Estimated Yield Loss Research Articles

Economic impact of clinical mastitis in a dairy herd assessed by stochastic simulation using different methods to model yield losses

The main aim of the present study was to examine the economic consequences of a reduction in the incidence of clinical mastitis (CM) at herd level under current Swedish farming conditions. A second objective was to ask whether the estimated cost of CM alters depending upon whether the model reflects the fact that in different stages of lactation, CM gives rise to different yield-loss patterns or postulates just one type of yield-loss pattern irrespective of when, during lactation, CM occurs. A dynamic and stochastic simulation model, SimHerd, was used to study the effects of CM in a herd with 150 cows (9000 kg of energy-corrected milk per cow-year). Four herd types, defined by production level and reproductive performance, were modelled to investigate possible interactions between herd type and response to a reduction in the risk of CM. Technical and economic results, given the initial incidence of CM (25.6 per 100 cow-years), were studied together with the consequences of reducing the initial risk of CM by 50% and 90% throughout lactation and the consequences of reducing the initial risk by 50% and 90% before peak yield. A conventional way of modelling yield losses – i.e. one employing a single yield-loss pattern irrespective of when, during the lactation period, the cow develops CM – was compared with a new modelling strategy in which CM was assumed to affect production differently depending on its lactational timing. The effect of the choice of reference level when estimating yield losses was investigated by comparing the results obtained using the potential yield of mastitic cows, had they not developed CM, with those obtained using the yield of non-mastitic cows. The yearly maximum avoidable cost of CM at herd level was estimated at €14 504, corresponding to 6.9% of the net return given the initial incidence of CM. Expressed per cow-year, the maximum avoidable cost was €97. The cost per case of CM was estimated at €428. Herd types all responded in a similar manner to the reduced relative risk of CM. There were no major differences in the results obtained using the new and the conventional modelling strategy, with the exception of the cost per case of CM. Similarities between the results obtained using the two methods were particularly evident when the mastitic cows’ own yield level, had they not developed CM, was used as the reference for production in healthy cows when yield losses were estimated. It was concluded that the conventional way of modelling yield losses is adequate and should, for the foreseeable future, be used in decision support systems.

Ozone in ambient air at a tropical megacity, Delhi: characteristics, trends and cumulative ozone exposure indices

Seven year data of hourly surface ozone concentration is analyzed to study diurnal cycle, trends, excess of ozone levels above threshold value and cumulative ozone exposure indices at a tropical megacity, Delhi. The ozone levels clearly exhibit a diurnal cycle, similar to what has been found in other urban places. A sharp increase in the ozone levels during forenoon and a sharp decrease in the early afternoon can be observed. The average rate of increase in ozone concentration between 09 and 12 h has been observed to be 7.1 ppb h−1. We find that the daily maximum and daytime 8-h (10–17 h) ozone levels are increasing at a rate of about 1.7 (± 0.7) and 1.3 (± 0.56) ppb y−1, respectively. The directives on ozone pollution in ambient air provided by United Nations Economic Commission for Europe and World Health Organization for vegetation (AOT40) and human health protection were used to assess the air quality. The present surface ozone levels in the city are high enough to exceed “Critical Levels” which are considered to be safe for human health, vegetation and forest. The human health threshold was exceeded for up to ~45 days per year. The AOT40 (Accumulated exposure Over a Threshold of 40 ppb) threshold was exceeded significantly during winter (D-J-F) and pre-monsoon (M-A-M) (Rabi crop growing season) season in India. Translating AOT40 exceedances during pre-monsoon into relative yield loss we estimate yield loss of 22.7%, 22.5%, 16.3% and 5.5% for wheat, cotton, soybean and rice, respectively.

