Field experiments were conducted in 1992 to 1993 and in 1995 to 1996 in Ibadan, Nigeria, to assess the effect of velvetbean and herbicides on maize (corn) and cogongrass growth and to assess regrowth of the weed 1 yr after treatment. In 1992 and 1995 cover cropping with velvetbean and imazapyr and glyphosate application reduced cogongrass density as much as the handweeded control. The smothering effect of velvetbean was equivalent to that of glyphosate at 1.8 kg/ha but was less than imazapyr even at the lowest rate of 0.5 kg/ha. Addition of adjuvant did not improve the efficacy of either herbicide. Maize grain yield was higher in velvetbean plots than in fallow plots dominated by cogongrass. Velvetbean and herbicide effects on cogongrass 1 yr later (1993 and 1996) followed a similar trend as observed in the year of application. Annual weed density was highest in glyphosate plots, followed by imazapyr, and least in plots previously seeded to velvetbean. Maize grain yield was higher in herbicide plots (average yield of 3,170 and 1,920 kg/ha in 1993 and 1996, respectively) than in velvetbean plots (2,800 to 1,180 kg/ha in 1993 and 1996, respectively) and handweeded plots (2,890 and 723 kg/ha in 1993 and 1996, respectively). In 1996 the lowest maize yield was in handweeded plots without velvetbean, suggesting that weeding four times suppressed cogongrass density and biomass, but was not sufficient to minimize the subsequent competition from annual weeds. Uncontrolled cogongrass reduced maize yield to zero. These studies suggest that planting velvetbean for cogongrass control may be a better alternative for farmers without the resources to purchase herbicides.

Mature seed samples from 35 populations of Echinochloa were collected in fields of the Eastern Iberian Peninsula and evaluated for nine morphologic traits. Four kernels per population were separately assayed for four isozyme systems. Genetic variability components were studied by correspondence analysis and chi-square distance using the isozyme pattern as variables. Genetic uniformity was found within populations as would be expected from their autogamous mating system. Intraspecific isozyme variability covered a wide spectrum, from none in E. colonum to very high in E. oryzoides. All the populations of E. colonum clustered together based on morphometric and isozymatic characters, and also those of E. oryzicola, but were distinct from the populations of all other species. Populations of E. crus-galli, E. hispidula, and E. oryzoides clustered within species based on morphology, but did not cluster based on isozymatic characters, being mixed in the isozymatic dendrogram. Our results support the hypothesis that E. hispidula and E. oryzoides are infraspecific taxa of E. crus-galli. The large between-population genetic variability may explain the differential response to herbicides within a given species and indicate that weed specialists should study the differences in response to a wide spectrum of Echinochloa populations to several herbicides instead of testing many plants from a small number of populations.

Dithiopyr was applied to ‘Penneagle’ creeping bentgrass seedlings 2, 4, and 8 wk after emergence (WAE) in separate studies in the summers of 1992 and 1993 to determine seedling tolerance. Dithiopyr emulsifiable concentrate (IEC) was applied at 0.14, 0.28, 0.42, and 0.56 kg ai/ha, and granular (G) dithiopyr (0.1G) was applied at 0.14, 0.21, 0.28, and 0.42 kg/ha. Dithiopyr applied 2 WAE caused unacceptable injury regardless of rate or formulation. Injury was characterized by stunting of plants, leaf tip die-back, yellowing of older leaves, and a visible decline in quality. Injury increased with increasing rate. In 1992, the EC and G formulation of dithiopyr caused similar responses, whereas in the summer of 1993, the EC caused greater turf injury. Dithiopyr applied 4 WAE caused less injury than when applied 2 WAE, and injury was acceptable. Dithiopyr applied 8 WAE only slightly injured creeping bentgrass at the high rate for both formulations in both years.

