The effect of johnsongrass [Sorghum halepense (L.) Pers.] on soybean [Glycine max (L.) Merr.] yields, grades, and net returns were determined by regression analysis of data from 252 field research plots from 1971 through 1976. Johnsongrass control from 0 to 100% was achieved by various combinations of summer fallow, dalapon (2,2-dichloropropionic acid) as a preplanting application at 8.3 kg/ha, or trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 0.8 to 1.7 kg/ha incorporated into the soil before planting. Repeated usage of trifluralin at 1.7 kg/ha, either with or without use of summer fallow, provided the most effective and most profitable soybean production. Foreign material in soybean seed samples was about 0.8% with 100% johnsongrass control and nearly 6% with no control. At least 70% johnsongrass control was required to avoid deductions from gross harvested weights caused by seed moisture levels exceeding 13%. Levels of johnsongrass control in excess of 60% tended to increase soybean test weights. With 100% johnsongrass control, about 1.2% damaged soybean seed occurred; whereas, without johnsongrass control, about 1.7% seed damage occurred. The level of johnsongrass control had little effect on the level of split soybean seed at harvest. Failure to control johnsongrass resulted in predicted soybean grades of 4.1; whereas, nearly 100% johnsongrass control was necessary to provide U.S. No. 1 grade soybeans. Soybean yields were increased 4.8 to 6.2% for each 10% increase in johnsongrass control when plots were not fallowed or after fallowing, respectively. Net returns in soybean production were nearly twice as great with 100% johnsongrass control as when johnsongrass was not controlled.

Experiments were conducted from 1973 through 1975 on Lucedale sandy loam to determine the influence of in-row cotton (Gossypium hirsutum L. ‘Stoneville 213’) densities on the competitiveness of low-level infestations of sicklepod (Cassia obtusifolia L.) and pigweed (Amaranthus spp.). Weeds were established at densities of 0, 4, 12, and 32 weeds per 15 m of row and allowed to compete the entire season with cotton grown at densities of 5, 10, or 20 plants/m of row corresponding to 47000, 94000 and 187000 cotton plants/ha. Conventional cultural practices were employed in these experiments. Cotton yields were inversely related to weed density; however, the density of cotton did not influence the competitive effect of sicklepod or pigweed. Pigweed or sicklepod dry weed weight was reduced when competing with 187000 cotton plants/ha.

Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid}, 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and 3,6-dichloropicolinic acid were applied to the foliage of juvenile crop plants at 0.002, 0.009, 0.03, 0.14, and 0.56 kg/ha. Corn (Zea mays L.), oat (Avena sativa L.), wheat (Triticum aestivum L.), grain sorghum [Sorghum bicolor (L.) Moench], and kleingrass (Panicum coloratum L.) were generally more tolerant to the herbicides than were peanuts (Arachis hypogaea L.), cotton (Gossypium hirsutum L.), cucumber (Cucumis sativus L.), and soybean (Glycine max [L.] Merr.). Triclopyr was usually more phytotoxic to corn, oat, grain sorghum, and kleingrass than either 2,4,5-T or 3,6-dichloropicolinic acid at 0.14 and 0.56 kg/ha, but few differences occurred among herbicides at lower rates. Kleingrass was not affected at any rate of 3,6-dichloropicolinic acid. Wheat tolerated most rates of all three herbicides. At 0.56 kg/ha, triclopyr and 3,6-dichloropicolinic acid caused greater injury to peanuts than did 2,4,5-T; whereas, 2,4,5-T and triclopyr were more damaging to cotton and cucumber than 3,6-dichloropicolinic acid. The three herbicides at 0.14 and 0.56 kg/ha killed soybeans. Soybean injury varied from none to severe at 0.002 to 0.03 kg/ha, depending upon species investigated, but many plants showed morphological symptoms typical of the auxin-type herbicides.

