Search

Ornamental flowering cherry trees are important landscape plants in the United States but are susceptible to several serious pests and disease problems. Cherry leaf spot, incited by the fungus Blumeriella jaapii, is characterized by defoliating susceptible trees in late summer, leading to weakening or even death of the tree. To identify resistant plants for use in landscape plantings and in our breeding program, we used a detached leaf assay to screen 69 diverse ornamental flowering cherry taxa for resistance to cherry leaf spot. We found clear differences in susceptibility among the accessions, with seven accessions developing essentially no symptoms at all. A variance decomposition showed that most of the variance (59%) occurred among accessions, indicating that genotype, even more than species, determined susceptibility. The detached leaf assay used in this study is an effective method for screening large numbers of plants for relative resistance to cherry leaf spot. These methods will be particularly useful to characterize germplasm and screen hybrids in breeding and selection programs.

The aim of this study was to demonstrate the 10% threshold level for cherry leaf spot incidence on 23 commercial sweet cherry cultivars in two training systems. Twenty three cherry cultivars were evaluated in the two training systems with a spacing of 4 x 1 m and with a spacing of 2 x 5 m. Results showed that leaves of many cultivars were heavily infected, e.g. cultivars (cvs) ’Biggareau Burlat’, ’Sunburst’, while others showed low disease incidence e.g. cvs ’Celeste’ and ’Blaze Star’. According to the 10 % threshold level, cv ’Celeste’ proved to be the most resistant cultivar to leaf infection, while cv ’Münchebergi korai’ exceeded extremely the 10% threshold level. Leaf spot incidence was affected by training system on most cultivars. Thirteen cultivars had less than 10% infection in the 4 x 1 m spacing (i.e. they did not reach the 10% disease threshold level). At the same time, only 3 cultivars showed less than 10% infection in the 5 x 2 m spacing.

Sour cherry generally holds limited resistance to attack by cherry leaf spot fungus (Blumeriella jaapii) but differences in field performance are found between cultivars and in breeding progeny. Traditionally the degree of attack is estimated visually together with the type of reaction on the leaves. A more precise and less subjective method of evaluation is of interest for screening germplasm. A method of drying leaves, scanning dried leaves and a digital picture analysis protocol was developed to provide exact data on the percentage area of attacked necrotic tissue per leaf and with options of analysing size distribution of single necrotic spots to reveal detailed patterns of infections. The new method was used to characterize leaf attack in autumn on 20 individual leaves from single trees from a sour cherry breeding genepool of over 100 genotypes in a non-sprayed situation with high inoculum present. The percentage of necrotic leaf surface varied highly within the 20 leaves from one genotype, being dependent on the level of inoculum dispersal and air humidity/precipitation over time and space. The mean percentage of attacked leaf surface varied from 0 to almost 35% of total leaf area and the maximum from 0 to 60% necrotic leaf area, indicating the potential large impact on photosynthetic capacity in attacked trees. The distribution of and absolute size of single necrotic spots demonstrated differences in how individual genotypes react to infections, from small spots in tolerant genotypes to large collapsing necrotic spots in very susceptible genotypes. A comparison of attack data with the percentage of remaining leaves on a tree in autumn revealed that some genotypes retain leaves very late even if attacked by leaf spot disease. These trees may maintain a fairly high photosynthetic capacity even if some percentages of the leaf have become necrotic. Sour cherry generally holds limited resistance to attack by cherry leaf spot fungus (Blumeriella jaapii) but differences in field performance are found between cultivars and in breeding progeny. Traditionally the degree of attack is estimated visually together with the type of reaction on the leaves. A more precise and less subjective method of evaluation is of interest for screening germplasm. A method of drying leaves, scanning dried leaves and a digital picture analysis protocol was developed to provide exact data on the percentage area of attacked necrotic tissue per leaf and with options of analysing size distribution of single necrotic spots to reveal detailed patterns of infections. The new method was used to characterize leaf attack in autumn on 20 individual leaves from single trees from a sour cherry breeding genepool of over 100 genotypes in a non-sprayed situation with high inoculum present. The percentage of necrotic leaf surface varied highly within the 20 leaves from one genotype, being dependent on the level of inoculum dispersal and air humidity/precipitation over time and space. The mean percentage of attacked leaf surface varied from 0 to almost 35% of total leaf area and the maximum from 0 to 60% necrotic leaf area, indicating the potential large impact on photosynthetic capacity in attacked trees. The distribution of and absolute size of single necrotic spots demonstrated differences in how individual genotypes react to infections, from small spots in tolerant genotypes to large collapsing necrotic spots in very susceptible genotypes. A comparison of attack data with the percentage of remaining leaves on a tree in autumn revealed that some genotypes retain leaves very late even if attacked by leaf spot disease. These trees may maintain a fairly high photosynthetic capacity even if some percentages of the leaf have become necrotic

