Studies were conducted to evaluate density-dependent effects of common ragweed on weed growth and peanut growth and yield. Common ragweed height was not affected by weed density and peanut canopy diameter. Weed height exceeded peanut height throughout the growing season, indicating that competition for light occurred between the two species. Common ragweed aboveground dry biomass per plant decreased as weed density increased, but total weed dry biomass per meter of crop row increased with weed density. The rectangular hyperbola model described the effect of weed density on percent peanut yield loss. With the asymptote constrained to 100% maximum yield loss, the I coefficient (yield loss per unit density as density approaches zero) was 68.3 ± 12.2%. Common ragweed did not influence the occurrence of tomato spotted wilt virus, early leaf spot (Cercospora arachidicola), southern stem rot (Sclerotium rolfsii), and Cylindrocladium black rot (Cylindrocladium crotalariae). However, as common ragweed density increased, the incidence of late leaf spot (Cercosporidium personatum) increased. Results indicate that common ragweed is one of the more competitive weeds in peanut and a potential economic threat to peanut growers.

Field margin weeds may contribute to the invasion and persistence of weeds in arable fields. Experimental studies of this hypothesis, however, have been inconclusive. We examined the role of field margin weed populations with a spatially explicit simulation model of Canada thistle population dynamics. We measured the contribution of field margin populations to weed pressure in the field across a wide range of parameter values and compared the weed control value of efforts applied to the field margin to that of similar efforts applied to the field. Under most combinations of parameter values, field margin weeds contributed little to weed pressure in the field, suggesting that controlling field margin weeds may often be of little value. Two conditions appeared to be necessary for field margin weeds to influence weed population dynamics within the field: the presence of unoccupied weed habitat, which increased the importance of dispersal to population growth, and high dispersal rates of field margin weeds relative to field weeds, which increased the relative contribution of field margin weeds to dispersal.

Treatment interactions affecting endemic populations of annual grass and broadleaf weeds, corn rootworm larvae (CRW), corn earworm (CEW), European corn borer (ECB), and common rust in sweet corn were investigated in three field studies near Arlington, WI, in 1996 and 1997. In all environments, weed biomass was affected only by the weed control treatments with cultivation resulting in the highest weed biomass. Corn root damage was affected only by the CRW insecticide treatments in the early- and late-planted environments in 1997 (E97 and L97). Both weed control and ear insect (CEW and ECB) control treatments affected corn ear damage by CEW and ECB. In E97 and L97, more insect ear damage occurred in plots with 1× herbicide treatments than in cultivation treatments. In L97, the ear insect treatment decreased ear damage 55% compared to untreated plots. The interaction between ear insect and weed control treatments affected the number of CEW found per 10 ears in L97. The interaction between hybrid rust and weed control treatments influenced common rust severity in all environments. A hybrid rust by CRW by ear insect treatment interaction also affected common rust severity in E97 and L97. ‘Jubilee’ hybrid (rust-susceptible) corn treated with both insecticides had greater common rust severity than nontreated Jubilee corn. Sweet corn yield was affected most by weed control in all environments, with the lowest yields occurring in cultivated plots. Sweet corn yield did not differ between the 1× and ⅓× herbicide treatments in all environments. The interaction among hybrid rust by CRW by ear insect treatments also affected yield in E97 and L97. An important component of this interaction was the CRW treatment, as sweet corn yield was higher in treated than nontreated plots. The interactions in this study indicate that the best chances for developing comprehensive thresholds for sweet corn pests in the Midwest are for CEW, ECB, and common rust.

Field experiments from 1997 to 1999 examined cotton cv. ‘Coker 312’ that was genetically transformed to tolerate glufosinate. None of the glufosinate treatments caused visible injury to the glufosinate-tolerant cotton, but treatments were lethal to nontransformed or nonexpressing cotton. No glufosinate treatment adversely affected plant height at maturity, total number of nodes, bolls per plant, or boll positions. Glufosinate applications of 0.6 kg ha−1 made at eight stages of growth, ranging from cotyledon stage to 50% open boll, did not adversely affect yield or fiber quality as measured by micronaire or fiber length and strength. Sequential glufosinate applications up to four stages of growth from the zero- to one-leaf stage to the 14- to 15-leaf stage or individual glufosinate applications at 3.3 kg ha−1 made at the two- to three-leaf stage of growth also did not adversely affect yield or fiber quality. Overall yields in these studies were low relative to normal Texas Southern High Plains cotton yield because these studies were conducted using a Coker 312 parental line, which is generally a poor performer in this region. This research indicated that the transformation events for glufosinate tolerance in cotton were successful and the glufosinate-tolerance gene was expressed throughout the growing season. Transformation and field testing of other cotton varieties are needed to improve varietal performance on the Texas Southern High Plains.

