The rates of foliar dark respiration and net photosynthesis in attached leaves of 25 C3, C4, and C3-C4 intermediate dicotyledonous weed species were determined using the infrared gas analyzer. The ratio of dark respiration to photosynthesis per unit leaf area in attached leaves of each species was inversely proportional to leaf age. Highly significant, positive linear correlation was observed between the rates of foliar dark respiration and net photosynthetic CO2 uptake in dicot weeds irrespective of the photosynthetic type. The higher foliar dark respiration rate found in some of the weed species can be attributed in part to the higher carbohydrate levels as generated by a rapid photosynthetic CO2 assimilation. The significance of higher dark respiration rate in relation to carbon and energy economy of weeds is discussed.

A survey was conducted at 88 sites in Montana in 1984 and 1985 to determine the distribution of Urophora affinis Frauenfeld and U. quadrifasciata (Meigen), two seed head flies released on spotted knapweed (Centaurea maculosa Lam. # CENMA) in North America. U. affinis, released in Montana during 1973 to 1977, was found at 40 of the 88 sites. The fly was concentrated within a short radius (about 5 to 8 km) of release sites, even at sites having well-established populations. U. quadrifasciata, released in British Columbia in 1972, but not in the United States, was found at 84 sites. The data suggest that the fly entered the state in the northwest corner and dispersed in a southeasterly direction. There was a strong positive relationship between mean number of galls per seed head and percent infestation for both fly species.

The persistence and germinability of jointed goatgrass (Aegilops cylindrica Host. # AEGCY) seed (caryopses) were studied over a five-year period between 1979 and 1984 at five locations in Colorado, Kansas, and Nebraska. Seed were buried in open-mesh packets and the sites were not disturbed for the duration of the study. Seed survival at burial depths of 5, 15, or 30 cm decreased rapidly over the first three years at all locations. By the third year, less than 7.4 ± 6.5% (mean ± SD) of the seed remained at 5 cm in the soil at all locations. By the third, fourth, and fifth year there was total loss of seed at one, two, and four sites at the 5-cm burial depth. Only three of five sites had total loss of seed at 30 cm after five years. The proportion of surviving seed that were germinable increased with time and was almost 100% after three years of burial. Because jointed goatgrass seed were relatively transient in the soil profile, fallowing of infested areas for a three-year period may significantly reduce populations of this weed or eradicate it, depending upon location.

Root buds of leafy spurge (Euphorbia esula L. # EPHES) were found to be quiescent during most of the growing season due to correlative inhibition rather than innate dormancy. Excised root buds taken from plants that were fully flowering showed reduced elongation, indicating a period of innate dormancy. This innate dormancy could be eliminated by chilling plants for 8 days at 4 C. Root buds from plants showing late summer regrowth were no longer innately dormant. IAA (indole-3-acetic acid) and NAA (1-napthaleneacetic acid) completely inhibited the growth of excised leafy spurge root buds at concentrations of 10−3 and 10−5 M, respectively. A significant increase in root bud elongation was produced by 1 mM TIBA (2,3,5-triiodobenzoic acid) applied to stem and root tissue. These data provide further evidence for the involvement of IAA in correlative control of root bud growth in leafy spurge.

The potential of mourning doves (Zenaida macroura L.) as dispersers of leafy spurge (Euphorbia esula L. # EPHES) seeds was investigated by examing digestive tract contents and feces. Very few intact seeds passed through the digestive systems of wild or captive adult mourning doves. An average of less than one intact leafy spurge seed/g was recovered from fecal material found in dove nests. These results suggest that adult mourning doves are primarily consumers of leafy spurge seeds and rarely act as dispersal agents. It appears that dispersal is only possible when seeds passing through the digestive tracts of nestlings are deposited in the nest and the nest later falls.