Tropospheric Ozone Effects on the Productivity of Some Crops in Central Saudi Arabia

This study was conducted to evaluate damaging degree of ambient ozone (O3) levels in certain economically important crops in typical areas of the central KSA (Riyadh). Daily mean ozone concentrations were recorded by portable O3 analyzers in the center of Batha, Naseem, Oleya and Industrial City, from the beginning of October, 2006 to middle of June, 2007. Maseef area was used as control because it is receiving fewer pollutants (O3 levels less than 40 nL L -1 ). Selected crops grown in pots were exposed to short-term of pollution at defined localities. These crops include Triticum aestivum L. cv. Giza 68 (wheat), Vicia faba L. cv. Lara, (broad bean), Phaseolus vulgaris L. cv. Giza 3 (kidney bean) and Pisum sativum L. cv. Perfection (pea). The exposure indicators of them are length, injury symptoms, biomass and yield. The maximum values of daily O3 were 125 nL L -1 , 77 nL L -1 , 95 nL L -1 and 166 nL L -1 , in all the four studied areas, respectively in mid June, 2007. Results showed that the estimated yield losses varied in all four studied areas, being 35, 9, 39 and 46%, respectively for wheat; being 16, 13, 21 and 33%, respectively for broad bean; being 22, 20, 28 and 45%, respectively for kidney bean and being 5, 3, 14 and 30%, respectively for pea. This research recommended that these plant species can be used to give bio-indicator significance to assess ambient ozone impacts of different examined areas in KSA.

Estimates of Yield and Economic Losses Associated with White Mold of Rain‐Fed Dry Bean in North Dakota

White mold [caused by Sclerotinia sclerotiorum (Lib.) de Bary] of dry bean (Phaseolus vulgaris L.) is the most important disease affecting rain‐fed dry bean yields in North Dakota. The economic impact of this disease in North Dakota was assessed through a survey of 250 fields during 2003 to 2005. Profitability of a single fungicide application for managing white mold also was examined. Yield loss was estimated by regressing the mean of white mold incidence per county and year with their respective estimated yields. The slope of the resulting equation was divided by its intercept and multiplied by 100 to express yield loss as percentage of potential yield. Results of these analyses indicated a loss of 14 kg/ha (R2 0.50; P = 0.03) for every unit of white mold incidence, which represents a loss of 0.8% of the potential yield. The economic impact of the disease was assessed using estimated hectarage with ≥20% white mold incidence in conjunction with yield and dry bean prices as reported by National Agricultural Statistics Service for North Dakota. Over the 3‐yr period, economic losses were highest in 2004 and least in 2005; yield loss averaged 524 kg/ha (range 424–722 kg/ha) while production loss averaged 6433 t (range 1,789–10,438 t). These represent an average economic loss of U.S. $2.95 million (range U.S. $.63–5.74 million) per year. Profitability of a fungicide application to manage white mold was heavily influenced by disease pressure and varied widely between years. In years with high disease pressure, like 2004, a fungicide application would have produced a positive return in 72% of the fields; but under moderate to low disease‐pressure, applying fungicides would have been a profitable practice in <20% of fields.

Root rot of common bean in Zanjan, Iran: major pathogens and yield loss estimates

In 2007, prevalence of root rot pathogens and disease yield losses were studied under prevailing environmental conditions in common bean fields at Zanjan. Root rot disease incidence varied by sampling time and location of a field. In the majority of fields, Fusarium solani was the predominant fungus, being isolated from 2.8 to 96% of root samples over the sampling time, followed by Rhizoctonia solani, Macrophomina phaseolina and F. oxysporum. At pod maturity, the mean values for investigated factors were: disease incidence, 4.7–95%; disease severity, 0.1–2; disease index, 0.1–29%; number of seeds, 3.3–19; number of pods per plant, 8.3–62; and 100-seed weight, 19–53 g. Regression analysis demonstrated that disease incidence, disease severity and disease index were negatively correlated with both the number of pods or seeds per bean plant, whereas there was a positive correlation between the disease and 100-seed weight. If the indicative relations obtained between the disease and yield components are confirmed by further studies, then findings may contribute to the future estimation of bean yield losses to root rots and selection for resistant cultivars.

