Three herbaceous regimes were established, using herbicides, to examine the effects of interference on growth and biomass partitioning in loblolly pine (Pinus taeda L.). Trees were sampled near Auburn and Tallassee, AL. Trees at the Auburn site grown with low weed interference (LWI) had 4, 10, 10, 8, and 4 times greater total aboveground biomass than did trees with high weed interference (HWI) for ages one through five, respectively. Medium weed interference (MWI, Auburn site only) resulted in three times greater biomass the first 4 yr and two times greater total biomass by the fifth year compared to trees grown with HWI. Trees growing with LWI were 5, 8, 10, and 6 times larger than those with HWI for ages one through four, respectively, at the Tallassee site. At all levels of interference, the percentage of total biomass in foliage decreased, and stem and branch components increased, with increasing tree size at both sites. Trees growing with HWI had a lower percentage of total biomass in foliage and a greater percentage of total biomass in stem than those growing with LWI when compared over a common size. Growth efficiency per tree, expressed as annual increase in stem biomass per unit leaf area (g m−2), was slightly greater for trees growing with LWI compared to HWI when leaf area index (LAI3, total surface) was less than 0.2. For LAI values greater than 0.2 the relationship was reversed. The latter contradicts the idea that growth efficiency can be used as a measure of vigor for young loblolly pine. Changes in carbon partitioning to the development of leaf area are suggested to be driving the accelerated growth responses associated with a reduction of weed interference.

A tandem mass spectrometric procedure was developed to detect sesbanimide A and its isomers in plant materials. Analysis of seed extracts from 10 Sesbania species using this procedure readily detected sesbanimides in Drummond rattlebush, rattlebush, and bagpod sesbania. The toxic sesbanimides were not detected in hemp sesbania or in other species with no known history of animal toxicity.

Chlorsulfuron and metsulfuron were effective on Texas whitebrush, killing 70 to 75% of the plants at 0.28 kg ai ha, marginally effective on Macartney rose, killing 15 to 43% of the plants at 1.12 kg ha, but ineffective on honey mesquite and huisache, killing no more than 10% of the plants at 1.12 kg ha. Sulfometuron was ineffective on all woody species at 1.12 kg ai ha. Clopyralid and picloram were effective, killing 70 to 92% of the huisache at 2.24 kg ae ha. Tebuthiuron killed 72% of the Texas whitebrush at 1.12 kg ai ha. Sulfometuron generally reduced herbaceous plant cover the year of application. Chlorsulfuron and metsulfuron often resulted in increased grass cover the year of application. Most herbicides reduced broadleaf weeds the year of application. Woolly croton often was the first prominent broadleaf species to return to areas treated with clopyralid and sulfometuron. Few differences occurred among herbicides in herbaceous weed cover the year following treatment.

In replacement experiments in the greenhouse, plant relative yield (PRY) of both eastern black nightshade and tomato increased as the proportion of nightshade plants increased in the pots, indicating that nightshade is less competitive than tomato. In field studies tomato yield was reduced by two-thirds if three nightshade plants m–1 of row were allowed to grow with tomato more than 6 weeks following tomato establishment The percent marketable fruit decreased linearly from 73% with no nightshade to 49% when nightshade were present for 12 weeks. When nightshade and tomato were transplanted together, tomato yield was 9000 kg ha–1 and 49% of the fruit was marketable, while tomato yields were 30 000 kg ha–1 and 70% of the fruit was marketable when nightshade was established 9 weeks after tomato planting.

A series of experiments was carried out on oat to test the efficacies of fluazifop and glyphosate against water-stressed plants, plants grown in low and high nitrogen (N), and plants treated with gibberellic acid (GA). In the laboratory, plants maintained at wilting point for 5 days before and 9 days after spraying with fluazifop (0.5 kg ae/ha) appeared healthy 32 days after herbicide application, while plants supplied with water throughout the experiment were completely chlorotic/necrotic and had main stem detachment from within the leaf sheaths. In the field, plants maintained unirrigated until 14 days after spraying with fluazifop (0.25 kg/ha) or glyphosate (0.18 kg ae/ha) showed greater tolerance of the herbicides than plants irrigated regularly. Under well-watered conditions in the laboratory and field, fluazifop (0.25 kg/ha) and glyphosate (0.18 kg/ha) were less toxic at low N than high N. Increased fluazifop activity at high N was associated with increased transport of herbicide to apical meristems. Addition of 200 μg GA into the leaf sheaths 2 days prior to spraying with fluazifop or glyphosate increased the efficacy of both herbicides at low N.