Leaflets of 1690 species of Old World and South American Astragalus collected from herbaria at Kew, England; Edinburgh, Scotland; Munich, Germany; and Vienna, Austria were analyzed qualitatively for toxic aliphatic nitro compounds. The catabolites of nitro compounds found in species of Astragalus (nitro-bearing), 3-nitro-1-propanol and 3-nitropropionic acid, are especially toxic to cattle and sheep. A total of 190 of 1624 (12%) Old World species, 30 of 66 (45%) South American species, and a single species of one Astragalus subgenus were positive for nitro compounds. Most Old World species that contained aliphatic nitro compounds were collected in the Middle East and the Union of Soviet Socialist Republics. Nitro compounds were detected in specimens of eight species collected between 1822 and 1836. The nitro-bearing species were chemotaxonomically related and grouped within taxonomic sections. The presence of two or three nitro-bearing species within a section indicated that other species within the same section might also be nitro-bearing.

Aerial applications of 20% tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N-dimethylurea} pellets at 2.2 kg/ha (ai) in the spring effectively controlled post oak (Quercus stellata Wangenh.), blackjack oak (Q. marilandica Muenchh.), water oak (Q. nigra L.), yaupon (Ilex vomitoria Ait.), winged elm (Ulmus alata Michx.), downy hawthorn (Crataegus mollis Scheele), gum bumelia [Bumelia lanuginosa (Michx.) Pers.], and willow baccharis (Baccharis salicina Torr. & Gray) in the Post Oak Savannah of Texas. Tree huckleberry (Vaccinium arboreum Marsh.), black hickory (Carya texana Buckl.), honeylocust (Gleditsia triachanthos L.) and cedar elm (Ulmus crassifolia Nutt.) were partially controlled by 2.2 kg/ha of tebuthiuron. Canopies of buckbrush (Symphoricarpos orbiculatus Moench), southern dewberry (Rubus trivialis Michx.), American beautyberry (Callicarpa americana L.), and persimmon (Diospyros virginiana L.) were reduced for about two growing seasons after which the woody species recovered. American beautyberry appeared to increase in abundance by the third growing season after control of the other woody species. Honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell], eastern redcedar (Juniperus virginiana L.), and Texas persimmon (Diospyros texana Scheele) were not controlled by tebuthiuron at 2.2 or 4.4 kg/ha, and saw greenbrier (Similax bona-nox L.) and peppervine [Ampelopsis arborea (L.) Koehne] apparently increased following application of tebuthiuron.

Six herbicides were evaluated at two rates on sweet potatoes [Ipomoea batatas (L.) Lam. ‘Georgia Red’, ‘Georgia Jet’] with and without cultivation from 1972 through 1976. Cultivation with a ground-driven rotary hoe about 2 weeks later improved the control of late-season broadleaf weeds such as Florida beggarweed [Desmodium tortuosum (Sw.) DC] and showy crotalaria (Crotalaria spectabilis Roth.). Cultivation improved weed control where vernolate (S-propyl dipropylthiocarbamate), DCPA (dimethyl tetrachloroterephthalate), and napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] were applied. The improved weed control in cultivated treatments resulted in increased sweet potato yields in 1972 and 1973, which also were the years with the highest weed populations.

Field and growth chamber experiments were conducted to determine the effects of surface soil moisture on the phytotoxicity of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] to grain sorghum [Sorghum bicolor (L.) Moench. ‘Funk 623 GBR’], which was unprotected or protected with CGA-43089 {α-[(cyanomethoxy)imino] benzeneacetonitrile}. In field tests, neither alachlor nor metolachlor was phytotoxic to unprotected grain sorghum when the surface soil remained dry until the sorghum had emerged. CGA-43089 protected sorghum emerging from moist soil that had been treated with alachlor or metolachlor at rates of 2.24 or 3.36 kg/ha. Growth chamber tests showed that CGA-43089 was less effective in protecting sorghum from herbicide injury when Ships clay was continuously wet [110% field capacity (FC)] from time of planting to emergence (3 to 5 days) than when soil was wet for only 1 or 2 days prior to emergence. In contrast, if the surface soil remained dry until the coleoptile reached the soil surface, alachlor and metolachlor had little effect on sorghum even when no protectant was present. When sorghum was planted in Arenosa sand containing 5% organic matter, protected sorghum grew as well as the control even under continuous high moisture conditions. Metolachlor incorporated into the root zone at a rate of 20 ppm had no effect on either protected or unprotected sorghum. Alachlor and metolachlor were most phytotoxic when placed in the surface 1.25 cm of moist soil or when incorporated. The coleoptile was the most susceptible plant part. Thus, the key to grain sorghum response to these herbicides was in herbicide placement and availability to the coleoptile. Under conditions normally leading to phytotoxic effects from alachlor or metolachlor, grain sorghum growth was significantly better from seed protected with CGA-43089 than from unprotected seed.

