Field studies were conducted to determine the effect of soil surface (upper 5 cm) pH and tillage on weed control and corn (Zea mays L.) yield using simazine [2-chloro-4,6-bis-(ethylamino)-s-triazine] as the herbicide for weed control. Soil pH, weed control, and corn yield were examined under no-tillage and conventional tillage systems with and without added lime and different rates of nitrogen. Increased soil pH significantly increased weed control as compared with added lime vs. no added lime, where the surface soil pH influenced the effectiveness of the applied simazine. Soil pH had a greater effect on weed control under no-tillage than under conventional tillage. Conventional tillage significantly (P<.01) increased weed control, yield, and soil pH over no-tillage. Additions of lime as compared to unlimed treatments resulted in significantly increased weed control (83% vs. 63%), yield (5,930 vs. 5,290 kg/ha) and soil pH (5.91 vs. 5.22). The poorest weed control was observed with no-tillage on unlimed plots. A significant tillage by linear effect of nitrogen interaction for all variables resulted from a greater decrease (P<.01) in weed control and soil pH and a greater increase in yield with increased nitrogen under no-tillage than with conventional tillage.

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.

Four flower-color phenotypes were observed in a population of musk thistle (Carduus thoermeri Weinm.). This plant has been commonly referred to as C. nutans L. The four phenotypes were: purple corolla and purple pollen, pink corolla and white pollen, white corolla and purple pollen, and white corolla and white pollen. In four generations, 177 self-pollinated individuals of these four phenotypes produced 2123 progeny plants that were classified. Results support the hypothesis that three independent gene pairs were involved in determining the four flower phenotypes. The gene pairs have been designated P/p, W/w, and Pi/pi. It was postulated that all three dominant alleles, P, W, and Pi, must be present to produce both purple corollas and purple pollen. The p allele prevents color development in both corollas and pollen; the w allele eliminates color in corollas but does not affect pollen color; and the pi allele dilutes corolla color from purple to pink and eliminates pollen color. Height measurements of progenies of self-pollinated plants indicated that decreased plant height was associated with inbreeding. On the basis of the evidence presented, the musk thistle plants used in these experiments appear to belong to a single species.

Six ecotypes of saltcedar (Tamarix pentandra Pall.), an introduced competitive phreatophyte, were collected from Wyoming to Texas and grown at Los Lunas, New Mexico. Cladophyll epicuticular alkane and fatty acid contents were analyzed by gas-liquid chromatography. Fatty acid and alkane contents varied among the six morphologically-indistinguishable ecotypes. Alkane content patterns varied on the basis or absence of C39 and other constituents. Fatty acid contents of the C16 to C22 were different among the ecotypes. Variation was not explicable on the basis of latitude, light intensity, temperature, nutrition, or water status. Thus, the chemical taxonomy hypothesis of uniform epicuticular alkane quality within a species is not substantiated in saltcedar, and a portion of the ecotypic resistance to postemergence herbicide sprays may be due to differences in epicuticular wax quantity and quality.

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.

Absorption and translocation of 14C-glyphosate [N-(phosphonomethyl)glycine] in johnsongrass [Sorghum halepense (L.) Pers.] and soybeans [Glycine max (L.) Merr. ‘Lee 68’] were evaluated under various environmental conditions. The toxicity of unlabeled glyphosate applied similarly was determined in soybeans under similar conditions. In johnsongrass, absorption of 14C-glyphosate nearly doubled and translocation increased as air temperature increased from 24 to 35 C. Translocation in johnsongrass and soybeans was often greater at a relative humidity (RH) of 100% than at 45% and at a soil moisture level of 20% (field capacity) than at 12% (near the wilting point). In soybeans, absorption of 14C-glyphosate increased about 100%, translocation increased between 100 and 1200%, and glyphosate toxicity increased more than 200% as temperature decreased from 35 to 24 C. At 35 C, translocation in soybeans was often greater at 20% than 12% soil moisture. Absorption of 14C-glyphosate in soybeans was greater when the herbicide was applied to mature rather than immature leaves and stems, but the age of the treated tissue had less effect on 14C translocation. The addition of surfactant plus KH2PO4 to the treatment solution increased glyphosate absorption and translocation in soybeans, but addition of surfactant alone reduced translocation and addition of KH2PO4 alone increased translocation. Injury to six soybean cultivars from application of unlabeled glyphosate at 0.4 kg/ha ranged from 37% to 95% while total absorption of 14C-glyphosate into treated leaves of the same six cultivars ranged from 23% to 74% of the amount applied.

