Sequential herbicide treatments of 3-[p-(p-chlorophenoxy)-phenyl]-1,1-dimethylurea (chloroxuron) with S-propyl dipropylthiocarbamate (vernolate) controlled weeds early in the season in soybeans (Glycine max (L.) Merr. ‘Dare’ or ‘Bragg’) better than when chloroxuron was applied in sequence with either α,α,α-trifluoro-2,6-dinitro-N,N dipropyl-p-toluidine (trifluralin) or 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin). The control of weeds late in the season was enhanced with split applications of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) or 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) when applied to plots previously treated with chloroxuron as early postemergence and trifluralin, nitralin, or vernolate applied preplant. In 1969 nitralin injured soybeans, and reduced stands and seed yields significantly more than trifluralin or vernolate. In 1970 sequential treatments of prometryne with chloroxuron and vernolate were more phytotoxic to soybeans than were the same postemergence treatments when applied with nitralin and trifluralin.

Surgical experiments were conducted on cultured five-node apical rhizome segments of quackgrass. Removal of scale leaves promoted an initial burst of growth within the axillary buds but did not support the continued growth of buds as effectively as removal of the rhizome apex. Replacement of detached scale leaves over denuded buds temporarily repressed the promotive effect of scale leaf removal. Aqueous extracts of scale leaf material inhibited apical growth in rhizome segments but did not inhibit bud growth. Anatomical sections revealed that removal of scale leaves promoted development of buds: cells enlarged, vascular tissues differentiated, and new nodes began to form within 4 days of the removal of scale leaves. It is suggested that scale leaves contribute to apical dominance by inhibiting the initial development of axillary buds.

Seven herbicides were evaluated for the control of yellow nutsedge (Cyperus esculentus L.) in cotton (Gossypium hirsutum L. ‘Acala SJ-1’) in three field experiments during 1970 and 1971. The herbicides, 2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide (alachlor); 2-chloro-2′,6′-diethyl-N-(butoxymethyl) acetanilide (CP-53619); 2,4-bis(isopropylamino)-6-methylthio)-s-triazine (prometryne); 2-(α-naphthoxy)-N, N-diethylpropionamide (R-7465); S-isopropyl 5-ethyl-2-methylpiperidine-1-carbothioate (R-12001); 4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3-(2H)-pyridazinone (San-6706); and 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (methazole), were applied broadcast and incorporated 10 cm deep into the soil before the preplanting irrigation. All herbicides controlled nutsedge for at least 1 month in two or more experiments. Cotton was most tolerant to applications of 2.24 and 4.48 kg/ha of CP-53619, 3.36 and 6.72 kg/ha of prometryne, 1.12 kg/ha of San-6706, and 2.24 kg/ha of methazole. Higher rates of San-6706 and methazole and all rates of alachlor, R-7465, and R-12001 reduced the yield of cotton in one or more experiments.

Tobacco (Nicotiana tabacum L. ‘Samsun N. N.’) leaves were treated with (2,4-dichlorophenoxy)acetic acid (2,4-D) at a concentration of 500 mg/L by the syringe infiltration technique and then sampled at regular intervals. Electron microscopic examination of the treated tissue revealed that the response of the mesophyll cells to 2,4-D was related to the age of the leaf at the time of treatment. Expanding leaves from the upper portion of the plant exhibited a high degree of tolerance to 2,4-D. Mature, fully-expanded leaves from the lower part of the plant were highly sensitive to the herbicide, with the mesophyll cells undergoing rapid structural breakdown. This breakdown involved a rupturing and disintegration of the tonoplast, plasmalemma, and membranes of chloroplasts and mitochondria.

Soybean (Glycine max (L.) Merr., ‘Hawkeye 63′) seedling segments from the zone of elongation and corn (Zea mays L., ‘Pioneer 3306) seedling segments were utilized to evaluate the antagonistic interaction of S-ethyl dipropylthiocarbamate (EPTC) and (2,4-dichlorophenoxy)-acetic acid (2,4-D). EPTC inhibited growth of the soybean and corn tissue, and 2,4-D in combination with EPTC caused an increase in growth compared to EPTC alone. The 2,4-D-enhanced growth in the presence of EPTC was due to an antagonism of the EPTC inhibition. Inhibition of soybean tissue growth by S-ethyl diisobutylthiocarbamate (butylate) also was antagonized by 2,4-D. Preincubation of soybean tissue in EPTC for 4 hr prior to the addition of 2,4-D did not prevent 2,4-D enhancement of growth. Conversely, the rate of growth was inhibited when EPTC was added after 4 hr of 2,4-D-enhanced growth. The addition of uridine to the incubation media with EPTC did not decrease the EPTC-inhibition of soybean tissue growth. This indicated that EPTC did not inhibit the synthesis of pyrimidine precursors. EPTC vapor losses from the incubation media reduced the inhibitory effect of EPTC to soybean tissue. Also, a growth reduction occurred when the amount of soybean tissue per unit of EPTC was increased.