Estimates of Yield and Economic Losses Associated with White Mold of Rain-Fed Dry Bean in North Dakota

White mold [caused by Sclerotinia sclerotiorum (Lib.) de Bary] of dry bean (Phaseolus vulgaris L.) is the most important disease affecting rain-fed dry bean yields in North Dakota. The economic impact of this disease in North Dakota was assessed through a survey of 250 fields during 2003 to 2005. Profitability of a single fungicide application for managing white mold also was examined. Yield loss was estimated by regressing the mean of white mold incidence per county and year with their respective estimated yields. The slope of the resulting equation was divided by its intercept and multiplied by 100 to express yield loss as percentage of potential yield. Results of these analyses indicated a loss of 14 kg/ha (R2 0.50; P = 0.03) for every unit of white mold incidence, which represents a loss of 0.8% of the potential yield. The economic impact of the disease was assessed using estimated hectarage with ≥20% white mold incidence in conjunction with yield and dry bean prices as reported by National Agricultural Statistics Service for North Dakota. Over the 3-yr period, economic losses were highest in 2004 and least in 2005; yield loss averaged 524 kg/ha (range 424–722 kg/ha) while production loss averaged 6433 t (range 1,789–10,438 t). These represent an average economic loss of U.S. $2.95 million (range U.S. $.63–5.74 million) per year. Profitability of a fungicide application to manage white mold was heavily influenced by disease pressure and varied widely between years. In years with high disease pressure, like 2004, a fungicide application would have produced a positive return in 72% of the fields; but under moderate to low disease-pressure, applying fungicides would have been a profitable practice in <20% of fields.

Biomass Yield Reductions in Switchgrass Due To Smut Caused by Tilletia maclaganii

Switchgrass (Panicum virgatum) is an attractive biomass crop for renewable energy, but there is little information on disease losses. Tilletia maclaganii causes a smut disease of switchgrass that results in stunting, premature flowering, and replacement of seeds by fungal sori. We conducted a study in naturally-infested fields to describe the impact of smut on biomass yield. Ten fields were sampled; smut incidence, stand density, and biomass yield were determined. Disease incidence varied from 0.7 to 55.4% (26% overall) and biomass varied from 174 to 617 g/m2. Mean biomass/tiller was significantly reduced by the disease in each field, by 38 to 82%. Yield loss was calculated based on the ratio of mean biomass/tiller for samples (actual yield) and mean biomass/tiller for healthy tillers (attainable yield). Yield loss estimates ranged from 1.7 to 40.1% among the fields. There was a strongly linear relationship (R2 = 0.95) between disease incidence and yield loss, and regression analysis estimated a 0.66% reduction in yield for every 1% increase in disease incidence. According to this model, yield loss for all sampled fields was estimated at 17.0%. This disease is having a significant impact on biomass production in Iowa, and there is a critical need for research on management approaches if switchgrass is to be successful as a feedstock for lignocellulosic ethanol production. Accepted for publication 2 January 2008. Published 17 March 2008.

PERDAS DE PRODUÇÃO PELA BROCA-DO-COLMO (Diatraea saccharalis Fabr. 1794) (LEPIDOPTERA: PYRALIDAE) EM GENÓTIPOS DE ARROZ DE TERRAS ALTAS

The impact of the Diatraea saccharalis natural infestation on yield of 24 genotypes of upland rice was studied in an experiment carried out in field conditions. The attack of D. saccharalis on stems and its effect on spikelet weight was determined using a yield loss index and by regression analysis. The index used quantifies the spikelet mass loss per bored stem in relation to spikelet mass no bored stem. The estimates obtained with these two methods were different. Less than 10% of genotypes showed a linear relationship between the infestation and stem borer damage. Estimated yield losses based on the index seemed more appropriate to the conditions of the experiment. Infestations by D. saccharalis did not visibly affect the weight of spikelets of five genotypes, caused a small reduction in two genotypes, and caused economic losses in the most of them (17 genotypes). The CNAs9023 genotype was the least infested and presented the highest weight of spikelets, and showed more resistance than CNAs9028, which was more infested and produced less. KEY-WORDS: Upland rice; stem borer; sampling; genotype evaluation.

