First Report of Powdery Mildew on Nandina domestica (Berberidaceae) in North America

Nandina domestica Thunb. (heavenly bamboo) is an ornamental plant that is widely planted in landscapes in California and other states. Since 1996, powdery mildew disease has been seen on outdoor landscape N. domestica in various regions of California (Alameda, Monterey, Riverside, and Santa Barbara counties). Symptoms consist of reddening of leaf and stem tissues colonized by the fungus and curling and twisting of infected leaves. The following observations were the same for all collected isolates. White ectophytic mycelium was observed on leaves and petioles. Mycelium on leaves was amphigenous, mostly epiphyllous, and effused or in patches. Hyphal appressoria were nipple-shaped to lobed and sometimes opposite in orientation. Conidiophores were cylindrical, straight, sometimes slightly flexuous, 22 to 32 × 6 to 8 μm in dimension, and followed by one to two shorter cells. Conidia were cylindrical, produced singly, and 27 to 42 × 11.5 to 14 μm in dimension. Fibrosin bodies were not observed. Conidial germ tubes were approximately twice the length of the spore, originated from the ends of the spore, and terminated in simple appressoria. Cleistothecia were not present. Based on these characteristics, the fungus was identified as Microsphaera berberidis (DC) Lév. (1). Pathogenicity was confirmed by gently pressing diseased leaves on leaves of healthy N. domestica plants. Plants were incubated in a humidity chamber at 22 to 24°C, and after 10 to 14 days, powdery mildew colonies developed. A voucher specimen was deposited in the University of California Herbarium (UC 1738622). Additional inoculation experiments showed that four other N. domestica cultivars were susceptible (Compacta Nana, Gulf Stream, Harbour Dwarf, and Royal Princess). Helfer (2) noted several possible candidates for the Nandina powdery mildew pathogen in the United Kingdom. However, due to the conidial characteristics of that fungus and the paucity of character descriptions for the several species mentioned, no species name was given to the Edinburgh isolate. In contrast, the mitosporic characteristics of our isolates fit the description for M. berberidis. This is the first report of powdery mildew on N. domestica in North America. References: (1) U. Braun. Nova Hedwigia 89:1, 1987. (2) S. Helfer. Plant Dis. 79:424, 1995.

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First Report of Powdery Mildew Caused by Podosphaera (Sphaerotheca) fusca on Euryops pectinatus in North America

Plant Disease ◽

10.1094/pdis.2000.84.9.1048a ◽

2000 ◽

Vol 84 (9) ◽

pp. 1048-1048 ◽

Cited By ~ 1

Author(s):

G. S. Saenz ◽

S. T. Koike ◽

N. Shishkoff

Keyword(s):

United States ◽

New York ◽

North America ◽

Powdery Mildew ◽

Fungal Growth ◽

The United States ◽

Voucher Specimen ◽

First Report ◽

Humidity Chamber ◽

Powdery Mildew Pathogen

Gray-leaved Euryops (Euryops pectinatus Cass., Asteraceae) is an evergreen shrub that is widely planted in landscapes in the United States. In the fall of 1999, powdery mildew was observed on E. pectinatus planted in landscapes in Redlands (San Bernardino County), CA. Symptoms consisted only of slight cupping of leaves. Fungal growth was observed on stems, leaves, petioles, and pedicels and was ectophytic and amphigenous. The white mycelium was patchy to effuse. Hyphal appressoria were indistinct (1). Conidiophore foot cells were cylindric and sometimes were tapered toward or constricted at the base. Foot cells measured 30 to 50 by 10 to 12 μm and were followed by one to two shorter cells. Conidia were cylindric to slightly doliform, borne in chains of two to three, and measured 26 to 38 by 14 to 18 μm. Conidial length to width ratios ranged from 1.7 to 2.4. Catenate conidia had crenate edge lines (3). Conidia possessed conspicuous fibrosin bodies and from their sides produced short germ tubes without appressoria. Cleistothecia were not observed. Based on these characters, the fungus was identified as Podosphaera fusca (Fr.) U. Braun & N. Shishkoff (Podosphaera sect. Sphaerotheca) (1,2). Pathogenicity was confirmed by gently pressing diseased leaves onto leaves of healthy E. pectinatus plants. Plants were incubated in a humidity chamber at 22 to 24°C and after 12 to 14 days powdery mildew colonies developed. E. pectinatus cv. Viridis, a cultivar that lacks the extensive pubescence of E. pectinatus, also developed disease when inoculated. This appears to be the first report of powdery mildew on E. pectinatus in North America. A voucher specimen has been deposited into the University of California Herbarium (accession # UC1738635). P. fusca was also observed on cv. Viridis in a nursery in New York in 1999. It is unclear where this pathogen originated. P. fusca parasitizes a large number of asteraceous species including dandelion (Taraxacum officinalis) and sowthistle (Sonchus spp.) weeds, which occur in the area and sometimes are infected with powdery mildew. The Euryops powdery mildew pathogen may be a race that is different than those found on other composites in the United States. The fungus was observed on plants in shaded areas but not on plants in full sun. References: (1) U. Braun. Nova Hedwigia 89:1, 1987. (2) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000. (3) H. D. Shin and Y. J. La. Mycotaxon 46:445, 1993.