A phytosociological study of weeds carried out at Ajmer in the semi-arid zone of India revealed the presence of Dactyloctenium-Cynodon-Chloris community during the monsoon season and Cynodon-Tribulus-Tephrosia community of weeds during the summer season, growing on coarse and sandy soils and in harmony with all biotic factors. The communities experience high summer and low winter temperatures with rainfall occurring only during the monsoon season (July to September). Other dominant weeds included Achyranthes aspera L., Amaranthus gracilis Desf., Tephrosia purpurea (L.) Pers., and Trianthema portulacastrum L. during the monsoon season, and Boerhavia diffusa L., Indigofera linifolia (L.) Retz., and Rhus mysurensis Heyne ex Wight. are dormant during the summer season.

Field experiments were conducted in 1977 and 1978 to determine susceptibility of rhizome johnsongrass [Sorghum halepense (L.) Pers.] to metriflufen3 {2-[4-(4-trifluoromethylphenoxy) phenoxy] propanoic acid, methyl ester} applied as preplant-incorporated, preemergence, or postemergence treatments. Rates of metriflufen applied preplant incorporated and preemergence were 1.12, 2.24, and 3.36 kg/ha. Postemergence treatments consisted of 0.56, 1.12, and 1.68 kg/ha of metriflufen plus a non-ionic polyethylene glycol alkyl ester, each applied to johnsongrass at growth stages of 30 to 38 cm, 60 to 75 cm, and heading. Johnsongrass control increased with each increase in rate of soil-applied metriflufen with no differences in control between preplant incorporated and preemergence treatments. Johnsongrass density was reduced by increased rates of metriflufen, and 1978 soil-applied treatments reduced densities by 62%. Preplant-incorporated and preemergence applications of 3.36 kg/ha of metriflufen resulted in higher soybean yields than did the two lower rates. Results from treatments with trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) were similar to those with metriflufen at the same rate. Metriflufen applied to 30-to 38-cm johnsongrass reduced stands by 60% in 1978, but stands increased by 51 and 71% in plots treated at the 60- to 75-cm or heading stages of growth. Soybean tolerance to postemergence applications of metriflufen was excellent for all stages of growth and rates of metriflufen.

Several regimes of supplying exogenous aromatic amino acids to intact, 3-day-old, soybean [Glycine max (L.) Merr. ‘Hill’] seedlings by root uptake were tested to determine if growth retardation caused by root-fed, 0.5 mM glyphosate [N-(phosphonomethyl) glycine] could be reversed. Generally, root-fed levels of aromatic amino acids just below growth-retarding levels (e.g. 1 mM phenylalanine + 0.1 mM tyrosine) reversed root growth inhibition caused by glyphosate to a small (ca. 10%) but significant extent. Feeding aromatic amino acids for 1 to 3 days before glyphosate exposure did not enhance the reversal. Uptake and metabolism of root-fed, aromatic amino acids in control and glyphosate-treated plants were verified by increased levels of hydroxyphenolic compounds (end products of aromatic amino acid metabolism) and by uptake and incorporation of 14C-labeled phenylalanine and tyrosine. On a fresh weight basis, glyphosate had no inhibitory effect on uptake or incorporation of these amino acids into protein or secondary phenolic compounds. After 3 days of exposure, glyphosate had no substantial effects on shikimate dehydrogenase activity in control or aromatic amino acid-fed seedlings. These data suggest that either root-fed aromatic amino acids are compartmentalized differently than the endogenous pools affected by glyphosate or that root-fed glyphosate exerts most of its effect on growth of soybean seedlings through means other than inhibition of aromatic amino acid synthesis.