Field experiments were established to determine the dose and timing of DPX-A7881 applied postemergence for control of weeds in winter rapeseed. Wild mustard and shepherdspurse were effectively controlled by DPX-A7881. Control of these weeds by DPX-A7881 was dependent upon growth stage. The later the growth stage at time of herbicide application the poorer the control. Fall applications of DPX-A7881 provided greater control of wild mustard and shepherdspurse seedlings compared to spring applications. The 0.010 kg ai ha-1 dose was as effective in controlling susceptible weed species as 0.030 kg ai ha-1. Control of common lambsquarters and redroot pigweed by DPX-A7881 was poor. Regardless of timing or amount of herbicide applied, DPX-A7881 did not significantly reduce dry weights of either barnyardgrass or green foxtail. Doses of DPX-A7881 ranging from 0.010 to 0.030 kg ai ha-1 did not injure or adversely affect winter survival of rapeseed seedlings. Rapeseed yield and seed quality were not affected by DPX-A7881 applied postemergence.

The overall degradation of chlorimuron was very similar at −0.1 and −1.5 MPa and slightly less in air-dry soil. Degradation rates increased with increasing temperature. The primary 14C-labeled compounds observed in moist-soil extracts were desmethyl chlorimuron and saccharin, while the primary 14C-labeled compound observed in air-dry soil extracts was saccharin. Saccharin is formed quantitatively from ethyl 2-(aminosulfonyl)benzoate (phenylsulfonamide) during extraction and therefore represents phenylsulfonamide formed in the soil as a result of chemical hydrolysis of the sulfonylurea bridge. These degradation products suggest that chemical hydrolysis of the sulfonylurea bridge is the primary mode of degradation in air-dry soil, while microbial degradation and chemical hydrolysis both occur in moist soil. These laboratory results demonstrate that chlorimuron will degrade in air-dry soil at a temperature-dependent rate by chemical hydrolysis.

Greenhouse and field studies were conducted to determine the effect of the isooctyl ester of MCPA on the activity of the ethyl ester of fenoxaprop in four grass species. In the greenhouse, wheat tolerated fenoxaprop better than barley, oat, and wild oat. Among wild oat populations, SH 430 was the most tolerant to fenoxaprop followed by MON 73, CS 40, the natural population, and AN 51. MCPA reduced fenoxaprop activity in wheat and barley, protecting the crops from herbicide injury. However, MCPA did not reduce the activity of fenoxaprop in most wild oat lines. In field studies, wheat and barley treated with fenoxaprop at 150 g/ha plus MCPA at 300 g/ha were not appreciably different from weed-free controls while fenoxaprop applied alone at 150 g/ha damaged the crops. Fenoxaprop applied at 150 g/ha in combination with 300 g/ha MCPA resulted in at least 78% wild oat control.

Several herbicides were evaluated for their ability to control duncecap larkspur, a serious poisonous plant on mountain rangelands in the western U.S. Duncecap larkspur density was reduced from 33 to 93% by triclopyr applied at 2.2, 4.5, and 9.0 kg ae/ha. Picloram applied at 2.2 and 4.5 kg ae/ha reduced density from 33 to 99%. Metsulfuron applied at 86 and 138 g ai/ha reduced density from 50 to 98%. Glyphosate was the most effective herbicide, reducing density by 90 to 100% when applied at 2.2 kg ai/ha. Glyphosate reduced the cover of grasses and perennial forbs but increased cover of annual forbs. All rates of picloram and metsulfuron reduced forb cover. Grass cover increased in most plots where duncecap larkspur and forbs were reduced.

Weed emergence and viable weed seed numbers were determined in field plots during a 5-yr period where reseeding was prevented. Known numbers of seeds of seven weed species were added to the native seed population at the beginning of the study. Plots were nontilled or tilled to depths of 0, 5, 10, and 15 cm early in the spring of each year. Velvetleaf, spurred anoda, hemp sesbania, morningglory species, and pigweed species emergence was significantly greater from the nontilled plots during the first year after seeds were added to the native seed population. Tillage, regardless of depth, reduced weed emergence during the first year where seeds were added to the plots but had no effect on emergence from plots where no seeds were added. Tillage during the second through the fifth year did not affect emergence regardless of the addition of seeds. of the 5-yr emergence totals, 61 to 88% of all weeds in all plots emerged during the first year and 9 to 23% emerged during the second year. The 5-yr decline rate for emergence of all weeds was exponential. Viable seeds of prickly sida, spurges, and pigweeds in the nontilled plots declined from 590, 1531, and 4346 m−2, respectively, to zero by the third year. Tillage did not affect the decline. However, weed emergence in the field indicated that a few (1.0 to 5.6 m−2) seeds of those weeds were still viable after 3 yr. In nontilled plots, many recently added seeds were on or near the soil surface and germinated during the first year. Tillage moved many seeds to sites that were unfavorable for germination and emergence during the first year.

