Hawaiian sugarcane cultivars (Saccharum L. hybrids) differed considerably in their tolerance to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). There was a greater concentration of diuron in the younger leaves of a sensitive cultivar, ‘H 53–263,’ compared with a tolerant cultivar, ‘H 50–7209′; degradation of diuron was more extensive in ‘H 50–7209′. The metabolites identified after applications of carbonyl-labeled diuron to the root system were 1-(3,4-dichlorophenyl)-3-methylurea (monomethyl-diuron) and 1-(3,4-dichlorophenyl)urea (demethylated diuron). Differences in diuron phytotoxicity to cultivars ‘H 53–263’ and ‘H 50–7209’ are at least partially explained by differences in the distribution and degradation of diuron.

Growth chamber studies were conducted to determine the influence of several pretreatment radiation, humidity, and temperature regimes on the response of peas (Pisum sativum L. ‘Alaska’) and velvetleaf (Abutilon theophrasti Medic.) to foliarly-applied (2,4-dichlorophenoxy)acetic acid (2,4-D). Under the conditions of these studies, growing peas under solar or fluorescent-incandescent lamp radiation, in high or low humidity, or in temperatures between 10 and 25 C prior to treatment did not influence their response to 2,4-D. The response of velvetleaf to 2,4-D was slightly greater when pretreatment growth was under solar radiation rather than under fluorescent-incandescent lamps. Similarly, high pretreatment humidities and temperatures produced slightly greater responses to 2,4-D in velvetleaf than low pretreatment humidities and temperatures. Herbicide uptake and translocation were greater when pretreatment pea growth was under solar radiation, but spray retention and rate of 2,4-D metabolism were not affected by pretreatment radiation. This study indicates that pretreatment light, temperature, and humidity conditions play only a minor role in determining the response of peas and velvetleaf to 2,4-D.

The response of close-spaced, pickling cucumbers (Cucumis sativus L.) to preplant incorporation treatments of O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide (bensulide), N-butyl-N-ethyl α,α,α-trifluoro-2,6-dinitro-p-toluidine (benefin), and dimethyl tetrachloroterephthalate (DCPA) and preemergence applications of 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) and the methyl ester of 3-amino-2,5-dichlorobenzoic acid (chloramben) has been evaluated over a 2-year period. DCPA and nitralin gave the best overall weed control, while benefin and the methyl ester of chloramben were less effective in controlling weeds. The poorest weed control performance was observed with bensulide. Nitralin, DCPA, benefin, and the methyl ester of chloramben caused crop injury if leaching rains followed application. Despite early herbicide injury, yields were usually not adversely affected.

Greenhouse and field studies were conducted with 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron). Tolerant soybean (Glycine max (L.) Merr.) and susceptible tall morningglory (Ipomoea purpurea (L.) Roth.) and ivyleaf morningglory (I. hederacea (L.) Jacq.) were studied with both root and foliar chloroxuron applications. Soybean tolerance to chloroxuron was reduced when treatments occurred in the unifoliate stage; greatest soybean tolerance was noted when soybeans were treated in either the cotyledonary or third trifoliage stage. Tall and ivyleaf morningglory were susceptible to chloroxuron until about 21 days of age (five true leaves), after which resistance increased. Root applications of chloroxuron were more phytotoxic than foliar applications for soybeans and both species of morningglory. In a 3-year study in the field, the following sequential herbicide treatments of either α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), 4-(methylsulfonyl-2,6-dinitro-N,N-dipropylaniline (nitralin), S-propyl dipropylthiocarbamte (vernolate), or 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) applied preemergence plus chloroxuron postemergence resulted in higher soybean yields than any single herbicide treatment. Weed control was better with the sequential combinations. All sequential combinations with chloroxuron caused soybean injury. Greatest soybean injury occurred when chloroxuron was applied in the first and second trifoliate stage than in the third trifoliate stage. Vernolate alone caused some injury in certain years.

Fenac [(2,3,6-trichlorophenyl)acetic acid] and 4-amino-3,5,6-trichloropicolinic acid (picloram) at 28 and 2.2 kg/ha, respectively, controlled woollyleaf bursage (Franseria tomentosa Gray) for 3 years in noncropped areas. Effective control of woollyleaf bursage was obtained when treated at the bud stage or earlier with an ester formulation of (2,4-di= chlorophenoxy)acetic acid (2,4-D) at 2.2 kg/ha or 3-amino-s-triazole (amitrole) at 4.5 kg/ha in an oil-water emulsion carrier or 3,6-dichloro-o-anisic acid (dicamba) at 2.2 kg/ha in a water carrier with 0.5% surfactant. Picloram, at 0.44 kg/ha or more, controlled woollyleaf bursage at any time of application.

