Picloram (4-amino-3,5,6-trichloropicolinic acid) applied at 0.6 to 1.2 kg/ha as 5 or 10% pellets during the summer or fall usually killed 90% or more of the rayless goldenrod [Isocoma wrightii (Gray) Rydb.] on sandy loam soils in western Texas, whereas the higher rates were necessary for 80% or greater control following winter applications. Acceptable control persisted for 4 yr. Applications of tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}at 1.1 kg/ha as 20% pellets during summer controlled 85% of the rayless goldenrod, but summer applications of tebuthiuron at 0.6 kg/ha or winter applications at 0.6 or 1.1 kg/ha did not control the weed effectively. Dicamba (3,6-dichloro-o-anisic acid) applied at 0.6 or 1.1 kg/ha as 5% granules did not control rayless goldenrod. Prescribed burning in late February reduced the density of rayless goldenrod 18 to 41%, but decreased control with soil-applied picloram or tebuthiuron. Reduction in rayless goldenrod densities of 75% or greater following applications of picloram or tebuthiuron pellets more than doubled the estimated carrying capacity of the arid rangeland.

Investigations were conducted to determine whether light, temperature, or their interaction stimulated primary basal-bulb formation on underground stems of yellow nutsedge (Cyperus esculentus L.) seedlings grown from tubers. Basal-bulb formation results when internodes shorten and leaves lengthen. When seedlings were grown without medium around the underground shoots, a temperature alternation of 10C stimulated basal-bulb formation; light did not affect the process. When seedlings were grown with medium around the underground shoots, either light or alternating temperature stimulated basal-bulb formation. Nine colors of light gave the same stimulus as white (fluorescent) light. Phytochrome did not appear to be the photoreceptor for the stimulus, as both red and far-red light responses were identical to that of white light.

Curly dock (Rumex crispus L.) seeds failed to germinate in the dark, but germinated readily in light at 15, 20, and 25C. A secondary dormancy was induced in these seeds by 6 days of dark or light incubation at 30C (thermodormancy), by 6 days of dark incubation at 15C, or by a prolonged soaking in −15.7 bar polyethylene glycol-6000 (PEG) solution at 15C in light. The secondary dormancy induced at 15C was partially removed by 2-chloroethylphosphonic acid (ethephon) in presence of light; however, when the dormancy was induced at 30C, an addition of gibberellin A4+7 (GA4+7) to ethephon was necessary for effective removal of the dormancy. The ability of growth regulators to remove the secondary dormancy induced by prolonged dark incubation at 15C decreased progressively in light as the duration of dark incubation increased. The water-potential studies indicate that the thermodormancy can be attributed, at least in part, to the inability of the embryonic cells to lower their water potential to a level sufficient to cause radicle protrusion.

The combustion apparatus described provides a rapid and inexpensive alternative for measurement of radioisotopes in plant parts. The apparatus utilized a nickel-chromium resistance wire connected to a low-voltage transformer to generate the heat required to ignite the plant tissue. The nickel-chromium wire also served as the sample holder. Combustion was performed in an O2-flushed liquid scintillation vial, and the combustion gases containing either 14CO2 or 3H2O were trapped in situ, scintillant was added, and the vials assayed for radioactivity. The percentage of the radioactivity recovered after combustion was 96.0 for 14C and 93.4 for 3H with standard deviations of 6.8 and 3.0%, respectively.

Glyphosate [N-(phosphonomethyl)glycine] was less phytotoxic when applied in 190 L/ha of well water with ionic strengths of 0.005 or greater than in distilled water. At a carrier volume of 24 L/ha, this inhibition of glyphosate was reduced or eliminated. Glyphosate was less phytotoxic when applied in 10-mM solutions of CaCl2, FeSO4, Fe2(SO4)3, MgSO4, NaHCO3, Na2CO3, and ZnSO4 than in distilled water. Adding H2SO4, HCl, HClO4, acetic, and lactic acids at 5, 10, and 50 mM to the spray solution resulted in variable increases in glyphosate phytotoxicity. H2SO4 was the most effective acid tested in increasing glyphosate phytotoxicity when added to well water. Lowering the pH of the spray solution by using potassium biphthalate and phosphoric acid buffers did not increase glyphosate phytotoxicity.