Field studies at Arlington, WI, and LeSueur, MN, were conducted in 1996 and 1997 to evaluate tolerance of six sweet corn hybrids to RPA 201772 applied preemergence at 79 to 210 g/ha. Both years the most sensitive hybrid at the Wisconsin site was ‘Zenith,’ with yield reductions of 14 and 22% at 210 g/ha (twice the labeled rate). ‘Excellency,’ ‘Green Giant 43,’ and ‘Jubilee’ tolerated RPA 201772 at 158 g/ha or less. The least tolerant hybrids in Minnesota were ‘Green Giant 6′ and Jubilee, and the most tolerant hybrids were Green Giant 43 and ‘Rogers 9056.’ Injury from RPA 201772 increased as application dose increased. The greatest risk of injury from RPA 201772 appear to be with Green Giant 6, Zenith, and Jubilee, especially on coarser textured soils with low organic matter. Excellency, Green Giant 43, and Rogers 9056 appeared to be the most tolerant. Because of the differential hybrid response to RPA 201772 across sites and years, more hybrid response data needs to be generated before RPA 201772 is labeled in sweet corn.

Reduced-rate herbicide strategies, which rely on treatment of small weed seedlings, are not effective under all situations. The consistency of reduced-rate treatments may be improved by adjustments in application variables. Field experiments were conducted at Kalispell, MT, during 1994 and 1995 to determine the effects of carrier volume on the efficacy of reduced-rate imazamethabenz applications for wild oat control in barley. Imazamethabenz was applied to two- and four-leaf wild oat plants at 0.26 and 0.52 kg ai/ha in carrier volumes of 75, 150, and 225 L/ha. Wild oat control generally increased as carrier volume increased, regardless of imazamethabenz rate or wild oat growth stage. However, increasing carrier volumes had a greater positive effect on wild oat control when imazamethabenz was applied to two-leaf vs. four-leaf wild oat seedlings. Barley yield was most affected by the duration of wild oat interference, with the greatest yield being observed with the earliest application. Barley yield tended to increase as carrier volume increased in 1 of 2 yr. These results indicate that wild oat control with imazamethabenz can be enhanced by increasing carrier volume, providing more consistent wild oat control from reduced imazamethabenz rates.

Field trials were conducted at two sites in 1996 and 1997 to evaluate weed control and crop response to herbicide programs in no-till soybean that include flumioxazin or sulfentrazone alone and each herbicide tank-mixed with either chlorimuron or imazaquin. A prepackaged mixture of metribuzin plus chlorimuron also was included for comparison. Cool, wet conditions after herbicide application in both years were conducive to soybean injury up to 21% at 3 wk after planting (WAP). Flumioxazin and sulfentrazone alone provided ≥ 89% control of velvetleaf, Pennsylvania smartweed, and common cocklebur. Sulfentrazone alone provided greater control of common waterhemp, common cocklebur, and ivyleaf and pitted morningglories than flumioxazin. Flumioxazin provided greater control of common ragweed than sulfentrazone. The addition of chlorimuron to flumioxazin or sulfentrazone provided greater control of velvetleaf than flumioxazin or sulfentrazone alone. The addition of imazaquin or chlorimuron to flumioxazin provided greater control of common cocklebur than flumioxazin alone. The addition of imazaquin or chlorimuron to sulfentrazone provided greater control of common ragweed than sulfentrazone alone. The addition of chlorimuron or imazaquin to sulfentrazone or flumioxazin provided little or no additional control of pitted morningglory, common waterhemp, or Pennsylvania smartweed. Metribuzin plus chlorimuron provided control of velvetleaf, Pennsylvania smartweed, common ragweed, and common cocklebur that was equal to or better than the control provided by sulfentrazone or flumioxazin plus chlorimuron or imazaquin.

