Olson, H. A., and Benson, D. M. 2011. Cbaracterization of Phytophthora spp. on floriculture crops in Nortb Carolina. Plant Dis. 95:1013-1020.Isolates of Phytophthora in floriculture crops were collected from North Carolina commercial greenhouse facilities in 2t)()7 and 2008, identified, and characterized for mating type and mefenoxam sensitivity. In all, 163 isolates from 13 host species at 11 locations were identified primarily as Phytophthora nicotianae (59%), P. drechsleri (23%), P. cryptogea (9%), and P. tropicalis (4%). Multiple Phytophthora spp. were found at five locations. DNA sequencing was more reliable for differentiating P. cryptogea and P. drechsleri. Only tbe A1 mating type of P. drechsleri was collected; bowever, both mating types of P. nicotianae. P. cryptogea, and P. tropicalis were found. Overall, 66% of Phytophthora isolates were resistant or intermediate in resistance to mefenoxam at 1 (jg a.i./ml. Tbree groups of P. drcchsleri isolates had effective concentration of mefenoxam providing 50% growth inhibition (EC51,) estimates over 7(K) \ig a.i./ml. EC,n estimates for P. nicotianae ranged from 246 to 435 |jg a.i./ml. Isolates of P. nicotianae exbibited phenotypic heterogeneity at several locations, suggesting multiple separate introductions to tbe facilities. In contrast, P. nicotianae and P. drechsleri isolates from two locations were pbenotypically identical to a previous survey, suggesting tbat tbe facilities bave Phytophthora spp. established onsite.

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2013. Diversity and mefenoxam sensitivity of Phytophthora spp. associated with the ornamental horticulture industry in the southeastern United States. Plant Dis. 97:86-92.Phytophthora isolates associated with ornamental plants or recovered from irrigation water in six states in the southeastern United States (Georgia, North Carolina, South Carolina, Tennessee, Texas, and Virginia) were identified and screened for sensitivity to mefenoxam. Isolates from forest and suburban streams in Georgia and Virginia were included for comparison. A new in vitro assay, utilizing 48-well tissue culture plates, was used to screen for mefenoxam sensitivity; this assay allowed high throughput of isolates and used less material than the traditional petri plate assay. In total, 1,483 Phytophthora isolates were evaluated, and 27 species were identified with Phytophthora nicotianae, P. hydropathica, and P. gonapodyides, the most abundant species associated with plants, irrigation water, and streams, respectively. Only 6% of isolates associated with plants and 9% from irrigation water were insensitive to mefenoxam at 100 (Jg a.i./ml. Approximately 78% of insensitive isolates associated with plants were P. nicotianae, and most of these (67%) came from herbaceous annual plants. Most of the insensitive isolates recovered from irrigation water were P. gonapodyides, P. hydropathica, P. megasperma, and P. pini, and 83% of the insensitive isolates from streams were P. gonapodyides. Overall, this study suggests that mefenoxam should continue to be a valuable tool in the management of Phytophthora diseases affecting ornamental plants in the southeastern United States.

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