Absorption and translocation of buthidazole [3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone] was determined in several plant tissues. Buthidazole caused slight effects on seed germination. Germination of soybean (Glycine max L. Merr. ‘Williams’) seeds was inhibited up to 15% and velvetleaf (Abutilon theophrasti Medic.) was stimulated up to 13%. Buthidazole was absorbed by germinating soybeans, velvetleaf, and corn (Zea mays L.) with rate of absorption increasing when roots were capable of absorption. Buthidazole concentrations of 0.5 μM or greater inhibited growth of soybean in the early second-trifoliolate growth stage when supplied to the roots in nutrient solution. Within 96 h, 29% of the buthidazole available to soybeans was absorbed from nutrient solution and 89% of that absorbed was found in the shoots. The expanded leaves of soybean accumulated the majority of the radioactivity. Radioactivity in roots of soybean approached a steady state condition within 96 h, whereas 14C continued to increase in shoots. Foliar absorption of buthidazole in soybean greatly increased when any one of several surfactants were used. Soybean dry weight reduction nearly doubled by adding surfactants. Over 60% of the 14C-buthidazole applied to soybean leaves was absorbed within 1.5 h, and increased to 73% by 96 h when the nonionic surfactant, AL-411-F3 [Phytobland Spray Oil (83%) plus ATPLUS 300F (17%)] was used compared to only 7% in 96 h without the surfactant. There was little or no movement of buthidazole from the treated leaves. Translocation was typical of apoplastic movement.

Greenhouse studies revealed that glyphosate [N-(phosphonomethyl)glycine] at 3.4 kg/ha or picloram (4-amino-3,5,6-trichloropicolinic acid) at 0.3 kg/ha more effectively reduced further growth of honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.] when treated at a height of 30 cm than did 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 1.1 kg/ha or dicamba (3,6-dichloro-o-anisic acid) at 0.6 kg/ha. Glyphosate or picloram applications were also more effective than 2,4-D or dicamba applications in reducing amount of regrowth that occurred after treated plants were cut at the soil surface. Glyphosate plus 2,4-D, glyphosate plus dicamba, glyphosate plus picloram or 2,4-D plus picloram combinations also effectively reduced further growth of treated plants and subsequent regrowth after plants were initially harvested. Greenhouse studies revealed that glyphosate plus ethephon [(2-chloroethyl)phosphonic acid] at 1.7 plus 0.6 kg/ha or glyphosate plus ammonium sulfate at 1.1 plus 6.7 kg/ha were no more effective than glyphosate alone at 1.7 kg/ha. Dowco 290 (3,6-dichloropicolinic acid) at up to 2.2 kg/ha did not effectively inhibit growth of honeyvine milkweed.

Based on an herbarium survey, clover broomrape (Orobanche minor J. E. Smith) was found to have an 116 yr history in the United States. It has been collected 98 times in a total of 32 counties in 12 states and the District of Columbia, and it appears to have become established in seaports and along railroads. It most commonly parasitizes red and white clover, but also burley tobacco, carrots, and several species of ornamental shrubs and herbs. Distribution of clover broomrape indicates either a pattern of repeated introductions from foreign sources, or a persistence in areas where the parasite has become established. While not presently a significant threat, the potential for damage to crops of economic importance cannot be ruled out. The flowers are autogamous.

Hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] was applied to honeylocust (Gleditsia triacanthos L.), honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell], huisache [Acacia farnesiana (L.) Willd.], live oak (Quercus virginiana Mill.), Macartney rose (Rosa bracteata Wendl.), post oak (Quercus stellata Wangenh.), saw greenbrier (Smilax bona-nox L.), whitebrush (Aloysia lycioides Cham.), and yaupon (Ilex vomitoria Ait.). Bromacil (5-bromo-3-sec-butyl-6-methyluracil) and tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} were used for comparison in some experiments. Hexazinone was required at the following rates to kill at least 75% of the following species: 1.1 kg/ha for live oak, 2.2 kg/ha for post oak, 4.5 kg/ha for huisache (at Bryan, Texas) and whitebrush, and 9 kg/ha for honeylocust. Hexazinone was ineffective at 9 kg/ha for control of honey mesquite, huisache (at Washington, Texas), Macartney rose, saw greenbrier, and yaupon. Tebuthiuron at 1.1 kg/ha killed 80% of the live oak, and as a subsurface spray at 4.5 kg/ha, killed huisache (at Washington, Texas). Bromacil was effective on huisache at 9 kg/ha.