Canola (edible rapeseed) crops are often infested by related weed species. This paper addresses effects that seeds from various Brassicaceae weeds may have on canola oil and meal quality. Seeds of common Brassicaceae weeds were collected from canola fields throughout northern Idaho. These were wild mustard, black mustard, birdsrape mustard, shepherd's-purse, flixweed, tumble mustard, and field pennycress. Collected seeds were physically described by weight, size, and shape and were analyzed for oil concentration, fatty acid composition, and glucosinolate concentration. Seed weights ranged from 0.1 to 2 g/1,000 seed. Oil concentration in the weed seeds ranged from 25 to 38%, with erucic acid levels ranging from less than 1 to 47%. Glucosinolate concentration in the mustard weed seeds was over 100 μmol/g oil-free meal, except for shepherd's-purse, which had only 3.4 μmol/g. Using these data, a simple model predicts that both canola oil and seed meal quality can be adversely affected by contamination with weed seeds. Increased erucic acid concentration in modeled admixtures was the most likely oil quality problem associated with weed seed contamination. Glucosinolate concentration in modeled admixtures was higher than acceptable only in those admixtures that also had erucic acid levels that exceeded canola quality standards. Canola-quality oil and seed meal can be maintained with conspicuous weed seed mixtures up to the 2% maximum allowed in U.S. No. 1 canola. However, canola-quality oil and seed meal was not achieved when a 5% weed seed mixture allowed in No. 2 canola was evaluated with the model.

Five cultivation implements (two flex-tine cultivators, brush hoe, and rolling and shovel cultivators) were evaluated for weed control and effect on broccoli, snap bean, and sweet corn yield. Each implement was used alone or in combination with flex-tine cultivators. Standard broadcast herbicide treatments were: broccoli, metolachlor at 2.3 kg ai/ha posttransplant; snap bean, metolachlor preemergence (PRE) at 2.3 kg ai/ha followed by fomesafen postemergence (POST) at 0.4 kg ai/ha; sweet corn, atrazine at 1.1 kg ai/ha plus metolachlor at 2.3 kg ai/ha PRE. In the snap bean trials, an additional treatment consisted of metolachlor at 2.3 kg ai/ha PRE applied in a 25-cm band over the crop row followed by fomesafen POST at 0.4 kg ai/ha directed at the crop row, with a subsequent shovel cultivation. In the sweet corn trials, all cultivation treatments received an application of atrazine at 1.1 kg ai/ha plus metolachlor at 2.3 kg ai/ha PRE in a 25-cm band over the crop row. In broccoli, weed control and yields with all cultivation treatments were comparable to those with broadcast herbicide. In snap bean, flex-tine cultivators failed to control weeds and prevent yield reductions compared to the broadcast herbicide treatment. When either the brush hoe or the shovel cultivator was preceded by flex-tine cultivation, weed control and snap bean yield were comparable to those with broadcast herbicides. Banded herbicides followed by shovel cultivation also controlled weeds and prevented yield reductions. In sweet corn, banded herbicides controlled in-row weeds, and despite variable between-row weed control, all cultivation treatments yielded as well as the broadcast herbicide treatment. Relative performance of the cultivators was influenced by soil type and rainfall as well as crop canopy characteristics.

There are limited options for controlling large crabgrass in spring-seeded cool-season turf. The objective of this experiment was to evaluate the safety and effectiveness of dithiopyr and quinclorac to control large crabgrass in spring-seeded Kentucky bluegrass and perennial ryegrass stands. Quinclorac at 0.84 kg/ha and dithiopyr at 0.56 kg/ha were applied separately at various times prior to seeding and after emergence of Kentucky bluegrass and perennial ryegrass. Quinclorac applied once at 2, 4, 8, or 12 weeks after emergence (WAE) or split-applied preplant incorporated (PPI) + 12 WAE will give season-long control of large crabgrass with no injury to spring-seeded Kentucky bluegrass or perennial ryegrass. Quinclorac applied PPI or 0 WAE is safe to use in spring seedings, but it will not provide season-long control of large crabgrass. Dithiopyr applied 2 or 4 WAE will control large crabgrass season-long while not injuring spring-seeded Kentucky bluegrass or perennial ryegrass. However, dithiopyr applied PPI or 0 WAE will severely limit germination of desirable turf, and dithiopyr applied 8 or 12 WAE will not control mature crabgrass.