Absorption, translocation, metabolism, and action of 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid (endothall) in annual bluegrass (Poa annua L.), Kentucky bluegrass (Poa pratensis L. ‘Merion’), and creeping bentgrass (Agrostis stolonifera L. ‘Penncross’) were studied. Selective action on annual bluegrass from root applications of endothall was attributed to differences in absorption and action of the herbicide. Morphological differences among species, spray retention, and endothall action contributed to selectivity following foliar applications.

Endothall (7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid) was evaluated for controlling annual bluegrass (Poa annua L.) infestations in Kentucky bluegrass (Poa pratensis L.) and creeping bentgrass (Agrostis stolonifera L.) turfs. Growth of annual bluegrass was selectively suppressed by three applications of 0.6 kg/ha of endothall, two or three applications of 1.1 and 2.2 kg/ha, and one application of 4.5 kg/ha made to the single plant sand cultures. Field treatments were variable and seasonably dependent. Endothall selectively killed annual bluegrass when applied to roots in sand culture at a concentration of 2.7 × 10−4 molar. A granular formulation of endothall provided selective control of annual bluegrass in field and greenhouse studies. High watering frequency prior to application, low organic matter content of the underlying soil, and predominance of the annual biotype of annual bluegrass enhanced the selective action at the lowest rates of endothall application.

Injection of undiluted dimethylamine salt of (2,4-dichlorophenoxy)acetic acid (2,4-D) containing 479 g/L killed several species of bottom-land hardwoods when applied in 1 or 2-ml dosages in injections spaced from edge-to-edge to 23 cm apart. Most hardwoods were easier to kill in June than in September or December. For greatest economy, treatments should be varied by species and seasons. A 4:1 mixture of triisopropanolamine salts of 2,4-D and 4-amino-3,5,6-trichloropicolinic acid (picloram) containing 305 g/L was effective on some species resistant to 2,4-D, including eastern persimmon (Diospyros virginiana L.), swamp privet (Forestiera acuminata (Michx.)Poir.), and bitter pecan (Carya x lecontei Little).

Barley (Hordeum vulgare L. ‘Coho’), rye (Secale cereale L. ‘MSU Exp.’) and oat (Avena sativa L. ‘Gary’) seedlings were grown in nutrient solutions containing 0 and 10−9 to 10−7 M concentrations of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine). In kinetic studies with rye and barley seedlings, simazine increased water and nitrate uptake after 3 days' exposure to 10−9 M simazine compared to controls; there was no effect from 10−7 M simazine. The effect was manifested in an increase in both plant weight and total protein. After 12 days, companion plants treated with 10−7 M simazine were the same size as controls but contained a higher protein concentration especially in the shoots. Regression analyses showed that the simazine-induced increases in total nitrogen content of the three grain species were closely related to the nitrate and water uptake, whether manifested by greater plant growth or more protein per gram of plant.

Four herbicides were applied at 6-month intervals, and incorporated by disking, to desert cropland soils at two locations. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) was applied at 0.9 kg/ha; and 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) were applied at 1.8 kg/ha. Following treatment the soils remained fallow without irrigation for 24, 18, 12, 6, or 0 months before planting eight crops. Sugarbeet (Beta vulgaris L.) growth was affected 24 months after applications of trifluralin. Growth of two or three crops at each location was affected 18 months after application of prometryne. Residues of atrazine and diuron usually caused greater injury to most crops than did prometryne or trifluralin. Six months after the first planting four additional crops were planted. In plots planted 30 months after treatment diuron reduced sorghum (Sorghum bicolor (L.) Moench) stands by 70% and reduced fresh weights of three crops at Mesa. Trifluralin reduced fresh weight of sorghum by 80% at Yuma. Crops responded differently to herbicide residues at the two locations. Injury to crops was most severe at Mesa despite higher rainfall during the fallow period at this location.

Triethylamine salts of 4-amino-3,5,6-trichloropicolinic acid (picloram) plus (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) (1:1) sprays were more effective for the control of huisache (Acacia farnesiana (L.) Willd.) than for the control of Macartney rose (Rosa bracteata Wendl.) at 13 dates of application in 1969 and 1970. Both species were more controlled effectively with the application rate of 1.12 than 0.56 kg/ha. Most effective control of huisache was obtained June 18, 1970, although other summer treatments in 1970 were effective. The herbicide was, on the average, more effective on huisache and Macartney rose when applied in the evening than morning or midday. Macartney rose was most effectively controlled by treatments applied in September and October of both years. Poorest control of the two species occurred when internal water stress was highest.