To minimize harmful effects of the fungicide application in sweet cherry orchards, it is necessary to use them in accordance with the good agricultural practice and to monitor presence of their residues. Cherry leaf spot caused by Blumeriella jaapii is a significant sweet cherry disease which control is heavily dependent on fungicide treatments. In this study, effects of fungicide treatments against B. jaapii and fungicide residues remaining in sweet cherry fruits after the treatments were evaluated, and the causal agent of cherry leaf spot was confirmed on cherry leaves from untreated control plots using conventional phytopathological techniques (isolation on nutrient media and morphological traits of developed fungal colonies). The trial was set up at two localities in south Serbia (District of Niš), in sweet cherry orchards, according to EPPO methods. Fungicides tested against B. jaapii were based on dodine (650 g a.i./kg) WP formulation, at concentration of 0.1% and mancozeb (800 g a.i./kg) WP formulation, at concentration of 0.25%. During the trial, two evaluations were carried out. Fungicide efficacy was determined according to Abbott. The obtained data were statistically processed by ANOVA and LSD test. In both sweet cherry orchards high efficacy in control B. jaapii was registered in case of dodine application efficacy of 96.3-98.9%, while mancozeb showed slightly lower efficacy of 91.0-95.6%. The results of the dissipation dynamic suggest that the dodine dissipation curves followed the first-order kinetic (Ct=6.23e−0.09, with R2=0.986) and its half-life in sweet cherry fruits was 7.7 days. The final residues in sweet cherry fruits were below the MRL (3 mg/kg) 21 days after the application. The results indicate that sweet cherry fruits can be safely consumed after dodine based fungicides applications at the recommended rate.

In two 3-year studies, the effect of two training systems (free spindle versus super spindle) and two tree-age periods (4–6 versus 13–15 years) were evaluated on cherry leaf spot (CLS) epidemics and tree defoliation for 12 sweet cherry cultivars in an integrated orchard. Then, relationships among CLS infection periods, CLS incidences and percent defoliation were determined for the training systems and tree-age periods. In addition, cultivars were classified into three CLS susceptibility and three defoliation categories (low, moderate, and high). Annual CLS and defoliation incidences of individual cultivars were lower, by 0.05–10.8% and by 0.1–9.1%, respectively, on trees pruned to super spindle compared to trees pruned to free spindle, except for defoliation incidences on cultivars ‘Biggareau burlat’ and ‘Muncheberger’, where training system had no effect. The three-year means of CLS and defoliation incidences ranged from 18.0 to 70.5% and from 14.1 to 47.9%, respectively, on the 4–6 years old trees; and from 8.7 to 34.7% and 5.4–25.5%, respectively, on the 13–15 years old trees. Leaf spot infection period, CLS incidence and defoliation incidence showed strong relationship in both training systems in those years when annual CLS incidences were high. Cherry leaf spot and defoliation classification categories of some cultivars were different for the two training systems and/or for the two three-year periods. Our study demonstrated that both training system and tree-age can impact the severity of leaf spot epidemics and tree defoliation for sweet cherry genotypes showing moderate susceptibility to leaf spot.

Cherry leaf spot (CLS) disease caused by Blumeriella jaapii is a significant constraint in nursery production of flowering cherries in the southeastern United States. The objectives of this study w...