Air pollution impact assessment on agroecosystem and human health characterisation in the area surrounding the industrial settlement of Milazzo (Italy): a multidisciplinary approach

In order to evaluate the impact of atmospheric pollutants emitted by the industrial settlement of Milazzo (Italy) on agriculture, sulphur dioxide and ozone levels in air were monitored and the data were used to estimate yield losses of the most widespread cultures. Trace element concentrations in crops and soils were also detected and metabolic profiles of soil microbial communities were considered. Vibrio fischeri test was used to appraise airborne pollutant ecotoxicity and epidemiological studies on causes of death distribution were carried out to characterize health state of people living in the area. All the sampling points were selected in farms on the basis of a theoretical meteo-diffusive model of industrial air pollutants. Experimental SO2 and O3 values mainly exceeded the threshold established by Italian and EU regulations to protect vegetation and they correspond to estimated significant crop losses. Conversely toxic element residues in soils and in agroalimentary products were generally lower than the fixed values. SO2 and O3 concentrations, toxic element contents and ecotoxicity levels of airborne pollutants were not related only to industrial site emissions, while the fluctuations on metabolic profiles of soil microbial communities seem to agree with the predicted deposition of xenobiotic compounds from the industrial plants. The epidemiological study evidenced a better health state of populations living in the investigated area than in the Messina province and the Sicily region but, inside the area, males living in the municipalities closest to the industrial settlement exhibited a worst health state than those in the very far ones.

A model of the effect of fungicides on disease‐induced yield loss, for use in wheat disease management decision support systems

AbstractA model of the effect of foliar‐applied fungicides on disease‐induced yield loss is described, parameterised and tested. The effects of fungicides on epidemics of Septoria tritici (leaf blotch), Puccinia striiformis (yellow rust), Blumeria graminis f.sp. tritici (powdery mildew) and Puccinia triticina (brown rust) on winter wheat were simulated using dose–response curve parameters. Where two or more active substances were applied together, their joint action was estimated using an additive dose model where the active substances had the same mode of action or a multiplicative survival model where the modes of action differed. By coupling the model with models of wheat canopy growth and foliar disease published previously, it was possible to estimate disease‐induced yield loss for a prescribed fungicide programme. The difference in green canopy area and, hence, interception of photosynthetically active radiation between simulated undiseased and diseased (but treated) crop canopies was used to estimate yield loss. The model was tested against data from field experiments across a range of sites, seasons and wheat cultivars and was shown to predict the observed disease‐induced yield loss with sufficient accuracy to support fungicide treatment decisions. A simple method of accounting for uncertainty in the predictions of yield loss is described. Fungicide product, dose and spray timing combinations selected using the coupled models responded appropriately to disease pressure and cultivar disease resistance.

Nitrogen fertilization at the rice panicle differentiation stage to compensate for rice water weevil (Coleoptera: Curculionidae) injury

A three-year study was conducted to determine the effect of nitrogen fertilizer rates applied at the panicle initiation stage of rice, Oryza sativa L., and insecticide applications on yield loss caused by rice water weevil, Lissorhoptrus oryzophilus Kushel, damage. Our estimates of yield loss caused by L. oryzophilus injury were, at the recommended nitrogen rate of 191 kg N per ha, 1.7% in 1997, 11.8% in 1998, and 9.9% in 1999. In 1998, doubling the panicle differentiation nitrogen rate from 67 to 134 kg N per ha significantly increased yield by 591 kg per ha, averaged across insecticide treated and untreated plots. In both 1998 and 1999, reducing nitrogen rate below the recommended rate significantly ( P<0.05) reduced rice yield, indicating the value of providing the rice plant with sufficient levels of nitrogen. In 1998 and 1999, insecticide treatment increased yield by 570 and 830 kg per ha, respectively. The interaction between insecticide treatment and fertilizer rate was not significant ( P>0.05) for yield in any year of our study, suggesting that increasing nitrogen at the panicle differentiation stage does not have a major impact on compensation of the rice plant for L. oryzophilus injury. Our results indicate that farmers should not increase nitrogen fertilizer at the panicle differentiation stage to compensate for L. oryzophilus damage.