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Powdery Mildew of Spearmint Caused by Erysiphe orontii in California

Plant Disease ◽

10.1094/pdis.1999.83.4.399c ◽

1999 ◽

Vol 83 (4) ◽

pp. 399-399 ◽

Cited By ~ 3

Author(s):

S. T. Koike ◽

G. S. Saenz

Keyword(s):

Powdery Mildew ◽

Fungal Growth ◽

The State ◽

Conidial Germination ◽

Mentha Spicata ◽

First Report ◽

Humidity Chamber ◽

Monterey County ◽

Germ Tubes

In 1997 and 1998, the white fungal growth of a powdery mildew was observed on leaves and stems of both nursery and landscape spearmint (Mentha spicata) growing in coastal California (Monterey County). Mycelia were conspicuous, amphigenous, and epiphytic with indistinct to nipple-shaped appressoria. Conidiophore foot cells were cylindrical, straight, nonconstricted at the base, 61 to 92 μm × 11 to 14 μm in size, and were followed by 1 to 3 cells. Doliiform conidia, which were borne in chains of at least 3 to 5 conidia, measured 28 to 33 μm × 17 to 22 μm. Catenate conidia had sinuate edge lines. Conidia lacked fibrosin bodies. Upon germination, conidia produced germ tubes that were mostly apically inserted and ended in club-shaped appressoria, which fit Braun's Cichoracearum-type of conidial germination (1). Cleistothecia were not observed. Based on these features, the pathogen was identified as Erysiphe orontii Cast. (1). Pathogenicity was demonstrated by gently pressing diseased leaves onto leaves of potted spearmint, incubating plants in a humidity chamber for 48 h, then maintaining plants in a greenhouse. The powdery mildew that later developed was morphologically identical to the original isolates. While powdery mildew on spearmint has been observed previously in the state, this is the first report of the disease and first characterization of the pathogen for California. Reference: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987.

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First Report of Powdery Mildew Caused by Oidium araliacearum on Ivy in California

Plant Disease ◽

10.1094/pdis.1998.82.1.127d ◽

1998 ◽

Vol 82 (1) ◽

pp. 127-127 ◽

Cited By ~ 3

Author(s):

G. S. Saenz ◽

S. T. Koike

Keyword(s):

Powdery Mildew ◽

Fungal Growth ◽

University Of California ◽

Accession Number ◽

Hedera Helix ◽

Moist Chamber ◽

First Report ◽

The University ◽

Germ Tubes ◽

English Ivy

Powdery mildew was observed on English ivy (Hedera helix L.) in Berkeley, CA, in the spring of 1997. Fungal growth was ectophytic and amphigenous on leaves and petioles and caused slight reddening and buckling of leaves. The mycelium was white, effuse to dense, and had hyphal diameters of 3.5 to 6.9 μm. Appressoria were nipple-shaped to lobed, and sometimes were opposite. The foot cells of the conidiophores were cylindric, sometimes slightly flexuous, and were 18.5 to 30.0 × 6.9 to 9.2 μm in diameter. The foot cells were followed by 1 or 2 cells. When only one cell followed the foot cell, this cell was longer and slightly wider than the foot cell and measured 20.8 to 46.2 × 6.9 to 9.2 μm. When two cells followed the foot cell, these cells were of similar length to the foot cell, with the second cell usually shorter. Conidia were formed singly, were cylindric to slightly doliiform, and measured 32.0 to 44.0 × 11.5 to 19.0 μm. Fibrosin bodies were not observed. Conidia germinated at the ends and germ tubes terminated in lobed appressoria, placing this fungus in the Polygoni-type germination category (2). Cleistothecia were not observed. Based on these characters, the fungus was identified as Oidium araliacearum U. Braun & E. Oehrens B. A specimen was deposited with the University of California at Berkeley herbarium (accession number UC1713247). Pathogenicity was confirmed by gently pressing infected leaves onto leaves of various stages of maturity on ivy vines (3 to 4 vines per plant; 4 plants). Inoculated plants were kept in a moist chamber for 48 h, and then maintained in a greenhouse. Powdery mildew developed on inoculated plants, primarily on leaves of intermediate maturity, after 14 days, while uninoculated plants did not develop disease. Phyllactinia guttata is the only other powdery mildew recorded on English ivy (2). O. araliacearum differs from P. guttata in conidial shape (cylindric vs clavate), germination habit (end vs side of conidia), and asexual genus (Oidium vs Ovulariopsis) (2). Previous to this report, O. araliacearum was described only on Pseudopanax valdiviensis, another Araliaceae plant, in Chile (1). This is the first report of a powdery mildew disease of ivy in California, and the first report of Hedera helix as a host of O. araliacearum. References: (1) U. Braun. Mycotaxon 25:259, 1986. (2) U. Braun. Nova Hedwigia 89:1, 1987.

