Results from greenhouse and growth chamber studies indicated that alachlor [2-chloro-2′,6-diethyl-N-(methoxymethyl) acetanilide] injury to ‘Superior’ potatoes (Solanum tuberosum L.) was related to time of herbicide application and temperature. Injury to the ‘Superior’ cultivar was observed when alachlor was applied just before potato emergence. Necrosis of shoots near the soil surface, shoot dieback, stem swelling, leaf crinkle, and plant stunting were characteristic symptoms of alachlor injury. Cool temperatures appeared to intensify the injury. ‘Superior’ potatoes outgrew injury within 41 days after treatment. Herbicide placement studies in the growth chamber suggested that alachlor or its metabolites were absorbed by the shoots of emerging ‘Superior’ potatoes. Under growth chamber conditions the ‘Katahdin’ cultivar was injured by preemergence applications of alachlor when the herbicide was applied just before plant emergence. Injury symptoms were similar to those observed on the ‘Superior’ cultivar. ‘Pungo’ and ‘Norchip’ potatoes were tolerant to preemergence applications of the herbicide regardless of time of application.

Inhibition and subsequent recovery of net CO2 exchange (NCE) by single leaves of 53 grass species of the subfamilies Festucoideae, Panicoideae, and Eragrostoideae was monitored following limited root uptake of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Rates of NCE recovery were correlated with rates of 14C-atrazine metabolism in leaf sections of festucoid and panicoid grasses but not eragrostoid grasses. Rates of NCE recovery among the nine festucoid and 12 eragrostoid species tested did not exceed 0.2 and 1.1 mg CO2 per dm2 per hr/hr, respectively, whereas for the 31 panicoid species, it ranged from 0.2 to 2.4 mg CO2 per dm2 per hr/hr. Selected species exhibiting NCE recovery rates exceeding 1.2 mg CO2 per dm2 per hr/hr were tolerant to 1.0 kg/ha preemergence and 1.25 kg/ha postemergence atrazine applications. These panicoid species included a number of common weed species belonging to the genera Digitaria, Panicum, and Setaria, as well as species belonging to Bracharia, Pennisetum, Sorghum, and Zea. Unchanged 14C-atrazine accounted for 11.3 to 92.7% of the total 14C-radioactivity extracted from 14C-atrazine infiltrated leaf sections following an 8-hr incubation period. N-dealkylation, hydroxylation, and peptide conjugation occurred in all species, although rates of these metabolic pathways varied widely among species. Recovery of NCE was correlated with formation on the glutathione-atrazine conjugate, and conjugation was the major detoxification pathway in species exhibiting tolerance to atrazine.

The degree of control of purple nutsedge (Cyperus rotundus L.) provided by Bactra verutana Zeller, a native moth, was evaluated for various stress conditions. Two, three, or four weekly infestations each with three larvae per live shoot, reduced purple nutsedge dry weight an average 77% compared with an average 55% for one infestation. Eight weekly infestations reduced plant dry weight 98%. Neither caging of the larvae on the plants nor osmotic stress with NaCl to −8 bars influenced larval efficacy, but nitrogen deficiency did reduce the effect of the larvae about 75%. Purple nutsedge had no effect on the dry weight of cucumber (Cucumis sativus L., ‘Straight Eight’) after 1 month, whether larvae were or were not present. Purple nutsedge did reduce the plant dry weight of okra (Abelmoschus esculentus (L.) Moench, ‘Clemson Spineless’) 64%, but repeated (eight) weekly infestations of larvae gave a plant weight of okra equal to that of okra grown without purple nutsedge. Purple nutsedge reduced the bulb and root dry weight of onion (Allium cepa L., ‘Big Valley’) 37%, but repeated weekly infestations of larvae gave onion growth equal to that of onion grown without purple nutsedge.

The site of uptake of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] was studied using a double pot technique. Sorghum [Sorghum bicolor (L.) Moench ‘RS610′] and pea (Pisum sativum L. ‘Alaska’) were the test plants. Herbicidal activity measured by the reduction in fresh weight of the roots and shoots of treated plants showed that exposure of the shoot zone to the herbicides caused much more injury to the plants than root exposure. Translocation of both compounds from root applications to tops of pea and sorghum was studied using 14C-labeled herbicides. There was very little movement of the compounds from the roots of both species. Translocation of the compounds from foliage application was studied using greenbean (Phaseolus vulgaris L. ‘Spartan Arrow’) and soybean [Glycine max (L.) Merr ‘Wayne’]. Almost all of the applied 14C-herbicides remained at the point of application.

