The effect of wheat straw incorporation on imazaquin concentration and biological activity in soil solution was determined as a function of herbicide rate and time of incubation. Etowah silt loam, amended with wheat straw (2 g/kg) or unamended, received imazaquin (0, 31, 62, or 124 μg ai/kg oven-dry soil). Soils incubated at 25 C were subsampled 0, 12, 24, 48, and 96 h after treatment and soil solutions were analyzed for imazaquin, pH, and electrical conductivity. Wheat straw amendment, imazaquin rate, and time of incubation influenced the concentration of imazaquin in the soil solution. Imazaquin concentration in soil solution exhibited gradual linear declines with time. Relative length of sunflower radicles declined with increased imazaquin rate. Regression of relative radicle length on activity of imazaquin anion in soil solution indicated differential response in the presence of wheat straw-amended versus unamended soil.

Chlorophyll content of wheat (Triticum aestivum L. ‘Mericopa’) and corn (Zea mays L. ‘Merit’) treated with the herbicide fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)-phenyl]-4(1H)-pyridinone} and grown under high light intensity (10.8 klux), was markedly reduced. Corn and wheat germinated from seeds treated with 10 uM fluridone and grown for 6 days were almost completely bleached. Under low light intensity (108 lux) the influence of fluridone on chlorophyll production was greatly reduced. Under very low light intensity (21.5 lux) this influence was almost completely lost. The effect of light on the activity of fluridone suggests that the inhibition of carotenoid production may represent the mode of action of this herbicide. This study shows that the carotenoid content of wheat or corn drops dramatically when these plants are treated with fluridone.

Concentrations of clomazone in nutrient solution causing 50% reduction in shoot fresh weights were 325 and 2 μM for soybean and velvetleaf, respectively. Root uptake of 14C–clomazone from nutrient solution and translocation to shoots were similar for the two species. Soybean and velvetleaf contained similar amounts of 14C per plant; however, because velvetleaf had lower tissue weights, concentration of 14C was higher in velvetleaf. Clomazone did not accumulate in roots but was rapidly translocated to shoots of both species. No more than 30% of absorbed clomazone remained in roots at any time in the experiment. Soybean and velvetleaf leaves contained 4.2 and 1.7 nmol clomazone g−1 fresh weight, respectively, and 3.7 and 6.1 nmol clomazone metabolites g−1 fresh weight, respectively. Thus, velvetleaf metabolized clomazone more rapidly than soybean did. Treatment of clomazone metabolites with β-glucosidase demonstrated that metabolism occurred by oxidative cleavage and conjugation of the benzyl moiety in both plant species. One aglycone cochromatographed with 2–chlorobenzylalcohol. The results suggest that reduced absorption or translocation or increased detoxication of clomazone by soybean seedlings is probably not responsible for their tolerance to this herbicide.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] (0, 0.56, 1.12, 1.68 kg/ha) applied the soybean (Glycine max (L.) Merr.) cultivars ‘Bragg,’ ‘Hampton,’ ‘Bienville,’ ‘Coker 318,’ ‘Coker 102,’ and ‘Hardee’ induced significant changes in total fatty acid concentration of soybean oil. Minor changes in soybean oil quality were induced by metribuzin but percent protein was not influenced.

In the presence of relatively high but non-toxic levels of phosphate, the suppression of corn (Zea mays L.) or squash (Cucurbita maxima Duchesne) seedling growth in the dark by 3-amino-2,5-dichlorobenzoic acid (amiben) or 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) was enhanced. This effect was not due to increased uptake of either herbicide in the presence of the phosphate by roots of corn, squash, soybeans (Glycine max (L.) Merr.), or redroot pigweed (Amaranthus retroflexus L.). A proportional decrease in herbicide uptake with increasing herbicide concentration was most evident for amiben and atrazine uptake by the roots of soybean plants grown in the light.

Studies were conducted on and in the vicinity of the U. S. Cotton Research Station at Shafter, California, to evaluate the prevalence of the insect Bactra verutana Zeller (Olethreutidae) and its potential for injury to yellow nutsedge (Cyperus esculentus L.). Field surveys during August 1966, and August and October 1967 revealed many infested yellow nutsedge plants. Other field studies indicated that the insect may significantly suppress the growth of yellow nutsedge, providing that the insect infestation is early, sufficiently severe, and present on both parent and subsequently emerging vegetative plants. Greenhouse studies further revealed that severely infested plants may survive to produce numerous vegetative plants and tubers. While Bactra verutana Zeller damaged yellow nutsedge plants late in the season, the absence of early infestation limited its usefulness as a biological control agent.