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First Report of Powdery Mildew Caused by an Oidium sp. on Papaver nudicaule in Italy

Plant Disease ◽

10.1094/pdis.2004.88.6.682b ◽

2004 ◽

Vol 88 (6) ◽

pp. 682-682

Author(s):

A. Garibaldi ◽

A. Minuto ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

Powdery Mildew ◽

Northern Italy ◽

Cut Flower ◽

Plant Leaves ◽

American Phytopathological Society ◽

Voucher Specimen ◽

First Report ◽

Erysiphe Cruciferarum ◽

Comprehensive Treatise ◽

The University

Iceland poppy (Papaver nudicaule L.) is grown on the Italian Riviera for export as a cut flower and its importance in the industry is increasing. During the spring of 2003, severe outbreaks of powdery mildew that had not been reported previously, occurred in several commercial plantings grown outdoors in containers near Imperia in northern Italy. Mycelium was observed on all green organs of the plant (leaves, stems, and petioles). Both surfaces on the leaves were affected, and heavily colonized leaves were distorted. As the disease progressed, diseased leaves turned yellow and died. The disease did not affect the flowers. Conidia were hyaline, cylindric, and measured 10.8 to 29.8 × 16.8 to 48.0 μm (average 13.7 × 37.3 μm). Foot cells were cylindric and appressoria unlobed. Fibrosin bodies were not present, and cleistothecia were not observed. The pathogen was identified as Oidium sp. subgenus Pseudoidium (1,2). Pathogenicity was confirmed by gently pressing leaves with visible sporulation onto the leaves of five 90-day-old P. nudicaule plants that were healthy and free of symptoms. Five noninoculated healthy plants served as controls. Inoculated and noninoculated plants were maintained in a growth chamber at 15°C with a 12-h photoperiod. After 7 to 10 days, typical symptoms of powdery mildew developed on inoculated plants but not on noninoculated plants. Previously, Erysiphe cruciferarum Opiz ex L. Junell has been reported on P. nudicaule in all continents, and E. cichoracearum DC. and E. polygoni DC. have been reported in several countries, including Italy, as a causal agent of powdery mildew on other species of Papaver including P. rhoeas and P. strigosum. To our knowledge, this is the first report of powdery mildew caused by an Oidium sp. on P. nudicaule in Italy. The voucher specimen is kept in the department collection at the University of Torino. References: (1) R. Belanger et al., eds. The Powdery Mildew A Comprehensive Treatise. The American Phytopathological Society, St Paul, MN, 2002. (2) U. Braun. Nova Hedwigia. 89:700, 1987.

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First Report of Powdery Mildew of Lycium chinense (Chinese Matrimony Vine) Caused by Arthrocladiella mougeotii in the Pacific Northwest

Plant Health Progress ◽

10.1094/php-2004-1208-01-hn ◽

2004 ◽

Vol 5 (1) ◽

pp. 16

Author(s):

Dean A. Glawe

Keyword(s):

North America ◽

Powdery Mildew ◽

Medicinal Plant ◽

Pacific Northwest ◽

Morphological Features ◽

Lycium Chinense ◽

First Report ◽

Landscape Plant ◽

The Pacific ◽

Plant Grown

Chinese matrimony-vine (Lycium chinense Mill.) is a traditional medicinal plant grown in China and used as a perennial landscape plant in North America. This report documents the presence of powdery mildew on L. chinense in the Pacific Northwest and describes and illustrates morphological features of the causal agent. It appears to be the first report of a powdery mildew caused by Arthrocladiella in the Pacific Northwest. Accepted for publication 10 November 2004. Published 8 December 2004.

