436 ppmw the least susceptible. There was some growth suppression with foliar application but primary activity on all species was attributed to root uptake. The most significant translocation of labeled tebuthiuron was to the tops of common ragweed (Ambrosia artemisiifolia L.) plants treated through the nutrient solution where 24.5% of the total amount recovered was detected after 24 h. Only 7.3% of the total amount recovered was detected in the top of rye (Secale cereale L. ‘Elbon’) plants with the same treatment. With both species, more than 90% of the radioactivity recovered following foliar treatments was still in the treated leaf after 24 h. Less than 5.5% of the recovered activity for both species was in the tops, less than 3% in the roots, and less than 1.5% was in the nutrient solution.

A 3.6 g/L solution of glyphosate [N-(phosphonomethyl)glycine] applied to selected parts of bermudagrass [Cynodon dactylon (L.) Pers.] shoots did not kill the entire plant. However, phototoxicity increased as more parts of the plant were treated. No differences were observed when solutions of 3.6 and 5.4 g/L glyphosate were applied at 94 and 373 L/ha. However, greater herbicide efficacy was obtained when 1.8 g/L solution was applied at the higher volume. Translocation of this herbicide appeared to follow the typical source-sink relationship. A 7.2 g/L solution of glyphosate applied at 373 L/ha was necessary to kill the plant.

In the field, surface applied cyanazine 2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] did not move below 5 cm in a Monona silty clay loam (Typic Hapludoll) which received 20 cm of water over a 54-day period. In hand-packed soil columns in the laboratory, surface-applied diuron and cyanazine penetrated to depths of 10 and 20 cm, respectively, when leached over a comparable time period and with amounts of water similar to that used in the field. Soil thin layer chromatography and adsorption isotherm studies showed that diuron was adsorbed more strongly than was cyanazine. In general, both compounds were degraded more rapidly at the higher temperatures when incubated at 5, 20, 35, and 50 C over a 20-week period. Degradation was slowest at 5 C in a Valentine loamy fine sand (Typic Ustipsamment). Diuron appeared to break down most readily at 35 C. Cyanazine was usually decomposed by the 10th week at 5 C and the 5th week at higher temperatures.

The type of growth chamber environmental regime used altered the response of sugarbeets (Beta vulgaris L. ‘USH-9′) to desmedipham [ethyl m-hydroxycarbanilate carbanilate(ester)]. No difference occurred in growth retardation following treatment at different times of day when standard growth chamber constant day/night temperature and light cycles were used. When temperatures were programmed and light intensity varied during the day/night cycles, approximating out-of-doors daily cyclic conditions, the herbicide caused greater injury following morning treatments and less injury following late afternoon treatments. Data obtained in the growth chamber under the typical constant day/night pattern did not agree with field derived information; data obtained using the programmed temperature and varying light regime agreed well with field data and with known action of desmedipham. Plants stressed for moisture after treatment were less retarded than plants turgid at treatment; but both showed relationships to time of day at treatment similar to those noted above. Moisture stress prior to treatment diminished growth retardation by desmedipham, and reversed the treatment time of day effect.

Products volatilized from arsenical-treated soil were identified and their rates of formation measured to determine if generation of alkylarsines by soils is part of a natural arsenic cycle. 74As-sodium arsenate, 14C-MSMA (monosodium methanearsonate), or 14C-cacodylic acid (hydroxydimethylarsine oxide), were added at 13.3 μMoles (10 ppmw As) to individual flasks containing 100 g of Mattapeake silt loam. Either air or N2 was used to sweep gases from the flasks and through trapping solutions. Arsenical content in the solutions was monitored by liquid scintillation and assayed for arsenic by atomic absorption spectroscopy. Volatile arsine gases were produced under all conditions. The organo-arsenicals formed volatile compounds most quickly under aerobic conditions. In 160 days, the trapping solutions contained 18.0%, 12.5%, and 1.0% of the activity from soils treated with cacodylic acid, MSMA, or sodium arsenate respectively, when flushed continuously with air, and 7.8%, 0.8%, and 1.8% when flushed with N2. The volatile gases were identified as dimethyl- and trimethylarsine (DMA and TMA) by ion exchange and gas chromatography, and mass spectroscopy. Methylarsine (MA) was not detected. Most of the extractable arsenic remaining in the soil was present as a trimethyl arsenical compound regardless of the treatment. Since arsenic was transferred to air regardless of arsenical treatment, the transfer of arsenic from soil to air is part of the natural arsenic cycle in soils.

