Greenhouse and laboratory experiments were conducted to determine the basis of imazethapyr tolerance in cowpea. Cowpea required more than 700 g ha−1 imazethapyr to reduce shoot growth 50% while corn required 70 g ha−1 to reduce growth 50% in greenhouse experiments. Extractable acetohydroxy acid synthase activity from cowpea 24 h after foliar imazethapyr treatment was only 20% of that of untreated cowpea but increased to control levels 72 h after treatment (HAT). The unifoliate leaves of cowpea absorbed 25% of the 14C-imazethapyr applied 72 HAT. Movement of 14C-imazethapyr out of the treated zone increased gradually to approximately 47% of the absorbed 14C 168 HAT. Parent imazethapyr decreased from 41 to 27% of the recovered 14C between 4 and 24 HAT, and continued to decrease to 14% by 168 HAT. Polar metabolites increased from 27 to 55% of the recovered 14C from 24 to 168 HAT. The polar metabolites of imazethapyr included hydroxyimazethapyr and conjugates of hydroxyimazethapyr. Tolerance of cowpea to imazethapyr is based on the plants ability to metabolize the herbicide to nontoxic metabolites.

The purpose here was to study fundamental aspects of polyphenoloxidase in dormant tubers.

Promising results of applications of α, α-dichloropropionic acid (Dalapon) to wild oats (Avena fatua) were first reported in May 1953 in Dow Chemical Company's Dalapon Bulletin No. 1. Encouraging results with Dalapon on wild oats were obtained by various workers during the summer of 1953. The work reported herein was conducted in 1954 to gain further information on the effects of Dalapon on wild oats.

Seeds of winged elm (Ulmus alata Michx.) stored under moist conditions lost viability rapidly. Under dry conditions the seeds lived longer. Winged elm seeds would not germinate at 4 C or 42 C but did at temperatures between these points. Salt concentrations above 20,000 ppm killed the seed; concentrations below this inhibited germination; twelve per cent manitol solutions (16 atmospheres osmotic pressure) prevented germination; pressures lower than this decreasingly affected germination. If the soil moisture level was below 2%, winged elm seeds would not germinate. Removal of the outer husk of the seed did not affect germination. Winged elm seedlings did not emerge if planted at depths below ¼ inch.

We compared various rates of 2,3,6-trichlorobenzoic acid (2,3,6-TBA), 3,6-dichloro-o-anisic acid (dicamba), and 4-amino-3,5,6-trichloropicolinic acid (picloram), and various methods of application on persimmon (Diospyros virginiana L.). Single rates of 2,3,6-trichlorophenylacetic acid (fenac) and (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) also were included. In one experiment, 8 lb/A of dicamba injected into the soil killed significantly more persimmon than the same rate applied to the soil in 4-inch bands. Otherwise, with given herbicides at comparable rates, defoliation and mortality of persimmon were similar with all methods of soil application. Foliage applications of dicamba or picloram at relatively low rates caused defoliation and mortality of persimmon equal to soil applications of dicamba or picloram at high rates. Dicamba was more effective than equal rates of 2,3,6-TBA for killing persimmon. Picloram at 2 lb/A and dicamba at 4 lb/A, as foliage applications, defoliated and killed persimmon to nearly the same extent. Fenac was relatively ineffective for killing persimmon. Soil treatments with picloram and dicamba killed 22 to 30% more persimmon when applied in summer than when applied in spring. Spring and summer foliage applications of dicamba and 2,3,6-TBA caused similar defoliation and mortality of persimmon, but mortality of persimmon was somewhat higher with spring than with summer foliage applications of picloram. Summer basal treatment with 2,4,5-T killed more persimmon than spring basal treatment.

The herbicide dichlobenil (2,6-dichlorobenzonitrile) inhibited soil nitrification significantly at 100 ppm following 1 and 2 weeks incubation but did not inhibit nitrification at the rates recommended for weed control.