Knowledge of how reduction in the rate of herbicide application or rotation of their mode of action influences weed growth will provide insight into how successful these practices will be in an integrated weed management program. Field experiments were conducted in 1996 and 1997 to quantify velvetleaf growth response to three postemergence herbicides, each with a different mode of action. A monoculture of velvetleaf was treated with halosulfuron, dicamba, and flumiclorac at 0, 0.10, 0.25, 0.50, 0.75, and 1.0 × the labeled rate for weed control in corn. Percent plant mortality increased with rate of application; the greatest mortality occurred in flumiclorac treatments in 1996 and in halosulfuron and flumiclorac treatments in 1997. Growth rate temporarily decreased as application rate increased. Maximum height decreased as rate of application increased, with the dicamba treatment resulting in the greatest (27%) reduction. Early-season leaf area index decreased with increasing rate of application, the greatest reduction occurring with halosulfuron (1997) and flumiclorac (1996 and 1997) treatments. The number of leaves produced per plant was temporarily reduced by all treatments, but treatment with dicamba later resulted in larger numbers of small leaves. The number of velvetleaf seed capsules produced per surviving plant was not reduced by any treatment, but the number of capsules per square meter was reduced by the 0.5 × rate of flumiclorac (1996) and the 0.5- and 1.0 × rates of halosulfuron (1997). Research is needed to evaluate whether the temporary suspension of velvetleaf growth after herbicide treatment is sufficient to prohibit crop yield reduction and velvetleaf capsule production.

Afterripening requirements and the possible occurrence of endogenously controlled germination rhythms in downy brome (Bromus tectorum L.) were investigated in the laboratory. Afterripening temperatures from 0 to 50 C, maintained for periods of 4 to 28 days, had little effect on the percentage and rate of downy brome germination when seeds were incubated at 15 and 20 C. However, at 30 C germination temperature, the percentage and rate of germination were significantly increased by short periods (4 to 7 days) of afterripening at 50 C. Similar results occurred at 20 to 40 C afterripening temperatures after 14 to 28 days exposure. In general, high temperature afterripening conditions (40 to 50 C) initially increased downy brome germination at 30 C incubation temperature, but prolonged exposure tended to decrease germination. No endogenously controlled germination rhythms were observed in downy brome caryopses.

A 3-yr field study was conducted to determine the effect of a biological control agent, Sclerotinia minor Jagger, and a common herbicide, Killex, on the population dynamics of dandelion and other broadleaf species and on the dandelion seed bank. Treatments were applied as one spring, one early autumn, or a spring plus an early autumn treatment per year. The response of the dandelion population to a spring herbicide treatment was similar to two applications per year (spring and early autumn). Significantly less dandelion control occurred after the first early autumn application of the herbicide. Two weeks after application, spring or early autumn treatments with S. minor were equally effective in suppressing dandelions. In the second year of the two applications per year of S. minor treatment, weed control was equivalent to the herbicide. By the third year of the one spring application of S. minor, weed control was equivalent to the herbicide. Generally over the study period, the early autumn application of S. minor was less effective than the spring or the spring and early autumn applications. The S. minor treatments significantly reduced the dandelion seed bank, and this effect was not significantly different from the Killex herbicide treatment. The rate, frequency, and seasonal timing of application had no effect on the dandelion seed-bank size, but terminating the application would gradually replenish the seed bank. Populations of white clover, broadleaf plantain, birdsfoot trefoil, and common ragweed were similarly suppressed by either the S. minor or the herbicide treatments. Yellow woodsorrel significantly increased after 1 yr of herbicide treatment compared with the S. minor and untreated control treatments, indicating a possible weed species shift. Turf quality was improved because of the herbicide and S. minor treatments, but grass injury and smooth crabgrass invasion were recorded in 17% of herbicide-treated plots.

The expression of a candidate auxin-responsive gene was evaluated for use in a diagnostic assay for plant growth regulator (PGR) herbicide injury in soybean leaves. Expression of GH3, a primary auxin-responsive gene, was evaluated in response to dicamba and clopyralid at the RNA and protein levels, and proteomic analysis evaluated global expression of proteins in response to dicamba. Expression of GH3 was also analyzed in response to heat, drought, salt stress, and infection by soybean mosaic virus (SMV) and bean pod mottle virus (BPMV) to determine the specificity of GH3 expression as a diagnostic marker for PGR herbicide injury. At the RNA level, GH3 was strongly induced by dicamba and clopyralid within 8 h after application. Expression peaked 1 to 3 d after treatment (DAT) in response to 10% and 1% of a labeled dose of dicamba and clopyralid, with higher expression levels detected at higher herbicide rates. At the protein level, GH3 expression was also strongly induced at 1, 2, and 3 DAT by 10% vs. 1% of a labeled dose of dicamba and clopyralid. Heat, drought, and salt stress and infection with SMV or BPMV had no effect on GH3 expression at either the RNA or protein level. Proteomic analysis identified three proteins that were up-regulated in response to dicamba. Two were induced for less than 7 DAT, and a third was identified as a stress-response enzyme (superoxide dismutase) that is likely not specific to PGR herbicide injury. Expression of GH3 was highly induced by PGR herbicides at the RNA and protein level and was not affected by environmental stresses or viral infection, indicating that GH3 expression has excellent potential for use in a diagnostic assay for PGR herbicide injury.

