Plant Disease (2014) 98, 937-942

Jerry E. Weiland, Luisa Santamaria and Niklaus J. Grünwald (2014)
Sensitivity of Pythium irregulare, P. sylvaticum, and P. ultimum from forest nurseries to mefenoxam and fosetyl-Al, and control of Pythium damping-off
Plant Disease 98 (7), 937-942
Abstract: Mefenoxam and fosetyl-Al are common fungicides used to supplement disease control of Pythium damping-off and root rot in forest nurseries of the western United States. However, it is unknown whether fungicide-resistant Pythium isolates are present or whether new fungicide and biological treatments might also provide supplemental disease control. Isolates of Pythium irregulare, P. sylvaticum, and P. ultimum from three forest nurseries were evaluated for in vitro sensitivity to mefenoxam and fosetyl-Al. A greenhouse study was also conducted to assess efficacy of fungicide and biological treatments in Douglas-fir (Pseudotsuga menziesii) seedlings inoculated with Pythium dissotocum, P. irregulare, and P. 'vipa´. P. irregulare was approximately three times less sensitive to mefenoxam (0.20 μg/ml) than P. sylvaticum (0.06 μg/ml) and P. ultimum (0.06 μg/ml), and two resistant isolates of P. ultimum were identified (>311 μg/ml). All three Pythium spp. were similarly sensitive to fosetyl-Al (1,256 to 1,508 μg/ml) and no resistant isolates were found. In the disease control efficacy trial, both fosetyl-Al and phosphorous acid consistently provided good protection against damping-off caused by P. dissotocum, P. irregulare, and P. 'vipa'. Other treatments, including mefenoxam, also provided good or intermediate protection but efficacy depended upon which Pythium sp. was used. Growers should consider rotating mefenoxam use with other fungicide chemistries or biological treatments to prevent further development and spread of mefenoxam-resistant isolates.
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Link to article at publishers website
Database assignments for author(s): Niklaus J. Grünwald

Research topic(s) for pests/diseases/weeds:
control - general

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Globisporangium ultimum
	Globisporangium irregulare
	Pythium dissotocum	Douglas fir (Pseudotsuga menziesii)	U.S.A. (NW)
	Globisporangium sylvaticum