Field experiments were carried out in northern Greece during 1994, 1995, and 1996 to study the effect of nitrogen fertilization on competition between sterile oat and wheat, barley, and triticale. Dry weight of all crops was not affected until early March by sterile oats (110 plants m−2), but wheat and triticale dry weight were significantly reduced by sterile oats competition after that time. Grain yield of both wheat and triticale was equally reduced by 61% due to the presence of sterile oats, whereas the reduction for barley grain yield was 9%. Nitrogen fertilization (150 kg N ha−1) slightly increased yield of all crops grown without weed competition compared to the control (0 kg N), whereas the same treatment increased sterile oats dry weight as well as its competitive ability against wheat and triticale. Split application of nitrogen (50 kg N ha−1 before planting and 100 kg N ha−1 in early March) caused a slightly higher increase in sterile oats dry weight compared to the control or one application (150 kg N ha−1) before planting, when grown with wheat and triticale. However, dry weight of sterile oats grown with barley was severely reduced by the interference of the crop. Total nitrogen content of all crop plants grown without sterile oats increased with nitrogen fertilization compared to the control. However, total nitrogen in crop plants grown with sterile oats was reduced compared to the weed-free control; percent reduction was greater in plants grown in plots treated with nitrogen than in the control. These results indicate that barley could be used for limiting sterile oats interference in areas where winter cereals are grown; time of nitrogen application could also be used for a slight reduction of sterile oats competitive ability against wheat or triticale.

Field experiments were conducted in 1996 and 1997 to evaluate the efficacy of combined cultural and biological weed control for management of Canada thistle in conservation tillage soybean production. For cultural control, we used a highly weed-competitive soybean variety (cv. ‘Kato’). The biological control agent was the phytopathogenic bacterium Pseudomonas syringae pv. tagetis (PST). The application of PST reduced Canada thistle survivorship, height growth, and seed production, although these reductions were usually less than those resulting from bentazon application. Only bentazon application resulted in significant reduction of biomass of Canada thistle plants that survived all season. These results suggest the value of PST for management of Canada thistle in conservation tillage systems due to its negative effects on survival, growth, and reproduction. However, the weed-competitive soybean variety did not affect Canada thistle performance differently than a less competitive variety used for comparison, and there was no indication of synergy between the effects of the two control methods.

Field studies were conducted in 1996, 1997, and 1998 to determine the effectiveness of several grasses as filter strips for reducing sediment and herbicide losses in runoff. Big bluestem, eastern gamagrass, switchgrass, and tall fescue reduced total runoff volume by at least 55, 76, 49, and 46%, respectively. Within the 127-d sampling period, each perennial grass filter strip investigated reduced total sediment loss in surface runoff by at least 66%. All four species reduced total fluometuron loss in runoff at least 59%. Big bluestem and eastern gamagrass reduced norflurazon loss in runoff 63 and 86%, respectively. When a filter strip was present, fluometuron and norflurazon losses did not exceed 5 and 3% of the total applied, respectively, compared to 12 and 5%, respectively, when a filter strip was not present.

Field studies at three sites and growth chamber experiments were conducted to determine the reproductive potential, flower phenology, seed viability and germination, and overall seedbank longevity of yellow starthistle in the Central Valley of California. At the three study sites, seedheads contained an average of between 65 and 83 achenes. Overall, 85% of the achenes were the interior pappus-bearing type, and the remaining 15% were the outer nonpappus-bearing type. Germinable seed did not initially develop until the late corolla senescence stage 8 d after flower initiation. Seed germination and viability 1 wk after dispersal were similar (86 and 91%, respectively). Comparison in flower phenology in 1996 and 1997 indicated that development from initial anthesis to achene dispersal more closely corresponded to days, rather than thermal units. In the field, germinable seed was produced when more than 2% of the total seedheads had initiated anthesis. To minimize seed production with late-season control methods, such as prescribed burning, mowing, or herbicide treatment, management strategies should be timed before the plant population has advanced beyond the 2% flower initiation stage. Over 84% of the seed germinated under growth chamber conditions 1 wk after seedheads reached the dispersal stage. This indicates that most yellow starthistle seed had little or no after-ripening requirements. In a field experiment, yellow starthistle seed germination corresponded to seasonal rainfall. A total of 44 and 39% of the pappus-bearing and nonpappus-bearing seed, respectively, germinated after one growing season. Of seed recovered from the soil after the first growing season, 88 and 81% of the pappus-bearing and nonpappus-bearing seed, respectively, was either damaged or degraded. From projected values based on recovered and germinated seed, it was estimated that over 97% of the total seed was removed from the soil seedbank after two growing seasons. These findings should assist land managers in developing long-term yellow starthistle management strategies.