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First Report of a Leaf Spot Caused by Alternaria brassicae on the Invasive Weed Lepidium draba in North America

Plant Disease ◽

10.1094/pdis-93-8-0846a ◽

2009 ◽

Vol 93 (8) ◽

pp. 846-846 ◽

Cited By ~ 1

Author(s):

A. J. Caesar ◽

R. T. Lartey

Keyword(s):

North America ◽

Chinese Cabbage ◽

Leaf Spot ◽

The United States ◽

Alternaria Brassicae ◽

Voucher Specimen ◽

First Report ◽

Leaf Spots ◽

Black Spots ◽

Lepidium Draba

The exotic, rangeland weed Lepidium draba L., a brassicaceous perennial, is widely distributed in the United States. For example, Oregon contains 100,000 ha of land infested with L. draba (2). Because it is capable of aggressive spread and has the potential to reduce the value of wheat-growing land (4), it is the target of biological control research. The application of multiple pathogens has been advocated for control of other brassicaceous weeds, including the simultaneous application of biotrophic and necrotrophic pathogens (3). In pursuit of this approach, in 2007, we discovered the occurrence of leaf spots on approximately 90% of L. draba plants near Shepherd, MT, which were distinct from leaf lesions caused by Cercospora bizzozeriana (1). The lesions were initially tiny, black spots enlarging over time to become circular to irregular and cream-colored around the initial black spots and sometimes with dark brown borders or chlorotic halos. Conidia from the lesions were light brown, elongate and obclavate, produced singly from short conidia, with 8 to 12 transverse septa, and 2 to 6 longitudinal septa. The spore body measured 25 to 35 × 200 to 250 μm with a beak cell 42 to 100 μm long. On the basis of conidial and cultural characteristics, the fungus was identified as Alternaria brassicae (Berk.) Sacc. Leaf tissues bordering lesions were plated on acidified potato dextrose agar. Colonies on V8 and alfalfa seed agar were black with concentric rings, eventually appearing uniformly black after 10 to 14 days. The internal transcribed spacer region of rDNA was amplified using primers ITS1 and ITS4 and sequenced. BLAST analysis of the 575-bp fragment showed a 100% homology with a sequence of A. brassicae Strain B from mustard (GenBank Accession No. DQ156344). The nucleotide sequence has been assigned GenBank Accession No. FJ869872. For pathogenicity tests, aqueous spore suspensions approximately 105/ml were prepared from cultures grown at 20 to 25°C for 10 to 14 days on V8 agar and sprayed on leaves of three L. draba plants. Inoculated plants were enclosed in plastic bags and incubated at 20 to 22°C for 72 to 80 h. In addition, three plants of the following reported hosts of A. brassicae were inoculated: broccoli, canola, Chinese cabbage, collards, broccoli raab, kale, mustard greens, radish, rape kale, and turnip. Within 10 days, leaf spots similar to those described above developed on plants of radish, canola, Chinese cabbage, and turnip and A. brassicae was reisolated and identified. Control plants sprayed with distilled water remained symptomless. These inoculations were repeated and results were the same. To our knowledge, this is the first report of a leaf spot disease caused by A. brassicae on L. draba in North America. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI No. 878750A). References: (1) A. J. Caesar et al. Plant Dis. 93:108, 2009. (2) G. L. Kiemnec and M. L. McInnis. Weed Technol. 16:231, 2002. (3) A. Maxwell and J. K. Scott. Adv. Bot. Res. 43:143, 2005. (4) G. A. Mulligan and J. N. Findlay. Can. J. Plant Sci. 54:149, 1974.

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First Report of Powdery Mildew Caused by Erysiphe aquilegiae var. aquilegiae on Aquilegia flabellata in Italy