Twenty years after aerial application of 2.24 kg ae/ha of the butoxy ethanol ester of 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] to release grass stage longleaf pine (Pinus palustris Mill.) seedlings, stocking was the same for each of three treated and control 4-ha plots. Treated plots, however, had significantly greater tree diameter (10%), taller trees (17%), and more merchantable tree volume/ha (40%). Merchantable tree volume differences 20 yr after treatment represent an 8 yr growth advantage for treated plots.

Field experiments were established in 1978 and repeated in 1979 to monitor quackgrass [Agropyron repens (L.) Beauv. ♯3 AGRRE] rhizome growth through a growing season. Quackgrass shoots grew most vigorously when temperatures were moderate. They elongated and differentiated an inflorescence in June. Rhizome apical tips remained belowground in late spring, early summer, and early fall. Quackgrass rhizome tips grew vertically and emerged from the soil in midsummer and late fall. Experiments conducted in growth chambers revealed that photoperiod, temperature, and nitrogen level affected quackgrass shoot and rhizome growth. Shoots grew vigorously at 21C and elongated to differentiate an inflorescence when exposed to a photoperiod of 14 h or longer. Rhizome apical tips remained belowground when plants were grown at 21 C and received 16 or 12 h of light, but the tips curved upward and emerged from the soil when quackgrass was grown at 32 or 10 C, or when the plants received 14 or less than 10 h of light. The temperature and photoperiod responses coordinated to partition the growing season into primary rhizome and rhizome-tiller growth periods.

Optimum germination of fringed sagebrush (Artemisia frigida Willd.) occurred at alternating temperatures of 10 to 20 C. Seeds were able to germinate (15%) in NaCl concentrations of 5000 ppmw. Light was important in seed germination; however, its absence could be overcome by adding 30 ppmw GA3 (gibberellic acid) to the germination medium. Optimum pH for germination was between 5.8 and 7.0. Depth of planting influenced seedling emergence; the greatest emergence occurred when seeds were planted on the soil surface; emergence was lower when seeds were buried at any depth in the soil. Osmotic potentials of −13 bars and greater reduced germination, but 6% of the seeds germinated at −15 bars. Fringed sagebrush seedlings tolerated average plant water potentials of −10 to −19 bars and died when water potentials were decreased to −22 bars. Mature fringed sagebrush plants were capable of producing from 16500 to 190000 seeds/plant.

Canada thistle is resilient to many control tactics, especially in undisturbed sites. Such sites are suitable for slow acting biological control agents, such as the bacterium Pseudomonas syringae pv. tagetis (PST), because complete control is usually not required in the short term. A new method of introducing or intensifying PST infection of Canada thistle was investigated. Sap of naturally infected Canada thistle was extracted and applied in water plus Silwet L-77 organosilicone surfactant with a backpack sprayer to healthy Canada thistle plants in the field. Application variables of time of the season, spray volume, concentration, and frequency were studied. When practical field rates were applied, infected sap concentration and spray volume did not affect the level of disease observed. This suggests that PST applications could be practical at the field scale because a single application caused apical chlorosis. However, multiple applications proved beneficial because four consecutive weekly applications caused greater disease incidence (50%) than one or two applications (28% and 30%, respectively). Disease symptomology was greatest when PST was applied in mid-July rather than mid-June or mid-August. However, the levels of disease expression were not adequate to effectively suppress Canada thistle. Increased toxin production, either by finding ways to support higher PST populations or by selecting strains that produce more toxin per bacterial cell, would improve this system.

The effects of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} on the metabolic activity of excised root tips of corn (Zea mays, L. ‘Goldencrossbantam′) were studied under laboratory conditions. Uptake and incorporation of 14C-labeled thymidine, uridine, leucine, glucose, and acetic acid into cell constituents, as well as respiration, increased continuously with time progressions during the incubation period. Sethoxydim did not affect either the uptake of any 14C-precursor into or respiration of the root tip tissue. Although RNA and protein syntheses were not affected by the herbicide, DNA and cell wall syntheses were inhibited 120 min after treatment with sethoxydim. Incorporation of 14C-acetic acid into lipid fraction was inhibited by sethoxydim in a time- and concentration-dependent fashion. This inhibition was observed at a shorter time after sethoxydim treatment than that of any other 14C-precursor. The effect was not observed in the nonproliferative regions of corn roots, whereas cerulenin (a fatty acid synthase inhibitor) inhibited the incorporation of 14C-acetic acid both in proliferative and nonproliferative regions. It is suggested that the inhibition of lipid synthesis by sethoxydim does not play a major role in the mode of action of this herbicide. The effects of sethoxydim, including those on lipid metabolism, are closely associated with proliferative conditions of susceptible graminaceous plants.

