March
2007
, Volume
91
, Number
3
Pages
294
-
300
Authors
Patricia S.
McManus
,
Department of Plant Pathology, University of Wisconsin, Madison 53706
;
Tyre J.
Proffer
,
Department of Plant Pathology, Michigan State University, East Lansing 48824 and Department of Biological Sciences, Kent State University, Salem, OH 44460
;
Raffaele
Berardi
,
Department of Plant Pathology, Michigan State University, East Lansing 48824 and Dipartimento di Protezione e Valorizzazione Agroalimentare, University of Bologna, Bologna, Italy
;
Barrett R.
Gruber
,
Department of Plant Pathology, University of Wisconsin, Madison 53706
;
James E.
Nugent
,
Northwest Michigan Horticultural Research Station, Traverse City 49684
; and
Gail R.
Ehret
,
Zhonghua
Ma
, and
George W.
Sundin
,
Department of Plant Pathology, Michigan State University, East Lansing 48824
Affiliations
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RelatedArticle
Accepted for publication 3 October 2006.
Abstract
ABSTRACT
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.
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© 2007 The American Phytopathological Society