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Ambrosia trifida L., known as giant ragweed, is native to North America and was introduced in Korea in the 1970s (4). It is now widely naturalized, and since 1999, has been designated as one of 11 most ‘harmful nonindigenous plants’ by the Korean Ministry of Environment because of its adverse effects on native plants. Various strategies to eradicate this noxious weed have been unsuccessful (4). In June 2008, leaf spot symptoms on this weed were found in Inje, Korea. Hundreds of giant ragweed growing along stream banks contained leaf spots with leaf yellowing and premature defoliation. Leaf lesions were 1 to 5 mm in diameter, angular to irregular, dark brown without a distinct margin, later becoming pallid with a brown margin. Between 2008 and 2011, the authors observed the same symptoms in Dongducheon, Yangku, Namyangju, and Pocheon, Korea. Voucher specimens have been housed in the herbarium of Korea University. Numerous black pycnidia were formed on the lesion. Pycnidia were amphigenous, globose, dark brown, ostiolate, and measured 80 to 130 μm in diameter. Conidia were filiform, straight to mildly curved, eguttulate, hyaline, 18 to 36 × 1.5 to 2.5 μm, one to three septate, subtruncate at the base, and tapering to a rounded apex. Single-conidial isolations onto potato dextrose agar formed dark grayish colonies. Pycnidia matured after 5 weeks when plates were incubated under fluorescent illumination for 12-h photoperiods at 25°C. On the basis of morphological and cultural characteristics, the fungus was identified as Septoria epambrosiae D.F. Farr (2). Three isolates were deposited in the Korean Agricultural Culture Collection (KACC). Preliminary morphological identification of the fungal isolates was confirmed by molecular data. The internal transcribed spacer (ITS) region of rDNA was amplified using the ITS1/ITS4 primers and sequenced. The resulting sequences of 449 bp obtained from the three isolates were identical to each other. They showed 100% similarity when compared with a sequence of S. epambrosiae (GenBank No. AF279582). The nucleotide sequence of a representative isolate (KACC43850) was deposited in GenBank (No. JN695498). Pathogenicity was confirmed by inoculating the leaves of three seedlings with a conidial suspension (~2 × 105 conidia/ml). Three noninoculated seedlings served as controls. Plants were maintained in a glasshouse at 100% relative humidity for 48 h. After 6 days, typical leaf spots, identical to the one observed in the field, started to develop on the leaves of the inoculated plants. No symptoms were observed on the control plants. The fungus was successfully reisolated from the symptomatic plants, fulfilling Koch's postulates. A leaf spot disease associated with S. epambrosiae has previously been recorded on A. artemisiifolia in Hungary (1–3) and A. trifida in North America (2,3). To our knowledge, this is the first report of S. epambrosiae on giant ragweed in Asia. Because of its potential as a biocontrol agent, further studies are needed. References: (1) G. Bohar and I. Schwarczinger. Plant Dis. 83:696, 1999. (2) D. F. Farr and L. A. Castlebury. Sydowia 53:81, 2001. (3) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , September 20, 2011. (4) S. M. Oh et al. Impacts of Invasive Alien Weeds and Control Strategies of Noxious Weeds in Korea. National Institute of Agricultural Science and Technology, Suwon, Korea, 2007.

Lamium purpureum L. (Lamiaceae), known as red dead-nettle, is native to Europe and Asia Minor. It has been widely naturalized in East Asia including Korea, where it is considered an invasive species. This plant is also known as one of primary overwintering sources for cucumber mosaic virus with a broad host range including many horticultural crops (Tomlinson et al. 1970). In May 2018, several hundred plants of red dead-nettle were found heavily infected with a powdery mildew in Gongju (36°19′59″N; 127°05′31″E), Korea. Symptoms first appeared as thin white colonies, which subsequently developed into abundant hyphal growth on both sides of the leaves. Voucher specimens were deposited in the Korea University herbarium (KUS-F30500). Hyphal appressoria were moderately lobed to multilobed. Conidiophores were 90 to 240 × 10 to 12 μm and produced two to six immature conidia in chains with a sinuate outline, followed by one to three cells. Foot cells of conidiophores were straight or slightly swollen at the base, cylindrical, and 30 to 60 μm long. Conidia were hyaline, cylindric oval to ellipsoid, measured 24 to 38 × 18 to 22 μm (length/width ratio = 1.3 to 2.1), and devoid of distinct fibrosin bodies. Primary conidia were rounded at the apex and subtruncate at the base. Germ tubes were produced on the perihilar position of conidia. No chasmothecia were observed during field survey until the plants were killed by frost damage in November. The structures described above were typical of powdery mildew Striatoidium anamorph of the genus Neoerysiphe. The measurements and morphological characteristics were compatible with those of N. galeopsidis (DC.) U. Braun (Braun and Cook 2012). To confirm the identification, the internal transcribed spacer (ITS) regions of KUS-F30500 were amplified by polymerase chain reaction using primers ITS5/P3 as described by Takamatsu et al. (2009) and sequenced directly. The resulting 579-bp sequence was deposited in GenBank (accession no. MK156132). A GenBank BLAST search using the Korean isolate showed 99% (575/579) similarity with those of N. galeopsidis isolates on Lamium purpureum (AB498942 from Ukraine and KY660982 from the United Kingdom). Pathogenicity was confirmed through inoculation tests by gently pressing a diseased leaf onto young leaves of three asymptomatic potted plants. Three noninoculated plants were used as controls. Plants were maintained in a glasshouse without temperature control, between about 20 and 40°C. Inoculated plants developed signs and symptoms after 7 days, whereas the control plants remained healthy. The fungus present on the inoculated plants was morphologically identical to that originally observed on diseased plants. The powdery mildew infection of L. purpureum associated with N. galeopsidis has been known in most European countries (Farr and Rossman 2018) and Japan (Takamatsu et al. 2008). Although N. galeopsidis has been recorded on Stachys affinis and Lamium amplexicaule in Korea, this is the first report of powdery mildew caused by N. galeopsidis on L. purpureum. The field observations suggest that the powdery mildew may limit the spread of this invasive weed in Korea.