The effects of herbicides on in vivo nitrate and nitrite reduction were determined by vacuum infiltrating sections of barley (Hordeum vulgare L.) or bean (Phaseolus vulgaris L.) leaves with solutions containing nitrate and herbicides. Herbicides causing a reduction of nitrite accumulation in the dark were considered to have inhibitory effects upon nitrate reduction and those causing an accumulation of nitrite in the light were considered to inhibit nitrite reduction. Only dinoseb (2-sec-butyl-4,6-dinitrophenol) and potassium azide significantly reduced nitrate reduction in both barley and bean. All of the herbicides which inhibit photosynthesis inhibited nitrite reduction but had no significant effect on nitrate reduction in barley and bean. Nitrite reduction in an atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] resistant pigweed (Amaranthus retroflexus L.) biotype was not affected by any triazine tested. However, these triazines significantly inhibited nitrite reduction in barley, bean, and the susceptible pigweed biotype. The results suggest that the in vivo nitrate reductase technique may be a useful technique for identifying chemicals which inhibit the flow of electrons to ferredoxin, thereby inhibiting nitrite reduction in light.

Yellow nutsedge (Cyperus esculentus L.) control with herbicides was evaluated with and without competition from turfgrasses. Postemergence applications of cyperquat (1-methyl-4-phenylpryidinium) provided safe selective control of yellow nutsedge in Kentucky bluegrass (Poa pratensis L. ‘Merion’), perennial ryegrass (Lolium perenne L. ‘Manhatten’), and red fescue (Festuca rubra L. ‘Pennlawn’). Pre- and post-emergence applications of perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide} controlled yellow nutsedge when rainfall or irrigation was adequate for good turfgrass growth. Under dry conditions, perfluidone slightly injured Kentucky bluegrass and gave poor control of yellow nutsedge. Bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one2,2-dioxide] was less effective than cyperquat or perfluidone for yellow nutsedge control and required split applications. Bentazon did not injure Kentucky bluegrass. Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] and Vel 3973 [N-(2,4-dimethyl-5-{[(trifluoromethyl)sulfonyl]amino}phenyl)acetamide] did not provide adequate yellow nutsedge control. Vel 5052 {2-chloro-N-(2,6-dimethyl-phenyl-N-[(1,3-dioxolan-2-yl)methyl] acetamide}showed promise for yellow nutsedge control.

A spray chamber was constructed to spray herbicides or growth regulators on small potted plants. Syphon-type pneumatic atomizing nozzles were used to eliminate the need to pressurize the spray solution. Two stationary overhead nozzles deliver the solution to plants rotating on a turntable. The chamber permits convenient and accurate regulation of volume and rate of chemical application for laboratory and greenhouse investigations.

Studies were conducted to determine the effect on absorption and metabolism of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] by atrazine-susceptible (S) and -resistant (R) biotypes of common lambsquarters (Chenopodium album L.) and redroot pigweed (Amaranthus retroflexus L.). The response of isolated chloroplasts of susceptible and resistant biotypes of each species was also studied. In both species the two biotypes absorbed atrazine equally well and were unable to differentially metabolize the herbicide. The photochemical activity of R chloroplasts isolated from each species was not inhibited by atrazine but S chloroplasts were severely inhibited.

Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] at 0.14 kg/ha and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)one] at 0.56 kg/ha applied under field conditions interacted synergistically to reduce soybean [Glycine max (L.) Merr. ‘Harsoy-63′] growth. In the greenhouse, a number of combinations with atrazine at 0.07 kg/ha or greater and metribuzin at 0.56 kg/ha and greater interacted synergistically to reduce soybean fresh and dry weights 30 days after planting. Over a soil pH range of 4.6, 5.6, and 6.7, atrazine–metribuzin interactions were more apparent as the soil pH values increased. Atrazine at 10-5 and 10-6 M concentration in the sand culture nutrient solution during the early growth of ‘Swift’ soybean seedlings decreased 14C-metribuzin uptake and movement into the 12-day-old soybean shoots during the 12-hr treatment period. However, 10-7 M atrazine increased 14C-metribuzin in the shoot by increasing stomatal aperture and subsequent transpiration. Conditions favoring the synergistic interaction were low atrazine residue levels which increase soybean transpiration, high metribuzin rates, and high soil pH levels.

A 3.6 g/L solution of glyphosate [N-(phosphonomethyl)glycine] applied to selected parts of bermudagrass [Cynodon dactylon (L.) Pers.] shoots did not kill the entire plant. However, phototoxicity increased as more parts of the plant were treated. No differences were observed when solutions of 3.6 and 5.4 g/L glyphosate were applied at 94 and 373 L/ha. However, greater herbicide efficacy was obtained when 1.8 g/L solution was applied at the higher volume. Translocation of this herbicide appeared to follow the typical source-sink relationship. A 7.2 g/L solution of glyphosate applied at 373 L/ha was necessary to kill the plant.

