Greenhouse and growth chamber studies were conducted to determine the cause of previously observed differences in the effectiveness of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] when applied at various times of the day to velvetleaf (Abutilon theophrasti Medic). Leaves of velvetleaf moved rhythmically from a near horizontal day position to a near vertical night position with the tip of the blade pointed downward. Plants were sprayed with bentazon at various times of day. The amount of spray retained and the degree of control decreased as the leaves moved toward the vertical downward night position. This suggested that a major cause of the time-of-day effect with bentazon treatments on velvetleaf is variation in the amount of spray intercepted and retained as a function of varying leaf angles.

Yields of birdsfoot trefoil (Lotus corniculatus L.) and red clover (Trifolium pratense L.) were increased during establishment after herbicide treatments. All treatments, which included preplanting application and incorporation of EPTC (S-ethyl dipropylthiocarbamate) at 2, and 4 kg/ha in all combinations with postemergence applications of dinoseb (2-sec-butyl-4,6-dinitrophenol) at 0.25 and 0.5 kg/ha, controlled weeds and increased yields over those of untreated plots during a 2-yr period. EPTC and dinoseb treatments alone and in combinations were economical in birdsfoot trefoil, using the cost for weed control and the value of the extra forage. However, with red clover only dinoseb proved economically feasible at hay prices less than $80/metric ton.

Greenhouse and field studies demonstrated that plants compete for soil-applied atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Oats (Avena sativa L. ‘Neal’) and soybeans [Glycine max (L.) Merr. ‘Clark 63’] were grown in greenhouse bioassay studies to study the effects of plant population on bioassay sensitivity. High plant populations were not as effective as low plant populations in detecting low levels of atrazine in soil. Conversely, by increasing plant populations or decreasing soil volumes quantitative measurement of higher atrazine concentrations can be determined. A 14C-labeled atrazine study showed that by increasing soybean populations from one to six per pot, atrazine uptake per plant was decreased 50%. When soybeans were planted at a rate of six plants per 100 cm2 in a field treated with atrazine at 1.1 kg/ha, soybean dry weight production was 97% of the untreated control; when planted at a rate of one plant per 100 cm2, dry weight was only 26% of the comparable untreated check. Thus, herbicide rates for optimum weed control may have to be increased with increasing weed populations or increased crop seeding rates or both.

Rhizomes of johnsongrass [Sorghum halepense (L.) Pers.], cut into 2.5-cm or 15-cm lengths, were planted in the field within and below a 7.5-cm layer of soil mixed with trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 0, 1.7, or 3.4 kg/ha. When planted 3.8- and 10-cm deep in nontreated soil, survival was 90% and 69%, respectively, for the longer rhizomes and only 39% and 10%, respectively, for the shorter ones. When planted within trifluralin-treated soil, 95% and 100% of the shorter rhizomes and 54% and 81% of the longer rhizomes were killed at 1.7 and 3.4 kg/ha, respectively. When planted below treated soil, only 11% or 19% of the longer rhizomes were killed. The shorter rhizomes planted below the treated soil survived at less than 10%.

Survival of hydrilla (Hydrilla verticillata Royle) plants and propagules after removal from water and desiccation under controlled conditions were studied. Both apical and sub-apical sections of hydrilla plants were physiologically alive after drying for 16 h at 30 C and 40% relative humidity. Tubers survived drying conditions longer than turions. There was 16.7% sprouting in tubers that had been dried for 64 h, while percent sprouting of turions decreased sharply as the drying period increased from 0 to 8 h.

Bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide], cyperquat (1-methyl-4-phenylpyridinium), and perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide} were evaluated for their potential use as postemergence herbicides for selective yellow nutsedge (Cyperus esculentus L.) control in Kentucky bluegrass (Poa pratensis L.) in field studies. High rates of these herbicides as single or split applications were effective and only slightly reduced verdure of Kentucky bluegrass, indicating excellent selectivity. In greenhouse studies perfluidone exhibited growth retardant properties. Shoot dry weight production was inhibited and root dry weight of treated plants was markedly reduced. These two factors are undesirable features for commercial sod production.

The germination of seeds (achenes) of milk thistle [Silybum marianum (L.) Gaertn.] was investigated. One month after harvest, milk thistle seeds had afterripening requirements related to germination temperature that limited germination to 10 to 20 C temperatures. The time required to satisfy afterripening requirements was dependent on germination temperature. Generally the higher the incubation temperature during germination, the longer the afterripening requirement (up to a maximum of 5 months). Once afterripening requirements were satisfied, milk thistle seeds germinated over a temperature range of from 0 to 30 C. Optimum germination occurred with 2 to 15 C 16-h cold periods alternating with 10 to 30 C 8-h warm periods. Emergence of milk thistle seedlings decreased with increased burial depth, but substantial emergence occurred from 8 cm. Germination on the surface of the soil or litter was greatly reduced compared to that with slight soil or litter coverage. Potassium nitrate (KNO3) added to the germination substrate at 1.0 mM enhanced the germination of milk thistle seeds at 2 and 5 C incubation temperatures.