Reductions in yields of processing tomatoes (Lycopersicon esculentum Mill. ‘H2653’ and ‘Earlirouge′) caused by interference from eastern black nightshade (Solanum ptycanthum Dun. # SOLPT) and hairy nighthsade (S. sarrachoides Sendt. # SOLSA) were estimated for transplanted and seeded tomatoes at two locations in southern Ontario. Tomato yield losses were significantly greater in seeded than in transplanted tomatoes. Stomatal conductance and transpiration rates of seeded tomatoes decreased more rapidly with increased nightshade density than did those of transplanted tomatoes. Percent yield losses also differed between sites. Seeded tomatoes grown at high density in twin rows (33 300 and 45 000 plants/ha) had higher yields and lower percent yield losses than did tomatoes grown at low density in single rows (12 500 to 22 500 plants/ha). Nightshade dry weight and seed production decreased per plant but increased per unit area with increasing nightshade density. Nightshade dry weights and seed production did not vary with site or method of tomato establishment. A hyperbolic model provided an excellent fit to data on both tomato yield losses and nightshade seed production as a function of nightshade density.

Plants of dormant and nondormant wild oat (Avena fatua L. # AVEFA) lines were grown under temperatures of 15, 20, and 25 C. A number of physiological and morphological characters in the plants and seed of both lines were influenced by temperature. Duration of dormancy in the progeny seed increased in both lines that had experienced low temperatures (15 C) during development, and decreased in seed of both lines that had experienced high temperatures (25 C) during development. High, compared to low, temperatures of development decreased plant height, vegetative and seed development time, seed numbers per plant, seed dry weight, and seed water content.

Plants produced by yellow nutsedge (Cyperus esculentus L. # CYPES) tubers planted in a field at the U.S. Cotton Research Station, Shafter, CA, at monthly intervals were harvested 2, 4, or 8 weeks after planting or at the end of a full season that varied from 12 to 37 weeks. In the 2 yr of the study, 1982 and 1983, tubers were slow to sprout in March and April, taking up to 8 weeks. From June through October about 60% of the plants emerged within 2 weeks of the planting date. Parent plants produced daughter plants by the 4-week harvest except for March, April, and October 1982, and March 1983 planting periods. All planting periods had daughter plants by the 8-week harvest. In 1982, plants of the June full-season planting had significantly more daughter plants than plants of other full-season treatments even though the June full season was 12 weeks shorter than the March full season. In 1983, the number of daughter plants produced by plants for the full-season harvest was equal for all monthly plantings regardless of the length of the full season. In 1982, for the May through September plantings, more tubers were produced by plants at the 8-week harvest than the number of tubers originally planted. In 1983, only plants of the June and August plantings produced more tubers by the 8-week harvest than had been planted. In both years, plants that grew for a full season produced more tubers than the number planted, up to 200-fold more.

Weed seeds were germinated in incubators at constant temperatures ranging from 4 to 32 C increments. Percent germination per day was regressed against temperature with the x-intercept representing the low threshold temperature for development. Low threshold temperatures for development (low TTD's) calculated for wild proso millet (Panicum miliaceum L. # PANMI), barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG], common lambsquarters (Chenopodium album L. # CHEAL), and redroot pigweed (Amaranthus retroflexus L. # AMARE) were 6.9, 9.7, 6.0, and 10.0 C, respectively.

Mechanical wounding broke dormancy and promoted germination of primary dormant pure-line wild oat (Avena fatua L. # AVEFA) caryopses that were in the first physiological stage of dormancy. Caryopses incubated in petri dishes responded to wounding by germinating more rapidly than wounded caryopses incubated in soil. There was no difference in germination between wounded and lanolin-covered wounded caryopses when incubated in soil. The less dormant AN265 caryopses responded to the wounding treatment more rapidly than the more dormant caryopses of M73 in both petri dish and soil incubation systems. Chlorocholine chloride (CCC), an inhibitor of gibberellic acid (GA) biosynthesis, reduced the germination rate of wounded AN265 and M73 caryopses above and at 1 mM, respectively. Application of 25 mM CCC to wounded dormant AN265 caryopses decreased the level of hexose in the embryo to 47% of the control level. There was no significant effect of CCC on the endosperm hexose, embryo and endosperm imbibed fresh weight, and sucrose and starch content. The results suggest GA or GA biosynthesis is the limiting factor to germination.

