Common lambsquarters is an important annual weed of many crops world-wide. Ascochyta caulina is a plant pathogenic fungus that, under natural conditions, causes necrotic spots on the leaves and stems of Chenopodium species. The objective of this study was to evaluate the effect of weed growth stage, relative humidity, dew period, and temperature on the infection of A. caulina isolates against common lambsquarters. In greenhouse experiments, replicated groups of common lambsquarters plants were sprayed with different isolates of A. caulina 2, 3, 4, 5, and 6 wk after emergence. Both disease severity and pathogen-induced dry weight reduction decreased with plant age. The efficacy of all isolates tested was reduced by high leaf-to-air vapor-pressure deficit. Disease severity was more responsive to relative humidity than temperature. However, a minimum dew period of 6 h was required to cause significant disease severity in common lambsquarters. Among all tested A. caulina isolates, W90–1 gave the highest disease scores under all conditions, with the exception of temperatures ≤15 C.

Acetolactate synthase (ALS), a common enzyme in the biosynthesis of branched-chain amino acids, is a target for the sulfonylurea, imidazolinone, triazolopyrimidine, pyrimidinylthiobenzoate, and the sulfonylaminocarbonyltriazolinone classes of herbicides. Widespread resistance to the ALS-inhibiting herbicides has been attributed to single-base mutations in the ALS gene. The objective of this study was to investigate the feasibility of using denaturing high-performance liquid chromatography (DHPLC), a recently developed method of mutation analysis, for the detection of three ALS mutations, Ala122Thr, Leu574Trp, and Ser653Thr, which confer herbicide resistance. The mutated variants of the ALS gene were isolated from herbicide-resistant biotypes of smooth pigweed and Powell amaranth using polymerase chain reaction (PCR). The PCR products were hybridized with a wild-type sample and subjected to DHPLC analysis. All three mutations could be detected using a modified High performance liquid chromatography system; however, the sensitivity of the method was strongly dependent on the melting temperature profile of the analyzed DNA fragment. Once the primers and the DHPLC conditions are optimized, the procedure is economical, rapid, and requires little sample preparation. Because of these favorable features, DHPLC can be used as an alternative to other commonly used mutation detection methods.

Indaziflam is a cellulose biosynthesis-inhibiting herbicide for annual weed control in various agricultural systems. Sporadic cases of unacceptable injury to desirable plants have been reported after indaziflam application, which may have been due to conditions favoring increased indaziflam–soil bioavailability. Research was conducted from 2013 to 2015 on a sandy soil to elucidate the effects of soil organic matter content (SOMC) and soil volumetric water content (SVWC) on indaziflam–soil bioavailability. Indaziflam was applied (50 or 100 g ha–1) at fall only, fall plus spring, and spring only timings to plots in a factorial arrangement of SOMC, pre–indaziflam application (PrIA) SVWC, and post–indaziflam application (PoIA) SVWC. After application, field soil cores were collected for a subsequent greenhouse bioassay experiment, where foliage mass reduction of perennial ryegrass seeded from 0 to 15 cm soil depth was used as an indicator of indaziflam–soil bioavailability throughout the profile. Significant edaphic effects were observed at 0 to 2.5, 2.5 to 5, and 5 to 7.5 cm depths, with increased bioavailability at low compared with high SOMC. Pre–indaziflam application SVWC did not affect bioavailability, whereas PoIA high SVWC increased indaziflam–soil bioavailability at 2.5 to 7.5 cm depth compared with PoIA low SVWC. Low SOMC–PoIA high SVWC decreased perennial ryegrass foliage mass 40 and 37% at 5 to 7.5 cm depth from cores collected 10 and 14 wk after treatment, respectively, whereas reductions from all other SOMC–PoIA SVWC combinations were < 12% and did not vary from each other. Pearson's correlation coefficients showed a moderate, positive relationship between perennial ryegrass mass reductions at 0 to 2.5, 2.5 to 5, 0 to 5, and 0 to 10 cm depths and hybrid bermudagrass cover reduction, which suggests conditions favoring increased indaziflam–soil bioavailability can adversely affect plant growth. Data from this research will aid land managers to use indaziflam effectively without adversely affecting growth of desirable species.

