If available for use on snap bean, pyroxasulfone would provide valuable preemergence control of troublesome weed species that currently contaminate the crop postharvest. The extent to which snap bean tolerates pyroxasulfone is poorly documented. The objective of this research was to quantify the extent to which pyroxasulfone tolerance exists in a large collection of snap bean cultivars. A snap bean diversity panel of 277 entries was screened for tolerance to sulfentrazone at a rate of 420 g ai ha−1 in a field trial in 2019 and 2020 near Urbana, IL. Snap bean cultivars exhibited variation in tolerance to pyroxasulfone. While a handful of cultivars were tolerant across variable environments, most cultivars were sensitive in the year that had 30% more water supply (rainfall plus sprinkler irrigation) within 3 wk of planting. Low estimates of broad-sense heritability reflect a large influence of the environment on seedling emergence and growth. With a few exceptions, currently, the margin of crop safety across diverse germplasm is insufficient for registration of pyroxasulfone use on snap bean crops.

Limited information exists on the global economic impact of glyphosate-resistant (GR) weeds. The objective of this manuscript was to estimate the potential yield and economic loss from uncontrolled GR weeds in the major field crops grown in Ontario, Canada. The impact of GR weed interference on field crop yield was determined using an extensive database of field trials completed on commercial farms in southwestern Ontario between 2010 and 2021. Crop yield loss was estimated by expert opinion (weed scientists and Ontario government crop specialists) when research data were unavailable. This manuscript assumes that crop producers adjust their weed management programs to control GR weeds, which increases weed management costs but reduces crop yield loss from GR weed interference by 95%. GR volunteer corn, horseweed, waterhemp, giant ragweed, and common ragweed would cause an annual monetary loss of (in millions of Can$) $172, $104, $11, $3, and $0.3, respectively, for a total annual loss of $290 million if Ontario farmers did not adjust their weed management programs to control GR biotypes. The increased herbicide cost to control GR volunteer corn, horseweed, waterhemp, giant ragweed, and common ragweed in the major field crops in Ontario is estimated to be (in millions of Can$) $17, $9, $2, $0.1, and $0.02, respectively, for a total increase in herbicide expenditures of $28 million annually. Reduced GR weed interference with the adjusted weed management programs would reduce farm-gate monetary crop loss by 95% from $290 million to $15 million. This study estimates that GR weeds would reduce the farm-gate value of the major field crops produced in Ontario by Can$290 million annually if Ontario farmers did not adjust their weed management programs, but with increased herbicide costs of Can$28 million and reduced crop yield loss of 95% the actual annual monetary loss in Ontario is estimated to be Can$43 million annually.

Biotypes of Palmer amaranth that are resistant to acetolactate synthase (ALS) inhibitor are becoming widespread in western Nebraska. There are limited effective postemergence (POST) herbicides labeled for ALS-inhibitor-resistant Palmer amaranth control in dry edible bean. The objective of this study was to evaluate the efficacy of dimethenamid-P in a sequential preemergence (PRE) fb followed by (fb) POST program at two POST application timings, the first and third trifoliate stages (V1 and V3, respectively), for controlling ALS-inhibitor-resistant Palmer amaranth in dry edible bean. A field study was conducted in 2019, 2020, and 2021 in Scottsbluff, NE. PRE-alone applications of pendimethalin + dimethenamid-P provided inconsistent Palmer amaranth control. Dimethenamid-P applied POST following a PRE application of pendimethalin + dimethenamid-P provided effective (>90%) Palmer amaranth control at 4 wk after V3 only at the V1 application timing in 2019. In 2020 and 2021 dimethenamid-P applied POST at V1 and V3 following a PRE application of pendimethalin + dimethenamid-P provided 99% and 98% Palmer amaranth control at 4 wk after V3, and 98% and 94% Palmer amaranth control at harvest, respectively. Palmer amaranth biomass was reduced by 95% to 99% and by 96% to 98% compared with the -nontreated control when dimethenamid-P was applied POST at V1 and V3, respectively, following a PRE application of pendimethalin + dimethenamid-P in 2020 and 2021. Application of a mixture of dimethenamid-P with imazamox + bentazon POST provided similar results to those of the fomesafen-containing treatments and dimethenamid-P alone POST. Dimethenamid-P applied POST following a PRE application of pendimethalin + dimethenamid-P resulted in similar yield as the fomesafen-containing treatments. If fomesafen is not an option due to the crop rotation interval restriction, using dimethenamid-P in a sequential PRE fb POST program is the only effective alternative to control ALS-inhibitor–resistant Palmer amaranth in Nebraska. The use of dimethenamid-P in a sequential PRE fb POST program, alone or mixed with foliar-active herbicides should be considered by dry edible bean growers who are dealing with ALS-inhibitor-resistant Palmer amaranth.