Solarization is a method of heating moist soil by covering it with plastic sheets to trap solar radiation. In field experiments in Israel during the summer, maximum soil temperature under plastic cover at the 5-cm depth averaged 46 to 49C. No weeds emerged under the plastic cover during solarization and weed emergence was reduced after its removal. The heating effect from solarization decreased with soil depth. Concentration of O2 in soil under plastic was similar to that in uncovered controls, but the concentration of CO2 was markedly higher than in control soil, rising up to 2.4%. Higher temperatures and better residual weed control were produced by transparent than by black plastic, with best results from thin (0.03 mm), transparent polyethylene. Under Israeli summer conditions, 2 to 4 weeks of solarization produced effective control of annual weeds that was still appreciable after 1 yr. Narrow sheets of 20 to 50 cm produced effective weed control in bands. on soil irrigated once before placing the plastic sheets, there was no need to irrigate during solarization. The response of weed species to solarization differed. Many annual weeds, both summer species such as pigweed (Amaranthus spp.) and common purslane (Portulaca oleracea L.) and winter species as henbit (Lamium amplexicaule L.) were well controlled by solarization. Broomrape (Orobanche crenata Forsk.) was controlled in one experiment. on the other hand, horseweed [Conyza canadensis (L.) Cronq.] and bull mallow (Malva niceaensis All.) were relatively resistant, and established perennials escaped the treatment.

Black nightshade (Solanum nigrum L.) planted in the field at monthly intervals from March through October at Shafter, California, began to emerge in March when soil temperatures at a depth of 5 cm reached 17C. With the exception of August plantings, emergence remained constant for all plantings. Average weights of plants of May, June, and July plantings at 12 weeks were 60% greater than March and August plantings and 30% greater than April plantings. Plants began flowering 7 to 9 weeks after planting for the March through June plantings and 5 to 6 weeks after planting for the July through September plantings. Killing frosts in November prevented black nightshade planted in October from flowering. Black nightshade planted in April through July produced an average of 1000 berries/plant, which was 40 to 95% greater than those planted in March, August, and September. Seed production ranged from 20000 to 30000 seed/plant for the May through July plantings, and 600 to 8000 seed/plant for the March, April, August, and September plantings.

Construction and use of a portable electronic metronome as an aid in maintaining the desired speed while spraying with an operator-propelled sprayer is described. Use of such a metronome should minimize fluctuations in spray application caused by variations in walking speed during spraying.

An increased rate of butylate (S-ethyl diisobutylthiocarbamate) degradation occurred on a Kennebec silt loam (sil) exhibiting rapid EPTC (S-ethyl dipropylthiocarbamate) breakdown in the field. Butylate degradation was not as rapid as EPTC degradation on field soils previously treated with EPTC. Addition of R-33865 (O, O-diethyl-O-phenol phosphorothioate) to butylate extended its persistence in field soils with and without prior EPTC application. Although microbial degradation of butylate, EPTC, and vernolate (S-propyl dipropylthiocarbamate) was increased on EPTC-pretreated soils, EPTC and vernolate degradation was much more rapid than butylate degradation. Addition of R-33865 to butylate, EPTC, or vernolate extended their soil persistence on soils pretreated with EPTC. In a laboratory experiment, a maximum rate of EPTC degradation resulted from one prior application. The rate of butylate degradation increased with each successive butylate application, but the degradation rate was not as high as those observed for EPTC on EPTC-pretreated soil.

Effects of temperature and interference were examined in a replacement series experiment with soybean [Glycine max (L.) Merr. ‘Ransom’], common cocklebur (Xanthium pensylvanicum Wallr.), and smooth pigweed (Amaranthus hybridus L.). Plants were grown in controlled-environment greenhouses at day/night temperatures of 32/23, 29/20, or 26/17C and harvested 14 and 34 days after planting. In all species, height, dry weight, and leaf area at both harvests, and dry matter and leaf area duration for the harvest interval, increased significantly with temperature. Net assimilation rate in all species peaked at 29/20C. Dry weight and leaf area at day 34, and dry matter production and leaf area duration for the harvest interval, were reduced in plants subjected to interference. Temperature modified the effects of interference upon growth in smooth pigweed, but not in the other species. Common cocklebur and soybean were roughly equivalent as competitors at all temperatures and were superior to smooth pigweed.