Radioactive sodium salt of 2,2–dichloropropionic acid (dalapon) was applied to the leaves or to the roots of sugar beets, a species tolerant of the herbicide, and yellow foxtail (Setaria glauca), a susceptible species. Autoradiographs indicated that dalapon entered through the leaves and roots, and moved throughout all portions of both species within 48 hours. Accumulation of dalapon was greatest in the younger tissues of both species. Paper chromatographic separations of aqueous extracts of the plants indicated no metabolic derivatives of dalapon in either species.

The herbicide, isopropyl N–(3–chlorophenyl) carbamate (CIPC), has proved to be efficient in eliminating certain weeds from several crops. The toxic mechanism of this herbicide is still somewhat doubtful. In order to further determine the reaction of plants to this herbicide the carbohydrate content of corn plants sprayed with CIPC was investigated.

Chlorsulfuron and metsulfuron were effective on Texas whitebrush, killing 70 to 75% of the plants at 0.28 kg ai ha, marginally effective on Macartney rose, killing 15 to 43% of the plants at 1.12 kg ha, but ineffective on honey mesquite and huisache, killing no more than 10% of the plants at 1.12 kg ha. Sulfometuron was ineffective on all woody species at 1.12 kg ai ha. Clopyralid and picloram were effective, killing 70 to 92% of the huisache at 2.24 kg ae ha. Tebuthiuron killed 72% of the Texas whitebrush at 1.12 kg ai ha. Sulfometuron generally reduced herbaceous plant cover the year of application. Chlorsulfuron and metsulfuron often resulted in increased grass cover the year of application. Most herbicides reduced broadleaf weeds the year of application. Woolly croton often was the first prominent broadleaf species to return to areas treated with clopyralid and sulfometuron. Few differences occurred among herbicides in herbaceous weed cover the year following treatment.

Leucaena [Leucaena leucocephala (Lam.) de Wit] is a perennial weed in more than 25 countries, including Australia. Knowledge regarding the seed biology of L. leucocephala could help in making weed management decisions. Experiments were conducted to study the effect of hot water (scarification), alternating temperatures, heat stress, salt stress, water stress, and burial depth on seed germination of two populations of L. leucocephala collected from Toowoomba and Gatton, Australia. The optimum duration of hot water treatment to break the hard seed coat dormancy was 2 min for both populations. The highest germination (92% to 98%) was recorded at 35/25 C for both populations, and similar germination occurred at 30/20 C. The Toowoomba population recorded greater germination at low temperature (15/5 to 25/15 C) than the Gatton population. Additionally, the Gatton population had higher germination than the Toowoomba population after 5 min of exposure to temperatures of up to 100 C, suggesting that the Gatton population may be more tolerant to heat stress. Germination was completely inhibited at pretreatment (5 min) temperatures of 150 to 250 C. The Toowoomba population recorded 17% greater germination than the Gatton population at a high salt concentration (160 mM NaCl), indicating its greater salt tolerance. At low moisture stress (−0.1 and −0.2 MPa), higher germination was observed in the Toowoomba population than in the Gatton population, whereas germination was similar for both populations at higher water stress levels (−0.4 MPa or lower). Germination was similar for both populations at shallow depths (0 and 1 cm) but higher emergence was recorded for the Toowoomba population at 2 to 8 cm than the Gatton population. Differential germination behaviors of both populations suggest that they adapted differently in their respective local environments. Knowledge gained from this study will help in formulating integrated management practices for L. leucocephala.

The selectivity of 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) in winter wheat (Triticum aestivum L., var. Nugaines), a resistant species, and coast fiddleneck (Amsinckia intermedia Fisch. & Mey.), a susceptible species, was concluded to be the result of a complex of interactions. Wheat was 109 times more tolerant of bromoxynil than was coast fiddleneck. More spray solution was retained by coast fiddleneck plants than by wheat. Bromoxynil penetrated more rapidly into leaves of coast fiddleneck than of wheat. However, these factors did not fully explain bromoxynil selectivity. When differential spray retention and bromoxynil penetration was accounted for, it was estimated that coast fiddleneck was 30 times more susceptible than wheat.