Dicamba is a synthetic auxin herbicide that may be applied over the top of transgenic dicamba-tolerant crops. The increasing prevalence of herbicide-resistant weeds has resulted in increased reliance on dicamba-based herbicides in soybean production systems. Because of the high volatility of dicamba it is prone to off-target movement, and therefore concern exists regarding its drift onto nearby specialty crops. The present study evaluates 12 mid-Atlantic vegetable crops species for sensitivity to sublethal rates of dicamba. Soybean, snap bean, lima bean, tomato, eggplant, bell pepper, cucumber, summer squash, watermelon, pumpkin, sweet basil, lettuce, and kale were grown in a greenhouse and exposed to dicamba at 0, 0.056, 0.11, 0.28, 0.56, 1.12, 2.24 g ae ha−1, which is, respectively, 0, 1/10,000, 1/5,000, 1/2,000, 1/1,000, 1/500, and 1/250 of the maximum recommended label rate for soybean application (560 g ae ha−1). Vegetable crop injury was evaluated 4 wk after treatment using visual rating methods and leaf deformation index measurements. Overall, snap bean was the most sensitive crop, with dicamba rates as low as 0.11 g ae ha−1 resulting in significantly higher leaf deformation levels compared with the nontreated control. Other Fabaceae and Solanaceae species also demonstrated high sensitivity to sublethal rates of dicamba with rates ranging 0.28 to 0.56 g ae ha−1 causing higher leaf deformation compared with the nontreated control. While cucumber, pumpkin, and summer squash were no or moderately sensitive to dicamba, watermelon showed greater sensitivity with unique symptoms at rates as low as 0.056 g ae ha−1 based on visual evaluation. Within the range of tested dicamba rates, sweet basil, lettuce, and kale demonstrated tolerance to dicamba with no injury observed at the maximum rate of 2.24 g ae ha−1.

Although Palmer amaranth is currently not widespread in most dry edible bean−producing states in the United States, it is widespread in western Nebraska, a major dry edible bean−producing region. There is currently a lack of research on management and biology of Palmer amaranth within dry edible bean production. The objective of this study was to quantify the impact of season-long Palmer amaranth interference on yield of dry edible bean and seed production of Palmer amaranth. A field study was conducted in Scottsbluff, NE, in 2020 and 2021. Palmer amaranth interference at densities of 0, 0.2, 0.3, 0.5, 1, and 2 plants m−1 row of dry edible bean was evaluated. Palmer amaranth interference reduced dry edible bean yield by 77% at a weed density of 2 plants m−1 row compared to the weed-free control, and a 5% yield reduction threshold was estimated to occur at a Palmer amaranth density of 0.02 plants m−1 row. Yield reduction occurred primarily through a reduction in the number of pods per plant as Palmer amaranth density increased. Palmer amaranth plants produced 91,000 to 376,000 seeds per plant depending on densities, and as many as 140,000 seeds m−2. Study results will help farmers and other stakeholders estimate Palmer amaranth interference within their fields, and may help justify the economic cost of incorporating additional Palmer amaranth management practices.

The critical timing of weed removal (CTWR) is the point in crop development when weed control must be initiated to prevent crop yield loss due to weed competition. A field study was conducted in 2018 and 2020 near Scottsbluff, NE, to determine how the use of preemergence herbicides affects the CTWR in dry bean. The experiment was arranged as a split plot, with herbicide treatment and weed removal timing as main and sub-plot factors, respectively. Herbicide treatments consisted of no-preemergence application, or pendimethalin (1,070 g ai ha–1) + dimethenamid-P (790 g ai ha–1) applied preemergence. Sub-plot treatments included season-long weed-free, weed removal at: V1, V3, V6, R2, and R5 dry bean growth stages, and a season-long weedy control. A four-parameter logistic model was used to estimate the impact of time of weed removal, for all response variables including dry bean yield, dry bean plants m–1 row, number of pods per plant, number of seeds per pod, and seed weight. The CTWR based on 5% yield reduction was estimated to range from the V1 growth stage [(16 d after emergence (DAE)] to the R1 growth stage (39 DAE) in the no-preemergence herbicide treatment. In the preemergence-applied treatment, the CTWR began at the R2 growth stage (47 DAE). Number of dry bean plants m–1 row was reduced in the no-preemergence treatment when weed removal was delayed beyond the R2 growth stage in the 2020 field season. The use of preemergence herbicides prevented a reduction in the number of pods per plant in 2020, and the number of seeds per pod in 2018 and 2020. In 2018, the number of pods per plant was reduced by 73% when no preemergence herbicide was applied, compared to 26% in the preemergence-applied treatment. The use of preemergence-applied soil-active herbicides in dry bean delayed the CTWR and preserved yield potential.