Levels of MSMA (monosodium methanearsonate) that simulated drift (0.2, 0.39, and 0.78 kg/ha) were applied over-the-top to rice (Oryza sativa L. ‘Vista’, ‘Starbonnet’, or ‘Labelle’) after flooding at four developmental stages between early tillering and late jointing. The MSMA rates used were equivalent to, or lower than, the 0.78-kg/ha rate that would be applied as an over-the-top application to cotton (Gossypium hirsutum L.) for early season weed control. Over-the-top applications of MSMA did not affect heading and maturity dates of filled grains regardless of the rate or application timing. Reductions occurred, however, in plant height, number of panicles, and yield. In addition, the percentage of erect panicles showing typical “straighthead” symptoms increased. Rice sensitivity to MSMA depended on MSMA rate and stage of growth with injury being most severe as rice approached the reproductive stages of development. Because aerial applications of MSMA to cotton are normally made before rice reaches the reproductive stage, injury resulting from MSMA drift should be minimal.

Toxicity of nonradiolabeled and translocation of 14C-labeled metriflufen3 {2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoic acid} in cotton (Gossypium hirsutum L. ‘Stoneville 213’) were evaluated under different environmental conditions as affected by surfactant and by the maturity of stem or leaf tissue at the place of herbicide application. Cotton was very tolerant to metriflufen, with the greatest tolerance at high temperatures. The herbicide entered the plant quite rapidly and autoradiographs indicated that radioactivity from the herbicide moved freely throughout the plant. Relative humidity (RH) between 40 and 100% had little effect on metriflufen toxicity. Two weeks after treatment with metriflufen at 0.5 kg/ha, cotton was essentially free of injury symptoms at 35 C, but injury was as great as 41 and 13% at 18 and 25 C, respectively. All plants recovered fully after 6 additional weeks in the greenhouse. When surfactant was added to the spray solutions, cotton injury was frequently increased during the first 2 weeks but not after 8 weeks. Accumulation of 14C at the site of 14C-metriflufen application was 31 to 65% after 48 h. Between 16 and 51% of the applied 14C moved from the treated area by translocation into other parts of the plant, or by volatilization into the atmosphere. Movement was greatest from stem tissue at 35 C and 100% RH. There was no correlation between 14C movement and herbicide toxicity within the plant. The selectivity of metriflufen to cotton probably results from deactivation by, or tolerance within, the plant rather than from differential absorption and translocation of the herbicide.

The soil activity of foliar-applied HOE 29152 {2-[4-trifluoromethyl-phenoxy)phenoxy] propanoic acid} and diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} on barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and yellow foxtail [Setaria lutescens (Weigel) Hubb.] was evaluated in the greenhouse. HOE 29152 was applied at 0.1, 1.2, 2.4, and 3.5 kg/ha; and diclofop was applied at 0.5, 2.7, 4.9, and 7.2 kg/ha. Both compounds applied to roots or shoots before emergence reduced growth. Neither compound had much, if any, effect on the germination of barnyardgrass or yellow foxtail; however, the survival of both weed species that germinated in solutions of these two compounds was reduced. The number of seedlings surviving for both weed species was reduced by both compounds. Seedling survival from germination imbibition by diclofop and HOE 29152 was influenced by the presence of light at the time of seed germination.

A procedure is described for the rapid analysis of leaf samples to determine triazine resistance. The technique uses a commercially available fluorometer and is based upon the fact that photosynthesis-inhibiting herbicides increase chlorophyll fluorescence (because of dissipation of absorbed radiant energy in the absence of useful photochemistry). Resistant and susceptible biotypes of six weed species were assayed. Fluorescence of susceptible leaf sections increased dramatically over a 1- to 3-h exposure to atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], but resistant leaf sections showed no fluorescence increase. Substantial fluorescence increases of both resistant and susceptible leaf sections were induced by diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. In the absence of herbicides, fluorescence was higher in resistant than in susceptible leaf sections, suggesting that the resistant biotypes are less efficient photosynthetically. Fluorescence analysis was used to characterize atrazine inhibition of photosynthesis in leaf sections of three crop species. Differences in atrazine-induced fluorescence between crop lines were relatively small and were not well correlated with atrazine tolerance. The fluorometer is a convenient device for monitoring photosynthesis inhibition, however, and could be useful in detecting plants having resistance to photosynthesis-inhibiting herbicides.