Major differences in above- ground biomass and tuber production of yellow nutsedge (Cyperus esculentus L. # CYPES) were not observed when corn (Zea mays L. “CO-OP S265”) was seeded on different dates (1st, 2nd, 3rd and 4th week of May; and 1st week of June). The final seedbed was prepared just prior to each seeding date and this cultivation stimulated dormant tubers to sprout. As a result, a large population of yellow nutsedge emerged with the corn at all seeding dates. Because fertilizer was banded near the corn row, yellow nutsedge biomass, tuber dry weight and number of tubers were higher within corn rows than between rows. Tuber size was affected by seeding date and shifted toward smaller tubers within corn rows and larger tubers between the rows as the corn was sown late. The optimum seeding date of corn was in the 3rd week of May when the highest corn yield was obtained and yellow nutsedge growth was generally reduced.

Tank-mix combinations of PRE and POST herbicides were applied to control emerged large crabgrass and goosegrass in common bermudagrass turf. Large crabgrass control was better when MSMA at 2.2 kg ai ha-1 was tank mixed with either pendimethalin at 1.7 kg ai ha-1 (≤ 85%) or dithiopyr at 0.3 kg ai ha-1 (≤ 94%), when compared with MSMA at 2.2 kg ai ha-1 (≤ 50%) alone. When MSMA plus metribuzin at 2.2 + 0.14 kg ai ha-1 was tank mixed with pendimethalin in 1992, large crabgrass control was better (≥ 96%) than when MSMA plus metribuzin was applied alone (≤ 73%). Quinclorac applied alone at 0.8 kg ai ha-1 controlled ≥ 94% large crabgrass, but control with diclofop was 32%. There was no increase in control when either quinclorac or diclofop was tank mixed with any PRE herbicide. Methyl ester of diclofop applied alone at 1.1 kg ai ha-1 provided 97% control of goosegrass at one location, but control was ≤ 62% at two other locations. Goosegrass control was better when diclofop at 1.1 kg ha-1 was tank mixed with dithiopyr at 0.6 kg ha-1 (≥ 77%) than when either diclofop (≤ 62%) or dithiopyr (≤ 50%) was applied alone. Goosegrass control was consistently better across years from combinations of dithiopyr plus diclofop at 0.6 + 1.1 kg ha-1 (82%) than from combinations of MSMA plus metribuzin with dithiopyr (34%) or pendimethalin (53%). Common bermudagrass injury at Griffin-Spalding Golf Course in 1991 was higher at 1 wk after combination treatments of MSMA plus metribuzin with dithiopyr (46 to 54%) or pendimethalin (50%) than with MSMA plus metribuzin applied alone (26%). Injury from the combinations was higher from single MSMA plus metribuzin treatment for 4 wk. Similar results occurred at the Georgia Station in 1992 from combinations of dithiopyr with MSMA plus metribuzin.

The cucumber (Cucumis sativus L.) accession PI 390244 tolerated up to 0.56 kg/ha atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] whereas most cultivars and accessions were killed by 0.14 kg/ha. The possible mechanisms for tolerance were investigated by comparing growth rates, effects on photosystem II in isolated chloroplasts, and differences in uptake and translocation of 14C-atrazine between tolerant PI 390244 and the susceptible cultivar Marketmore 70. PI 390244 had significantly more leaf area than Marketmore 70, but less root biomass. Isolated chloroplast preparations from both cultivars were equally susceptible to the herbicide. Although PI 390244 absorbed more total 14C-atrazine, it translocated less radioactivity from the roots. While the concentration of 14C found in the PI 390244 roots was 10 to 30% greater than in Marketmore 70, the amount of radioactivity in the cotyledons, and first and second true leaves of Marketmore 70 were 53, 34, and 55% higher, respectively, after 48 h.

Because environmental factors facilitating the breaking of dormancy of seed of catclaw mimosa (Mimosa pigra L. ♯ MIMPI) under field conditions were unknown, the effect of constant temperatures (2 to 44 C) on germination of scarified and unscarified seeds, and the effect of diurnally fluctuating temperatures on unscarified seeds were examined. Temperatures fluctuated diurnally by 10 and 20 C in these latter experiments. Germination was less than 10% at all constant temperatures except 44 C, which had 40% germination. Scarification increased germination to 100% at constant temperatures greater than 12 C. Germination of unscarified seed was significantly lower (0 to 23%) when day/night temperature ranges fluctuated by 10 C than when they fluctuated by 20 C. Optimum temperature for germination was 40/20 C, where 93% germination occurred within 4 days.