The relationship between species richness and sample area has been characterized in many natural communities but has rarely been examined in crop–weed communities. We determined the species–area relationship in short-term (≤4 yr) and long-term (>15 yr) moldboard-plowed (MP), chisel-plowed (CP), and no-tillage (NT) fields cropped to corn and in short-term MP, CP, and NT fields cropped to soybean. A total of 10 corn fields and 10 soybean fields were sampled for species richness in 14 nested sample areas that ranged from 0.0625 to 512 m2. The influence of sample area on frequency of species occurrence was also determined. Species richness was greater in long-term NT fields than in tilled or short-term NT fields. The species–area relationship in tilled and short-term NT fields was best described by an exponential function. In contrast, a power function was the best fit for the species–area relationship in long-term NT fields. The functional minimum area required to represent 75% of the total weed species in tilled and short-term NT fields was 32 m2. A functional minimum area could not be determined in long-term NT fields because species richness continued to increase over the range of sample areas. Regression functions predicted that sample areas of 1 m2 would contain less than 50% of the observed maximum species richness in these fields. Sample areas of 36 m2 in tilled and short-term NT fields and 185 m2 in long-term NT fields were predicted to measure 75% of observed maximum species richness in these fields. Pigweed species and common lambsquarters occurred at high frequencies and were detected in most sample areas. This information could be used to better define sample area requirements and improve sampling procedures for species richness of weed communities.

California arrowhead is a broadleaf weed widespread in water-seeded rice. Bensulfuron is the only herbicide currently available for use throughout the California rice growing region that provides complete control of California arrowhead; however, resistance to bensulfuron has been detected in California arrowhead and in several other weed species. Growers have herbicide alternatives for weed species other than California arrowhead but continue to use bensulfuron year after year for control because they believe California arrowhead reduces rice yields. However, damage thresholds have not been determined for this weed, and the crop may be able to tolerate relatively high California arrowhead densities. In this work, the damage thresholds for California arrowhead were determined in field and greenhouse experiments. Water-seeded rice was grown in mixture with California arrowhead in a 1992 greenhouse experiment and in field experiments in 1992 and 1998. Rice tiller density and grain yields were not affected by California arrowhead densities up to 200 plants m−2 in any year. Rice was taller than California arrowhead throughout the growing season in all experiments, and the weed senesced well before rice maturity. The ability of the crop to overtop the weed and grow weed-free during the latter part of the season may explain why California arrowhead is such a weak competitor with water-seeded rice. The results suggest that growers may be able to tolerate California arrowhead densities up to 200 plants m−2 without detectable yield losses. Implications for weed management are discussed.

Geostatistical techniques were used to describe and map the spatial distribution of crenate broomrape populations parasitizing broad bean over 6 yr (from 1985 to 1990). In the first year, the spatial distribution was random, but from 1986 to 1989, crenate broomrape populations were clearly aggregated. The crenate broomrape infection severity (IS: number of emerged broomrape m−2) increased every year, from an average of 0.45 in 1985 to 29.4 in 1989, with a slight decrease the following year (IS = 27.4). Spherical functions provided the best fit because the cross-validation criteria were accomplished in all study cases. Kriged estimates were used to draw contour maps of the populations. About 34.3, 43.3, and 74.3% of the field plot surface exhibited an IS ≥ 1 (economic threshold) in 1985, 1986, and 1987, respectively, and nearly 100% of the area exceeded the economic threshold from 1988 to 1990; 1985 and 1986 were key years for control of the parasitic weed population. The percentage of infested area at different IS intervals in each year's map obtained by kriging was used to estimate the percentage of yield losses in each infested area (YA) with the equation: YA = A ∗ Ymax ∗ (1 − IS ∗ 0.124), where A is the infested area at a given IS interval and Ymax is the expected broomrape-free broad bean yield. Yield losses under different IS intervals were compared with yield loss attributable to a uniform distribution of crenate broomrape. Results showed that yield loss assuming a uniform distribution of crenate broomrape was clearly overestimated, which is important to avoid overuse of herbicides.