Dicamba is a synthetic auxin herbicide that is prone to off-target movement, including drift and volatilization. Due to the increased acreage of dicamba-resistant soybean to control glyphosate-resistant weeds, dicamba drift injury to neighboring vegetable crops is of concern. A method to quantify leaf deformation (often referred to as leaf cupping) caused by dicamba injury was developed and compared to visual rating techniques to determine its accuracy and suitability. A second objective was to determine the relative dicamba sensitivity of several economically important vegetable crops. Soybean, snap bean, tomato, and cucumber were grown in a greenhouse and exposed to dicamba at 0, 56, 112, 280, 560, 1,120, and 2,240 mg ae ha−1, which is, respectively, 0, 1/10,000, 1/5,000, 1/2,000, 1/1,000, 1/500, and 1/250 of the maximum recommended label rate for soybean application (560 g ae ha−1). Plants were evaluated visually and using an imaging analysis technique that measures the leaf deformation index (LDI) with a leaf area scanner. LDI is calculated by dividing the two-dimensional projection of the area of the leaf in its natural configuration by the area of the flattened leaf. Across all four crops, log-logistic regression analysis indicated the LDI method had lower I50 values with lower standard error, demonstrating that the LDI method gives more precise estimates of sensitivity. This novel method provides an objective, quantitative method for measuring dicamba drift injury and determining relative sensitivities of valuable specialty crops.

Evaluating the effects of crop successions in no-tillage system (NTS) is essential for the correct recommendation of agronomic practices, such as top-dressing nitrogen fertilization. The aim was to evaluate the effect of the crop succession and the splitting of top-dressing N fertilization on the agronomic performance and economic viability of common bean crop. The experiment was conducted in southeastern Brazil for two agricultural seasons in an area under NTS, using a split-plot in randomized complete block design. The plots represented three cropping successions (maize in sole crop, maize intercropped with Urochloa ruziziensis and U. ruziziensis in sole crop) and the subplots composed of ten combinations of splitting of top-dressing N, at the stages V3, V4 and R5 of the common bean crop. In relation to the single application of the N dose of 90 kg ha−1, the common bean had higher response as a function of the N splitting schemes adopted, regardless of the previous cropping succession. The cropping successions evaluated did not interfere with the seed yield of common bean as subsequent crop, even at the beginning of the establishment of NTS. To obtain higher seed yield and economic viability, the N dose of 90 kg ha−1 indicated for the crop must be split and applied among the phenological stages V3, V4 and R5.

Understanding the effects of crop management practices on weed survival and seed production is imperative in improving long-term weed management strategies, especially for herbicide-resistant weed populations. Kochia [Bassia scoparia (L.) A.J. Scott] is an economically important weed in western North American cropping systems for many reasons, including prolific seed production and evolved resistance to numerous herbicide sites of action. Field studies were conducted in 2014 in a total of four field sites in Wyoming, Montana, and Nebraska to quantify the impact of different crop canopies and herbicide applications on B. scoparia density and seed production. Crops used in this study were spring wheat (Triticum aestivum L.), dry bean (Phaseolus vulgaris L.), sugar beet (Beta vulgaris L.), and corn (Zea mays L.). Herbicide treatments included either acetolactate synthase (ALS) inhibitors effective on non-resistant B. scoparia or a non–ALS inhibiting herbicide effective for both ALS-resistant and ALS-susceptible B. scoparia. Bassia scoparia density midseason was affected more by herbicide choice than by crop canopy, whereas B. scoparia seed production per plant was affected more by crop canopy compared with herbicide treatment. Our results suggest that crop canopy and herbicide treatments were both influential on B. scoparia seed production per unit area, which is likely a key indicator of long-term management success for this annual weed species. The lowest germinable seed production per unit area was observed in spring wheat treated with non–ALS inhibiting herbicides, and the greatest germinable seed production was observed in sugar beet treated with ALS-inhibiting herbicides. The combined effects of crop canopy and herbicide treatment can minimize B. scoparia establishment and seed production.