Research was conducted to evaluate the effects of primary tillage (moldboard plowing and chisel plowing), secondary tillage (row cultivation), and herbicides on weed species changes in the soil seed bank in three irrigated row cropping sequences over a 3-yr period. The cropping sequences consisted of continuous corn for 3 yr (CN), continuous pinto beans for 3 yr (PB), and sugarbeets for 2 yr followed by corn in the third year (SB). A comparison between moldboard and chisel plowing indicated that weed seed were more prevalent near the soil surface after chisel plowing. The density of certain annual weed seed over the 3-yr period increased more rapidly in the seed bank after chisel plowing compared to moldboard plowing. Species exhibiting the most pronounced increase included hairy nightshade and stinkgrass in the PB cropping sequence and redroot pigweed and common lambsquarters in the SB sequence. Conversely, kochia seed density in the SB sequence decreased more rapidly in chisel-plowed plots. Row cultivation generally reduced seed bank densities of most species compared to uncultivated plots. Herbicide use in each cropping sequence produced a shift in the weed seed bank in favor of species less susceptible to applied herbicides. In particular, seed of hairy nightshade became prevalent in the PB cropping sequence, and seed of kochia, redroot pigweed, and common lambsquarters became prevalent in the SB sequence.

Field studies were conducted to determine the effect of green foxtail density and location on the yield of potato under dryland conditions. Total and marketable tuber yields were reduced by green foxtail densities of less than 75 plants m-2. Marketable yields were affected more by increasing green foxtail density than were total yields. Increasing weed density reduced both the number and size (tuber weight) of marketable tubers but not the specific gravity or the sucrose content of the tubers at harvest. Green foxtail growing between crop rows was as competitive with potato as plants growing within the row. The effect of weed competition on total and marketable tuber yields was more pronounced in drought years than years with normal precipitation.

Field research was conducted at Arlington, WI, and Janesville, WI, in 1986 and 1987 to evaluate the effect of conventional-tillage, chisel plow, and no-till systems on the density and control of annual weed species in solid-seeded soybean. Common lambsquarters densities were not greatly influenced by tillage systems, but redroot pigweed densities were generally highest in the chisel plow system. Conventional tillage always had greater velvetleaf densities than no-till and no-till always had greater giant foxtail densities than conventional tillage. Giant foxtail and redroot pigweed became more difficult to control when tillage was reduced, while velvetleaf became less of a problem. This response was not observed with all herbicide treatments evaluated and several herbicide treatments provided excellent weed control. Soybean yield was not affected by tillage systems under weed-free conditions and differences in soybean yield appeared to be due to differences in weed control.

Laboratory and greenhouse studies were conducted to determine imazaquin and imazethapyr adsorption, mobility, and efficacy in Sharpsburg silty clay loam, Holdrege silt loam, and Tripp sandy loam soils after adjusting pH to 5, 6, and 7. Both herbicides were more strongly absorbed, less mobile, and less efficacious at a lower pH. Observations were attributed to ionic bonding resulting from protonation of basic functional groups on the herbicide molecules as pH decreased. Adsorption was greatest in the silty clay loam and least in the sandy loam soil. Conversely, the herbicides were more efficacious and mobile in the more coarse-textured soils. Imazethapyr was less mobile, more highly adsorbed, and more phytotoxic than imazaquin. Greater adsorption of imazethapyr was attributed to a stronger basic pKa and steric factors.

Adsorption and desorption isotherms for atrazine and two metabolites, hydroxyatrazine (HA) and S-glutathione atrazine (GSHA), were determined by batch equilibration on Plano and Waukegan silt loam soils at two soil pH levels (Plano, 6.1 and 4.5; Waukegan, 6.1 and 4.0). Freundlich adsorption isotherms were not affected by soil type except for GSHA at pH 4.0 to 4.5. When averaged over both soils, the order of adsorption at pH 6.1 was atrazine (Kf = 3.7) < GSHA (Kf = 7.3) << HA (Kf = 25) and at pH 4.0–4.5 was atrazine (Kf = 6.1) << HA (Kf = 58) ≤ GSHA (Kf: Plano = 35; Waukegan = 78). The average slope of the adsorption isotherms (1/nads) was 0.81. The slopes of all desorption isotherms (1/ndes) were less than their respective 1/nads, indicating hysteresis. Atrazine desorbed into soil solution (1/ndes > 0.0). With the exception of GSHA which desorbed from the pH 6.1 Plano silt loam (1/ndes = 0.15), desorption of HA and GSHA from other treatments was negligible (1/ndes = 0.0). Consequently, leaching of HA and GSHA in these and similar soils is not likely, due to high adsorption and low desorption.

