Modification of the cropping environment to make weed seed more susceptible to fatal germination or decay processes is based, in part, on the premise that seed longevity is affected by the crop-influenced environment in which seed is produced, hereafter, called the maternal crop environment. The objective of this investigation was to determine the influence of maternal crop environment on wild-proso millet seed production, germinability, and seed coat tone (i.e., lightness), a trait previously associated with seed longevity in wild-proso millet. Maternal corn environments were established by growing wild-proso millet plants in four morphologically different sweet corn hybrids in four replicates over 2 yr. Wild-proso millet seed was collected at sweet corn harvest, enumerated, characterized for seed coat tone, and tested for germination. Principal component factor analysis reduced six sweet corn traits measured between silking and harvest into a single maternal corn environment factor that accounted for 84% of the variation among crop canopies. Functional relationships between maternal corn environment factor scores and wild-proso millet seed characteristics were clarified by fitting linear models. For each unit decrease in maternal environment factor score, wild-proso millet seed production increased 1,535 seed m−2, germination increased 2.2%, and seed coat tone was 1.8% lighter. These results show the size and germinability of wild-proso millet seed was highest in less-competitive maternal corn environments characterized by a short time to crop maturity and a small crop-canopy size.

The amount of lipid present on leaves of Canada thistle (Cirsium arvense (L.) Scop.) varied due to ecotype, site where grown, and date of sampling. Thistles from a site with the greatest wind movement and greatest evaporation produced the most lipid per unit area of leaf. The relative lipid yield of ecotypes was similar at different locations. Deposition of lipid on the leaves of Canada thistle increased from the early bud stage to the first bloom and late bloom stages of growth. The amount of lipid on the leaves and previous data on the response of these ecotypes to (2,4-dichlorophenoxy) acetic acid (2,4-D) were highly correlated. Three ecotypes with the most lipid were most resistant and four ecotypes with the least lipid were most susceptible to 2,4-D spray. Two ecotypes were inconsistent in that comparison.

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.

Field experiments were conducted during 1981 and 1982 in Ontario, Canada, on the effects of quackgrass [Agropyron repens (L.) Beauv. # AGRRE] interference in soybean [Glycine max (L.) Merr.] and the usefulness of infrared thermometry in predicting critical periods of weed interference. Soybean seed yield, dry weight, number of leaves, height, and number of pods were substantially reduced due to quackgrass interference. High levels of P and K fertility did not overcome the quackgrass interference. Part of the competitive effects of quackgrass was alleviated by irrigation. Infrared thermometry successfully detected the first occurrence of quackgrass-induced stress during the early soybean flowering stage, when the quackgrass was in the four-leaf gtowth stage. This coincided with the onset of the first significant soybean yield loss. No additional soybean yield loss occurred after quackgrass reached the five-leaf growth stage. There was an inverse relation between accumulated stress degree days and soybean yield reductions due to quackgrass interference. The use of the stress degree day concept may be a valuable tool in predicting soybean yield losses due to quackgrass interference.

Excised roots of corn (Zea mays L. ‘B73 × Mo 17′) and oat (Avena sativa L. ‘Goodfield’) and potato (Solanum tuberosum L. ‘Kennebec’) tuber slices absorbed 14C-atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] in a similar manner during short (1 to 30 min) absorption periods. Within 30 min, atrazine concentrations in tissues and ambient solution were equal. After 24 h of absorption, corn roots contained the most 14C, followed in order by velvetleaf (Abutilon theophrasti Medic.) roots, oat roots, and potato tuber slices. Corn and velvetleaf accumulated 14C to concentrations above the ambient solution. Efflux of 14C was slower for corn than oat, potato, and velvetleaf. Metabolism of atrazine to hydroxyatrazine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine] accounted for accumulation and slow efflux of 14C in corn. These experiments show that initial, rapid absorption of atrazine is comparable, but long-term accumulation differs among these tissues.

Studies on the development of leafy spurge (Euphorbia esula L.) were conducted in the field and growth room. Sixteen months after planting in field plots, leafy spurge plants arising from underground bud-producing root segments, transplanted seedlings, or seeds averaged 96, 83, and 136 shoots per plant, respectively, when grown free of interference from other vegetation. A number of plants arising from each source flowered the first year, and all plants flowered and produced seed the second year after planting. When grown in a perennial grass sod consisting of crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult.] and smooth brome (Bromus inermis Leyss.), no plant flowered or produced additional shoots. Soil moisture was less where a dense sod was present. In the growth room, total dry matter of tops and roots was greatest at a soil temperature of 18.3 C or higher, and plant height was greatest at 33.3 C. An early emerging crop might suppress leafy spurge by utilizing the available soil moisture early in the growing season.

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.