Three thousand accessions of the U.S. Dep. Agric. World Collection of Avena sp. germ plasm were screened for their ability to exude scopoletin (6-methoxy-7-hydroxy coumarin), a naturally occurring compound shown to have root growth inhibiting properties. Twenty-five accessions exuded more blue-fluorescing materials than a standard oat cultivar (Avena sativa L. ‘Garry’). Analysis of the exuded materials revealed that four accessions exuded up to three times as much scopoletin as ‘Garry’. When PI 266281 was grown with wild mustard [Brassica kaber (D.C.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler] for 16 days in sand culture, the growth of the wild mustard was significantly less than that obtained when the weed was grown with ‘Garry’. Wild mustard plants grown in close association with PI 266281 exhibited severe chlorosis, stunting, and twisting which appeared indicative of chemical or allelopathic effects rather than simple competition. Analysis of the culture solution indicated that levels of scopoletin were too low to cause the observed effects and it is postulated that the final toxic effects were possibly due to the exudation of scopoletin and other allelopathic compounds.

The capacity for photosynthetic acclimation to light intensity in Sakhalin knotweed (Polygonum sachalinense F. Schmidt) was studied by growing plants in four light environments [out-of-doors in full sun and under 50% shade, and in a growth chamber at 800 μE m2 sec-1 photosynthetically active radiation, 400 to 700 nm (PAR) and 150 μE m-2 sec-1 PAR], and then determining, with an infrared gas analyzer (IRGA), the photosynthetic rates of single leaves exposed to a range of light intensities from 100 to 2000 μE m2 sec-1 PAR. The plants grown in high light had higher photosynthetic rates throughout the range of 100 to 2000 μE M-2 sec-1 PAR. Maximum photosynthetic rates were 37 mg CO2 dm-2 h-1 for plants grown in full sun out-of-doors and 16.5 mg CO2 dm-2 h-1 for plants grown in low light in the growth chamber. There was no indication of positive adaptation to low light intensity in Sakhalin knotweed. Differences in light-saturated photosynthetic rates were closely related to differences in mesophyll conductance and chlorophyll content per unit leaf area.

Diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], and prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] were applied postemergence in cotton (Gossypium hirsutum L.) 50 cm high as directed sprays covering (a) the furrow and base of cotton plants or (b) covering the lower half of cotton plants. Herbicides directed to the base of plants caused little or no chlorosis of cotton foliage. When applied to the lower half of cotton plants, linuron caused the most injury to foliage; diuron, the least symptoms. Herbicides directed to base or lower half of cotton plants did not significantly reduce yields, alter boll components or fiber properties, and controlled broadleaved weeds.

The relative susceptibility of ‘Alaska’ and ‘Perfection’ cultivars of peas (Pisum sativum L.) to trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) was studied in excised roots, and in greenhouse and field plantings. Elongation of excised Alaska and Perfection pea roots was reduced 32 and 25%, respectively, by 4 mg/L dosages of trifluralin in aseptic culture, and 25 and 10% by 1.68 kg/ha dosages in greenhouse-grown plants. Seedling emergence in the greenhouse and field was reduced or delayed in both cultivars by 1.68 kg/ha trifluralin. Yields of field-grown Alaska and Perfection peas were reduced by trifluralin dosages equal to and exceeding 0.84 and 1.68 kg/ha, respectively, when there was a June water deficit (8 cm). Yields were not reduced in either cultivar when June rainfall was near normal (10.9 cm).

A sinking leaf-disk technique enabled detection of differences among potato (Solanum tuberosum L.) varieties in herbicide tolerance within 24 hr. Susceptibility of varieties to field application of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5-(4H)-one] was correlated (r = 0.76∗∗) to the number of sunken disks in a metribuzin solution in a growth chamber with continuous light at 30 klux. Varieties that were very tolerant, very susceptible, or intermediate in tolerance to field application of metribuzin were generally in these same categories when evaluated by the sinking leaf-disk technique. Speed of this response was dependent upon herbicide concentration and solution temperature, but the varietal relationships did not change. It was necessary to use leaves of nearly the same age as determined by relative size and position on the plant. Other factors influencing results included plant growth stage, soil moisture, and atmospheric temperature. Results from the sinking leaf-disk test of winter-grown greenhouse plants of the same clones were correlated (r = 0.86∗) to estimated metribuzin injury to field-grown plants. This method, with adequate modification of technique, may have potential use for studying other plant species and other relationships between plants and photosynthesis-inhibiting herbicides.