Yaupon (Ilex vomitoria Ait. ♯ ILEVO) in the Post Oak Savannah of Texas was treated with liquid and dry formulations of herbicides. Sprays of Bay Met 1486 {N-[5-(ethylsulfonyl)-1,3,4-thiadiazol-2-yl]-N, N′-dimethylurea} and picloram (4-amino-3,5,6-trichloropicolinic acid), sprays and pellets of tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and boluses of hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1N,3H)-dione] at 4.5 kg ae or ai/ha were the most effective treatments, reducing the canopy 87 to 99% and killing 68 to 93% of the yaupon after 2 yr. The percentage of dead yaupon after 1 yr was similar to that found 2 or 3 yr after treatment. Most herbicides, except clopyralid (3,6-dichloro-2-pyridinecarboxylic acid), reduced the yaupon canopy sufficiently to allow an increase in understory grass and broadleaf vegetation, particularly 1 yr after treatment.

Experiments were conducted to compare the drift of low-expansion foam and conventional sprays in a low-speed horizontal wind tunnel under controlled environmental conditions. Dimensions of the tunnel were 1.30 m high, 0.61 m wide, and 7.32 m long. Wind speed was maintained at 1.52 m/sec. Drift was compared for spray solutions, with and without foam adjuvants, using several different types and sizes of air-inducting nozzles and three sizes of conventional fan nozzles. Large drops produced by the air-inducting nozzles, with and without foam adjuvant, resulted in significantly less drift beyond 1.83 and 6.10 m than sprays from the conventional fan nozzles. The addition of foam adjuvant to the spray solution resulted in increased drift beyond 1.83 m for sprays from the air-induction nozzles in several comparisons but did not result in a significant increase in the drift beyond 6.10 m.

Chlorpropham (isopropyl m-chlorocarbanilate) at 6.7 kg ai/ha controlled a mixture of field dodder (Cuscuta campestris Yunck. ♯3 CVCCA) and largeseed dodder (Cuscuta indecora Choisy ♯ CVCIN) for 3.0 and 4.3 weeks in two greenhouse experiments. The insecticide carbaryl (1-naphthyl N-methylcarbamate) at 0.8 kg ai/ha applied with chlorpropham extended control by 0.7 and 1.8 weeks, and PCMC (p-chlorphenyl N-methylcarbamate) at 0.8 kg ai/ha extended it by 2.7 and 2.8 weeks. Both additives also improved dodder control by chlorpropham in the field, with carbaryl having less effect than PCMC.

Versatile mist chambers, framed with aluminum and glass and having access from top and sides, permit culture of an extensive number of, and different types of, vegetative plant organs as well as seeds and plant pathogens. Pneumatic atomizing nozzles are staggered to permit division of the chamber, and the spray emitted can be regulated from each nozzle. The amount of water vapor emitted is regulated by changing the air pressure or siphon height. Gauge-monitored pressure regulators and solenoid valves control the air and spray system. Timing devices can be used to inject water vapor at desired intervals. Air passing through a condensation tube is recycled past cone heaters, providing temperature from ambient to 90 F, and a duct and baffle system provides uniformity of temperature throughout. A combination recorder and controller maintains the desired temperature.

Relatively pure stands of eight weed species were maintained under field conditions on a Goldsboro loamy sand at Lewiston, North Carolina, for all or part of a 6-year period. Herbicides evaluated as preemergence surface treatments for these species were 2-sec-butyl-4,6-dinitrophenol (dinoseb), isopropyl m-chlorocarbanilate (chloropropham), 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea (diuron), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), and 3-amino-2,5-dichlorobenzoic acid (amiben). S-ethyl dipropylthiocarbamate (EPTC) and a,a,a-trifluro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) were evaluated as preemergence incorporated treatments. The first four herbicides were evaluated in 1961, 1964, and 1966 while the last three were evaluated in 1962, 1963, and 1965. A series of rates was used for each chemical with three replications. With the exception of diuron which failed to control goosegrass (Eleusine indica (L.) Gaertn.), all of the herbicides provided at least a moderate degree of control of goosegrass, smooth crabgrass (Digitaria ischaemum (Schreb.) Muhl.), and redroot pigweed (Amaranthus retroflexus L.) at the respective typical field use rates. In general, trifluralin and amiben gave the best grass control and dinoseb the poorest. None of the herbicides effectively controlled common cocklebur (Xanthium pensylvanicum Wallr.) or ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.). Trifluralin and EPTC did not control Pennsylvania smartweed (Polygonum pensylvanicum L.), common ragweed (Ambrosia artemisiifolia L.), and common lambsquarters (Chenopodium album L.). Chloropropham was ineffective on common ragweed. Simazine, chloropropham, and amiben controlled Pennsylvania smartweed while diuron, simazine, dinoseb, and amiben were especially effective on common lambsquarters. Distinctive patterns of nematode infestations were observed as a function of weed species.

