Epidemics of apple powdery mildew (Podosphaera leucotricha) in a mixed cultivar orchard

Epidemics of apple powdery mildew were monitored on leaves of vegetative extension shoots in a mixed-cultivar orchard in 1979. 1980 and 1981. Cultivars Cox's Orange Pippin. Golden Delicious. Ida Red and Suntan were very susceptible but little mildew developed on cv. Discovery in any year. Results with cvs Crispin and Spartan were less consistent due, in part, to differing patterns of vegetative growth. The rankings of cultivars for disease incidence (proportion of leaves with mildew), number of colonies and mildewed area were similar, and were also consistent on fungicide-sprayed and unsprayed trees in 1981. Less disease occurred on fungicide-treated Golden Delicious than on Cox's Orange Pippin. Most infections occurred on the rolled leaves at the shoot tip. Spore production was greatest on leaves at positions -1 to -4 where leaf 0 was the youngest and leaf - 1 the adjacent and older unrolled leaf.     

Spatial and temporal spread of powdery mildew (Erysiphe pisi) in peas (Pisum sativum) varying in quantitative resistance

A field experiment was conducted to assess the progress in time and spread in space of powdery mildew (caused by Erysiphe pisi ) in pea ( Pisum sativum ) cultivars differing in resistance to the disease. Disease severity (proportion of leaf area infected) was measured in 19 × 23 m plots of cultivars Pania and Bolero (both susceptible) and Quantum (quantitatively resistant). Inoculum on infected plants was introduced into the centre of each plot. Leaves (nodes) were divided into three groups within the canopy (lower, middle, upper) at each assessment because of the large range in disease severity vertically within the plants. Disease severity on leaves at upper nodes was less than 4% until the final assessment 35 days after inoculation. Exponential disease progress curves were fitted to disease severity data from leaves at middle nodes. The mean disease relative growth rate was greater on Quantum than on Pania or Bolero, but it was delayed, resulting in an overall lower disease severity on Quantum. Gompertz growth curves were fitted to disease progress on leaves at lower nodes. Disease progress on Quantum was delayed compared with Pania and Bolero. The average daily rates of increase in disease severity from Gompertz curves did not differ between the cultivars on these leaves. Disease gradients in the plots from the inoculum focus to 12 m were detected at early stages of the epidemic, but the effects of background inoculum inputs and the rate of disease progress meant that these gradients decreased with time as the disease epidemic intensified. Spread was rapid, and there were no statistically significant differences between cultivar isopathic rates (Pania 2.2, Quantum 2.9 and Bolero 4.0 m d⁻¹).     

Resistance in water yam (Dioscorea alata) cultivars in the French West Indies to anthracnose disease based on tissue culture-derived whole-plant assay

Reactions of 60 water yam ( Dioscorea alata ) cultivars to three isolates of the yam anthracnose fungal pathogen ( Colletotrichum gloeosporioides ) were evaluated using tissue culture-derived whole-plant assay. Three disease parameters: single score on a scale of 0–6 at the seventh day after inoculation (SD7); area under the disease progress curve (AUDPC); and disease progress rate ( R _d) were compared, and cultivars were classified into disease-response groups using a rank-sum method based on AUDPC scores for the two most virulent isolates. A wide range of variation in resistance of the D. alata cultivars, and significant effects of pathogen isolate and isolate–cultivar interactions, were observed for all disease parameters. The three disease parameters were positively correlated; however, four cultivars showed great dispersions from the regression lines for comparisons of SD7 with the multiple assessments based AUDPC and R _d. The 60 cultivars were separated into resistant ( n  = 12), moderately resistant ( n  = 19), moderately susceptible ( n  = 18) and susceptible ( n  = 11) groups. The potential of the tissue culture-derived whole-plant assay to resistance breeding programmes and further understanding of the yam anthracnose pathosystem is discussed.     