A linear uptake of 14C-labeled 6,7-dihydrodipyrido (1,2-a:2′,1′-c)pyrazinediium ion (diquat-14C) at 1 ppmw by hydrilla (Hydrilla verticillata Casp.) occurred during a 10-day period under controlled conditions. Plant tissue contained higher amounts of radioactivity after treatment with combinations of 0.1 or 0.5 ppmw of diquat-14C plus 1 ppmw of copper than did tissue of plants in solutions of diquat-14C alone. Plants in a 1 ppmw of diquat-14C solution contained 2,123 cpm/mg after 8 days; however, 5,857 cpm/mg were measured in plant tissue taken after the same period from solutions containing diquat-14C plus 2 ppmw copper as copper sulfate pentahydrate (CSP). An increase in CSP from 3 to 10 ppmw did not significantly increase the uptake of diquat-14C over the 2 ppmw. Results with an organic copper complex (copper sulfate triethanolamine) in combination with diquat-14C were the same as those obtained with diquat-14C plus CSP.

Six Setaria species and varieties and three Panicum species were allowed to absorb 14C-labeled 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine), and/or 2-chloro-4,6-bis (ethylamino)-s-triazine (simazine). The grasses metabolized the herbicides to water-soluble derivatives. Peptide conjugates were the only major metabolites formed by each species or variety; however, hydroxyderivatives of the herbicides were detected. The order of ability of the Setaria and Panicum species and varieties to metabolize atrazine and/or propazine was similar to the order of their tolerance to atrazine and/or propazine. Several Setaria and Panicum species and varieties formed peptide conjugates of atrazine and/or propazine to which they are resistant, more rapidly than they formed peptide conjugates of simazine, to which they are susceptible.

Field studies were conducted with giant foxtail (Setaria faberii Herrm.) under shade intensities of 0, 30, 60, 70, 80, and 98%. Seed weight, dry weight of plant tops exclusive of seed, and total dry weight per plant decreased linearly with increasing shade intensities. These decreases were due primarily to decreases in number of leaves, number of stems per plant, and number of heads per plant. Height of main culm was less affected than other morphological characteristics. Shading affected the length of internodes but had little influence on number of internodes on the main culm. The amount of shade required to control giant foxtail completely, once it is established, appears to be above 95%. Expressed as 2-year means, plants grew to as much as 135 cm, had as many as 188 leaves, 41 stems, and 31 heads, and produced 73 g of dry matter per plant including 6 g of seed. Maximum number of seeds per head was 1405.

Systems of weed control composed of (a) intensive cultivation only, (b) herbicides only, or (c) herbicides plus cultivation controlled weeds in soybeans (Glycine max (L.) Merr.) with acceptable crop tolerance. On Ocilla sandy loam, systems with S-propyl dipropylthiocarbamate (vernolate) as a preplanting treatment and 3[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron) as an early postemergence treatment, followed by either sweep cultivations or directed postemergence applications of other herbicides, controlled yellow nutsedge (Cyperus esculentus L.) satisfactorily and controlled 99 to 100% of the common cocklebur (Xanthium pensylvanicum Wallr.) and Florida beggarweed [Desmodium tortuosum (Sw.) DC.]. As directed postemergence treatment, 2-seobutyl-4,6-dinitrophenol (dinoseb) controlled common cocklebur and Florida beggarweed about as well as 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron). However, for the broad spectrum of weeds encountered on the Greenville soil, linuron was superior to dinoseb, especially on Texas panicum (Panicum texanum Buckl.). Systems containing only cultivation controlled 84 to 98% of the common cocklebur and 78 to 99% of the Florida beggarweed. On Greenville sandy clay loam, several systems of weed control significantly reduced the stand but not the yield of soybeans. Vernolate reduced stands when used as a preplanting incorporated treatment but not when injected at planting. No significant yield differences among the weed control systems were apparent in the 3-year averages. Costs of weed control ranged from $20 to $30/ha for cultivation only, from $55 to $73/ha for herbicides only, and from $45 to $53/ha for herbicides combined with cultivation. Uncontrolled weeds, primarily common cocklebur and Florida beggarweed, in the weedy check plots reduced the average yield of soybeans 74% on the Ocilla soil during the 3-year period. The different systems of weed control did not affect commercial quality of soybean oil.