A new biotype of common cocklebur, called multiple-seeded cocklebur (MSC), was found in Bell County, TX, in 1994. MSC has up to 25 seeds per bur, usually producing up to nine seedlings, whereas normal common cocklebur (NCC) has two seeds per bur which usually produce only one seedling. MSC burs are large, round, covered with hairy spines or prickles, and flattened on one end, with each seed terminated by a beak. Leaf morphology differs among the biotypes, and stems of MSC are straighter and smoother than NCC. Apomixis occurred with MSC but not with NCC. Both biotypes have potential dormancy with germination occurring in the second growing season. MSC produces increased numbers of seedlings which increases the difficulty in controlling common cocklebur.

Field research was conducted to evaluate the response of soybean to various herbicides applied at rates to simulate drift damage. Dicamba, glyphosate, glufosinate, and the sulfonylurea herbicides CGA-152005, primisulfuron, nicosulfuron, rimsulfuron plus thifensulfuron, and CGA-152005 plus primisulfuron were applied to soybean at the two to three trifoliolate leaf stage in 1997 and 1998 at and ⅓ of the recommended use rates. The order of yield reduction after herbicide treatment was CGA-152005 > dicamba > CGA-152005 plus primisulfuron > rimsulfuron plus thifensulfuron > primisulfuron. Soybean yields were not reduced by glyphosate, glufosinate, and nicosulfuron. Applications of all herbicides at rates higher than of the use rate caused injury symptoms within 30 d after treatment. However, soybean plants had partially or fully recovered by the end of the growing season. Therefore, early-season injury symptoms from herbicide drift are not reliable indicators for soybean yield reduction.

Soil-applied herbicides alone or followed by postemergence (POST) applications of CGA-277476 were evaluated for season-long weed control in soybean. Common cocklebur, hemp sesbania, and pitted morningglory control was not consistently improved with a soil-applied herbicide followed by a POST application of 79 g ai/ha CGA-277476. However, in locations with heavy weed pressure, a tank-mix of chlorimuron + metribuzin + trifluralin or imazaquin + pendimethalin followed by CGA-277476 improved common cocklebur, hemp sesbania, and pitted morningglory over CGA-277476 alone. Sequential application of CGA-277476 following SAN 582 improved weed control over SAN 582 alone. When weed pressure was not severe, there were no differences in control from CGA-277476 alone or following soil-applied herbicides. A POST application of CGA-277476 following soil-applied herbicides did not consistently improve soybean yield over CGA-277476 alone. Yield from soybean treated with SAN 582 was improved when CGA-277476 was applied. In contrast, when chlorimuron + metribuzin + trifluralin or imazaquin + pendimethalin were applied at planting, yield was similar with or without POST application of CGA-277476.

Cloransulam-methyl applied postemergence (POST) following various preplant-incorporated (PPI) herbicides was evaluated in four experiments for weed control in North Carolina soybean over a 2-yr period at three locations. Acifluorfen plus bentazon or chlorimuron alone applied POST injured soybean more than cloransulam-methyl when following any soil-applied herbicide. When following trifluralin PPI, cloransulam-methyl controlled common ragweed, entireleaf morningglory, and pitted morningglory comparable to acifluorfen plus bentazon or chlorimuron. Common lambsquarters and prickly sida control was higher when acifluorfen plus bentazon was applied POST following trifluralin PPI compared to trifluralin PPI followed by cloransulam-methyl or chlorimuron. Acifluorfen plus bentazon or chlorimuron POST controlled yellow nutsedge and smooth pigweed more than cloransulam-methyl POST when following trifluralin PPI. When trifluralin was applied PPI in mixtures with chlorimuron plus metribuzin, flumetsulam, or imazaquin, control of most species was similar regardless of POST treatment used. Soybean treated with cloransulam-methyl yielded 250 kg/ha more than treatments with chlorimuron when these herbicides followed trifluralin plus flumetsulam or trifluralin plus imazaquin. Net returns with different herbicide systems followed trends similar to soybean yield.