Relationship between leaf emergence and optimum spray timing for leaf blotch (Rhynchosporium secalis) control on winter barley

For wheat, the optimum time to apply fungicide to control disease on a given leaf layer is usually at, or shortly after, full leaf emergence. Data from field experiments on barley were used to investigate whether the same relationship was applicable to control of leaf blotch on barley. Replicated plots of winter barley were sown in the autumns of 1991, 1992 and 1993 at sites in southwest England with high risk of Rhynchosporium secalis infection. Single fungicide treatments at four doses (0·25, 0·5, 0·75 or 1·0 times the label rate) were applied at one of eight different spray times, starting in mid-March in each year, with intervals of 10–11 days between spray timings. Disease was assessed every 10–11 days and area under the disease progress curve (AUDPC) values were used to construct fungicide dose by spray time response surfaces for each of the upper four leaves, for each year. Spray timings shortly before leaf emergence were found to minimize the AUDPC for each year and leaf layer, and also the effective dose (the dose required to achieve a specified level of control), similar to wheat. Fungicide treatments on barley were effective for a longer period before leaf emergence than afterwards, probably because treatments before emergence of the target leaf reduced inoculum production on leaves below. This partly explains why fungicides tend to be applied earlier in the growth of barley compared with wheat.     

Effect of Fungicides on Septoria nodorum and Wheat Green Leaf Area1

Fungicides applied at different growth stages were compared for the control of wheat glume blotch, caused by Septoria nodorum (Berk.) Berk. In glasshouse and small-scale field tests, 11 commercially used fungicides, when applied to fully emerged wheat ears, cv. Hobbit, gave only partial control of ear infection by spores applied immediately after spraying. They gave better control of infection of leaves by a similar inoculum. Larger field trials, moreover, indicated better foliar and ear disease control from fungicide applications made before ear emergence, compared with those applied later. In another field trial, nine fungicides were applied to replicated plots of winter wheat, cultivars Atou and Hobbit at GS 31, GS 39, GS 55 or GS 71. On five occasions from anthesis (25 June) until 30 July disease was assessed and green leaf area measured. The trial was harvested on 22 August 1980. Significantly greater yields and grain weights were obtained from plots sprayed with fungicide at GS 39 than from those sprayed at any other time or left unsprayed. Treatments made before symptoms of infection by S. nodorum developed (i.e. before GS 55) prolonged the duration of green leaf areas during the post-anthesis period. Grain weight and yield increases were related closely to the duration of green leaf area above 75 96, but not to the amount of green leaf area at any single assessment nor to the subsequent degree of disease development. The data on which this abstract is based form part of a continuing research programme, the results of which will be published in full at a later date. Full details on the 1980 results referred to above appear in the Annual Report of Long Ashton Research Station (1980).     

Effects of bean rust (Uromyces appendiculatus) epidemics on host dynamics of common bean (Phaseolus vulgaris)

Epidemics of bean rust ( Uromyces appendiculatus ) and their effects on host dynamics of common bean ( Phaseolus vulgaris ) were studied in three controlled greenhouse experiments, with and without fungicide sprays, on two susceptible bean cultivars, Dufrix and Duplika. Bean plants were artificially inoculated with a suspension of 10⁵ U. appendiculatus urediniospores mL⁻¹ water and temporal disease progress, as well as host growth dynamics (leaf size and defoliation), were monitored on a leaflet basis in comparison with non-inoculated plants, which were sprayed with deionized water. Progress curves of bean rust, expressed as the proportion of leaf area occupied by pustules (uredinia), or as the proportion occupied by total lesion area (= halo areas + pustule area), were well described by logistic functions with maximum disease levels clearly lower than 1. Bean rust epidemics substantially affected host growth by reducing the total leaf area formed by 17·4–35·6% and 35·3–46·2% compared with healthy plants for cvs Dufrix and Duplika, respectively. Fungicide sprays mitigated the negative effect of bean rust, leading to a gain in leaf area of 17–21% compared with unsprayed plants in both cultivars in two experiments, while in another experiment, disease control had no effect in Dufrix, but a clear effect in Duplika. In addition to the growth depression, bean rust also led to pronounced losses of leaf area as a result of reduced leaf size (leaf shrivelling) and accelerated defoliation.     

Changes in populations of the eyespot fungi Tapesia yallundae and T. acuformis under different fungicide regimes in successive crops of winter wheat, 1984–2000