Early weed and crop interference was examined in a greenhouse pot experiment combining aspects of additive, substitutive, and diallel designs. Cotton (Gossypium hirsutum L. 'Stoneville 213′) and four weeds {purple nutsedge (Cyperus rotundus L.), large crabgrass [Digitaria sanguinalis (L.) Scop.], velvetleaf (Abutilon theophrasti Medic.) and prickly sida (Sida spinosa L.)} were grown singly and in all possible combinations of pairs including reciprocals for 5 weeks in 10-cm plastic pots. After 5 weeks large crabgrass was the tallest species in all combinations except when grown with purple nutsedge. Purple nutsedge, however, had more leaf area and greater dry weight than all other species. Height, leaf area, and dry weight were lowest in prickly sida. Mean relative yields in mixtures (a measure of competitive ability) were 1.90, 1.15, 1.13, 0.86, and 0.41 for purple nutsedge, large crabgrass, cotton, velvetleaf, and prickly sida, respectively, when grown with the other four species as associates. Conversely, purple nutsedge and cotton as associates depressed mean relative yields of competing species to 0.59 and 0.94. Large crabgrass, velvetleaf, and prickly sida as associates increased mean relative yields of competing species to 1.17, 1.18, and 1.55, respectively. Analysis of these data and replacement-series diagrams indicated that purple nutsedge was the most competitive, prickly sida the least, and the other species were intermediate and approximately equivalent in competitive ability.

A compact incorporator-planter, which incorporates herbicides into moist soil simultaneously with planting of cotton (Gossypium hirsutum L.), was constructed and evaluated over 3 yr using six herbicides. Weed control was consistent with that reported for large, cumbersome units utilizing standard planters and incorporating units from ground-driven rotary tillers and was enhanced in seasons in which rain fell during the first 3 weeks after planting. Among the dinitroaniline herbicides, dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) controlled barnyardgrass [Echinochloa crus-galli (L.) Beauv.], and redroot pigweed (Amaranthus retroflexus L.) most effectively. Cotton stands and yields were equivalent to those obtained using standard cotton-planting methods.

Seven herbicides and two herbicide combinations were applied once either preplant or postplant to control perennial grasses and forbs as planting-site preparation for 2-yr-old seedlings of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) and Douglas fir [Pseudotsuga menziesii var. glauca (Beissn.) Franco] at locations in Washington and Oregon. Hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H, 3H)-dione] applied at 2.2 kg/ha provided most effective and lasting herbaceous weed control in both states. A combination of dalapon (2,2-dichloropropionic acid) and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] applied at 9.0 + 4.5 kg/ha also proved similarly effective. In Washington, each conifer species responded with exponential growth increases over a 6-yr period. For ponderosa pine and Douglas fir, respectively, hexazinone treatment increased tree height by 58 and 70%, stem diameter by 70 and 69%, and stem-volume yield by 387 and 650% as compared to untreated checks. Corresponding gains for the two conifers associated with dalapon + atrazine were 73 and 54% in height, 63 and 46% in diameter, and 421 and 349% in yield.

Terbacil (3-tert-butyl-5-chloro-6-methyluracil) metabolism was evaluated as a possible basis of tolerance in two species, strawberry (Fragaria × ananassa Duchesne) and goldenrod (Solidago fistulosa Miller). Reported cultivar variation in strawberry tolerance to terbacil was examined by comparing herbicide metabolism patterns in an established tolerant cultivar, 'Sunrise’, with those of the reported susceptible cultivar, ‘Guardian’. A terbacil-sensitive plant, cucumber (Cucumis sativus L. ‘Chipper’), was also used as a basis for comparison. Using gradient elution high performance liquid chromatography (HPLC), two terbacil metabolites were separated and quantitated from methanol extracts of the three species treated with 14C-terbacil via roots in solution culture. The minor metabolite was identified as the non-phytotoxic derivative, 3-tert-butyl-5-chloro-6-hydroxymethyluracil, based on its co-migration with authentic 3-tert-butyl-5-chloro-6-hydroxymethyluracil in two chromatographic systems. The major metabolite was a glycoside, which yielded the hydroxylated derivative upon β-glucosidase hydrolysis. In all species, metabolites accumulated more rapidly and extensively in roots than in leaves. Metabolism was greater in the two tolerant species than in cucumber. However, the greater tolerance of goldenrod to terbacil compared to that of strawberry was apparently unrelated to differences in herbicide metabolism.