Dinoseb (2-sec-butyl-4,6-dinitrophenol) and certain dinitroaniline herbicides suppressed root rot caused by Aphanomyces euteiches Drechs. and other fungal pathogens in peas (Pisum sativum L.). Dinoseb was the most effective. At 6.72 kg/ha pre-plant incorporated (PPI) it reduced the disease severity index (DSI) in glasshouse bioassays to the level considered safe for general use by commercial growers. In fields tests disease severity was reduced and yield of peas was increased with dinoseb. Dinitroaniline herbicides reduced DSI values to the level considered safe for early crop peas. A simplified DSI method of measuring root rot based on mid-season root symptoms was found to be effective. Weed control was superior with the dinitroanilines and propachlor (2-chloro-N-isoproylacetanilide). Dinoseb significantly reduced weed populations relative to untreated plots. Several dinitroaniline treatments caused stunting and stand reduction.

Preemergence application of chloramben (3-amino-2,5-dichlorobenzoic acid) at 5.0 and 6.7 kg/ha, chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea] at 2.2 kg/ha, and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] + nitralin [4-(methyl-sulfonyl)-2,6-dinitro-N,N-dipropylaniline] at 1.1 + 1.1 kg/ha controlled 95% or more of the barnyardgrass [Echinochloa crus-galli (L.) Beauv.], common lambsquarters (Chenopodium album L.), red-root pigweed (Amaranthus retroflexus L.), Powell amaranth (A. powellii S. Wats.), and hairy nightshade (Solanum sarachoides Sendt.), but reduced stands and injured direct-seeded asparagus (Asparagus officinalis L. ‘UC-66’). Linuron at 1.1 kg/ha controlled only 84% of the barnyardgrass and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] at 0.6 kg/ha controlled about 50% of the hairy nightshade. Activated carbon applied at 56 and 112 kg/ha in a 3-cm band over the seeded row protected the asparagus from chloramben at 5.0 kg/ha, chlorbromuron at 2.2 kg/ha, and linuron + nitralin at 1.1 + 1.1 kg/ha. Weed control generally was reduced about 10% in the carbon band, but control was still 85 to 90%. Metribuzin reduced asparagus stands and vigor severely, even when 112 kg/ha of activated carbon was applied.

Sainfoin (Onobrychis viciaefolia Scop. ‘Melrose’) seedlings tolerated at 15:1 commercial formulation of the sodium salts of MCPB {4-[(4-chloro-o-tolyl)oxy] butyric acid} and MCPA {[(4-chloro-o-tolyl)oxy] acetic acid} applied at rates up to 2.2 kg/ha in the greenhouse and 3.4 kg/ha in the field. Broadleaf weed control was only fair. Applications of 1.1 kg/ha, 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] ester caused moderate damage to sainfoin initially, but no reduction in yield. Weed control was fair to good. Higher rates of 2,4-DB caused excessive injury unless a heavy growth of weeds protected the sainfoin from contact with the spray. The use of 2,4-D [(2,4-dichlorophenoxy) acetic acid] amine damaged sainfoin severely, although weed control was fair. Nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) at 3.4 kg/ha caused spotting on sainfoin leaves with no reduction in growth. Initial weed control was good, but sainfoin seedlings did not suppress new weed growth. Herbicide applications made when sainfoin had 1 to 3 leaves provided the best combination of crop tolerance and weed control.

After land was plowed in the spring and prepared for planting, yellow nutsedge (Cyperus esculentus L.) was allowed to develop to heights of 10 to 12 and 20 to 25 cm. Either glyphosate [N-(phosphonomethyl)glycine] or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) was applied to emerged yellow nutsedge and other annual weeds at rates of 0.5, 1, 2, and 4 kg/ha. Half of the plots were double-disked 3 days after herbicide applications, and then all plots were planted with alfalfa (Medicago sativa L. ‘Cayuga’). Disking alone and application of glyphosate or paraquat alone did not satisfactorily control all weeds. However, the combination of a herbicide and disking controlled weeds enough to allow excellent establishment of alfalfa. In the year after establishment, the first cutting yields from the better combination treatments ranged from 3000 to 4400 kg/ha, which is normal for mid- to late-summer plantings in the region. Glyphosate was better than paraquat for control of grass weeds. Paraquat approached glyphosate in effectiveness when a supplemental disking treatment was added. Disking was as effective as the herbicide treatments for control of yellow nutsedge but not for control of broadleaf or annual grass weeds.

Vapor pressures of technical-grade triallate [S-(2,3,3-trichloroallyl)diisopropylthiocarbamate] were calculated from the vapor density measurements determined at seven different temperatures, using a gas-saturation technique and solid adsorbent traps. The equation Log10P = 11.05 – (4401/T) delineated the relationship between the apparent vapor pressure and temperature, giving the triallate vapor pressure values from 1.083 × 10−4 to 16.371 × 10−4 mm Hg over the temperature range of 20 to 45 C. The vapor flux of triallate from glass surfaces was of the order of 5.7 μg cm−2 h−1 at 25 C.