Effects of regular treatments with the fungicides carbendazim and prochloraz applied to whole plots divided into subplots with different initial population mixtures of carbendazim-sensitive or carbendazim-resistant Tapesia yallundae or T. acuformis were studied in successive crops of winter wheat from 1984/85 to 1999/2000. In unsprayed and carbendazim-sprayed whole plots, a stable coexistence of about 50% each of T. yallundae and T. acuformis developed within five seasons, but in whole plots sprayed with prochloraz or prochloraz plus carbendazim, the proportion of T. acuformis increased to > 80%. A discrete time difference equation model was derived from knowledge of the biology of eyespot and competition theory to describe the population changes. The model was fitted to the data from treatments where coexistence occurred [subplots in unsprayed (1985–92) and carbendazim-sprayed (1985–89) whole plots], using nonlinear least squares regression. The optimized value of the resource overlap coefficient was small, suggesting niche differences between the two species. Populations were nearly 100% carbendazim-resistant in carbendazim-sprayed whole plots by July 1985 (one season) and in whole plots sprayed with prochloraz plus carbendazim by July 1986 (two seasons). In prochloraz-sprayed whole plots, the proportion of carbendazim-resistant isolates decreased more rapidly than in unsprayed whole plots in the 1980s, but by July 1992 a shift in populations in unsprayed and prochloraz-sprayed whole plots towards predominantly carbendazim-resistant strains had occurred.     

Post‐spray effects of an aerial application of fenitrothion on the pine beauty moth,Panolis flammea (Denis & Schiffermüller)

Abstract

Panolis flammea that had survived an aerial spraying programme of fenitrothion were compared in a series of laboratory experiments with moths that had not been within the sprayed area, to assess the effects of sub‐lethal spray application on various life history parameters. Emergence success was not significantly different between the two treatments and the sex ratio in both cases approximated 1:1. The bionomics of moths surviving in the sprayed plots were different in several respects from those taken from unsprayed plots. The former emerged from pupae later, had lower levels of fecundity and a longer pre‐oviposition period. Females from sprayed plots were also heavierthan males and their weight was positively correlated with fecundity, whereas neither of those traits were shown by unsprayed moths. A number of other bionomic traits were not significantly different in sprayed or unsprayed groups. Analysis of the population growth rates of P. flammea from areas of the forest where control was either ineffective or effective, revealed no significant differences. The implications of these results for the population dynamics of P. flammea are discussed.     

Foliar resistance of cacao (Theobroma cacao) to Phytophthora palmivora as an indicator of pod resistance in the field: the effect of light intensity and time of day of leaf collection

Resistance of cacao leaves to Phytophthora palmivora was studied with regard to the time of leaf collection (morning, afternoon) and the degree of exposure of the leaves to light in the field (low, medium and high). The efficiency of leaf disc inoculations in predicting field resistance of nine clones was compared with that of detached and attached pod inoculations. Significant effects were observed, with leaves exposed to high light intensity and collected early in the afternoon showing highest susceptibility. The effect of time of leaf collection was reduced when leaves were stored overnight and leaf discs prepared and inoculated the following day, as compared to inoculations on the day of collection. Interactions between the main factors were significant, though less substantial than the clone effects. The most significant correlations with pod resistance ( r  = 0·70 to 0·97) were obtained for leaves collected early in the morning and exposed to intermediate shade conditions in the canopy. For other treatments, the correlations with pod resistance were still positive ( r  = 0·23 to 0·83) but often not significant. Pod inoculations in the laboratory were better correlated with field resistance ( r  = 0·92) than pod inoculations in the field ( r  = 0·72). Detached pod inoculations were also better correlated with leaf disc inoculations than those of attached pods. The results confirm the validity of laboratory inoculations of leaves and pods to assess field resistance to Phytophthora . Standardization of the leaf disc test is essential to obtain reliable results.     

Effect of pea plant architecture on spatiotemporal epidemic development of ascochyta blight (Mycosphaerella pinodes) in the field

The effect of pea canopy structure on epidemics of Mycosphaerella pinodes was investigated in four spring pea cultivars (Bridge, Obelisque, Solara and Athos) in two field experiments. These cultivars had similar levels of susceptibility to ascochyta blight and presented different architectural features (branching, standing ability and stem height). Stem height ranged from 77 to 95 cm in 1999 and from 72 to 92 cm in 2000, while leaf area index (LAI) ranged from 3·8 to 5·1 in 1999 and from 3·8 to 4·7 in 2000. Internode lengths varied from 4·6 to 6·0 in 1999 and from 3·8 to 4·7 in 2000. Mean distance between nodes in the canopy (MDN) ranged from 12·2 to 15·3 cm in 1999 and from 11·2 to 13·9 cm in 2000. Canopies with different architecture differed in disease progression on stipules and mainly on pods. The levels of disease on stipules and pods were strongly correlated. Moreover, if disease was considered as a function of stipule height up the stem, large differences in vertical disease distribution were observed between cultivars. Three architectural features acted on disease development: cumulative LAI above the node on which disease was assessed (LAIcum) and large MDN favouring disease development, and large internode length reducing disease severity. Modifying LAI distribution and plant organization could be one way to reduce the impact of ascochyta blight, by direct or indirect effects on environmental and dispersal conditions.     