Dodder (Cuscuta) species are obligate shoot parasites that attach to stems and leaves of plants belonging to diverse families, diverting water, minerals, and metabolites, resulting in suppression of crop plants and yield reduction. Lespedeza dodder has the most diverse and numerous host range among the Cuscuta genus and is a major weed problem in tomato production in certain parts of the world, including California. At present, few resistant varieties of normally susceptible plant species have been developed or identified, and none are available in California. In this study, greenhouse and field studies were conducted to test and characterize the tolerance of commercial hybrid tomato varieties to lespedeza dodder. In greenhouse studies, Heinz varieties ‘9492’, ‘9553’, and ‘9992’ exhibited tolerance to the parasite, compared to the susceptible variety, ‘Halley 3155’. Lespedeza dodder germinated, made contact, twined around tomato stems, and adhered to them, but in most cases, haustoria failed to penetrate into the stem, eventually leading to the death of the parasite. In field studies, lespedeza dodder attachments were 75% less on tolerant varieties, and dodder growth was reduced by more than 70%.

The influence of tillage, crop rotation, and weed management regimes on the weed seedbank in land previously under the conservation reserve program (CRP) for 8 yr was determined from 1994 through 1997. The study was a split-plot design with four replications, two tillage systems, two crop rotations, and three weed management treatments. Eleven weed species were recorded in 1994 and 1995, and 13 in 1996 and 1997. The weed seedbank was dominated by broadleaf species. In 1994, the first year after CRP, the seed population density in the top 15 cm of the soil profile was 51,480 seeds m−2, of which 60 and 20% were pigweed and common lambsquarters. The population density of pigweed seeds in the seedbank increased over time and reached 51,670 seeds m−2 in 1996. In contrast, the seed population density for foxtail species was only 417 seeds m−2 in 1994, but it increased to 7,820 seeds m−2 in 1997. The large increase in foxtail species seed population density in the 4-yr period was mainly in the no-herbicide weed management treatment. The weed seedbank was reduced similarly by band and broadcast herbicide treatments. Tillage and crop rotation did not influence the weed seedbank or Shannon's diversity index, nor did they interact with the weed management treatments in any of the years. The weed seedbank population density varied with the years and time of soil sampling. Weed seed population densities tended to be greater in the fall but declined significantly by time of the spring sampling. The no-herbicide treatment had a more diverse weed seedbank compared with band and broadcast herbicide weed management treatments. An average of one grass and three broadleaf weed species were identified in the three weed management treatments. Band and broadcast herbicide treatments reduced the weed seedbank population density but did not affect the number of broadleaf weed species observed.

Field experiments were conducted in 1998 and 1999 at Five Points, CA, in the San Joaquin Valley under irrigated conditions to study competition between four commonly grown tomato cultivars and velvetleaf and to identify cultivar characteristics associated with greater tolerance to velvetleaf. The effect of velvetleaf competition varied with both year and tomato cultivar. When grown with 5 velvetleaf plants m−1 of row, marketable yield of tomato was reduced 8% in 1998 and 60% in 1999 for cultivar H8892 and 58% in 1998 and 80% in 1999 for cultivar H9661, compared to cultivars grown in monoculture. Across velvetleaf densities, height of tomato cultivars was not reduced compared to that of cultivars grown in monoculture. However in 1999, canopy width of tomato cultivars grown with velvetleaf was less than that of cultivars grown in monoculture. At early stages of growth, the leaf area index of tomato cultivars grown with velvetleaf was less than that of cultivars grown in monoculture. Crop growth rate and aboveground dry biomass of tomato cultivars grown with velvetleaf were generally less than those of cultivars grown in monoculture. Yield loss at high weed density was similar among cultivars, whereas yield loss at low weed density varied among cultivars. Cultivar tolerance to velvetleaf varied with year. However, cultivar H8892 had low yield loss and cultivar H9661 high yield loss at low weed density in 1998 and 1999. For cultivar H8892, leaf area expansion rate was also among the greatest for both years.