Effect of Tobacco Budworm (Lepidoptera: Noctuidae) Infestation Level on Budworm-Resistant and -Susceptible Varieties of Flue-Cured Tobacco in North Carolina

Field experiments were conducted from 1972 to 1978 and from 1998 to 1999 to evaluate tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae), larval feeding on flue-cured tobacco, Nicotiana tabacum (L.), yield in eastern North Carolina. In the earlier studies, using variety Coker 319, treatment plots were evaluated when either 0 or 100% of plants in a plot were infested with H. virescens larvae. Treatment differences based on actual yield loss (kilograms per hectare) were compared with estimations of yield loss based on leaf consumption and leaf loss. Results indicate actual yield loss when 100% of plants were infested was less than the corresponding estimates of yield loss. In the later experiments, two tobacco budworm-resistant lines, ‘CU 263′ and ‘CU 370′, were compared with a commercial susceptible variety, K 326, when 0, 10, 20, or 40% of plants were infested (1998) and 0, 10, 40, 75, or 100% of plants were infested (1999). Although significant increases in leaf equivalents consumed were associated with infestations exceeding the recommended threshold, differences were not detected for yield (kilograms per hectare), quality (dollars per kilogram), and value (dollars per hectare) within each tobacco line. Additionally, there was not a significant correlation between value and infestations level for any of the tobacco lines. These results provide economic support for tolerance of a higher treatment threshold. Although K 326 sustained more leaf equivalent loss than CU 263 and CU 370, the value of K 326 harvested was higher than that of CU 263 and CU 370. To justify use of resistant varieties, the combination of pest pressure and the benefit of host plant resistance must be greater than the capacity of a susceptible variety to produce competitive yields, despite sustaining significantly higher loss.

Effect of Tobacco Budworm (Lepidoptera: Noctuidae) Infestation Level on Budworm-Resistant and -Susceptible Varieties of Flue-Cured Tobacco in North Carolina

Field experiments were conducted from 1972 to 1978 and from 1998 to 1999 to evaluate tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae), larval feeding on flue-cured tobacco, Nicotiana tabacum (L.), yield in eastern North Carolina. In the earlier studies, using variety Coker 319, treatment plots were evaluated when either 0 or 100% of plants in a plot were infested with H. virescens larvae. Treatment differences based on actual yield loss (kilograms per hectare) were compared with estimations of yield loss based on leaf consumption and leaf loss. Results indicate actual yield loss when 100% of plants were infested was less than the corresponding estimates of yield loss. In the later experiments, two tobacco budworm-resistant lines, 'CU 263' and 'CU 370', were compared with a commercial susceptible variety, K 326, when 0, 10, 20, or 40% of plants were infested (1998) and 0, 10, 40, 75, or 100% of plants were infested (1999). Although significant increases in leaf equivalents consumed were associated with infestations exceeding the recommended threshold, differences were not detected for yield (kilograms per hectare), quality (dollars per kilogram), and value (dollars per hectare) within each tobacco line. Additionally, there was not a significant correlation between value and infestations level for any of the tobacco lines. These results provide economic support for tolerance of a higher treatment threshold. Although K 326 sustained more leaf equivalent loss than CU 263 and CU 370, the value of K 326 harvested was higher than that of CU 263 and CU 370. To justify use of resistant varieties, the combination of pest pressure and the benefit of host plant resistance must be greater than the capacity of a susceptible variety to produce competitive yields, despite sustaining significantly higher loss.