Visual and PCR assessment of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) cultivars

Methods to assess light leaf spot ( Pyrenopeziza brassicae ) on winter oilseed rape cultivars were compared in laboratory, controlled-environment and field experiments. In controlled-environment experiments with seedling leaves inoculated at GS 1,4, the greatest differences in percentage area affected by P. brassicae sporulation were observed with inoculum concentrations of 4 × 10³ or 4 × 10⁴ spores mL⁻¹, rather than 4 × 10² or 4 × 10⁵ spores mL⁻¹, but older leaves had begun to senesce before assessment, particularly where they were severely affected by P. brassicae . In winter oilseed rape field experiments, a severe light leaf spot epidemic developed in 2002/03 (inoculated, September/October rainfall 127·2 mm) but not in 2003/04 (uninoculated, September/October rainfall 40·7 mm). In-plot assessments discriminated between cultivars best in February/March in 2003 and June in 2004, but sometimes failed to detect plots with many infected plants (e.g. March/April 2004). Ranking of cultivar resistance differed between seedling experiments done under controlled-environment conditions and field experiments. The sensitivity of detection of P. brassicae DNA extracted from culture was greater using the PCR primer pair PbITSF/PbITSR than using primers Pb1/Pb2. P. brassicae was detected by PCR (PbITS primers) in leaves from controlled-environment experiments immediately and up to 14 days after inoculation, and in leaves sampled from field experiments 2 months before detection by visual assessment.     

Substantial reductions in winter wheat diseases caused by addition of straw but not manure to soil

Over a period of 3 years, five agronomically distinct crops of winter wheat were grown in plots in which straw (1 kg m⁻²), manure (4 kg m⁻²) or nothing were incorporated into the soil. Plant establishment and height, but not leaf area per tiller, were lower in straw-treated plots. Fertilizer regimes differed between years. Soil and leaf nitrogen were recorded; there was no obvious link between N and any disease or soil amendment. The numbers of leaf layers scorable for disease were similar in all treatments. At the end of the season, plants from straw-treated plots had consistently reduced septoria tritici blotch (caused by Mycosphaerella graminicola ), powdery mildew [caused by Erysiphe ( Blumeria ) graminis ], brown rust (caused by Puccinia recondita ) and foot rot (caused by Fusarium spp.). Early on, M. graminicola was worse in straw-treated plots. In manure-treated plots, P. recondita was reduced but effects on other diseases were inconsistent and slight. A fungicide, chlorothalonil, was applied in one crop; its effects did not interact with those of other treatments. Mycosphaerella graminicola was not suppressed by straw in outdoor pot experiments. Late in the season, straw-treated plants had significantly higher leaf silica ( P  < 0·01). In a glasshouse experiment, plants supplied with silicon had less E. graminis infection ( P  < 0·001) and higher leaf silica, but effects on M. graminicola were inconsistent. A prior inoculation of M. graminicola primed plant defences against a subsequent attack of E. graminis , but only in the presence of adequate Si. It is postulated that straw acts in the field by increasing Si availability.     

Threshold values for chemical control of powdery mildew (Erysiphe cruciferarum) on Brussels sprouts

To establish control thresholds for chemical control of powdery mildew (Erysiphe cruciferarum) on Brussels sprouts, mildew intensity on leaves and buds was observed on the cultivars Lunet, Tardis and Asgard during three years in unsprayed plots. Mildew infection on the leaves was observed from late August onwards, increasing to moderate or high levels. In one year light infestation of the buds was observed, but no reduction in quality occurred. These preliminary results indicate, that from late August onwards the following levels of leaf injury by powdery mildew can be tolerated: T=5+0.42^*(Julian date — 235), in which T is the tolerable leaf injury in percentage leaf area covered. When sampling the crop to assess powdery mildew infection, care must be taken that leaves are sampled from all stem positions, as top leaves tend to be much less infected.     