Different growth rates of young seedlings (genets) and plants grown from root pieces (ramets) of yellow toadflax could influence their respective competitive ability and their susceptibility to management techniques. Shoot production was similar for genets and ramets (approximately 10 shoots were produced 12 or 13 wk after transplanting or cotyledon appearance, respectively), but the rate of shoot biomass accumulation was higher for genets than for ramets. Genets consistently produced more underground shoots than ramets. Replanted underground shoots separated from their roots were able to produce new shoots and roots. Rate of elongation for roots 0.5 to 1.5 mm in diameter was higher for ramets than for genets, but their shoot production potential was the same. Root pieces from genets did not have the ability to produce daughter shoots until 3 wk after cotyledon appearance. This indicates that very young genets would be more susceptible than older genets or ramets to management control systems.

Representative herbicides of the substituted ureas, uracils, s-triazines, benzonitriles, and bipyridyls, which are potent inhibitors of photosynthetic electron transport, markedly accelerated photooxidations (chlorophyll bleaching and lipid peroxidation) normally occurring in isolated intact chloroplasts. Other herbicides, which are not potent inhibitors of photosynthesis, did not accelerate photooxidations. The photooxidations, whether in the presence or absence of herbicides, were completely prevented by exogenously supplied NADH or NADPH but not by sucrose or mannitol. Herbicide-induced injury to barley (Hordeum vulgare L.) seedlings treated with paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) was diminished by allowing the seedlings to absorb NADPH. These results provide additional support to the hypothesis that depletion of the source of reducing potential (NADPH) is responsible for chloroplast photooxidations and plant death following treatment with photosynthesis-inhibiting herbicides.

The uptake, translocation, and metabolism of 14C-alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] by germinating and emerged snap bean (Phaseolus vulgaris L.) seedlings were monitored under 16-h daylength (21 klux) comparing 16 C night/21 C Day and 27 C night/32 C day temperature regimes. Total uptake of 14C-alachlor by germinating snap beans was greater under the higher temperature, however, the compound was localized primarily in the roots where it was rapidly metabolized. At the lower temperature, the label was located in approximately equal amounts in all plant parts except cotyledons and significantly less of the alachlor was metabolized. Root uptake of 14C-alachlor and translocation of labeled compounds to the shoots were significantly greater under the higher temperatures. Approximately 60% of 14C-alachlor was shown to volatilize from a watchglass after 48 h at 27 C. After volatilization, uptake of 14C-alachlor occurred in adjacent snap bean plants in a closed system.

Relationships between volunteer barley plant density and both pea and volunteer barley yield were determined in field experiments conducted over 2 yr at Vegreville and Lethbridge, Alberta. Nonlinear regression analysis indicated that severe pea yield losses due to volunteer barley occurred at both locations. Averaged over both years, pea seed yield losses per volunteer barley plant (initial slopes) varied from 1.7% at Vegreville to 5.4% at Lethbridge. Based on certain assumptions, economic thresholds calculated from the equations were approximately 2 and 6 volunteer barley plants m−2 at Lethbridge and Vegreville, respectively. Revenue from the volunteer barley seed partially alleviated the monetary losses caused by the reduced pea seed yield. The effects of pea density on pea and volunteer barley yield were inconsistent and marginal. This suggested that there was little advantage, in terms of increasing pea yield or reducing volunteer barley interference, to seeding pea above the recommended rate of 100 plants m−2.