Cherry leaf spot (Blumeriella jaapii) is the most dangerous disease of orchards and nurseries of stone fruit trees, especially sour cherries. Chemical method is the primary tool for controlling cherry leaf spot. Dodine, benzimidazole and triazole fungicides are the most commonly used. The frequent application of these fungicide groups resulted in the development of resistant forms of the causal agent to their active substances. In years 2012–2015 in 33 selected sour cherry orchards located in central Poland, the occurrence of resistant forms of B. jaapii to dodine and benzimidazoles was determined by using a spore germination test on the poisoned agar medium. The study showed high resistance to thiophanate-methyl in 15 orchards, and to dodine in 5 orchards. The medium resistance to thiophanate-methyl and dodine occurred in 7 orchards. Low level of resistant forms to thiophanate-methyl was found in 11 orchards, and to dodine – in 21. The obtained results will be the basis for implementation of cherry leaf spot control programs in regard to appropriate antiresistance guidelines.

Practical resistance to sterol demethylation inhibitor (DMI) fungicides among populations of Blumeriella jaapii, the cherry leaf spot (CLS) pathogen, was documented in 2005. In the present study, strategies to reduce selection for DMI-resistant strains of B. jaapii and adapt to possible restrictions on the use of chlorothalonil are described. Ten field trials were conducted on the sour cherry cultivars Balaton and Montmorency to test the efficacy of integrating respiration-inhibitor and copper-based fungicides into spray programs. Programs that included up to three sprays of copper-based fungicides were among the most effective for controlling CLS, although leaf phy-totoxicity was sometimes observed. Under high disease pressure, eliminating chlorothalonil compromised CLS control. ‘Balaton’ and ‘Montmorency’ did not differ in the percentage of leaves with CLS or defoliation resulting from CLS. The physical modes of action of representative DMI, QoI, and copper-based fungicides were evaluated in a leaf disk assay. Trifloxystrobin, a QoI fungicide, provided the best protection against infection by B. jaapii. All fungicides were more effective than water when applied 46 h postinfection, although differences were not statistically significant in one of two trials. Tebuconazole, a DMI, was the only fungicide that was more effective than water in preventing resporulation from existing lesions in both trials. Isolates of B. jaapii, which varied in DMI-sensitivity, all were sensitive to copper in vitro.

Sweet and sour cherries are fruit with great potential in the agroecological conditions of Serbia, taking into account its climatic and geographical conditions. In the production of these plant species, a number of leaf pathogens may occur. One of the most significant is Blumeriella jaapii occurring mainly on commercial cultivars present in Serbia. The occurrence and development of this pathogen mostly depends on climatic conditions. Under favorable climatic conditions, infection progressively develops through the season and causes premature defoliation resulting in decreased fruit quality and increased bud sensitivity to frost, reduced yield and fruit size, as well as tree die-back the following season. In addition to chemical control, agrotechnical and other measures must be employed. Several active ingredients are registered against cherry leaf spot in Serbia: mancozeb, dodine, prochloraz, dithianon, and the mixture of primary and secondary potassium phosphate+chlorothalonil. There are eight registered products based on the above-mentioned active ingredients. The risk of resistance development to fungicides registered against B. jaapii in Serbia is low. Nonetheless, implementation of resistance management strategy is proposed.

The intensive use of site-specific fungicides in agricultural production provides a potent selective mechanism for increasing the frequency of fungicide-resistant isolates in pathogen populations. Practical resistance occurs when the frequency and levels of resistance are great enough to limit the effectiveness of disease control in the field. Cherry leaf spot (CLS), caused by the fungus Blumeriella jaapii, is a major disease of cherry trees in the Great Lakes region. The site-specific sterol demethylation inhibitor fungicides (DMIs) have been used extensively in the region. In 2002, CLS control failed in a Michigan orchard that had used the DMI fenbuconazole exclusively for 8 years. That control failure and our observations from around the state suggested that practical resistance had developed in B. jaapii. Field trial data covering 1989 to 2005 for the DMIs fenbuconazole and tebuconazole supported observations of reduced efficacy of DMIs for controlling CLS. To verify the occurrence of fungicide-resistant B. jaapii, monoconidial isolates were collected in two surveys and tested using a fungicide-amended medium. In one survey, 137 isolates from sites with different DMI histories (no known history, mixed or alternated with other fungicides, and exclusive use) were tested against 12 concentrations of fenbuconazole, tebuconazole, myclobutanil, and fenarimol. Isolates from sites with no prior DMI use were DMI sensitive (DMIS = no colony growth at 0.2 μg/ml a.i.) whereas the isolates from the site with prior exclusive use showed growth at DMI concentrations 3 to >100 times higher, and were rated as DMI resistant (DMIR). A second survey examined 1,530 monoconidial isolates, including 1,143 from 62 orchard sites in Michigan, where DMIs had been used to control CLS. Resistance to fenbuconazole was detected in 99.7% of the orchard isolates. All isolates from wild cherry trees were sensitive and isolates from feral and dooryard trees showed a range of sensitivities. A polymerase chain reaction (PCR)-based detection method for identifying B. jaapii and DMIR was developed and tested. The species-specific primer pair (Bj-F and Bj-R) based on introns in the CYP51 gene of B. jaapii, and the DMIR-specific primer pair (DMI-R-Bj-F and DMI-R-Bj-R) based on an insert found upstream of CYP51 in all DMIR isolates, provided an accurate and rapid method for detecting DMIR B. jaapii. The PCR-based identification method will facilitate timely decision making and continued monitoring of DMIR subpopulations in response to management programs.