An experiment examining the effect of burcucumber emergence date and corn competition on burcucumber fecundity was conducted in 1997 and 1998 in central Pennsylvania. Burcucumber seedlings were transplanted in the field in approximately 10-d intervals starting in late May through mid-August with or without competition from corn. Burcucumber plants grown without competition from corn produced 716 g dry matter and 4,500 seeds plant−1 in 1997 and 607 g dry matter and 1,800 seeds plant−1 in 1998. Biomass was greatest for plants established in late May, whereas seed production was greatest for plants established in mid-June. Although seed numbers were reduced in comparison to the May and June establishment periods, plants established as late as August still produced seed. Burcucumber established in corn produced 96% less dry matter and seed than the plants in a noncompetitive environment in both years of the study. Although the growth and seed production of burcucumber grown in corn was drastically reduced, plants established in mid-July still produced seed.

Accurate weed population estimation and yield loss prediction are important components of integrated weed management. Field experiments using Italian ryegrass as a weed in broccoli were conducted from 1994 to 1997 to compare weed density to other methods of weed population estimation, to evaluate the performance of weed population estimates in yield description models, and to study the affect of environmental variability on the predictive ability of models. A strong linear relationship was obtained between Italian ryegrass density and direct leaf area (r2 = 0.60 to 0.99). For Italian ryegrass, density and estimates of canopy from the optical device (crosswire device) had a hyperbolic relationship with high coefficients of determination (r2 > 0.72). Both direct leaf area and canopy estimates described broccoli yield as well as or better than Italian ryegrass density. The Li-Cor LAI-2000 Plant Canopy Analyzer (PCA) provided poor estimates of Italian ryegrass population (r2 from 0.00 to 0.63) that failed to describe broccoli yield. No relationship was observed between estimates of light interception through the plant canopy obtained with the Li-Cor LI-191-S Line Quantum Sensor (LQS) and either Italian ryegrass density or broccoli yield. The low performance of the PCA and lack of performance of the LQS were likely due to the smaller size of the plants and larger gaps in the plant canopy caused by wide bed spacing. At similar densities, Italian ryegrass competition with broccoli was stable from year to year. Under high Italian ryegrass density, water supply affected competition. This may limit construction of robust yield prediction models, especially in areas where water is mainly from rainfall.

A field study was conducted to determine the effects of giant ragweed emergence time and population density on corn grain yield, giant ragweed seed production, and giant ragweed predispersal seed losses. When weeds and crop emerged concurrently, hyperbolic regression of percent corn yield loss on giant ragweed population densities of 1.7, 6.9, and 13.8 weeds per 10 m2 gave a predicted loss rate of 13.6% for the first weed per 10 m2 in the linear response range at low densities and a maximum yield loss of 90% at high weed densities. Crop yield loss response to weed density was linear when giant ragweed emerged 4 wk after corn, and the regression coefficient indicated a yield loss rate of 1% per unit increase in weed density. A larger proportion of the variation in corn yield loss was explained by weed density (r2 = 0.99) than by weed biomass (r2 = 0.81). There was a positive linear relationship between giant ragweed seed production and weed density at each weed emergence time. When giant ragweed emerged with corn, regression equations for 1997 and 1998 gave a predicted seed rain of 146 and 238 seeds m−2 per unit increase in weed density, respectively. In both years when giant ragweed emerged 4 wk after corn, predicted seed rain was 16 seeds m−2 per unit increase in weed density. Viability of total giant ragweed seed was 56 and 38% in 1997 and 1998, respectively, and was not affected by weed emergence time or weed density. Feeding by insect larvae accounted for 13 to 19% of giant ragweed seed viability losses. Granivorous insects infesting giant ragweed seed were identified as a fruit fly (Diptera: Tephritidae), two weevils (Coleoptera: Curculionidae), and a moth (Lepidoptera: Gelechiidae).