Field experiments were conducted in 1996 and 1997 at five locations in southwestern Ontario to develop dose-response curves for SAN 1269H (SAN 835H plus dicamba) for weed control and crop tolerance in corn. SAN 1269H controlled wild buckwheat (Polygonum convolvulus L.), common ragweed (Ambrosia artemisiifolia L.), common lambsquarters (Chenopodium album L.), pigweeds (Amaranthus retroflexus L. and A. powellii S. Wats.), barnyardgrass [Echinochloa crus-galli (L.) Beauv.], and yellow foxtail [Setaria glauca (L.) Beauv.]. Biologically effective doses of SAN 1269H (BAS 662H) were 440, 430, 180, and 40 g/ha for yellow foxtail, barnyard grass, wild buckwheat, and common ragweed, respectively. The biologically effective dose (that which provides 90% reduction in weed dry matter) for common lambsquarters was 560 g/ha when SAN 1269H was applied preemergence (PRE) and 110 g/ha when applied postemergence (POST). When applied PRE at a rate of 420 g/ha, pigweed was controlled, whereas only 85 g/ha was required when applied POST. Grain yield increased with dose of SAN 1269H and did not differ with time of application. Temporary crop injury was observed when SAN 1269H was applied at the four- to six-leaf growth stage. Optimum corn yields were achieved with doses of 100 to 250 g/ha.

Field trials were conducted to evaluate weed control and crop safety with postemergence-applied herbicides in two cultivars of low-tannin seedling sericea lespedeza (Lespedeza cuneata). Two applications of either 2,4-D amine at 0.28 kg ae/ha or 2,4-DB amine at 0.56 kg ae/ha controlled sicklepod (Senna obtusifolia) ≥ 90%. Equivalent control of smallflower morningglory (Jacquemontia tamnifolia) required either two applications of 2,4-D or three of 2,4-DB. Three applications of either herbicide were required for comparable spotted spurge (Euphorbia maculata) control. Sericea lespedeza was not adversely affected when either herbicide was applied up to three times per season over two consecutive seasons. Tolerance to 2,4-D and 2,4-DB was equal between two sericea lespedeza cultivars. Absorption of foliar-applied 14C-2,4-D was greater in sicklepod and smallflower morningglory than in sericea lespedeza. Translocation of absorbed 14C-2,4-D was equivalent between sicklepod and sericea lespedeza but greater in smallflower morningglory than in sericea lespedeza. Absorption and translocation of foliar-applied 14C-2,4-DB was equivalent between sicklepod and sericea lespedeza. Furthermore, 14C-2,4-DB absorption was less in smallflower morningglory than in sericea lespedeza.

Agrichemical interactions between propanil; the herbicides HOE 30374, pendimethalin, piperophos, quinclorac, and thiobencarb; and the insecticide carbaryl were evaluated under field conditions to find synergistic or additive interactions useful to control a barnyardgrass biotype resistant to propanil (R-BYG) without injuring rice. Propanil and each compound were evaluated at four rates for a total of 16 rate combinations for each additive. Averaged over all experiments, 2- to 3-leaf R-BYG control with propanil alone at 0.83, 1.65, 3.3, and 6.6 kg ai/ha was 33, 53, 62, and 81% at 7 d after treatment (DAT). Propanil-susceptible barnyardgrass (S-BYG) response to propanil alone at similar rates was 52, 73, 88, and 94% control. HOE 30374, carbaryl, piperophos, or pendimethalin in combination with propanil produced synergistic effects on R-BYG. For each compound tested, at least one rate combination with propanil controlled R-BYG > 80% with minimal rice injury (< 20%) at 7 DAT. Use of these combinations of compounds could provide more effective control of this resistant biotype and help prevent its spread.