Gas exchange in cherry leaves infected with Blumeriella jaapii , the causal agent of cherry leaf spot disease, was studied. Infection reduced net photosynthesis during all stages of disease development. Throughout the course of this study there was a continuous decrease in carboxylation and the maximum electron transport rate. Carboxylation was always the most affected parameter, and it seems likely that the infection interferes mainly with the enzymatic processes in the Calvin cycle. There was also a drastic decrease in assimilation, transpiration and stomatal conductance before any visible symptoms occurred on cherry leaves.

The aim of this study was to evaluate the cherry leaf spot (CLS) incidence on 12 sweet cherry cultivars in integrated sweet cherry production in three consecutive years from 2010 till 2012. Assessed cultivars (cvs.) were ’Aida’, ’Axel’, ’Biggareau burlat’, ’Blaze Star’, ’Celeste’, ’Germersdorfi 3’, ’Izabella’, ’Katalin’, ’Krupnoplodnaja’, ’Linda’, ’Sunburst’, ’Vera’Results showed that year had an essential effect on the CLS disease incidence. Cultivars showed great differences within years. Cultivar ’Celeste’ showed the lowest disease incidence on leaves in all years lower than 10%. The largest disease incidence on leaves was on cv. ’Sunburst’ in 2010, on cv. ’Germersdorfi 3’in 2011 and on cv. ’Axel’ in 2012. Disease incidence on these cultivars ranged between 10 and 25%.

The aim of this study was to evaluate the effectiveness of reduced spray programmes against cherry leaf spot in integrated and organic sour cherry orchards. Altogether four spray programmes were performed i) standard integrated: sprays followed by forecasting systems during the season, ii) reduced integrated: sprays followed by forecasting systems but only 75% of the spray numbers used during the season-long spray programme, iii) standard oragnic: sprays applied every 7–14 days during the season and iv) reduced organic: 60 % of the spray numbers used during the season-long spray programme. Our study showed that cherry leaf spot did not increase above 3.1, 7.4, and 8.9% in 2008, 2009, and 2010, respectively, in the integrated orchards. However, leaf spot incidence was above 20% in all years in the organic field. Reduced spray programme did not increase significantly cherry leaf spot incidence in the integrated field in either years. However, leaf spot incidence increased significanly (above 20%) in the reduced spray programme for the organic orchard.

In this review, some aspects of disease management of cherry leaf spot (Blumeriella jaapii) are summarised with special reference to pesticide use. In the first part of the review, we show the non-chemical control approach (e. g. removal of fallen leaves, planting resistant cultivar) against leaf spot. In the second part of the review, the effect of pesticides including fertilizers (urea) and fungicides on cherry leaf spot are discussed. Special attention are given to the fungicides of copper, dodine, captafol, captan, benomil, chlorothalonil, sterol demethylation inhibitors (e.g. fenarimol, fenbuconazole, myclobutanil, tebuconazole), and strobilurins about their effectiveness against cherry leaf spot. In the final part of the review, possibilities of cherry leaf spot control are discussed in integrated and organic cherry orchards.

In this review, some important features of biology are summarised for cherry leaf spot (Blumeriella jaapii). In the first part of the review, the geographical distribution of the pathogen and the causal organism are described. Disease symptoms and disease cycle of cherry leaf spot are also shown. Special attention is given to hosts and then several cherry cultivars.are described in relation to their susceptibility to cherry leaf spot.