Field studies were conducted from 2009 through 2011 at the Sustainable Agriculture Research and Extension Center near Lingle, Wyoming, to evaluate great northern bean response to PRE flumioxazin mixed with either trifluralin, pendimethalin, or ethalfluralin. Seven treatments were arranged in a randomized complete block with three or four replicates y−1. The soil texture of the study site was loam in 2009 and 2011, and sandy loam in 2010. Soil organic matter ranged from 1.4% to 1.8%. Treatments included flumioxazin plus trifluralin, flumioxazin plus pendimethalin, flumioxazin plus ethalfluralin, ethalfluralin plus EPTC, imazamox plus bentazon (POST), hand-weeded control, and nontreated control. Dry bean density 4 wk after planting differed among herbicide treatments (P < 0.001). Treatments that included flumioxazin reduced dry bean density 54% compared with treatments without flumioxazin. Dry bean yield was influenced by dry bean density; on average, yield in flumioxazin-containing herbicide treatments was 30% less than treatments not containing flumioxazin, even though weed control was generally greater in flumioxazin treatments.

The occurrence of herbicide tank contamination with dicamba or 2,4-D will likely increase with the recent commercialization of dicamba- and 2,4-D-resistant soybean. High-value sensitive crops, including dry bean, will be at higher risks for exposure. In 2017 and 2018, two separate field experiments were conducted in Michigan to understand how multiple factors may influence dry bean response to dicamba and 2,4-D herbicides, including 1) the interaction between herbicides applied POST to dry bean and dicamba or 2,4-D, and 2) the impact of low rates of glyphosate with dicamba or 2,4-D. Dry bean injury was 20% and 2% from POST applications of dicamba (5.6 h ae ha−1) and 2,4-D (11.2 g ae ha−1), respectively, 14 days after treatment (DAT). The addition of glyphosate (8.4 g ae ha−1) did not increase dry bean injury from dicamba or 2,4-D. Over 2 site-years the addition of dry bean herbicides to dicamba or dicamba + glyphosate (8.4 g ae ha−1) increased dry bean injury and reduced yield by 6% to 10% more than when dicamba or dicamba + glyphosate was applied alone. The interaction between 2,4-D (11.2 g ae ha−1) and dry bean herbicides was determined to be synergistic. However, 2,4-D (11.2 g ae ha−1) had little effect on dry bean with or without the addition of a dry bean herbicide program. These studies document that synergy also occurs between dicamba and dicamba + glyphosate and both common dry bean herbicide programs tested: 1) imazamox (35 g ha−1) + bentazon (560 g ha−1), and 2) fomesafen (280 g ha−1). The synergy between dry bean herbicide and dicamba and dicamba + glyphosate can increase plant injury, delay maturity, and reduce yield to a greater extent than dicamba or dicamba + glyphosate alone. This work emphasizes the need to properly clean out sprayers after applications of dicamba to reduce the risk of exposure to other crops.

Earlier reports have summarized crop yield losses throughout various North American regions if weeds were left uncontrolled. Offered here is a report from the current WSSA Weed Loss Committee on potential yield losses due to weeds based on data collected from various regions of the United States and Canada. Dry bean yield loss estimates were made by comparing dry bean yield in the weedy control with plots that had >95% weed control from research studies conducted in dry bean growing regions of the United States and Canada over a 10-year period (2007 to 2016). Results from these field studies showed that dry bean growers in Idaho, Michigan, Montana, Nebraska, North Dakota, South Dakota, Wyoming, Ontario, and Manitoba would potentially lose an average of 50%, 31%, 36%, 59%, 94%, 31%, 71%, 56%, and 71% of their dry bean yield, respectively. This equates to a monetary loss of US $36, 40, 6, 56, 421, 2, 18, 44, and 44 million, respectively, if the best agronomic practices are used without any weed management tactics. Based on 2016 census data, at an average yield loss of 71.4% for North America due to uncontrolled weeds, dry bean production in the United States and Canada would be reduced by 941,000,000 and 184,000,000 kg, valued at approximately US $622 and US $100 million, respectively. This study documents the dramatic yield and monetary losses in dry beans due to weed interference and the importance of continued funding for weed management research to minimize dry bean yield losses.