Laboratory experiments were conducted to determine the effects of nonionic surfactants and reaction media (water, glass, and corn leaf residue) on photolysis and subsequent phytotoxicity of chlorimuron and metsulfuron residues. Oxysorbic and octoxynol enhanced rates of chlorimuron and metsulfuron photolysis in aqueous solution and on glass slides compared to controls with no surfactant. Enhanced photolysis of chlorimuron by surfactants was greatest on glass, where 93 and 89% loss occurred after 48 h exposure to ultraviolet light in the presence of oxysorbic and octoxynol, respectively, compared to 38% loss with no surfactant. Similarly, surfactant-enhanced metsulfuron photolysis was greatest on glass with 37 and 67% loss after 48 h exposure in the presence of oxysorbic and octoxynol, respectively, compared to 9% loss with no surfactant. Photolysis of herbicides deposited on corn leaf residue was significantly slower than that on glass or in aqueous media at all exposure times and metsulfuron photolysis on corn residue was enhanced by surfactants only after 144 h exposure. Bioassays confirmed that phytotoxicity of photolyzed herbicide residues was negatively correlated (r=-0.94 for chlorimuron and r=-0.92 for metsulfuron) with loss of parent herbicide as measured by liquid chromatography.

The absorption and translocation of 14C-terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine] and 14C-fluometuron [1,1-dimethyl-3-(α,α,α,-trifluoro-m-tolyl) urea] in cotton (Gossypium hirsutum L. ‘SJ-1′) and snapbean (Phaseolus vulgaris L. ‘Tenderette’) were studied. 14C-terbutryn supplied to the roots accumulated in the root system of both species. However, snapbean plants (sensitive) absorbed and translocated more 14C to the shoots than cotton (tolerant), followed by rapid distribution in the leaf mesophyll tissue. In cotton, the translocated 14C-terbutryn accumulated in stems, petioles, and leaf veins. Excised cotton roots absorbed more 14C-terbutryn than excised snapbean roots. The uptake and distribution pattern of root-applied 14C-fluometuron was similar in both species. Foliar application to the primary leaf of snapbeans and to one cotyledon of cotton resulted in 2% of 14C-terbutryn transported acropetally to younger leaves with no basipetal movement. Translocation of 14C-fluometuron from the site of foliar application was two or three times faster than terbutryn with significant basipetal transport in both species.

Horsenettle is a deep-rooted perennial weed that cannot be easily controlled by mechanical means or by a single chemical application. A study was conducted at two sites for two consecutive years to identify biological factors that might limit its growth. Insects, nematodes, and plant pathogens were collected from horsenettle growing in bermudagrass pastures. The insects most commonly found included the Colorado potato beetle and the eggplant flea beetle. An unidentified lepidopteron, family Gelechiidae, was found at very low frequency as pupae in hollow leaf chambers constructed at the apices of flowering meristems. Infested apices bore no fruit. Seven genera of nematodes were found in the soil at both sites, but only very low numbers of lesion nematodes were recovered from horsenettle roots, and these had caused little damage. Root rot was observed under wet soil conditions on plants damaged by trampling. A downy mildew was prevalent at both sites in both years in October.

Aerial applications of 20% tebuthiuron JA/-[5-(1,1- dimethylethyl) - 1, 3, 4 - thiadiazol-2 -yl] -N, N' dimethylurea pellets at 2.2 or 4.4 kg/ha in the spring to heavy brush cover in Texas Post Oak Savannah did not increase the amount of grass, compared to that of untreated pastures, until the growing season after application. By the second growing season after tebuthiuron application, however, native grass stands were composed of a higher proportion of perennial species of good-to-excellent grazing value than were stands on adjacent, untreated rangeland. Tebuthiuron at 4.4 kg/ha did not improve botanical composition of grass stands, but increased the amount of grass during the second and third growing season after application compared to those where 2.2 kg/ha were applied. Daily steer gains were increased in one experiment in the fall after application of 2.2 kg/ha of tebuthiuron in the spring, but were unchanged after two growing seasons in another. Days of available grazing were increased, however, by the second or third growing season after treatment with 2.2 kg/ha of the herbicide in both experiments.

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.

The influence of acid scarification on the responsiveness of curly dock (Rumex crispus L. ♯ RUMCR) seeds to physical and chemical factors was studied. Scarification made the seeds responsive to GA4+7 (a mixture of gibberellin A4 + A7) and markedly improved the responsiveness to light, moist-chilling, and a 1-h 40-C temperature shift. Scarification reduced the mechanical restraint of the seedcoat by 0.4 to 0.8 MPa. Removal of the entire pericarp induced 69% germination in the dark. Moist-chilling treatment of seeds reduced the soaking period needed for maximum response to the high-temperature shift from 24 to 6 h. The embryo growth potential generated by moist-chilling was less in magnitude than that by the reduction in seed coat restraint by scarification. Induction of secondary dormancy was prevented to a marked degree in scarified (chilled or unchilled) seeds during polyethylene glycol-6000 (PEG) treatment in light or in the presence of GA4+7 while intact seeds rapidly became secondarily dormant in light. The ability of scarified seeds to remain germinable or nondormant for a longer period than the intact seed in low water potential imbibing medium may be due to a net reduction (by 0.4 to 0.8 MPa) in the impact on the embryo of germination-preventing forces (low water potential plus mechanical restraint of the seed coat).