Wild oat (Avena fatua L.) seedlings from mature seeds emerged in silt loam from depths up to 17.5 cm in the greenhouse or 15 cm under field conditions. No emergence occurred from greater depths. Under field conditions, the greatest percentage of shoots emerged from seeds planted 5 cm deep. Wild oat in a space-planted nursery produced an average of 19 tillers, reached a maximum height of 79 cm, and produced an average of 1072 seeds. The number of tillers per plant, the number of seeds per panicle, and the total number of seeds per plant increased with an increase in annual precipitation. Wild oat seeds harvested as early as 3 days after anther extrusion germinated, but seeds harvested 6 or 7 days after anther extrusion germinated more rapidly.

Scarification of freshly harvested redweed (Melochia corchorifolia L.) seed for 15 to 30 s in an electric scarifier equipped with 100- to 120-grit emery cloth resulted in the best germination. Scarified seed germinated best at 35 and 40C. At 10 and 45C there was no germination even after 7 days. Seven days after planting in silt loam soil there was 80 to 90% emergence of redweed from depths of 1 to 5 cm, whereas no emergence was observed from depths of 0, 8, or 10 cm.

In greenhouse and growth-chamber studies, increasing the level of either light or temperature increased bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] phytotoxicity to cucumber (Cucumis sativus L.). Light had a greater influence on phytotoxicity than did temperature. Light and temperature conditions after bentazon application had a greater influence on phytotoxicity than did light and temperature conditions before application. Maximum phytotoxicity was obtained from treatment with low light level before application and high light level after application.

Tillage plus trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and prometryn [2,4-bis (isopropylamino)-6-(methylthio)-s-triazine] and tillage plus trifluralin and fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] applied as soil-incorporated preplanting treatments were compared with tillage alone in cotton (Gossypium hirsutum L.) grown in 51-cm and 102-cm rows on fine sandy loam soil. Over 3 yr, cotton grown in 51-cm rows yielded 15% more than cotton grown in 102-cm rows. Final cotton emergence was not altered by weed-control treatment or by planting pattern. Weed-control treatments with herbicides provided essentially complete, season-long control of grass and broadleaf weeds. At cotton layby, more weeds were in no-herbicide plots with 51-cm rows compared with 102-cm rows, but at cotton harvest numbers of weeds in both row patterns were essentially equal.

Uptake, translocation, and metabolism of 14C-MBR-18337 {[N-[(4-ethylthio)-2-(trifluoromethyl)phenyl] methanesulfonamide]} in soybean [Glycine max (L.) Merr.] and johnsongrass [Sorghum halepense (L.) Pers.] plants and cell cultures were studied. Sixty-five percent of the 14C recovered from soybean (65% of applied) was on or in the treated leaf, compared to 81% of the 14C recovered from johnsongrass (43% of applied). Translocation of the 14C from the treated leaf of soybean was greater than from the treated johnsongrass leaf, and was primarily to the apical leaves of both species. MBR-18337, its sulfoxide, sulfone, and an unidentified polar component(s) were isolated from intact plants and cell cultures of both species. Soybean plants and cells contained greater proportions of the polar component(s) than johnsongrass plants and cells.

The effect of moderate moisture stress on the activity of the methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} applied to wild oat (Avena fatua L.) and the influence of morphological and physiological factors on the activity of the herbicide on stressed plants were investigated in growth-room experiments. Wild oat was grown in very fine sandy loam brought to a gravimetric soil moisture content (SMC) of 20% (water potential of -0.3 bars) or 10% (-6.5 bars) prior to herbicide treatment. The activity of diclofop on wild oat was slightly, but significantly, reduced when the SMC was increased from 10 to 20% immediately after spraying. Maintaining the SMC at 10% after spraying further reduced the activity of the herbicide. Wild oat plants grown at 20% SMC had 22% greater leaf area and retained 23% more herbicide than plants grown at 10% SMC. Penetration of the methyl ester of 14C-diclofop into wild oat grown at 20 or 10% SMC did not differ significantly 12, 24, or 48 h after application. Stressed and unstressed plants did not differ significantly in the metabolism of the methyl ester of 14C-diclofop. However, growth at a low SMC prior to treatment decreased the proportion of the radiolabeled herbicide recovered in the apex, third leaf, and tillers of wild oat. This may partially account for the reduced activity of this herbicide on wild oat subjected to moisture stress.