The effect of soil residues of flumetsulam plus clopyralid on several vegetable crops grown in rotation with field corn was investigated over 2 yr. The effect of soil residues of flumetsulam plus clopyralid on sweet corn cultivars of varying sensitivity to acetolactate synthase (ALS)-inhibiting herbicide was also investigated. Flumetsulam plus clopyralid was applied preemergence (PRE) to field corn at 0, 50 + 135, and 100 + 270 g ai/ha, respectively, in 1993 and 1994. Cucumber, tomato, cabbage, potato, pepper, pea, and sweet corn were planted each spring, both 1 and 2 yr following the herbicide application. Cabbage was very sensitive and showed visible injury symptoms and yield reductions both years following flumetsulam plus clopyralid application. Pepper showed a yield reduction only in 1995. All other crops showed no injury or yield reductions. Flumetsulam plus clopyralid was applied PRE and postemergence (POST) to six sweet corn cultivars in 1995. These six sweet corn cultivars were replanted into the same site 1 yr later. Flumetsulam plus clopyralid severely injured three of six sweet corn cultivars in 1995, the year of application. Soil residues 1 yr later, however, did not injure or reduce yield of any sweet corn cultivars, including cultivars sensitive to ALS-inhibiting herbicides.

Studies were conducted at Clayton, Goldsboro, and Rocky Mount, NC, to evaluate weed and cotton response to herbicide programs in glyphosate-resistant cotton. Just prior to cotton harvest, programs containing norflurazon, trifluralin, fluometuron, glyphosate, MSMA, cyanazine, and/or pyrithiobac in various combinations controlled common lambsquarters, common ragweed, goosegrass, ivyleaf morningglory, and smooth pigweed at least 94%. Glyphosate-resistant cotton injury was no more than 5%. Yields for glyphosate programs differed only at Clayton, where glyphosate programs containing residual herbicides yielded more than glyphosate alone. Depending on location, programs utilizing glyphosate as needed required a minimum of two and a maximum of four applications to prevent yield loss when minimal soil-applied herbicides were used. Other as-needed programs required one-three glyphosate applications, depending on location. For comparison based on application, herbicide, and adjuvant costs, the standard program of trifluralin preplant incorporated (PPI), pyrithiobac postemergence (POST), and fluometuron plus MSMA postemergence-directed (PD) was $119/ha compared with trifluralin PPI followed by (fb) two applications of glyphosate ($54/ha) or four applications of glyphosate ($94/ha).

Producers in the central Great Plains are seeking alternative strategies to manage weeds because of herbicide resistance, narrow profit margins, and a lack of registered herbicides in some crops. Thus, we evaluated the impact of cultural systems in winter wheat and tillage on weed dynamics in corn, sunflower, and proso millet planted the year following wheat harvest. Weed seedling densities were 25 to 30% lower in a no-till system compared with minimum-till with a sweep plow. With no-till, cultural systems that produced more crop residue reduced weed densities an additional 15 to 30%, compared with the conventional system. Cultural system effect was eliminated in dry years and by tillage. Weed biomass was 10-fold less in proso millet than in corn. Crop residue management, critical for successful cropping in semiarid regions, also will help weed management by reducing weed density in summer annual crops, especially in no-till systems.

Soil moisture, relative humidity (RH), and the addition of bentazon were examined for effects on absorption and translocation of 14C-imazethapyr in common ragweed. When common ragweed was growing under conditions of low soil moisture (-300 kPa), absorption of 14C-imazethapyr was reduced from 51 to 42%. Translocation of 14C-imazethapyr was not affected by soil moisture. In the absence of bentazon, absorption and translocation of 14C-imazethapyr was similar at 65 and 85% RH 48 and 168 h after treatment. Bentazon decreased absorption of 14C-imazethapyr from 61 to 26% at 65% RH and from 65 to 57% at 85% RH 168 h after treatment. Bentazon decreased translocation of 14C-imazethapyr from 35 to 9% at 65% RH and from 30 to 21% at 85% RH when averaged over time. This reduction in the absorption and translocation of 14C-imazethapyr when bentazon was added may result in a reduction in common ragweed control compared to imazethapyr alone when RH is 65% or lower.