Four new biodegradable alkylpolyoxyethylene glycol surfactants (15-S-9, DN-65, 15-S-3, and 15-S-3A) provided excellent visual wetting of corn foliage in spray solutions of 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat), 2,2-dichloropropionic acid (dalapon), and 3-amino-1,2,4-triazole (amitrole) and many combinations were equal or superior to standard surfactants Tween 20, X-77, and Osamul 95 in enhancing phytotoxicity. Exceptions were observed, apparently due to specific but incompletely understood herbicide-surfactant-plant surface interactions. All four biodegradable surfactants and Osamul 95 were slightly toxic when sprayed alone on corn foliage.

Soldier thistle [Picnomon acarna (L.) Cass.] is widely distributed throughout rainfed fields across western Iran, where it decreases crop yields and interferes with harvest operations. This study was conducted to determine the influence of different factors on seed germination and seedling emergence of P. acarna. Freshly harvested seeds were dormant and required an after-ripening period for breaking dormancy. Seed germination was greatly promoted by light. Germination occurred over a wide spectrum of constant and fluctuating temperature regimes, ranging from 5 to 35 C, with highest germination at constant (74%) and fluctuating (94%) temperatures of 20 and 20/10 C. Seed germination of P. acarna was tolerant to osmotic potential, while salt stress significantly inhibited its germination percentage. pH was not an inhibiting factor for germination of P. acarna seeds. Seedling emergence decreased exponentially with an increase in seed burial depth in the soil; at soil burial depths of 4 cm or greater, no seedlings were able to reach the soil surface. The results suggest that significant seed germination of P. acarna in rainfed fields is possible, and the weed has great potential to spread throughout rainfed systems in western Iran. Based on these results, effective control of P. acarna can be achieved by applying interrow cultivation in row crops and deep tillage at seedbed preparation.

The herbicidal and desiccant properties of 1:1′–ethylene–2:2′–bipyridylium dibromide have been reported by Brian et al. (1). This substance appears to be a rapid acting translocated herbicide, effective on a wide range of plant species (1,2).

To minimize the chance of surface water contamination by herbicides, farmers need alternative ways to manage weeds in field crops, such as field corn, that reduce herbicide use. Zone herbicide application (ZHA) reduces herbicide use compared with conventional broadcast herbicide application by (1) banding low herbicide rates between corn rows (≤ 1× normal broadcast registered rate), (2) managing crops to favor crop competition, and (3) banding very low herbicide rates over crop rows (≪ 1× normal rate). The research goal was to compare the relative effectiveness of reduced-rate ZHA with broadcast herbicide application on in-row (IR) and between-row (BR) summer annual weed cover (chiefly giant foxtail and waterhemp species), grain yields, and net returns resulting from herbicide application in field corn. Preemergence ZHA of atrazine + metolachlor + clopyralid + flumesulam was made in zones (i.e., even width bands) at different rates between and over crop rows for three site-years in Missouri, and the 1× rate was 2.24 + 1.75 + 0.211 + 0.067 kg ai ha−1, respectively. Best ZHA treatments (0.29× to 0.30× IR herbicide rates + 0.74× to 0.80× BR herbicide rates) outperformed all reduced-rate broadcast herbicide treatments (0.25×, 0.5×, and 0.75×) based on net returns in partial budget analysis. Yields for highest yielding ZHA could not be distinguished from the 1× broadcast treatments in two of three site-years. Net returns due to herbicide application for the highest yielding ZHA were comparable with the 1× broadcast treatment in all three site-years. For the best ZHA, the 3-yr average for total herbicide applied per unit was 53% of the 1× broadcast rate. ZHA may provide row crop farmers with a new generic option for reducing herbicide rates and input costs while maintaining net returns and reducing the chance of surface water contamination by herbicides.

Amitrole-5-C14 was rapidly degraded in unsterile soil but underwent only minor modification in sterile soil. An unidentified chemical product of amitrole was formed in both sterile and unsterile soil. The principle metabolic product of amitrole was carbon dioxide; however, at least 13 additional compounds were formed. One or more metabolic compounds formed from amitrole are tenaciously bound to the soil and appear to be resistant to degradation.