The concentrations of 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] in four species of vegetation varied from 11 to 115 ppmw immediately after application at 2.24 kg/ha but were less than 0.5 ppmw after 1 yr. The 2,4,5-T level in forest floor declined 90% during the first 6 months after application and less than 0.02 kg/ha remained after 1 yr. There was little leaching of 2,4,5-T from the forest floor into soil and no residues were found deeper than 15 cm. Maximum soil residues did not exceed 0.1 ppmw. Residue levels and dissipation rates of 2,4,5-T were similar after one and two successive annual applications.

The persistence of 2,4-D [(2,4-dichlorophenoxy) acetic acid] and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] was studied in the chaparral environment. Chamise (Adenostoma fasciculatum H. & A.), grass and forbs, soil surface litter, and soil were sampled for up to 360 days after herbicide (4.5 kg/ha) application. Over 50% of the 2,4-D and 2,4,5-T recovered was found on soil surface litter while 18 to 31% was found on vegetation. Much less herbicide (0.1 to 0.2%) was found in soil (0 to 5 cm) than in foliage or litter. No herbicide residues were found below the 0 to 5 cm soil sample zone. Herbicide residues on foliage and litter decreased rapidly (up to 93%) within 30 days after application but remained constant thereafter until winter rainfall began. Residues of both herbicides were evident in chamise foliage (0.01 to 0.02%), surface litter (0.01 to 0.03%), and soil (0.01%) up to 360 days after application.

Emulsifiable cationic (CM-4,CRS-1H,CSS-1,CSS-1H) and anionic (SS-1H) asphalts mixed with bromacil (5-bromo-3 sec-butyl-6-methyluracil) varied in their toxicity to green foxtail [Setaria viridis (L.) Beauv.] and velvetleaf (Abutilon theophrasti Medic). Bromacil, picloram (4-amino-3,5,6-trichloropicolinic acid), prometone [2,4-bis(isopropylamino)-6-methoxy-s-triazine], and tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N-dimethylurea} mixed with CRS-1H or CSS-1H gave excellent control of green foxtail and velvetleaf. In greenhouse experiments prometone leached readily from SS-1H while bromacil, picloram, and tebuthiuron leached the least. Leachate from picloram and tebuthiuron at 10,000 ppmw gave excellent control of green foxtail and velvetleaf. After leaching combinations of bromacil or tebuthiuron in SS-1H asphalt with 554 cm of water, enough herbicide still remained in the asphalt to control green foxtail and velvetleaf. Results indicate control would persist for 7 yr if annual rainfall was 76 cm or less and the herbicides were applied at 10,000 ppmw. Bromacil, picloram, prometone, and tebuthiuron moved laterally and resulted in more vegetation kill along a highway shoulder than on a level smooth brome (Bromus inermis Leyss.) area. Herbicide rates of 1,000 and 10,000 ppmw often resulted in excessive lateral movement and vegetation kill 2 yr after treatment. Combining herbicides with asphalt appears to be a feasible method of controlling weed growth, reducing lateral herbicide movement, and lengthening herbicide persistence.

Sugarcane (Saccharum interspecific hybrids) grown without cultivation but maintained relatively weed-free with herbicides and hand hoeing, produced yields of sugarcane/ha and sugar/ha in the plant, first-ratoon, and second-ratoon crops that were 100%, 95%, and 88%, respectively, of the yield of sugarcane cultivated two to four times annually. Standard cultural practice involves at least two cultivations, namely, the off-barring and the fertilizational cultivations. Additional cultivations did not substantially increase yield. When sugarcane yield was affected either by cultivation or herbicide treatment, stalk population rather than stalk weight was affected the most. Johnsongrass [Sorghum halepense (L.) Pers.] and annual weeds were controlled effectively in both cultivated and non-cultivated sugarcane with broadcast, preemergence application of fenac [(2,3,6-trichlorophenyl)acetic acid] at 5 kg/ha or terbacil (3-tert-butyl-5-chloro-6-methyluracil) at 1.8 kg/ha. Purple nutsedge (Cyperus rotundus L.), however, was controlled only with a combination of fenac or terbacil and periodic cultivation.