Field trials were conducted in 1986 and 1987 to determine the effects of moisture on herbicidal activity of cinmethylin applied preemergence at 0.0, 0.3, 0.6, and 0.9 kg ai ha to both dry and moist sandy loam soil. Herbicide application was followed by varying amounts of irrigation. Weed species included velvetleaf, prickly sida, green foxtail, and barnyardgrass. When cinmethylin was applied to a moist soil or when 2.5 cm of irrigation was applied 5 days after cinmethylin application to a dry soil, overall weed control was reduced. Optimum weed control resulted from cinmethylin application to dry soil followed either by a 2.5-cm irrigation within 8 h or a 7.6-cm irrigation within 36 h.

A study was conducted under controlled environmental conditions to determine the effect of soil temperature, soil moisture, and depth of seed burial on the emergence of round-leaved mallow. Emergence occurred from 5 to 30 C but was optimal at 15 to 20 C. Soil moisture had a greater effect than soil temperature on percentage emergence. Emergence progressively declined below a soil water content of −0.28 MPa, with less than 20% emergence attained at −1.03 to −1.53 MPa. In contrast, rate of emergence of round-leaved mallow was affected more by soil temperature than by moisture. A decrease in temperature from 30 to 5 C increased the time to reach 50% emergence by 10 to 12 days over the moisture regime of this study. Emergence was greatest at depths of 0.5 to 2 cm. No emergence occurred at 8 cm or below. The potential of using the findings of this study to develop cultural control strategies for round-leaved mallow is discussed.

Greenhouse experiments were conducted to evaluate effects of sicklepod planting depths and chlorimuron, imazaquin, and metribuzin incorporation depths on sicklepod seedling emergence and growth. There was 35 and 90% sicklepod seedling emergence from 0- and 2-cm planting depths, respectively, in untreated soil 26 days after planting; emergence decreased with each additional increment below 2 cm. Chlorimuron at 63 g ai ha reduced the number of plants present 11 days after planting at 1- and 2-cm planting depths except when unincorporated. However, deeper sicklepod planting required chlorimuron incorporation to at least 6 cm for maximum reduction of plants. Imazaquin at 140 g ai ha was not as effective as chlorimuron, but a reduction in the number of plants was noted at 1- and 2-cm planting depths when imazaquin was incorporated to 4, 6, or 8 cm. Metribuzin at 420 g ai ha consistently reduced the number of plants at all incorporation depths except when unincorporated but had little effect on emergence. Chlorimuron and imazaquin reduced sicklepod dry weight most for all planting depths when incorporated 4 to 10 and 6 to 10 cm, respectively. Metribuzin reduced sicklepod biomass at all incorporation depths.

Herbicide desorption isotherms may be affected by the amount of nondesorbable herbicide present in soil. Nondesorbable alachlor (as determined after methanol extraction) generally increased on a Waukegan silt loam (Typic Hapludolls) and a Ves clay loam (Udic Haplustolls) during five 0.01 M CaCl2 desorptions. Atrazine was totally extracted with methanol from the Waukegan soil after one desorption using 0.01 M CaCl2. However, after five desorptions with 0.01 M CaCl2 an average of 5.5 and 15.5% of the total recovered atrazine from two atrazine application rates was methanol nondesorbable from the Waukegan and Ves soils, respectively. Freundlich desorption isotherms adjusted for nondesorbable herbicide accounted for as much as 71 % of the difference between adsorption and desorption isotherms. Only a portion of the hysteresis observed can be attributable to nondesorbable herbicide.

The establishment and management of nine cover crops in Kentucky production systems were evaluated in field experiments over a 2-yr period. ‘Wheeler’ rye, ‘Barsoy’ barley, and ‘Tyler’ wheat cereal grains produced greater biomass (180 to 260 g/m2) than the pasture species tall fescue, creeping red fescue, and white clover (55 to 110 g/m2). ‘Kentucky 31’ tall fescue, creeping red fescue, and white clover proved most difficult to control, and significant regrowth occurred regardless of herbicide or rate applied. HOE-39866 (1.7 kg ai/ha) was effective in rapidly controlling all cover crops except tall fescue by 30 days after application. Sethoxydim and fluazifop (0.4 and 0.3 kg ai/ha, respectively) effectively controlled the cereals and two ryegrass species. Glyphosate applied at 1.1 and 2.2 kg ai/ha was also effective, while 0.6 kg ai/ha controlled only cereal grain growth adequately. After chemical control, pasture grass plots contained fewest weeds/m2 with some reductions likely due to density and regrowth of the sods. Cover crops were effective in suppressing weed growth at 45 days after chemical control. However, significant weed growth existed in all cover crop plots by 60 days after kill. Row crop establishment increased linearly with increasing glyphosate rate. Cereal grain covers provided the most compatible planting situations for greatest seedling establishment, with rye and wheat providing greatest weed suppression. Generally, increased weed suppression provided by a cover crop was accompanied by reduced row crop establishment, with greatest reductions observed in pasture grass plots. Cucumber was most easily established while snap pea was most difficult.