GAF 141 [(2-chloroethyl)phosphonic acid plus N-methylpyrrolidone] increased basipetal translocation of glyphosate [N-(phosphonomethyl)glycine], dicamba (3,6-dichloro-o-anisic acid), and acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxyl]-2-nitrobenzoic acid} in bean seedlings (Phaseolus vulgaris L. 'Stringless Greenpod′). The GAF 141 was applied as a foliar treatment before or at the same time as herbicide injection into the cotyledonary node. GAF 141 applied 24 h prior to glyphosate, dicamba, or acifluorfen injection enhanced basipetal translocation to the roots and inhibited acropetal translocation to the young shoots. GAF 141 applied simultaneously with the herbicide injection did not have substantial effects on translocation. Greater basipetal translocation of acifluorfen occurred at high (75 ± 5%) than at low relative humidity (35 ± 5%).

Pseudomonas syringae pv. phaseolicola formulated with an organosilicone surfactant was tested as a potential bioherbicide for kudzu. Greenhouse studies were performed to determine the effect of kudzu plant age and leaf age on disease severity and growth of the bacterium in planta. Eight-week-old plants were more diseased 4 wk after spraying and had a higher potential for regrowth 7 wk after spraying than 12-wk-old plants. Young leaves developed water-soaked lesions earlier than older leaves and supported higher populations of bacteria. Data from field experiments at two separate locations indicated that single applications in late spring were as effective as multiple applications in early spring and were enhanced by repeat application. Three months after the beginning of the experiment, extensive regrowth occurred for all bioherbicide treatments and no differences were noted between treatments and the nontreated control.

The basis for increased phytotoxicity of foliar-applied atrazine at high temperature in common bean and redroot pigweed was investigated. Plants were grown under low (15/10 C), medium (25/20 C), or high (35/30 C) temperature regimes. Atrazine absorption by plants grown under different temperatures increased with increasing temperatures in both species. Greater than 90% of absorbed atrazine remained in treated leaves and translocation was not altered by temperature in both species. Metabolism of atrazine by both hydroxylation and glutathione-conjugation was greater in plants grown at 35/30 than 15/10 C in both species. Foliar-applied atrazine reduced extractable photosystem II (PS II) activity as temperature increased in both species. Studies were also conducted on thylakoid membranes from plants not treated with atrazine. The I50 for atrazine inhibition of PS II decreased and affinity of atrazine binding to thylakoid membranes increased as temperature increased in both species. We concluded that the increased phytotoxicity of atrazine at high temperatures is caused by enhanced foliar absorption and greater affinity of atrazine for the binding site.

Five field trials were conducted over a 2-yr period (2007, 2008) at various locations in Ontario to evaluate the tolerance of black, cranberry, kidney, otebo, pink, pinto, small red Mexican (SRM), and white bean to halosulfuron applied PPI, PRE, and POST at 35 and 70 g ai/ha. There was minimal injury (3% or less) with halosulfuron applied PPI or PRE in dry bean. At Exeter and Ridgetown, halosulfuron applied POST at 35 and 70 g/ha caused 3 to 5% and 4 to 8% injury in dry bean, respectively at 1 wk after herbicide application (WAA). The injury was transient with no significant injury at 2 and 4 WAA. At Harrow, halosulfuron POST at 35 and 70 g/ha caused as much as 4% injury at 35 g/ha and 14% injury at 70 g/ha in dry bean. Halosulfuron applied PPI, PRE, and POST at 35 and 70 g/ha caused no decrease in plant height of dry bean except for kidney bean, which was reduced 6% at 70 g/ha, and white bean, which was reduced 3% at both 35 and 70 g/ha. Halosulfuron applied PPI, PRE, and POST at 35 and 70 g/ha caused no decrease in dry bean yield except for kidney bean, which was reduced 9% at 35 g/ha and 10% at 70 g/ha; otebo bean, which was reduced 3% at 70 g/ha; and white bean, which was reduced 7% at both 35 and 70 g/ha. On the basis of these results, there is an adequate margin of crop safety in dry bean to halosulfuron applied PPI or PRE at 35 and 70 g/ha. In addition, there is an adequate margin of crop safety in black, cranberry, pink, pinto, and SRM bean to halosulfuron applied POST at 35 and 70 g/ha. However, further research is required to ascertain the tolerance of kidney, otebo, and white bean to halosulfuron applied POST.