Ozone and Water Stress: Effects on the Behaviour of Two White Clover Biotypes

ozone pollution, water stress, stomata conductance, ozone uptake, clover, OTC.Ozone is a strong oxidizing pollutant which derives by alteration of the photolytic NOx cycle and it accumulates in the troposphere spreading in rural areas and therefore determining injuries on natural vegetation and crops. Since its penetration occurs mainly through stomata, all factors which alter plant-atmosphere relations could be able to modify plant response to ozone. Interaction between ozone and water stress in Mediterranean environment was studied on ozone resistant and sensitive biotypes of white clover, which were grown in charcoal filtered and notfiltered Open Top Chambers in factorial combination with different levels of water supply. Measurements of biomass, leaf area and stomatal conductance were made during the growth period. Ozone injuries were estimated as not-filtered/filtered OTC yield ratio; the stomatal flux of ozone was estimated multiplying stomata conductance x diffusivity ratio between ozone and water vapour (0.613) x ozone hourly concentrations. The hourly values of ozone uptake were cumulated throughout the cropping periods of the two years. In the sensitive biotype, water stress reduced yield losses due to ozone from 38% to 22%, as well as yield losses due to water stress were reduced by the presence of ozone from 43% to 29%, while no interaction between ozone and water stress was observed in the resistant biotype. Biomass yield losses of the sensitive biotype were strictly correlated to cumulated ozone uptake (R2 = 0.99), while biomass yield losses of the resistant biotype were not affected by the ozone fluxes variations created by the treatments. Flux based models could better estimate yield losses due to ozone in Mediterranean environments in which other stresses could be contemporary present; therefore, the new European directives might replace the actual thresholds based on ozone concentration with others based on ozone flux models.

Estimate of milk and curd yield loss of sheep and goats with intrammamary infection and its relation to somatic cell count

Equations for predicting milk and curd loss due to intramammary infection in sheep and goat herds were derived. The empirical equations were derived from previously published studies conducted by this team with Assaf sheep and crossbreeds of goats in Israel. From these equations, it appears that infection of 25, 50 and 75% of the udders in a given herd was associated with loss of 4.1–12.2.5% milk in sheep and 0.8–2.3% in goats; whereas curd loss was 5.2–15.5% in sheep and 3.3–9.8.9% in goats. Based on percent of udder infection and projected SCC, the following categories are suggested for classification of sheep and goat milk: i. High-quality milk <800,000 SCC/mL, associated with infection of ∼25%; ii. Medium quality milk <1,500,000 SCC/mL, associated with infection rate between 25 and 50%; iii. Low-quality milk >1,500,000 SCC/mL, associated with infection rate above 50%; iv. Milk containing >3,500,000 SCC/mL should not be accepted for human consumption.

Disease Expression and Ecophysiological Yield Components in Sunflower Isohybrids with and without Verticillium dahliae Resistance

ABSTRACTVerticillium wilt (Verticillium dahliae Kleb.) is an important disease affecting sunflower (Helianthus annuus L.) in most production areas in Argentina, Canada, and the United States. Estimation of yield losses produced by the disease is difficult because of the absence of highly efficient chemical control and resistant hybrids of comparable yield potential. In this work nine pairs of isohybrids with and without resistance to V. dahliae were sown at five different locations and evaluated under natural infection to determine disease induced yield reductions across environments with varying V. dahliae incidence. The effects of the disease on physiological components of growth were studied in a separate trial with three pairs of isohybrids. Disease incidence and severity for resistant isohybrids (R) were zero or nearly zero independently of their genetic background in all locations, indicating the isohybrids were highly resistant or immune. In the most severe environments, grain and oil yield of susceptible isohybrids (S) were nearly 30% less than those of the resistance couterparts. The incorporated resistance resulted in an increased percent radiation interception and radiation use efficiency (RUE). However, the effect of the disease on crop growth rate was evident after flowering. Up to that phenological stage, leaf expansion, radiation interception and photosynyhetic rate did not differ between R and S isohybrids.

Modeling the effect of cultivar resistance on yield losses of winter wheat in natural multiple disease conditions

The use of winter wheat ( Triticum aestivum L.) cultivars resistant to diseases may make it possible to reduce yield losses without the need to use fungicides, which are expensive and may damage the environment. The cultivar resistances favored depend on the region considered and the nature of the most widespread diseases in that region. We have constructed a statistical linear model for the estimation of relative yield loss due to diseases, making it possible to assess the effects of winter wheat cultivars in various disease conditions. We considered the interactions “potential disease intensity × winter wheat cultivar” for four main fungal diseases: septoria tritici blotch ( Mycosphaerella graminicola), brown rust ( Puccinia triticina), yellow rust ( Puccinia striiformis) and powdery mildew ( Erysiphe graminis). This model can therefore be readily adapted to different regions with diverse combinations of these diseases. The potential intensity of each disease in each trial was calculated based on the symptoms observed on susceptible cultivars not treated with fungicide. The cultivar effect was characterized by the ratings of cultivar susceptibility to each disease and by cultivar earliness. The parameters of the model were estimated from 276 wheat cultivar trials carried out over 12 years (1991–2002) in the major wheat-growing areas of France. This model can help to choose from the cultivars resistant to several diseases (but very rarely resistant to all the diseases), those cultivars best adapted to a given environment, according to the hierarchy of potential disease intensities encountered.