The cross-tolerance of imidazolinone-tolerant (IMI-tolerant) rice to various acetolactate synthase (ALS)-inhibiting herbicides at one and two times labeled rates was studied. The IMI-tolerant rice is cross-tolerant to imazaquin, imazapyr, nicosulfuron, pyrithiobac, thifensulfuron plus tribenuron, and triasulfuron; is partially tolerant to imazamethabenz and metsulfuron; and is susceptible to chlorimuron, flumetsulam, imazamox, imazapic, primisulfuron, and rimsulfuron. In the greenhouse, IMI-tolerant rice injury with 70 and 140 g ai ha−1 imazethapyr was 17 and 34%, respectively, 28 DAT. Both rates of imazapyr, imazaquin, rimsulfuron, nicosulfuron, thifensulfuron plus tribenuron, and pyrithiobac, and 25 g ai ha−1 triasulfuron, injured rice the same as imazethapyr. Red rice control with 70 and 140 g ha−1 imazethapyr was 97 and 98%, respectively, 28 DAT. At label and two times the label rate, all imidazolinones, nicosulfuron, and primisulfuron controlled red rice equivalent to imazethapyr. Red rice control with 28 g ai ha−1 rimsulfuron was similar to control with 70 and 140 g ha−1 imazethapyr 28 DAT. In the field, barnyardgrass control with two times the labeled rate of imazamox, imazapic, imazapyr, imazaquin, imazamethabenz, rimsulfuron, and nicosulfuron was equal or greater than control with imazethapyr 30 DAT; however, at two times the labeled rate of imazamox, imazapic, and rimsulfuron, injury was greater than imazethapyr. Of all the herbicides tested, only nicosulfuron, imazaquin, and imazapyr offer a combination of low rice injury and high red rice control compared with imazethapyr.

Annual emergence and seed persistence of common waterhemp, velvetleaf, woolly cupgrass, and giant foxtail were characterized in central Iowa for 4 yr following burial of seeds collected and buried in autumn 1994. First-year emergence as a percentage of the original seed bank ranged from 5 to 40%, and the relative order was common waterhemp < velvetleaf < giant foxtail < woolly cupgrass. During the second and third years, there were no differences in percent emergence among species, with emergence percentages ranging from 1 to 9% of the original seed bank. During the fourth year, seedlings continued to emerge from only the velvetleaf and common waterhemp seed banks. A greater percentage of common waterhemp seed persisted each year and 12% of the original seed was recovered after 4 yr of burial. Five percent of the velvetleaf was recovered at the end of the fourth year. No woolly cupgrass and giant foxtail seed was recovered after the third and fourth years. The proportion of the seed that was accounted for from year to year through emergence and seed recovery varied by species and year. Total recovery of velvetleaf ranged from 61 to 87%, common waterhemp from 50 to 81%, woolly cupgrass from 29 to 79%, and giant foxtail from 23 to 79%. Based on the results of this research, velvetleaf and common waterhemp form more persistent seed banks than woolly cupgrass and giant foxtail. Therefore, woolly cupgrass and giant foxtail should be more amenable to management through seed bank depletion than velvetleaf and common waterhemp.

Cogongrass is a difficult weed to control in small-scale farming systems and often causes significant crop yield reduction. Field experiments were conducted from 1996 to 1999 at three sites located in the forest/savanna transition zone of Nigeria to determine the influence of intercropping cover crops on cogongrass, corn, and cassava growth. Total cogongrass biomass (shoots and rhizomes) at the onset of the study was highest at Ijaiye (889 g m−2), followed by Umumba (445 g m−2), and least in Ezillo (138 g m−2). Velvetbean had the highest percent ground cover at Umumba and Ijaiye (67 to 89%) 10 wk after planting and shaded the ground longer at all locations. Twelve months after planting, plots with cover crops had 66, 71, and 52% lower cogongrass biomass than the weedy control without cover crops at Ijaiye, Umumba, and Ezillo, respectively. Velvetbean at all locations, L. purpureus at Ijaiye, and tropical kudzu at Umumba and Ezillo were the cover crops most effective in reducing rhizome biomass of cogongrass. Annual weeds dominated the plots sown to cover crops after 2 to 3 yr. At Ijaiye and Umumba, cogongrass competition affected the yield of cassava more than the yield of corn. At all locations, cover crops and weeded control treatments had 27 to 52% more corn grain yield than the weedy control. At Ijaiye, corn grain yields from velvetbean and L. purpureus plots were similar to that from the weeded control plot. At Umumba, all plots with cover crops had corn grain yields similar to that of the weeded control. At all locations, almost all cover crop treatments had cassava root yields higher than the weedy control. Except at Ijaiye, root yields from weeded control plots were 17 to 88% higher than in cover-cropped treatments, suggesting competition between cover crops and cassava.