Silverleaf sunflower (Helianthus argophyllus Torr. & Gray) is a weed in the sandy soils of south and southeast Texas. The young plant parts are densely white-tomentose. This pubescence greatly increased laboratory and field-measured light reflectance over the 0.5- to 2.5-μm waveband compared with the sparsely-hairy leaves of common sunflower (Helianthus annum L.). This increased reflectance caused silverleaf sunflower's image on Eastman Kodak Aerochrome infrared color type 2443 film to be “pinkish” compared with darker magenta images for other plant species. Therefore, aerial photography may be useful to distinguish silverleaf sunflower plants from other plant species to locate its endemic areas, monitor its spread, and delineate areas needing weed control.

Seven herbicides were tested for their effect on growth of Pyricularia oryzae Cavara, Hypochnus sasakii Shirai, and Xanthomonas oryzae Uyeda & Ishiyama Dowson on agar media and for subsequent influence on disease intensity on rice plants (Oryza sativa L.) in the greenhouse. The herbicides studied were: propanil 3′,4′-dichloro-propionanilide), NTN 5$006 [O-(2-nitro-4-methylphenyl)-O-ethyl-N-isopropyl-phosphor-amidothioate], simetryn [2,4-bis(ethylamino)-6-)methylthio)-s-triazine], terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine], nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether), molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate), and aglypt (4-amino-3-methylthio-6-phenyl-1,2,4-triazine-5-on). The growth of P. oryzae, H. sasakii and X. oryzae on culture media containing 10 μg/ml commercial formulation of propanil was reduced to approximately 50% of the control. The other herbicides tested were less effective. Differences in disease severity produced on rice plants treated with the previously mentioned herbicides were in agreement with the results obtained by the culture method. The effect of simetryn and nitrofen on disease severity was stronger than expected from the small direct action on the pathogen in culture. It is suggested that the influence of these two compounds on the disease intensity is due to their effect on the host plant rather than the pathogen directly. Propanil was effective only if applied immediately or up to 1 day before inoculation, indicating that this herbicide is degraded on or within the rice leaves.

Glyphosate [N-(phosphonomethyl)glycine] toxicity to bermudagrass [Cynodon dactylon (L.) Pers.] increased significantly with each rate increase from 0.14 to 1.12 kg/ha. Under greenhouse conditions approximately 50% bermudagrass control was obtained at 0.56 kg/ha glyphosate. Visible toxicity and fresh wt of treated plants and regrowth of plants clipped at the soil surface 24 h after treatment were used as indices for penetration and translocation of glyphosate. Visible injury to bermudagrass with 0.56 kg/ha glyphosate was greater at 100% than at 40% relative humidity (RH) at both 22 and 32 C. Fresh wt data indicated that 0.56 kg/ha glyphosate was more toxic at 32 C than at 22 C at 40% RH, but no difference was observed at 100% RH. Less than 10% of the applied 14C-glyphosate penetrated the treated bermudagrass leaf at 22 C and 40% RH; whereas, more than 70% penetrated the treated leaf at 32 C and 100% RH. Five to six times more 14C-label was translocated into the plant at 100% than at 40% RH. Significantly more 14C-label translocated out of the treated leaf and into the plant at 32 C than at 22 C at 40% RH but no significant increase was observed at 100% RH.

The impact of annual preemergence herbicide usage on the rooting potential of seven commercially important woody ornamental species was studied. Granular formulations of dichlobenil (2,6-dichlorobenzonitrile), diphenamid (N,N-dimethyl-2,2-diphenylacetamide), simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine] employed as dormant season or spring applications had no inhibitory effects on the rooting of plants following transplantation. Season of transplanting influenced subsequent root growth of Japanese holly (Ilex crenata Thunb. var. convexa Makimo), Rosebud azalea (Rhododendron X ‘Rosebud’), and Hicks' yew (Taxus media Rehd. var. hicksii Rehd.) more than herbicide treatment. Hardwood cuttings taken from plants grown in herbicide-treated soil rooted as well as those from untreated controls. Plants grown in full sunlight or 55% shade exhibited similar root growth and insensitivity to preemergence herbicides.

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.

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 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.