The interference and seed production potential of pitted morningglory (Ipomoea lacunosa L. # IPOLA) with conventional-row (1 m) and narrow-row (20 cm) ‘Hill’ soybeans [Glycine max (L.) Merr.] was studied for 2 yr. Pitted morningglory densities were 3.3, 10, 20, and 40 plants/m2 while soybean densities were 23 and 50 plants/m2 in conventional and narrow rows, respectively. Pitted morningglory interfered with soybean growth earlier in conventional-row soybeans than in narrow-row soybeans due to its rapid increase in leaf area index (LAI) and biomass from 4 to 8 weeks after emergence. Soybeans were competitive with pitted morningglory until the soybean reproductive stage began at 7 weeks after emergence. Pitted morningglory reduced soybean yields 17% more in a dry year than in a wet year. Yield of narrow-row soybeans was equal or greater than yield of conventional-row soybeans at all pitted morningglory densities. Conventional-row soybean yields were reduced an average of 42 and 81% at pitted morningglory densities of 3.3 and 40/m2, respectively, but yield of narrow-row soybeans was reduced only 6 and 62% at equivalent densities. Pitted morningglory grown without soybean interference produced an average of 52.3 million seeds/ha. Total seed production of pitted morningglory growing in soybeans increased as pitted morningglory density increased and was greater in conventional rows than in narrow rows. Narrow rows reduced total seed production an average of 90 and 68% at pitted morningglory densities of 3.3 and 40/m2, respectively.

Spotted knapweed (Centaurea maculosa Lam. # CENMA) communities were sampled to determine the relationship between age and the number of root rings, and the population age structure. Spotted knapweed taproots add one ring of secondary xylem annually. In 1984, populations were expanding with high densities of individuals in the early age classes, followed by a steady decline in the older classes. In 1985, the majority of the individuals in knapweed populations were in the older age classes. This change in the population age structure was attributed to high mortality among the young age classes due to a drought in 1985. The maximum age class at the sites ranged from 5 to 9 yr. The percentage of plants with floral stalks increased with age to a peak of 75% in the fifth year in 1984 and in the seventh year in 1985.

Palmer amaranth (Amaranthus palmeri S. Wats. # AMAPA) planted in a field at monthly intervals from March through October at Shafter, CA, began to emerge in March when soil temperatures at a depth of 5 cm reached 18 C. With the exception of March and April plantings, at least 50% of the seed of later plantings produced seedlings within 2 weeks after planting. Although growth of plants was initially slower for early plantings, plantings from March to July reached 2 m or greater in height by fall. Due to longer growing times, plantings from March to June eventually produced more dry matter and a greater number of inflorescences than later plantings. Plants began flowering 5 to 9 weeks after planting in March through June and 3 to 4 weeks after planting in July through October. Some viable seed was produced as early as 2 to 3 weeks after flowering began. Total seed production in the fall ranged from 200 000 to 600 000 seed/plant for the March through June plantings, and 115 to 80 000 seed/plant for the July through September plantings. Killing frosts in November prevented Palmer amaranth planted in October from producing seed.