Poisonous plants and noxious weeds are often chemically examined to determine concentrations of secondary metabolites which are responsible for their toxic or biological activity. This study examined sample size requirements and sample methods necessary to quantify accurately the concentrations of individual and total toxic alkaloids in two tall larkspur populations. A high performance liquid chromatography analytical method was utilized to determine toxic alkaloid concentrations in all leaves from three individual plant stems and leaves from the remaining stems (remainder) from each of 50 plants in each population. To obtain high precision in quantifying toxic alkaloids in the larkspur populations (within 2.5 to 5% of the population mean, 0.95 confidence), very large numbers of samples (>50–200) were required. However, lower precision (within 10% of the population mean, 0.90–0.95 confidence) required only 20 samples. Similarly, testing parameters relating to toxin concentration in tall larkspur populations within 5 or 10% of the population mean also required hundreds of samples at power levels of 0.95 and α-levels of 0.05. Relaxing power and α-level requirements to 0.80 and 0.1 respectively, reduced sample size to about 30. The means obtained by four different sampling methods were similar (P>0.05). Alkaloid concentrations in leaf samples from single stems were highly correlated to whole-plant leaf (remainder) samples (r2≥0.76), indicating that harvesting leaves from single stems provided representative samples of the entire plant. The results indicate the difficulty in obtaining accurate information about toxins in poisonous plant populations for risk assessment by livestock producers or extension agents and demonstrate the necessity for efficient analytical methodology. Researchers evaluating concentrations of plant compounds in other weeds or toxic plants should consider variability, sampling procedure, and sample size before experiments begin.

Biotypes of common cocklebur were identified, which were assumed to differ only with respect to sensitivity to MSMA. Water use of these biotypes when grown as isolated plants in a growth chamber was determined with stem flow gauges. The MSMA-tolerant biotype exhibited less whole-plant sap flow at media moisture levels above 17%. Furthermore, only in the tolerant biotype did sap flow differ between the upper and lower canopy; the upper canopy had greater sap flow. Field experiments were conducted to compare growth parameters, water use and competitive ability toward cotton of the MSMA-sensitive and -tolerant biotypes. Sensitive biotype plants were taller and had greater leaf area than those of the tolerant biotype; dry weight was equivalent. The tolerant biotype used less water and reduced seed cotton yield more than the sensitive biotype.

Experiments were conducted at Lincoln and North Platte, Nebraska, during 1967 and 1968 to determine the effect of early preplant applications of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) on sorghum [Sorghum bicolor (L.) Moench ‘Nebraska 505′] and weed yields. Atrazine at 2.24 kg/ha was applied on separate plots preplant and incorporated about April 15, April 30, and May 15, and also preemergence without incorporation about May 17, after sorghum was planted. Sorghum grain yields were highest on plots where atrazine was applied preemergence rather than preplant due mainly to better weed control. Sorghum planted with planter units equipped with furrow openers, set to remove 2.5 to 5 cm of surface soil, had better sorghum stands and smaller weed yields than sorghum planted without removing surface soil. Sorghum population was the lowest following the April 30 atrazine application due to stand loss at North Platte, but grain yields were not significantly different from other preplant treatments since stand loss was compensated for by more heads per plant, larger heads, and larger seed.

Seven herbicides were tested for their effect on growth of Pyricularia oryzae Cavara, Hypochnus sasakii Shirai, and Xanthomonas oryzae Uyeda & Ishiyama Dowson on agar media and for subsequent influence on disease intensity on rice plants (Oryza sativa L.) in the greenhouse. The herbicides studied were: propanil 3′,4′-dichloro-propionanilide), NTN 5$006 [O-(2-nitro-4-methylphenyl)-O-ethyl-N-isopropyl-phosphor-amidothioate], simetryn [2,4-bis(ethylamino)-6-)methylthio)-s-triazine], terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine], nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether), molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate), and aglypt (4-amino-3-methylthio-6-phenyl-1,2,4-triazine-5-on). The growth of P. oryzae, H. sasakii and X. oryzae on culture media containing 10 μg/ml commercial formulation of propanil was reduced to approximately 50% of the control. The other herbicides tested were less effective. Differences in disease severity produced on rice plants treated with the previously mentioned herbicides were in agreement with the results obtained by the culture method. The effect of simetryn and nitrofen on disease severity was stronger than expected from the small direct action on the pathogen in culture. It is suggested that the influence of these two compounds on the disease intensity is due to their effect on the host plant rather than the pathogen directly. Propanil was effective only if applied immediately or up to 1 day before inoculation, indicating that this herbicide is degraded on or within the rice leaves.