Soil Water Availability Modulation Over Estimated Relative Yield Losses in Wheat (Triticum aestivumL.) Due to Ozone Exposure

The approach developed by Fuhrer in 1995 to estimate wheat yield losses induced by ozone and modulated by the soil water content (SWC) was applied to the data on Catalonian wheat yields. The aim of our work was to apply this approach and adjust it to Mediterranean environmental conditions by means of the necessary corrections. The main objective pursued was to prove the importance of soil water availability in the estimation of relative wheat yield losses as a factor that modifies the effects of tropospheric ozone on wheat, and to develop the algorithms required for the estimation of relative yield losses, adapted to the Mediterranean environmental conditions. The results show that this is an easy way to estimate relative yield losses just using meteorological data, without using ozone fluxes, which are much more difficult to calculate. Soil water availability is very important as a modulating factor of the effects of ozone on wheat; when soil water availability decreases, almost twice the amount of accumulated exposure to ozone is required to induce the same percentage of yield loss as in years when soil water availability is high.

Relationship between abundance of rodents and damage to agricultural crops

Developing a relationship between pest abundance and damage to crops is essential for the calculation of economic injury levels (EIL) leading to informed management decisions. The crop modelling framework, APSIM, was used to simulate the impact of mouse damage on yield loss on wheat where a long-term dataset on the density of mice was available (1983–2003). The model was calibrated using results from field trials where wheat plants were hand clipped to imitate mouse damage. The grazing effect of mice was estimated using the population density, daily intake per mouse and the proportion of wheat grain and plant tissue in the diet to determine yield loss. The mean yield loss caused by mice was 12.4% (±5.4S.E.; range −0.5 to 96%). There were 7/21 years when yield loss was >5%. A damage/abundance relationship was constructed and a sigmoidal curve explained 97% of variation when accounting for different trajectories of mouse densities from sowing to harvest. The majority of damage occurred around emergence of the crop when mouse densities were >100 mice ha −1. This is the first time that field data on mouse density and a crop simulation model have been combined to estimate yield loss. The model examines the efficacy of baiting and how to estimate EILs. Because the broadscale application of zinc phosphide is cheap and effective, the EIL is very low (<1% yield loss). The APSIM model is highly flexible and could be used for other vertebrate pests in a range of crops or pastures to develop density/damage relationships and to assist with management.

Incidence of and yield loss caused by maize rayado fino virus in maize cultivars in Ecuador

Three sowing date trials, each planted with one cultivar, were performed to measure the natural incidence of the Maize rayado fino virus (MRFV). The lowest incidences (1–6%) were obtained at the sowing dates normally practised in the tested regions. Earlier or later sowing dates had higher to much higher incidences (up to 18 and 32%). Two cultivar trials, one with four cultivars and one with eight cultivars, showed significant differences in incidence, ranging from 14.0% in ‘Iniap-160’ to 2.0% in ‘Cadet-2’. In one trial with plots of 1000 m2, the cultivar Iniap-122 was sown at three sowing dates. In each plot, plants that developed MRFV symptoms at the 8–10 leaf stage, at the 12–14 leaf stage and at the emergence of tassels were marked. Marked MRFV-affected plants were compared with non-MRFV-affected plants in their neighbourhood to estimate yield loss due to MRFV. The yield losses at the three sowing dates were 2.5, 1.6 and 4.8%, respectively. It was concluded that the yield loss due to MRFV is quite small provided sowing is restricted to the normal sowing period.