In the field, surface applied cyanazine 2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] did not move below 5 cm in a Monona silty clay loam (Typic Hapludoll) which received 20 cm of water over a 54-day period. In hand-packed soil columns in the laboratory, surface-applied diuron and cyanazine penetrated to depths of 10 and 20 cm, respectively, when leached over a comparable time period and with amounts of water similar to that used in the field. Soil thin layer chromatography and adsorption isotherm studies showed that diuron was adsorbed more strongly than was cyanazine. In general, both compounds were degraded more rapidly at the higher temperatures when incubated at 5, 20, 35, and 50 C over a 20-week period. Degradation was slowest at 5 C in a Valentine loamy fine sand (Typic Ustipsamment). Diuron appeared to break down most readily at 35 C. Cyanazine was usually decomposed by the 10th week at 5 C and the 5th week at higher temperatures.

Wild oat (Avena fatua L.) and California burclover [Medicago polymorpha L. var. vulgaris (Benth.) Shinners] are two important ruderal as well as rangeland species in California, with their wide adaptability correlated with several widespread genetic polymorphisms. In order to clearly demonstrate the role of genetic variation in their population dynamics, natural selection was studied at two of the polymorphic loci (B/b in wild oat and D/d in California burclover) which represent a useful class of marker genes governing seed coat morphology. Since parental seed coat often remains attached to the offspring seedling, two generations can be scored simultaneously during the population census in successive stages of the life cycle. Data are presented to provide direct evidence for natural selection at these loci and to argue for their wider use in such population studies. In wild oat, black lemma class (B-) germinated at a significantly higher rate than the gray class (bb) in mesic patches at one of the sites and seemed to be negatively density-dependent whereas density-dependent reproductive rates generally favored the gray class. Similarly, germination and seed output provided the balancing selection to maintain polymorphism at locus D/d in California burclover. Such processes of localized selection and population regulation may have significant implications in the management of weed populations.

Greenhouse studies were conducted to study the competition between soybeans [Glycine max (L.) Merr. ‘Vansoy’] and barnyardgrass [Echinochloa crus-galli (L.) Beauv.]. The competition was initiated or terminated when soybeans were 2, 3, 4, 5, 6, 7, 8, 9, and 10 weeks old. The reproductive efficiency of soybeans was not lowered by 4 to 7 weeks of competition after planting of soybeans. Competition between the two species for the entire growing season resulted in a significant decrease in plant height of soybeans. The total dry matter per plant was negatively correlated with an increase in the length of competition. Competition during the first 5 to 9 weeks of the life cycle of soybeans was more deleterious to soybean productivity than the last 5 to 9 weeks of its life cycle.

Phytochrome was assayed in vivo in the rhizomes of 12 to 14-week old johnsongrass [Sorghum halapense (L.) Pers.] plants. The phytochrome levels decreased basipetally from the apex through the eighth node. The decrease was logarithmic on a dry weight basis, but less rapid on a per segment basis. On a dry weight basis, higher phytochrome measurements were obtained with samples from the interior of the rhizome than from the external regions. The far-red absorbing form of phytochrome (Pfr) was shown to be very labile at 25 C in johnsongrass rhizomes. These results provide a basis for examining photomorphogenic responses of rhizomes to light and for correlating these responses to phytochrome photophysiology.

When the insecticide fonofos (O-ethyl-S-phenylethylphosphonodithioate) was added to a nutrient solution containing 14C-terbacil (3-tert-butyl-5-chloro-6-methyluracil), movement of total radioactivity into leaves of peppermint (Mentha piperita L. cv. ‘Todd's Mitchum’) during a 3-day treatment period approximately doubled. In addition, a higher percentage of this total radioactivity was identified as intact terbacil. Total radioactivity in the leaves was not significantly increased when terbacil was added to 14C-fonofos in nutrient solution. Studies also were conducted to measure the effect of fonofos upon the rate of terbacil metabolism in peppermint. Peppermint plants were treated for 3 days with nutrient solution containing 14C-terbacil alone or 14C-terbacil plus fonofos. The percentage of total radioactivity which remained as intact terbacil at the end of the treatment period was five times as high in plants treated with the combination as in those treated with terbacil alone. The relative rate of degradation during the succeeding 11 days was approximately the same in plants subjected to the two treatments. These results could account for damage to peppermint from closely timed applications of fonofos and terbacil in the field.