Weak selection by field sprays for flutriafol resistance in Septoria tritici

Change in sensitivity of populations of Septoria tritici resulting from single sprays of the sterol demethylation-inhibiting fungicide flutriafol was measured. Field trials were conducted over 3 years at two sites separated by about 15 km, on cvs Mercia and Riband at each site, in plots at least 10 × 12 m. Treatments included the full recommended rate and a reduced dose of flutriafol and a mixture of flutriafol with chlorothalanil. Sprays were applied at GS37; samples were taken just before spraying and as soon as lesions appeared on leaf 2, which had had no visible disease at the time of spraying. Epidemiological evidence suggests that sprays acted both curatively and as protectants. Significant shifts in sensitivity occurred after spraying in both water-sprayed and fungicide-sprayed plots; all plots became less sensitive. Disease severity after spraying clearly decreased with increasing fungicide concentration and with the use of a mixture of flutriafol and chorothalanil. However, after correction for the shifts in the water-sprayed plots, no dose produced a significant change in population sensitivity level, although sample sizes were large. There was no trend in sensitivity in the population over the 3 years of the experiment.     

Application of real-time and multiplex polymerase chain reaction assays to study leaf blotch epidemics in barley

ABSTRACT Leaf blotch, caused by Rhynchosporium secalis, was studied in a range of winter barley cultivars using a combination of traditional plant pathological techniques and newly developed multiplex and real-time polymerase chain reaction (PCR) assays. Using PCR, symptomless leaf blotch colonization was shown to occur throughout the growing season in the resistant winter barley cv. Leonie. The dynamics of colonization throughout the growing season were similar in both Leonie and Vertige, a susceptible cultivar. However, pathogen DNA levels were approximately 10-fold higher in the susceptible cultivar, which expressed symptoms throughout the growing season. Visual assessments and PCR also were used to determine levels of R. secalis colonization and infection in samples from a field experiment used to test a range of winter barley cultivars with different levels of leaf blotch resistance. The correlation between the PCR and visual assessment data was better at higher infection levels (R(2) = 0.81 for leaf samples with >0.3% disease). Although resistance ratings did not correlate well with levels of disease for all cultivars tested, low levels of infection were observed in the cultivar with the highest resistance rating and high levels of infection in the cultivar with the lowest resistance rating.     

Spiders in sprayed and unsprayed cotton fields in Israel,their interactions with cotton pests and their importance as predators of the Egyptian cotton leaf worm,spodoptera littoralis

Densities of spiders in sprayed and unsprayed cotton fields were determined during 1981 and 1982. Eighteen families were found in an unsprayed field and 13 in sprayed fields. Species of Clubionidae, Gnaphosidae and Philodromidae comprised more than half of the total number collected. The mean weekly number of spiders per meter of cotton row was 9.1 in the unsprayed field and 5.1–5.6 in sprayed fields. Spider populations fluctuated similarly in sprayed fields in both observation years, with only one peak in July, whereas there were two peaks in the unsprayed field. Spiders played an important role in suppressing pest populations and in delaying pest outbreaks early in the cotton growing season. Thus, early pesticide applications to cotton fields are unnecessary. In a biocontrol experiment, spiders suppressed larvae of the Egyptian cotton leaf worm,Spodoptera littoralis (Boisd.), thereby reducing damage to cotton leaves.     

Analysis of head and leaf reaction towards <Emphasis Type="Italic">Microdochium nivale</Emphasis>

This research examined the variation in the response of eight commercial wheat cultivars to Microdochium nivale isolates using both in vivo FHB tests (AUDPC and RHW measurements) and in vitro detached leaf assays (LGR). Irrespective of fungal variety, the two Italian cvs Fortore and Norba exhibited the greatest amount of visual disease symptoms (mean AUDPC=2.2 and 2.3, respectively), being significantly more susceptible than the other six cultivars (AUDPC 1.24) (P < 0.05). Irrespective of fungal variety, the Italian cv. Norba and the Irish cv. Falstaff were more susceptible than the other cultivars (except Fatima 2) in terms of RHW (P < 0.05), while the cvs Fortore, GK Othalom and Consort were more resistant than the other five cultivars (P < 0.05). In the detached leaf assay, the Hungarian cv. GK Othalom and the Italian cv. Norba were more susceptible (mean LGR=0.79 and 0.81 mm day^–1, respectively) to M. nivalethan the other six cultivars (mean LGR=0.51–0.72) (P < 0.05). Analysis of the relationship between head and leaf reaction to M. nivaleinfection revealed no significant correlation.     