Applications of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] at rates from 0.3 to 1.4 kg/ha were made in the field to soils of 2 and 30% (w/w) soil moisture. After 2 to 4 days, all soils were irrigated to establish stands of either sweet corn (Zea mays L. ‘Jubilee’) or winter wheat (Triticum aestivum L. ‘Stephens’) used as bioassay species for ethofumesate activity. Ethofumesate, at most rates, was significantly less effective on both corn and wheat when applied to dry soil than to wet soil. In greenhouse studies, ethofumesate activity was significantly greater when incorporated into soil of 12% than 2% (w/w) moisture 2 or 4 days prior to irrigation. An increase in herbicide activity was apparent as the length of time between herbicide application and wetting increased from 2 to 4 days. Analysis of wet (20%, w/w) and dry (2%, w/w) soils treated with equal levels of ethofumesate revealed no loss of herbicide applied to wet soil over a 12-day period, but in the dry soil, the amount extracted after 12 days was 10% of the amount extracted at 0 days. These data and other considerations suggest that chemical degradation of ethofumesate is the most likely mechanism for the activity loss in dry soil.

Residual herbicidal action of 3-amino-2,5-dichlorobenzoic acid (amiben), the methyl ester of amiben, 3-acetamido-2,5-dichlorobenzoic acid (N-acetyl amiben), 3-propionamido-2,5-dichlorobenzoic acid (N-propionyl amiben), 3-benzamido-2,5-dichlorobenzoic acid (N-benzoyl amiben), and the methyl ester of N-benzoyl amiben after 0, 1, 2, 4, and 6 hr irradiation was measured by oats (Avena sativa L., var. Markton) bioassay. In a greenhouse study, amiben and N-benzoyl amiben were applied to the soil surface, exposed to sunlight for 7.5 hr, and similarly bioassayed. Amiben, the methyl ester of amiben, and N-acetyl amiben lost 40 to 60% of their original herbicidal activity after 2 to 4 hr irradiation in the laboratory. N-benzoyl amiben and its methyl ester retained over 90% of their activity after 6 hr irradiation. Solar illumination reduced the herbicidal activity of amiben applied to the surface of wet soil by 11 to 14% but had no effect on N-benzoyl amiben. On a dry soil, the losses of amiben and N-benzoyl amiben were not significant.

A single application of 0.56 or 0.84 kg ai/ha tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl) oxirane] plus 2.3 kg ai/ha of atrazine [6-chloro-N-ethyl-N′-(1-niethylethyl)-1,3,5-triazine-2,4-diamine] at the one-to three-leaf stage controlled large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] and fall panicum (Panicum dichotomiflorum Michx. #PANDI) 96% or more. A sequential application of 1.1 kg/ha of atrazine, in addition to the above single application, was required for control of the two grass species at the four-to six-leaf stage. Application of tridiphane plus atrazine to large crabgrass and fall panicum beyond the six-leaf stage was ineffective. Tridiphane at 0.75 kg/ha, applied alone, reduced the shoot dry weight of large crabgrass by 71%. The response of tridiphane and atrazine combinations at the four- to five-leaf stage of large crabgrass was additive.

Absorption of 2,4-D [(2,4-dichlorophenoxy) acetic acid], dicamba [3,6-dichloro-o-anisic acid], and the isopropylamine salt of glyphosate [N-(phosphonomethyl) glycine] by excised honeyvine milkweed [Cynanchum laeve (Michx.) Pers.] leaves was determined. Experimental variables included leaf position (terminal vs. basal), a surfactant, 4-isopropenyl-1-methylcyclohexane plus unspecified emulsifiers (SA-77), and leaf collection dates. Absorption of the three herbicides by terminal and basal leaves was increased by the addition of the surfactant. However, the surfactant increased absorption into basal leaves more than into terminal leaves. The surfactant reduced surface tension and increased drying time of water droplets on adaxial leaf surfaces by 50%. The pH of the herbicide solutions was reduced from about 5.8 to about 3.9 by SA-77. Absorption of all three herbicides was greater into terminal than into basal leaves when the surfactant was not present, but the difference disappeared when the surfactant was added. Generally, no differences were observed in the absorption of 2,4-D and dicamba. Glyphosate absorption was greater in terminal leaves collected after a period of adequate moisture than after a period of dry soil conditions.