There is little information on the sensitivity of dry beans to flumioxazin. Tolerance of eight cultivars of dry beans representing four market classes (black, cranberry, kidney, and white beans) to preplant incorporated (PPI) and preemergence (PRE) applications of flumioxazin at the rate of 52.5, 70, and 140 g ai/ha were studied in three field experiments in Ontario in 2002 and 2003. There were no differences (P < 0.05) between two cultivars within a market class in their responses to flumioxazin. However, the four market classes differed in their responses to flumioxazin. Black and white beans were more sensitive to the PRE application of flumioxazin than cranberry and kidney beans. Flumioxazin applied PRE at 140 g/ha caused as much as 34% visual injury and reduced plant height by 23 to 28%, shoot dry weight by 35 to 39%, and yield by 20 to 30% in black and white bean market classes. Flumioxazin-applied PPI did not injure any market class. On the basis of this research, there is an acceptable margin of crop safety in these black and white bean cultivars only when flumioxazin is applied PPI. The two cranberry and kidney bean cultivars were tolerant to all rates of flumioxazin applied both PPI and PRE.

Whole-plant bioassays using sugar beet, lettuce, cucumber, green bean, pea, and soybean as test crops were used to detect mesotrione residues in the soil. The test crops were planted in soil treated with mesotrione in the field the previous year at rates of 0 to 560 g ai ha−1 and in nontreated soil from the same field, with mesotrione added at concentrations of 0 to 320 μg kg−1. Experiments were conducted in the greenhouse for a 21-d period. Values for the dose giving a 50% response (I50) were predicted using a log-logistic nonlinear regression model. I50 values (mean ± SE) of 8.6 ± 1.8, 14.9 ± 2.0, 29.8 ± 11.0, 41.6 ± 7.3, 52.9 ± 6.4, and 67.9 ± 30.3 g ai ha−1 for sugar beet, lettuce, green bean, cucumber, pea, and soybean, respectively, indicate that these crops were effective bioassay test species for quantifying mesotrione residues. A greenhouse bioassay was a simple and sensitive tool to detect mesotrione at concentrations of less than 1.0 μg kg−1 with sugar beet and lettuce being the most sensitive test species. The I50 values for soil treated with known concentrations of mesotrione were lower than for field soil treated with mesotrione the previous year. Knowing the level of mesotrione residues in the soil, growers have flexibility in crop rotations following mesotrione use on corn. Growers can use this information to minimize risk of crop injury by choosing appropriate rotation crops that suffer little or no yield reduction.

Fall-planted cover crops offer many benefits including weed suppressive residues in spring sown crops when controlled and left on the soil surface. However, vegetable growers have been slow to adopt direct-seeding (no-till) into cover crop residues. Field studies were conducted in 2009 and 2010 near Paterson, WA and Urbana, IL to evaluate mortality of rye and common vetch (WA) hairy vetch (IL) cover crops, weed density and biomass, and snap bean growth and yield following four cover crop control methods utilizing a roller–crimper. Rye had higher mortality than common and hairy vetch by roller-crimping, and carfentrazone applied after roller crimping only slightly increased vetch mortality. Heavy residues of rye and escaped vetch were difficult to plant into, often resulting in lower snap bean populations. Rye and hairy vetch residues suppressed final weed biomass, while common vetch reduced weed biomass 1 of 2 years. Escaped plants of both vetch species became a weed. Snap bean yields were inconsistent and often lower following cover crops compared with a fallow treatment. Being able to completely control cover crops and to plant, manage escaped weeds and mechanically harvest in the presence of heavy residues are challenges that deter vegetable growers from readily adopting these systems.

The diversity and abundance of insect predators of the bean aphid, Aphis fabae Scop. (Homoptera: Aphididae) on common beans, Phaseolus vulgaris L., were evaluated in Central Kenya. Predators included species in the Orders Coleoptera, Diptera, Hemiptera and Neuroptera. Coccinellidae were the most abundant and diverse group and several species, such as Hippodamia variegata Goeze and Platynaspis capicola Crotch, had hitherto not been recorded on common beans in Kenya. Higher numbers of predators developed on beans during the short rains (up to 540/100 m2 plot) as compared to the long rain season (182/plot) of 1985. In both seasons, numbers of coccinellid larvae were high after the fourth week of bean growth. The study provides evidence of an important build-up of insect predators on beans.