The short-run economic consequences of bans on herbicides commonly applied to corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.] on a typical Indiana farm were analyzed. A dinitroaniline ban reduced soybean yields and net farm income 17 and 32%, respectively. A triazine ban reduced corn and soybean yields 3 and 20%, respectively, and net farm income by 38%. A simultaneous ban on all dinitroaniline, triazine, and amide herbicides reduced corn and soybean yields 14 and 17%, respectively, and net farm income by 65%. Harvest delays attributable to less effective weed control resulted in a loss in efficiency, yields, and profits, and increased machinery and labor requirements. Hence, herbicide bans under typical Indiana conditions would inflict substantial, short-run economic losses on individual farmers. This study did not measure any potential public benefits or costs of herbicide bans, however.

Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] applied with simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] reduced by 47 to 82% the severity of simazine symptoms on California privet (Ligustrum ovalifolium Hassk.), staghorn sumac (Rhus typhina L.), and ‘Moonlight’ broom (Cytisus X praecox Bean). Oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) had a similar but smaller effect (40% reduction) when applied with simazine on broom in a field experiment and an effect equal to napropamide with simazine on privet in a greenhouse experiment. Both napropamide and oryzalin prevented some of the growth reduction from simazine on privet, broom, and ‘Baltic’ ivy (Hedera helix L. ‘Baltica’) in field experiments. In the greenhouse study with privet, napropamide prevented much of the growth-reducing effects of simazine on both shoots and roots of privet. Oryzalin appeared to have a similar effect.

Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] has considerable potential for yellow nutsedge (Cyperus esculentus L.) control in crops commonly produced in the Texas High Plains. Little information is available, however, concerning adsorption characteristics of metolachlor in soils of this region. Adsorption and movement of metolachlor were determined in three commonly occurring soils of the Texas High Plains. Organic carbon contents of the soils by weight varied from 0.3 to 0.5%, and the clay fraction ranged from 16 to 33%. Freundlich adsorption isotherms exhibited two linear regions for each soil, suggesting the possibility of multilayer adsorption. K′oc values and coefficients of determination for organic carbon and clay content vs. Freundlich K values indicated that organic matter was the predominant adsorbent for metolachlor in the soils studied. Desorption, soil column leaching, and thin-layer plate studies demonstrated metolachlor to be sufficiently mobile in scils low in organic matter to cause possible crop injury or loss of efficacy.

In a 2-yr field study with preplanting-soil-incorporated treatments of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], tolerance of soybeans [Glycine max (L.) Merr.] to these herbicides, as measured by seed yield, was increased by increasing the seeding rate one-and-one-half or two times that normally recommended. These results agree with suggestions in the literature that plants can compete for herbicide in the soil, and suggest that increased seeding rates of soybeans can partially reduce the adverse effects of atrazine carryover or excessive metribuzin application.

The influence of common ragweed (Ambrosia artemisiifolia L.) interference on soybean [Glycine max (L.) Merr. ‘Ransom’] yield was studied in the field utilizing naturally occurring weed populations. The damage-threshold population for a full-season, in-row common ragweed infestation was four weeds/10 m of row, which resulted in an 8% yield loss. Soybeans kept weed-free for 2 weeks or longer after emergence in a dry year produced normal yields, but 4 weeks of weed-free maintenance was required when adequate moisture was available early in the growing season. Soybean yield was not reduced by a natural population of common ragweed if the period of interference was limited to 6 weeks or less after crop emergence. By 8 weeks after emergence, common ragweed height averaged 25 cm taller than soybeans, and the weed canopy intercepted 24% of the photosynthetically active radiation.

A method is described for the large-scale production of a granular formulation of Alternaria macrospora Zimm. The granular preparation consisted of spores, mycelia, and vermiculite. This formulation of A. macrospora, applied preemergence or postemergence, controlled spurred anoda (Anoda cristata Schlecht.) plants in greenhouse and field tests. The pathogen did not significantly affect emergence or dry weight production of cotton (Gossypium hirsutum L. ‘Stoneville 213’) seedlings. The fungicides PCNB (pentachloronitrobenzene) and ETMT [5-ethoxy-3-(trichloromethyl)-1,2,4-thiadiazole] did not significantly affect spurred anoda control with A. macrospora. The method for production and formulation of A. macrospora was modified to produce spores and granular formulations of other Fungi Imperfecti: Drechslera sp. and Fusarium spp. (Moniliales), Colletotrichum spp. (Melanconiales), and Phyllosticta sp. (Sphaeropsidales).