Application of 112 to 336 kg/ha N as ammonium nitrate [NH4(NO−3)] failed to affect population numbers of common lambsquarters (Chenopodium album L.), giant foxtail (Setaria faberi Herrm.), velvetleaf (Abutilon theophrasti Medic.), jimsonweed (Datura stramonium L.), or redroot pigweed (Amaranthus retroflexus L.). Common lambsquarters seeds harvested from NO−3-treated plots were less dormant than control seeds. Seed germination in the laboratory increased from 3.0% for control seeds to 34.0% for seeds harvested from plots treated with 280 kg/ha N as NH4(NO−3). Nitrate concentration in common lambsquarters seeds increased as nitrogen fertilization increased. Seeds from nonfertilized plots contained 18.7 μg/g NO−3, while seeds from plots fertilized with 280 kg/ha N contained 126.3 μg/g. Adding exogenous NO−3 to the germination medium brought the germination of most seed lots to a similar level, except for control seeds which germinated at a lower rate. In contrast to common lambsquarters, nitrogen fertilization did not greatly affect dormancy or NO−3 accumulation in velvetleaf seeds. Exogenous NO−3 failed to stimulate velvetleaf germination because dormant velvetleaf seeds did not imbibe.

Karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-1,1-dimethylurea] residues were monitored in Texas Post Oak Savannah soils immediately at the point of deposition of spheres containing approximately 0.765 g active ingredient (50%, w/w). Karbutilate residues (1.1 ppmw) were detected after 194 days in clay loam to 90 cm deep directly beneath the point of impact of the spheres. Although in one of two studies trace amounts (0.1 ppmw) of karbutilate residues were detected to 45 cm deep at 90 cm away from the point of impact after 111 days, vertical movement through the soil profile was much more evident than lateral displacement. After 191 days and at the point of sphere deposition, about twice as much residual karbutilate was detected in the surface 30 cm of a clay loam as in a loamy sand.

The potential losses from spray applications of glyphosate [N-(phosphonomethyl)glycine] with and without the inclusion of a polymer thickening agent were evaluated in field tests, applied under identified weather conditions with a boom-nozzle ground sprayer, helicopter, and fixed-wing aircraft. The downwind transport and diffusion of the spray loss was assessed by means of Mylar fallout sheets, high volume air samplers, and 4-leaf wheat (Triticum aestivum L. ‘Anza’) plants. Lowest drift losses occurred, under 0.01 g/ha on fallout sheets at 100 m, with deflector fan nozzles (KGF) operating at a low pressure (7 kPa) on the ground sprayer. Drift losses from a helicopter equipped with micro-jet nozzles were only slightly higher, less than 0.03 g/ha on fallout sheets at 100 m. Drift losses from 8003 nozzles mounted on a ground sprayer and D-6 jet nozzles directed back on fixed wing aircraft produced much higher drift deposits, from 0.2 to 1.0 g/ha on fallout sheets at 100 m. The highest levels of drift losses were obtained with D-4 jet nozzles directed down on a helicopter, 5 g/ha on fallout sheets at 100 m. Some evidence of reduced airborne drift was apparent where the polymer thickening agent was used with aircraft and ground equipment. The test results indicate that significant reduction in drift losses were obtained with proper application equipment; however, the use of a polymer thickening agent reduced drift only slightly for certain applications.

Seed lots of Macartney rose (Rosa bracteata Wendl.), yaupon (Ilex vomitoria Ait.) huisache [Acacia farnesiana (L.) Willd.], and honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] were exposed for various periods to radiofrequency (RF) dielectric heating by electromagnetic fields of 10 and 39 megahertz (MHz) at various field intensities in attempts to increase their germination. Both continuous-wave and pulse-modulated exposures were used at 39 MHz. Seed samples were preconditioned at temperatures from 24 to −43 C before exposure. Sixty-Hz a-c and d-c electrical treatments were included in some experiments. Although significant increases in germination were obtained by RF treatment of huisache and honey mesquite seed in some experiments, results with different huisache seed lots were inconsistent. The germination of Macartney rose seed was not increased, and no germination was observed in yaupon, regardless of the treatment employed.

Toxicity of nonradiolabeled and translocation of 14C-labeled glyphosate [N-(phosphonomethyl)glycine] in cotton (Gossypium hirsutum L.) were evaluated under different environmental conditions as affected by surfactant and by the maturity of the plant tissue at the place of herbicide application. Toxicity was affected primarily by temperature with 21 to 40% greater cotton injury at 25 C than at 35 C. The addition of surfactant often increased toxicity under environmental conditions where toxicity was initially low. Absorption and translocation of 14C was affected primarily by relative humidity (RH). At constant temperature and rate of surfactant, an increase in RH from 40 to 100% resulted in a 3- to 6-fold increase in translocation of 14C. Autoradiograms indicated that the movement of the 14C-label was primarily into leaves above the treated area. Translocation of 14C was significantly greater following application to the mature lower stem than to the mature lower leaves or to immature upper stem or leaves of cotton.