A typical scotoactive stomatal behavior was noticed in Carissa spinarum L.; Gymnosporia emarginata Laws; Maba buxifolia Cl.; Flacourtia sepiaria Roxb.; Dodonaea viscosa L. and Randia malabarica Lamk. This stomatal behavior was reversed artificially by foliar application of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at 100 ppmw or 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] at 2000 ppmw. The size of the stomatal aperture, stomatal conductance and the rates of transpiration were enhanced significantly by the herbicide treatment. The physiological basis for the induction of desiccation and death of plant organs is thought to be the excessive stimulation of stomatal aperture, stomatal conductance and consequently high rates of transpiration observed here. The data suggest that herbicide-induced desiccation is the consequence of inhibition of scotoactive behavior and increased water loss with attendant desiccation and death of leaves.

The initial dormancy in mature seeds of 12 out of 14 species of grass weeds studied was significantly overcome by pretreatment of the dry seeds at 50 C in stoppered vials. The time required for maximum effect varied depending upon species and lots within species. The procedure, termed accelerated after-ripening, can produce seeds in various stages of dormancy simply by varying the duration of the pretreatment. One of the first stages that becomes apparent is an increased response to light.

The effects of intraspecific competition on the growth and development of purple nutsedge (Cyperus rotundus L.) were studied under greenhouse conditions. Increases in plant density increased the dry weight accumulation on a per pot basis but decreased the dry weight accumulation on a per plant basis. The partitioning of dry weight, whether on a per pot or per plant basis, indicated a shift in the method of reproduction as to density. Under low density conditions more dry weight was partitioned into inflorescences than into tubers. However, under high density conditions more dry weight was partitioned into tubers rather than inflorescences. Dry weight partitioned into rhizomes did not vary as to density. Dry weight partitioned into shoots and roots decreased with the concomitant increase in dry weight partitioned into reproductive structures. This shift to vegetative reproduction under stress conditions caused by competition provides further insight into the difficulties of controlling purple nutsedge.

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.

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.

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.

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.

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.

A water-soluble linseed oil formulation was compared with emulsifiable linseed oil as an additive to bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2,2-dioxide] for redroot pigweed (Amaranthus retroflexus L.) control. A water-soluble linseed oil formulation as an additive to bentazon controlled redroot pigweed better than did an emulsifiable linseed oil additive. Further, the water-soluble linseed oil additive enhanced redroot pigweed control with bentazon more than the emulsifiable linseed oil when a simulated rainfall followed application, or when humidity was low (30 to 45%) or spray volume high (170 to 340 L/ha). Redroot pigweed control with bentazon plus the water-soluble linseed oil additive followed by simulated rainfall in 4 h was similar to control with bentazon applied alone without a simulated rainfall.

Burley tobacco (Nicotiana tabacum L. ‘Kentucky 14′) was grown as a no-tillage crop in 1974 and 1975 by planting tobacco directly into an existing stand of orchardgrass (Dactylis glomerata L.) or rye (Secale cereale L.). Paraquat (1,1′-dimethyl-4,4′bipyridium ion) and glyphosate [N-(phosphonomethyl)glycine] were used to kill existing vegetation. Benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), oryzalin (3,5-dinitro-N4,N4-dipropylsulfaniiamide), metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)one], and chlorbromuron [3-(4-bromo-3-chlorophenyl), 1-methoxy-1-methylurea] were used to control annual grasses and broadleaf weeds.

Glyphosate was generally more effective than paraquat in killing existing vegetation. There was some injury to the tobacco associated with the glyphosate and paraquat treatments, but this was generally confined to those plants which came into contact with the treated herbage. Metribuzin caused severe damage to the tobacco and was discontinued after the first year. Chlorbromuron caused little injury if kept on the surface but injured the tobacco if incorporated by cultivation as in conventional tillage. Benefin and oryzalin caused little or no injury to the tobacco. All four herbicides gave adequate control of annual grasses and broadleaf weeds.

Persistence of 1.12, 2.24, and 3.36 kg/ha of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] applied preemergence to corn (Zea mays L. ‘Funk's 4761′) was determined in three soils, each providing a range of pH from 5 to 7. Samples of surface soil from each plot were collected at intervals after atrazine application until there was no evidence of phytotoxicity to oat (Avena sativa L. ‘Florida 501′) in bioassay. Persistence (Y50) was defined as the number of days following atrazine application until bioassay indicated 50% relative growth of oats (no atrazine = 100% growth). This period ranged from 24 to 178 days, depending upon soil type, pH, and atrazine rate. Persistence of atrazine increased with increasing soil pH. The effect of soil pH was essentially the same at each atrazine rate and did not vary appreciably with years in a given soil. In McLaurin sandy loam, atrazine persisted 8 to 9 days longer with each unit increase in soil pH. In Hartsells fine sandy loam and Decatur silt loam, atrazine persistence increased 9 to 13 days and 29 days, respectively, with each unit pH.

The effects of soil-applied and stem-injected herbicidal techniques of forest conversion on soil moisture, pine establishment and understory vegetation were determined in an Appalachian hardwood forest. Grid applications of fenuron (1,1-dimethyl-3-phenylurea) at 11.2 kg/ha were as effective in killing tops and controlling sprouting of hardwood species as the injection application with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and fuel oil. Survival of white pine (Pinus strobus L.) was higher with 5.6 kg/ha than with 11.2 kg/ha of fenuron pellets. The growth in height of pines growing under reduced competition was considerably greater than for pines growing in competition with hardwoods. During the second growing season after treatment significantly more soil moisture was present in the plots treated with fenuron and 2,4,5-T than in the untreated ones. Herbaceous vegetation and understory woody plants increased after the herbicide treatments. The third season following herbicide treatment twenty-seven species were recorded on the treated areas that were not present on the untreated control areas.