Cherry Leaf Spot Disease Management in Ornamental Cherries in Mid-Tennessee.

Abstract

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 were to evaluate six commercial cultivars for host resistance to CLS and identify effective fungicides that can be recommended to growers. Out of six cultivars 'Kwanzan', 'Okame', 'Autamnalis', 'Snowgoose', 'Yoshino', and 'Akebono' evaluated for host resistance, only 'Kwanzan' displayed moderate resistance with the least amount of disease symptoms in a shade-house environment, followed by 'Autamnalis'. 'Yoshino' was most susceptible to CLS in both the shade-house and field experiments. Out of seven fungicides evaluated individually and in rotations, captan in rotations with tebuconazole and trifloxystrobin and captan in rotations with chlorothalonil and acibenzolar-S-methyl were most effective in controlling CLS. A biopesticide (neem seed oil extract) and a biological control isolate (Stenotrophomonas spp.) were also effective in controlling CLS either alone or in rotation with conventional fungicides. This study identified effective fungicides, a biopesticide, and a biological agent that can be used along with resistant cultivars in CLS disease management.Résumé : La tache foliaire du cerisier (TFC) attribuable à Blumeriella jaapii est une maladie qui nuit passablement à la culture des cerisiers ornementaux dans les pépinières du sud-est des États-Unis. La présente étude avait pour but d'évaluer la résistance de six cultivars commerciaux à la TFC et d'identifier les fongicides efficaces que l'on pourrait recommander aux producteurs. Sur les six variétés testées (Kwanzan, Okame, Autamnalis, Snowgoose, Yoshino et Akebono), seule Kwanzan a illustré une résistance modérée à la maladie, caractérisée par la manifestation du plus petit nombre de symptômes en serre froide. Venait ensuite Autamnalis. Le cultivar Yoshino est le plus sensible à la TFC, autant en serre froide qu'au champ. Parmi les sept fongicides examinés, séparément et en rotation, le captan employé en rotation avec le tebuconazole ainsi que la trifloxystrobine et le captan utilisés en rotation avec le chlorothalonil et l'acibenzolar-S-méthyle s'avèrent les plus efficaces. Un pesticide biologique (extrait de l'huile de graines de margousier) et l'isolat d'un agent de lutte biologique (Stenotrophomonas spp) ont également permis de contrôler la TFC, seuls ou en rotation avec des fongicides classiques. Cette étude a permis d'identifier des fongicides efficaces, un antiparasitaire organique et un agent de lutte biologique susceptibles d'être utilisés avec les cultivars résistants pour combattre la TFC. [Traduit par la Rédaction]

Screening Ornamental Cherry (Prunus) Taxa for Resistance to Infection by Blumeriella jaapii

“…For example, accessions of Prunus maackii (three tested), Prunus takesimensis (six tested), and Prunus incisa (seven tested) were among the most susceptible and the most resistant plants tested. Our results on host resistance among cultivars is in agreement with those of Joshua et al (2017), who tested six ornamental Prunus cultivars and found that Yoshino (P. yedoensis) was among the most susceptible and Kwanzan (Kanzan in our study) was the most resistant. Our study broadens the scope of this previous work on ornamental cherries to provide resistance/susceptibility data for more taxa that are important in landscapes, the nursery trade, and our breeding program.…”

“…Wharton et al (2003) found that using a detached leaf assay to screen sour cherries for resistance to B. jaapii gave comparable results to whole plant inoculations. Similarly, our results are in agreement with those of Joshua et al (2017) who tested some of the same taxa that we tested, but used whole plant evaluations. We conclude, therefore, that our detached leaf assay is an effective method for screening large numbers of plants for relative resistance to CLS.…”

“…Symptomatic trees have decreased photosynthetic metabolism (Gruber et al, 2012) and less vigorous growth (Stanosz, 1992), which can decrease winterhardiness, leading to winter injury and even loss of the tree. The disease can be controlled partly by cultural practices, such as removal of leaf litter in which the pathogen overwinters (Holb, 2013;Joshua and Mmbaga, 2015) and by frequent and well-timed fungicidal applications (Jones et al, 1993;Joshua et al, 2017;McManus et al, 2007). However, fungicide-resistant strains have arisen Proffer et al, 2006).…”

“…Disease-resistant taxa have been found for use in sour and sweet cherry breeding programs (Stegmeir et al, 2014;Wharton et al, 2003), and detached leaf assays have been developed (Wharton et al, 2003). A field screening of six popular ornamental cultivars revealed differential resistance in those taxa as well (Joshua et al, 2017). The objectives of the present study were 2-fold: 1) to screen a large and diverse base of ornamental flowering cherry germplasm to identify the most resistant taxa for use in landscape plantings and in our breeding program, and 2) to verify that our detached leaf assay for this fungus was effective for flowering cherry taxa, where whole tree assays are often impractical.…”