Selected biological and physiological parameters of hydrilla [Hydrilla verticillata (L.f.) Royle # HYLLI] biotypes were compared in growth chambers, glasshouse, or outside aquaria. Salinity tolerance was similar for both biotypes with an injury threshold of approximately 13 parts per thousand (ppt). The registered aquatic herbicides diquat (6,7-dihydrodipyrido [1,2-α:2′,1′-c] pyrazinediium ion) and dipotassium and monoamine salts of endothall (7-oxabicyclo [2.2.1] heptane-2,3-dicarboxylic acid)4 produced similar injury to both biotypes. Biomass of the monoecious plants, growing in controlled environments, declined under short days. Tuber production in monoecious plants was greatest under short days and was significantly higher than in dioecious plants under the same conditions. Growth response to temperature was similar among all plants and was retarded at 15 C. Tuber germination occurred at lower temperatures in the monoecious plants, which was indicative of a lower temperature tolerance. Vegetative propagules were the only perennating structures observed in the monoecious biotype, and regrowth was entirely from tubers and turions. The annual growth habit, in conjunction with rapid and abundant propagule production, adapts the monoecious biotype to northern areas with short growing seasons.

Barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] spikelets were collected from greenhouse-grown plants at various developmental stages. Caryopses contained in a single spikelet were dormant at maturity, but dormancy was overcome when the spikelets were dry afterripened at 23 C or were treated with high temperatures, acid scarification, or punctured with a scalpel. The season at which anthesis occurred affected the length of time for afterripening. Enhanced germination due to puncturing and scarification was not related to removal of a restriction to water entry. The effectiveness of puncturing in overcoming dormancy depended on moisture content of the spikelets at the time of puncturing. Above 18% moisture content germination percentage was low regardless of the dormancy-releasing treatment.

In field and greenhouse experiments, sicklepod (Cassia obtusifolia L. # CASOB) control with postemergence application of imazaquin {ammonium salt of 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} was similar with spray volumes of 50, 185, and 360 L/ha. Application of DPX-F6025 {ethyl ester of 2-[[[[(4-chloro-6-methoxypyrimidin-2-yl) amino] carbonyl] amino] sulfonyl] benzoate} in 50 L/ha resulted in greater control than application in 185 or 360 L/ha in the greenhouse, but no effect of spray volume was noted in field studies. In the greenhouse, control was 25 and 63% less with imazaquin applied to three- and five-leaf plants, respectively, compared to one-leaf plants; control was 40 and 62% less with DPX-F6025 applied to three- and five-leaf plants, respectively, compared to one-leaf plants. In the field, initial control was greater with imazaquin and DPX-F6025 applied to one-leaf plants than to three- or five-leaf plants. Following cultivation, control was similar regardless of plant size at time of application. In the field, postemergence applications of imazaquin and DPX-F6025 were equally phytotoxic following preplant-incorporated application of vernolate (S-propyl dipropylcarbamothioate) or preemergence application of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide]. A synergistic interaction was observed in the greenhouse with imazaquin applied postemergence to sicklepod grown in vernolate- or alachlor-treated soil and with DPX-F6025 applied to sicklepod grown in alachlor-treated soil. Antagonism was observed with DPX-F6025 applied postemergence to sicklepod grown in vernolate-treated soil.

The ethyl ester of fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy] phenoxy] propanoic acid} was applied to rice (Oryza sativa L.) that was heavily infested with barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] during a 3-yr study. Applications were made to two- to three-leaf, three- to four-leaf, five- to six-leaf, or tillering barnyardgrass. Barnyardgrass control at 9 weeks after final treatment was greater than 90% for all growth stages except the 0.1 kg ai/ha rate applied to three- to four-leaf barnyardgrass in 1983. In 1984, the sequential application of fenoxaprop made at the three- to four-leaf stage controlled more than 95% when rated at 9 weeks. Rates of 0.17 and 0.2 kg ai/ha and the sequential treatment of 0.1 kg ai/ha followed by 0.1 kg ai/ha 7 to 10 days later controlled greater than 90% at 9 weeks when applied to three- to four- and five- to six-leaf barnyardgrass in 1985. In general, barnyardgrass was controlled by fenoxaprop rates greater than 0.1 kg ai/ha when applied to any growth stage evaluated up through the five- to six-leaf stage. However, acceptable control of tillering barnyardgrass was achieved in only 1 of 3 years. Yields were increased due to barnyardgrass control all years with all treatments except those applied at tillering. However, control was sufficient to increase yields over that of the check for all tillering treatments except the 0.1 kg ai/ha rate in 1984 and 1985 and the 0.17 kg ai/ha treatment in 1985.