Applying control measures when carbohydrate levels are low can decrease the likelihood of plant survival, but little is known about the carbohydrate cycles of dewberry (Rubus spp.), a problematic weed group on cranberry (Vaccinium macrocarpon Aiton) farms. Weedy Rubus plants were collected from areas adjacent to production beds on commercial cranberry farms in Massachusetts, two locations per year for 2 yr. For each site and year, four entire plants were collected at five phenological stages: budbreak, full leaf expansion, flowering, fruit maturity, and after onset of dormancy. Root sections were analyzed for total nonstructural carbohydrates (TNC; starch, sucrose, fructose, and glucose). Overall trends for all sites and years showed TNC were lowest at full leaf expansion or flowering; when sampled at dormancy, TNC concentrations were greater than or equal to those measured at budbreak. Starch, a carbohydrate form associated with long-term storage, had low levels at budbreak, leaf expansion, and/or flowering with a significant increase at fruit maturity and the onset of dormancy, ending at levels higher than those found at budbreak. The concentration of soluble sugars, carbohydrate forms readily usable by plants, was highest at budbreak compared with the other four phenological samplings. Overall, our findings supported the hypothesis that TNC levels within the roots of weedy Rubus plants can be predicted based on different phenological growth stages in Massachusetts. However, recommendations for timing management practices cannot be based on TNC cycles alone; other factors such as temporal proximity to dormancy may also impact Rubus plants recovery, and further research is warranted. Late-season damage should allow less time for plants to replenish carbohydrate reserves (before the onset of dormancy), thereby likely enhancing the effectiveness of weed management tactics over time. Future studies should consider tracking the relationship between environmental conditions, phenological stages, and carbohydrate trends.

The influence of manure and herbicide applications on weed-free fieldbeans (Phaseolus vulgaris L.) and root rot of fieldbeans was studied during 1978 and 1979 at Scottsbluff, Nebraska. Rates of cattle feedlot manure used were 0, 30000, 56000, 112000, or 168000 kg/ha. Preplant herbicide treatments used were alachlor [2-chloro-2′6′-diethyl-N-(methoxymethyl)acetanilide] at 3.4 kg/ha, EPTC (S-ethyl dipropylthiocarbamate) at 3.4 kg/ha, EPTC + trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 2.2 + 0.6 kg/ha, or dinoseb (2-sec-butyl-4,6-dinitrophenol) at 6.7 kg/ha. Manure rates of 56000 kg/ha or higher reduced fieldbean yields both years, but did not increase electrical conductivity or soil exchangeable sodium enough to explain these yield reductions. In 1978, but not in 1979, height and yield of weed-free fieldbeans were reduced by EPTC, EPTC + trifluralin, and alachlor treatments. A significant interaction between manure and herbicide treatments was not detected and none of the treatments increased the severity of root rot in either year.

Tank mixtures of herbicides for control of emerged winter weeds and preemergence control of large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] were evaluated on bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’ # CYNDA] fairways over a 2-yr period. Glyphosate [N-(phosphonomethyl)glycine] applied at 0.28 kg ai/ha in tank mixtures with DCPA (dimethyl tetrachloroterephthate) at 11 kg ai/ha controlled a higher percentage of parsley-piert (Alchemilla microcarpa Boiss. Reut. # APHMI) than either herbicide alone. When applied for spur weed (Soliva spp.) control, DCPA was antagonistic in the tank mixture with simazine [2-chloro-4,6-bis(ethylamino)-s-txiazine]. During one yr of the 2-yr study period, control of large crabgrass was less in plots treated with combination of DCPA and glyphosate than in plots treated with DCPA alone. Less large crabgrass control was obtained in plots treated with bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] at 11 kg ai/ha in combinations with either paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) or 2,4-D [(2,4-dichlorophenoxy)acetic acid] plus mecoprop {2-[(4-chloro-o-tolyl)oxy]propionic acid} plus dicamba (3,6-dichloro-o-anisic acid) than when treated only with bensulide.