Investigations were made on 12 sweet cherry cultivars (‘13-S-22-8’, 'Sunburst', `Kozerska'., 'NY 13791', 'Royalton', 'NY 13688', 'Hartland', `Sumerset', 'Pollax', 'Patriotka Krima', 'Castor', and `Lapins') in an experimental orchard of cherry cultivar collection in the Institute of Agriculture at Kyustendil, Bulgaria during the period of 1997-2003. The trees were planted in 1996. All cultivars were grafted on Prunus mahaleb. Four biological properties of the cultivars were assessed such as blooming time, resistance to late spring frost, fruit ripening and fruit mass. Among cultivars, a good resistance to late spring frost was observed on cultivar 'Sunburst'. The fruit mass varied between 4.2 g (cv. 'Patriotka Krima') and 8.5 g (cv. `Sunburst'). The susceptibility of the cherry cultivars to cherry leaf spot caused by Blumeriella jaapii was assessed in mid-September in each year. The estimation of the rate of attack was made according to the grade of Townsend and Neuberger. All cultivars showed symptoms of cherry leaf spot but the degree of susceptibility was different. Cultivar `Patriotka Krima' was the least susceptible, while cultivar `Somerset' was the most susceptible to Blumeriella jaapii.

We examined Blumeriella jaapii (Rehm) v. (Arx) infection on 21 sweet cherry cultivars in the cultivar-collection of the Experimental Station Pallag of the University of Debrecen, in 2004 and 2005. Considerable differences were detected in the infection degree of the different cultivars. In 2005, due to the more humid weather, the average infection highly exceeded data of the previous year. No symptomless cultivars were detected in either year. The least sensitive ones were Linda and the cultivar 11/106. The most sensitive cultivars were Early Müncheberg, Biggareau burlat and Round Solymári. Infection degrees of Alex, Rita and Vega were different from those of other cultivars on the basis of the two experimental years. It is important to consider both the specific weather conditions of the year and cultivar resistance at planning the plant protection system. It is recommended for each cultivar to perform a fungicide-spaying after the harvest.

Leaf spot disease on wild cherry (Prunus avium L.) was frequently observed in plantations for timber production in central Italy. Acervuli and conidia of Phloeosporella (= Cylindrosporium) padi (Lib.) Arx were detected. Since the presence in Italy of its teleomorph, Blumeriella jaapii (Rehm) Arx (1), has never been reported, the life cycle of the pathogen was investigated. In the autumn of 1996, in some diseased leaves in different locations, microconidia were observed in the same acervuli that produced macroconidia. Also, in a plantation near Rome, fallen leaves with dark, stromatic spots were present. Leaf samples were put into plastic net bags and laid onto the ground under the trees, to be observed after overwintering in the field. In March, fully developed apothecia were present on the lower leaf surface, containing asci and ascospores that matched the description of B. jaapii. To verify the capability of the ascospores produced in nature to infect the host, overwintered leaf fragments with mature apothecia were fixed to the underside of the lids of petri dishes, above healthy cherry leaves laid upside down on moistened filter paper. Uninoculated, healthy leaves kept in petri dishes served as control. Dishes were incubated at room light and temperature conditions. The ascospores were readily discharged and dark spots with hypophyllous or amphigenous acervuli of P. padi developed on infected leaves 20 days later. No symptoms were present in the control leaves. In conclusion, B. jaapii can complete its life cycle in wild cherries in Italy. The possibility of spring infection by ascospores should be considered in disease management programs. Reference: (1) S. Kaszonyi. Acta Phytopathol. Acad. Sci. Hung. 1:93, 1966.

A study was conducted to quantify the effect of leaf spot caused by Blumeriella jaapii on black cherry seedlings in a nursery. The severity of leaf spot, which had developed from naturally occurring inoculum, was visually estimated on leaves collected from untreated and benomyl-treated subplots in August 1990. Leaves were counted and seedling height, caliper, and area of collected leaves were measured. The number of seedlings with diameters ≥0.40 cm (5/32 in.), the minimum acceptable, was determined before seedlings were lifted in spring 1991 (.)