Effect of different levels of mannitol-induced water stress on the tolerance of cultivated oat (Avena sativa L.) to didofop-methyl

The effect of degree of water stress in Avena sativa on diclofop-methyl efficacy was assessed. Within 24 h of applying stress by adding mannitol to the root medium (0 to 12.5%), the rate of leaf extension of the youngest leaves (leaves 3 and 4) decreased with increasing mannitol concentration. Without water stress, application of diclofop-methyl had little effect on extension rate of leaves 3 and 4 during the first 4 days after spraying. Subsequently, it caused a significant decrease in the extension rate of leaf 4 with more pronounced effects on later leaves. Diclofop-methyl had little effect on leaf extension rate of plants given mannitol. Shoot dry weight at harvest for unsprayed plants decreased with increased mannitol concentration and for sprayed plants it was greater without mannitol than with mannitol (all levels). However, at mannitol concentrations greater than 4%, shoot dry weight for sprayed and unsprayed plants was not significantly different. Sprayed plants exposed to 2–8.5% mannitol produced seed heads but those at zero mannitol did not. When the root medium of all treatments was flushed of mannitol one week after spraying, then main-tained without mannitol, shoot dry weight at harvest for unsprayed plants decreased slightly with increased mannitol concentration applied initially. However, shoot dry weight for sprayed plants increased with increased mannitol concentration. Without mannitol two weeks after spraying, chlorophyll concentrations of leaves 3 and 4 were greater and water saturation deficit (WSD) values were lower for unsprayed plants than sprayed plants but there were no differences at 6.2% mannitol. It is proposed that tolerance to diclofop-methyl by A. sativa as a result of water stress, is primarily due to a decreased rate of leaf expansion resulting in lower demand for membrane synthesis and less strain on membranes damaged by the herbicide.     

Organochlorine pesticide residues - a review of some recent findings

Investigations to determine the optimum timing and placement of a supplementary food spray, Envirofeast® on the abundance of predatory insects on cotton was conducted in irrigated commercial cotton fields at Yarral near Narrabri, New South Wales, Australia, in 1998 v - v 99. Plots treated with the supplementary food product at the four-true leaf stage recorded a significantly higher number of predatory beetles, bugs and lacewings per metre compared with plots treated at two, six and eight-true leaf stages and unsprayed (control) plots. The cumulative total number of predatory beetles, bugs and lacewings recorded throughout the season in both treated and control plots was 23.81 per m. Of this total, plots treated at four true leaf stage recorded the highest (7.15 per v m) (i.e 30.03%), followed by two true leaf (5.81 per m) (24.41%), six true-leaf (4.31 per v m (18.12%), eight true-leaf stage (4.63 per v m) (i.e. 19.44%) and the unsprayed (control) plot recorded the lowest (1.91 per m (8.03%). The number of spiders per metre were not significantly different ( p v > v 0.05) among treatments and the control plots. The number of predators recorded in cotton crops treated with the supplementary food product as a band spray (33 v - v 50% band) or skip row spray (i.e. to every second row) was not significantly different ( p v > v 0.05) from plots where the product was applied as a solid spray to the entire crop (no skip row and/or no banding). Thus, tailoring Envirofeast® treatment in this way will ultimately reduce the quantity of product used, the cost of the product and allow cotton growers to adopt a multiple-use pattern for the product to support integrated pest management programmes in cotton.     

Angular leaf spot of phaseolus beans: relationships between disease, healthy leaf area, and yield

ABSTRACT Five field experiments were conducted to investigate the relationship between the severity of visible disease (X), area under the disease progress curve (AUDPC), healthy leaf area index on any given day (HLAI), radiation intercepted by healthy leaf area on any given day (HRI), healthy leaf area duration (HAD), total healthy leaf area absorption (HAA), and yield of Phaseolus beans, cultivars Rosinha and Carioca, inoculated with Phaeoisariopsis griseola at several doses. In general, yield was not related to disease severity (X) or AUDPC. In contrast, the highest yields were always related to the highest values of HAD and HAA. The relationship between yield and HAD was linear in each of five trials (29.9 < R(2) < 70.2%, P < 0.001). The relationship between yield and HAA was linear in four of the trials (52.3 < R(2) < 70.3%, P < 0.001) and exponential in one of them (in which the plant canopy was the largest). Singlepoint models using HRI to estimate yield at various times during the crop season were developed. The slope of the yield-HRI relationship proved to be stable (26.8 +/-2.4 g MJ(-1)), regardless of cultivar, locale, planting date, and bean growth stage (from R5 to R8). The yield-HLAI relationship proved to be less consistent. HRI is proposed as a key explanatory variable for a transportable system of disease management; it may be useful in producing precise recommendations at the farm level.