Several herbicides were evaluated for control of white locoweed (Oxytropis sericea Nutt. T & G # OXRMA) and changes in botanical composition on two sites on high-elevation rangeland. White locoweed was more abundant and its population more stable on the rocky subalpine wind-swept ridge site than on the subalpine loam site. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) at 0.6 and 1.1 kg ae/ha, and 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 2.2 and 4.5 kg ae/ha eliminated white locoweed on the subalpine loam site, although the population on this site declined naturally. Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was the most effective herbicide on the subalpine wind-swept site. Clopyralid at 0.3 and 0.6 kg ae/ha, dicamba (3,6-dichloro-2-methoxybenzoic acid) at 2.2 kg ae/ha, and 2,4-D at 1.1 kg ae/ha plus clopyralid or picloram at 0.3 kg/ha killed all white locoweed plants. Lower rates of clopyralid (0.1 kg/ha), dicamba (0.6 and 1.1 kg/ha), 2,4-D (2.2 and 4.5 kg/ha), and triclopyr {[(3,5,6-trichloro-2~pyridinyl)oxy] acetic aicid)} (0.6, 1.1, and 2.2 kg ae/ha) killed 45 to 84% of white locoweed plants. Grass cover increased on most treated areas where white locoweed, forbs, and sagebrush declined. Cattle consumption of white locoweed declined following application of 2,4-D.

Absorption and translocation of 14C-ethalfluralin (N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine) were measured in cucumber plants in the field and greenhouse. In field enclosures, cucumbers treated with 1.68 or 3.36 kg ai/ha preemergence soil-surface applications of 14C-ethalfluralin accumulated significantly more 14C in leaves than in petioles, stems, or fruits. In greenhouse studies, 14C-ethalfluralin vapor was absorbed by both cucumber seedling stems and cotyledons. Seedlings absorbed 14C-ethalfluralin from a nutrient solution and translocated 14C into all plant parts. Cucumber absorbed 14C-ethalfluralin topically applied to the stem and translocated 14C acropetally, while only limited basipetal translocation occurred. Although cotyledons absorbed 14C-ethalfluralin, very little 14 C moved out of the treated tissue.

A relatively inexpensive, cold-temperature germination bar was constructed. The optimum temperature gradient of the bar for our low-temperature seed germination studies ranged from −4 to 11 C. An independent compressor and a chest-type deep freeze were compared for cooling sources. Alumnium foil Petri dishes were developed for use on the bar.

Fall applications of 0.14 kg/ha of picloram (4-amino-3,5,6-trichloropicolinic acid) to musk thistle (Carduus nutans L.) rosettes controlled musk thistle stems better and more consistently than fall applications of 2.2 kg/ha of 2,4-D amine [(2,4-dichlorophenoxy)acetic acid], 0.6 kg/ha of dicamba (3,6-dichloro-o-anisic acid), or a mixture of 0.3 kg/ha dicamba + 1.1 kg/ha of 2,4-D. Dry conditions in 1975 and cool conditions in November, 1976, hampered control with all herbicides except picloram. In spring applications when growing conditions were favorable, herbicide differences were usually not significant. For all herbicides, treatment of bolted stems did not control musk thistle satisfactorily. Picloram was superior for reducing stems 12 to 18 months after application in 2 of 3 yr. Residual control resulted principally because the herbicide killed many seedlings and first-year rosettes at the time of application.

The influence of soil-applied phosphorus on the phytotoxicity of soil-applied 3-amino-s-triazole (amitrole) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) for corn (Zea mays L.), ryegrass (Lolium multiflorum L.), rye (Secale cereale L.), snapbeans (Phaseolus vulgaris L.), soybeans (Glycine max (L.) Mers.), sorghum (Sorghum vulgare Pers.), wheat (Triticum aestivum L.), cotton (Gossypium hirsutum L.), peanuts (Arachis hypogaea L.), and peas (Pisum sativum L.) was studied under greenhouse conditions. All species except cotton and peanuts indicated an amitrole-phosphorus interaction. Greater phytotoxicity was found for a given rate of amitrole as the soil phosphorus level was increased. A diuron-phosphorus interaction was observed for cotton and soybeans only.

The existing method for the analysis of 3-tert-butyl-5-chloro-6-methyluracil (terbacil) has been modified so that electron capture gas chromatography may be used for quantitation. The crop extract was applied to a powdered cellulose column, the interferences were eluted with hexane, and the terbacil was subsequently eluted with ethyl acetate. The ethyl acetate fraction may be used for analysis directly.

A soil sampler was constructed for moisture and pesticide residue determinations that will retrieve soils with rocky and heavy clay layers. The sampler consisted of a commercially constructed worm-gear driven auger mounted in a 3.7-m-tall vertical frame. Depth, speed, accuracy, and ease of sample retrieval were substantially increased, compared to manual sampling.