Fluorochloridone {3-chloro-4-(chloromethyl)-1-[3-(trifluoromethyl)phenyl]-2-pyrrolidinone} effectively controlled wild mustard (Sinapis arvensis L. # SINAR) in sunflowers (Helianthus annuus L. ‘Hybrid 894′). Preemergence (pre) treatments were more effective than preplant-incorporated (ppi) treatments at rates of 0.3 to 1.1 kg ai/ha. Applied as a foliar spray, fluorochloridone at rates of 0.12 to 0.25 kg ai/ha controlled 96% or more of wild mustard but some crop injury occurred. When fluorochloridone was mixed with trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] or EPTC (S-ethyl dipropyl carbamothioate) and applied ppi, several annual grasses as well as wild mustard were controlled.

Foliar absorption of imazaquin {ammonium salt of 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} following postemergence application was not necessary for control of sicklepod (Cassia obtusifolia L. # CASOB). Application of imazaquin to the soil resulted in control similar to application to the soil plus foliage. A 0.6-cm simulated rainfall 0.05 h after postemergence application of 140, 280, or 560 g ae/ha of imazaquin did not reduce sicklepod control. Foliar absorption was necessary for control with postemergence application of DPX-F6025 {ethyl ester of 2-[[[[(4-chloro-6-methoxypyrimidin-2-yl)amino]-carbonyl] amino] sulfonyl] benzoate}. Application of DPX-F6025 to the foliage resulted in control similar to application to the soil plus foliage. Sicklepod control resulting from postemergence application of 18 g ae/ha of DPX-F6025 was reduced when 0.6 cm of simulated rainfall was received 1 h after application but not when received 4 h after application. With application of 9 g/ha of DPX-F6025, simulated rainfall 24 h after application reduced control. Sicklepod control resulting from postemergence application of sublethal rates of imazaquin and DPX-F6025 was greater when plants were exposed to 3 or more days of 24/18 C day/night temperature than when grown at a continuous 32/24 C temperature. Exposure to low temperature for 3 days immediately before imazaquin application resulted in greater enhancement of control than did exposure for 3 days immediately after application. The reverse was found with DPX-F6025. Control obtained with both imazaquin and DPX-F6025 increased as the number of days of exposure to low temperature increased from 3 to 6. Enhancement of control with low temperature diminished as the herbicide application rate increased.

Foliar applications of 14C-bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] with PPA (polymeric polyhydroxy acid) at 1 or 2% (v/v) or nonoxynol (9.5 POE) [α-(p-nonylpheny1)-ω-hydroxypoly(oxyethylene)] at 1% (v/v) or mixtures of PPA and nonoxynol did not increase absorption or translocation of 14C-bentazon in soybeans [Glycine max (L.) Merr. ‘Lee 74′] or common cocklebur (Xanthium strumarium L. # XANST). PPA alone at 1 to 2% (v/v) did not significantly affect absorption or translocation of 14C-bentazon in smooth pigweed (Amaranthus hybridus L. # AMACH), but PPA with nonoxynol significantly increased translocation out of the treated leaf. Both PPA and nonoxynol decreased absorption and movement of 14C-MSMA [monosodium salt of methylarsonic acid] out of the treated leaf of johnsongrass [Sorghum halepense (L.) Pers. # SORHA]. In greenhouse research, PPA at 0.25 and 0.5% (v/v) did not increase the level of control of common cocklebur obtained following postemergence applications of bentazon at 0.24 and 0.48 kg ai/ha. Similarly, PPA at 0.25 and 0.50% (v/v) did not increase the toxicity of MSMA at 0.3 and 0.6 kg ai/ha to either johnsongrass or common cocklebur.