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.

The basis for 2,4-D [(2,4-dichlorophenoxy)acetic acid] antagonism of diclofop-methyl {methyl 2-[4-(2,4-dichlorophenoxy) phenoxy] propanoate} toxicity to wild oat (Avena fatua L.) was investigated by studying changes in the metabolism of diclofop-methyl in vitro. An esterase from wild oat, which hydrolyzes diclofop-methyl to the acid diclofop, was extracted, partially purified, and the reaction characterized. The rate of hydrolysis of 14C-diclofop-methyl was 0.14 ηmoles/2 h at standard assay conditions of 0.25 mg lyophilized enzyme preparation (19.6% protein) in 0.1 ml phosphate buffer (0.1 M, pH 7.0), substrate 5 μM. The addition of 2,4-D to this reaction did not inhibit 14C-diclofop formation. Higher levels of 2,4-D stimulated enzymic hydrolysis. 14C-diclofop-methyl was rapidly metabolized to 14C-diclofop and polar 14C-conjugates when vacuum-infiltrated into wild oat leaf segments. The addition of 2,4-D caused small increases in the rates of both 14C-diclofop-methyl de-esterification and 14C-diclofop conjugation. It is concluded that 2,4-D does not inhibit the in vitro de-esterification of diclofop-methyl.

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.

Viability of enzymatically isolated and purified oat (Avena sativa L. ‘Markton’) mesophyll protoplasts was established by their ability to photosynthetically fix CO2 and to accumulate neutral red. When protoplasts were treated with 10-3 M alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], barban (4-chloro-2-butynyl m-chlorocarbanilate), dalapon (2,2-dichloropropionic acid), dicamba (3,6-dichloro-o-anisic acid), glyphosate [N-(phosphonomethyl)glycine], oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), picloram (4-amino-3,5,6-trichloropicolinic acid), or trifluralin [α,α,α-trifluroro-2,6-dinitro-N,N-dipropyl-p-toluidine), only alachlor and barban caused significant leakage of 14C-labeled material from the protoplasts as compared to controls. An abrupt increase in leakage occurred when protoplasts were treated with Tween 20 (polyoxyethylene 20 sorbitan monolaurate) at concentrations above 0.01% (v/v). The amount of leakage from protoplasts treated with dalapon or paraquat in combination with Tween 20 appears to be equivalent to the sum of the individual treatments. Treatment of the plasma membrane ATPase with the above named herbicides during the assay period shows that alachlor, barban, and dicamba reduces enzyme activity whereas glyphosate increases the activity. Pretreatment of the membrane ATPase with the herbicides in assay buffer [36mM Tris [tris-(hydroxymethyl)-aminomethane]-MES [2-(N-morpholino)ethanesulfonic acid], 3mM MgSO4, 50mM KC1] did not inhibit the enzyme activity during the assay period. Pretreatment with dicamba, glyphosate, and picloram in gradient buffer [1mM Tris-MES, 1mM MgSO4, 1mM dithiothreitol] did inhibit enzyme acitivty during the assay period. However, these herbicides cause the pH of the gradient buffer to be acidic.

Field experiments were conducted to study the effects of varying velvetleaf (Abutilon theophrasti Medic.) densities and planting dates on the growth and yield of soybeans [Glycine max (L.) Merr. ‘Amsoy 71’]. Velvetleaf densities ranging from 2.5 to 40 plants/m2 caused reductions in the dry weight of soybean leaves, stems, roots, and pods and seeds, and in the leaf area index, pod number, and seed yield when velvetleaf and soybean plants emerged at the same time. The magnitude of reduction in soybean growth and the time at which the reduction was first observed was dependent on weed density. Soybean growth reductions caused by high velvetleaf densities were less when conditions of high soil moisture content minimized the effects of competition for water. Velvetleaf emerging 21 and 23 days after soybean emergence did not reduce crop growth or yield.