Plant Disease ◽

10.1094/pdis.2004.88.6.681a ◽

2004 ◽

Vol 88 (6) ◽

pp. 681-681

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

United States ◽

Powdery Mildew ◽

The United States ◽

Northern Italy ◽

American Phytopathological Society ◽

First Report ◽

Powdery Mildews ◽

The Family ◽

White Mycelium ◽

The University

Aquilegia flabellata Sieb. and Zucc. (columbine) is a perennial garden species belonging to the family Ranunculaceae. During the summer of 2003, a severe outbreak of a previously unknown powdery mildew was observed in several gardens near Biella (northern Italy). Upper surfaces of leaves were covered with a white mycelium and conidia, and as the disease progressed infected leaves turned yellow and died. Foot cell was cylindric and appressorium lobed. Conidia were hyaline, ellipsoid, and measured 31.2 to 47.5 × 14.4 to 33 μm (average 38.6 × 21.6 μm). Fibrosin bodies were not present. Cleistothecia were globose, brown, had simple appendages, ranged from 82 to 127 (average 105) μm in diameter, and contained one to two asci. Ascocarp appendages measured five to eight times the ascocarp diameter. Asci were cylindrical (ovoidal) and measured 45.3 to 58.2 × 30.4 to 40.2 μm. Ascospores (three to four per ascus) were ellipsoid or cylindrical and measured 28.3 to 31.0 × 14.0 to 15.0 μ;m. On the basis of its morphology, the pathogen was identified as Erysiphe aquilegiae var. aquilegiae (1). Pathogenicity was confirmed by gently pressing diseased leaves onto leaves of five, healthy A. flabellata plants. Five noninoculated plants served as controls. Inoculated and noninoculated plants were maintained in a garden where temperatures ranged between 20 and 30°C. After 10 days, typical powdery mildew symptoms developed on inoculated plants. Noninoculated plants did not show symptoms. To our knowledge, this is the first report of the presence of powdery mildew on Aquilegia flabellata in Italy. E. communis (Wallr.) Link and E. polygoni DC. were reported on several species of Aquilegia in the United States (2), while E. aquilegiae var. aquilegiae was previously observed on A. flabellata in Japan and the former Union of Soviet Socialist Republics (3). Specimens of this disease are available at the DIVAPRA Collection at the University of Torino. References: (1) U. Braun. Nova Hedwigia, 89:700, 1987. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St Paul, MN, 1989. (3) K. Hirata. Host Range and Geographical Distribution of the Powdery Mildews. Faculty of Agriculture, Niigata University, 1966.

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First Report of Powdery Mildew of Platanus occidentalis caused by Microsphaera platani (Erysiphe platani) in Washington State

Plant Health Progress ◽

10.1094/php-2003-0818-01-hn ◽

2003 ◽

Vol 4 (1) ◽

pp. 33 ◽

Cited By ~ 2

Author(s):

Dean A. Glawe

Keyword(s):

North America ◽

Powdery Mildew ◽

Native Species ◽

Washington State ◽

Eastern North America ◽

First Report ◽

Platanus Occidentalis

American sycamore (Platanus occidentalis L.) is a common native species in eastern North America and is planted widely as a landscape tree in other regions. During a survey of powdery mildew diseases in Washington State, the fungus Microsphaera platani Howe was found on American sycamore trees in Madison Park, Seattle. This report documents the presence of M. platani in Washington State and presents information on the fungus. Accepted for publication 30 July 2003. Published 18 August 2003.

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First Report of Powdery Mildew on Dipsacus sylvestris Caused by Sphaerotheca dipsacearum in North America

Plant Health Progress ◽

10.1094/php-2006-0607-02-br ◽

2006 ◽

Vol 7 (1) ◽

pp. 54

Author(s):

Frank M. Dugan ◽

Dean A. Glawe

Keyword(s):

North America ◽

Powdery Mildew ◽

Causal Agent ◽

European Species ◽

First Report ◽

Dipsacus Sylvestris ◽

Noxious Weed

Common teasel (Dipsacus sylvestris) is a European species introduced into North America, and is now widely established and regarded as a noxious weed. In October 2005, a powdery mildew was observed on D. sylvestris in two locations in Pullman, Whitman Co., WA. Examination of diseased material confirmed that the causal agent was S. dipsacearum. This report provides the first documentation of S. dipsacearum on D. sylvestris in North America. Accepted for publication 20 April 2006. Published 7 June 2006.

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First Report of Powdery Mildew on Corylus avellana caused by Phyllactinia guttata in Washington State

Plant Health Progress ◽

10.1094/php-2005-1121-01-br ◽

2005 ◽

Vol 6 (1) ◽

pp. 22 ◽

Cited By ~ 4

Author(s):

Sierra Hartney ◽

Dean A. Glawe ◽

Frank Dugan ◽

Joseph Ammirati

Keyword(s):

North America ◽

Powdery Mildew ◽

Corylus Avellana ◽

Washington State ◽

State University ◽

Washington State University ◽

Ornamental Tree ◽

Western Washington ◽

The University ◽

First Time

Contorted hazelnut is an ornamental tree introduced to North America from Europe. In the fall of 2004 and 2005, powdery mildew caused by Phyllactinia guttata (Wallr.:Fr.) Lév. was observed on contorted hazelnut (‘contorta’) located on the campus of Washington State University, Pullman, and on several C. avellana trees (unknown cultivar) on the campus of the University of Washington, Seattle. This report documents for the first time the occurrence of P. guttata on C. avellana in both eastern and western Washington. Accepted for publication 18 October 2005. Published 21 November 2005.

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