@article{lookabaugh_kerns_shew_2021, title={Evaluating Fungicide Selections to Manage Pythium Root Rot on Poinsettia Cultivars with Varying Levels of Partial Resistance}, volume={105}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS-04-20-0807-RE}, abstractNote={ Pythium aphanidermatum is the predominant species causing Pythium root rot of commercially grown poinsettia (Euphorbia pulcherrima Willd. ex Kotzch) in North Carolina. Pythium root rot is managed primarily through a combination of sanitation practices and preventative fungicide applications of mefenoxam or etridiazole. Insensitivity to mefenoxam is common but growers continue to rely on it from lack of inexpensive and efficacious alternatives. This research was conducted to identify alternative fungicides for Pythium root rot control and to evaluate their efficacy on poinsettia cultivars with varying levels of partial resistance. Greenhouse studies were conducted to assess efficacy of fungicide treatments in seven poinsettia cultivars inoculated with a mefenoxam-sensitive isolate of P. aphanidermatum. One study examined control with a single fungicide drench made at transplant and a second study examined repeat fungicide applications made throughout the experiment. Treatments containing etridiazole, mefenoxam, fenamidone, and cyazofamid provided control of Pythium root rot across all cultivars in both experiments whereas Fosetyl-al, potassium phosphite, and Trichoderma spp. failed to offer satisfactory control. Azoxystrobin, pyraclostrobin, and propamocarb reduced disease on some cultivars but failed to control Pythium root rot on highly susceptible cultivars. Four isolates of P. aphanidermatum cultured from plants growing in commercial greenhouses were evaluated for in vitro sensitivity to fungicides labeled for Pythium root rot control at four rates. Etridiazole, fosetyl-al, and potassium phosphite completely inhibited mycelial growth, whereas isolates varied in response to mefenoxam, cyazofamid, propamocarb, fenamidone, azoxystrobin, and pyraclostrobin in vitro. Twenty-one additional isolates then were evaluated at label rates of these fungicides. Seven isolates were insensitive to label rates of all three quinone outside inhibitors and one isolate was insensitive to the quinone outside inhibitors and mefenoxam. These results provide guidelines for selecting fungicides to maximize control of Pythium root rot on poinsettia cultivars. }, number={6}, journal={PLANT DISEASE}, author={Lookabaugh, Emma C. and Kerns, James P. and Shew, Barbara B.}, year={2021}, month={Jun}, pages={1640–1647} }
 @article{koehler_lookabaugh_shew_shew_2017, title={First report of pythium root rot of stevia caused by Pythium myriotylum, P. irregulare, and P. aplzanidermatum in North Carolina}, volume={101}, number={7}, journal={Plant Disease}, author={Koehler, A. M. and Lookabaugh, E. C. and Shew, B. B. and Shew, H. D.}, year={2017}, pages={1331–1332} }
 @article{lookabaugh_ivors_shew_2015, title={Mefenoxam Sensitivity, Aggressiveness, and Identification of Pythium Species Causing Root Rot on Floriculture Crops in North Carolina}, volume={99}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-02-15-0232-re}, abstractNote={ Herbaceous ornamental plants exhibiting symptoms of Pythium root rot were collected from 26 greenhouses in 21 counties in North Carolina (NC) from 2010 to 2012. Plant symptoms ranged from mild stunting to severe wilting, root rot, and death. Roots were plated on selective media, and 356 isolates of Pythium were recovered from 34 host species. Selected isolates were identified by sequencing of the internal transcribed spacer (ITS) rDNA gene region. Seventeen Pythium species were identified, with P. aphanidermatum, P. irregulare, and P. myriotylum comprising 75% of the 320 isolates sequenced. Twelve of the 26 greenhouses had more than one species present. Mefenoxam sensitivity was tested in vitro by growing isolates in wells of microtiter plates containing clarified V8 agar amended with 100 µg a.i./ml mefenoxam. Colonization was scored after 24 to 48 h using a scale of 0 (no growth) to 5 (entire well colonized). Fifty-two percent of the isolates were resistant to mefenoxam (mean score ≥4). All 32 isolates of P. myriotylum were sensitive, whereas sensitivity varied among isolates of P. aphanidermatum and P. irregulare. Resistant and sensitive isolates of the same species were found within the same greenhouses. The aggressiveness of P. aphanidermatum and P. irregulare isolates was evaluated on poinsettia, Gerbera daisy, and petunia. P. aphanidermatum was more aggressive than P. irregulare on poinsettia and petunia; symptoms were mild and no differences in aggressiveness were observed on Gerbera daisy. Sensitivity to mefenoxam was not related to aggressiveness. }, number={11}, journal={PLANT DISEASE}, author={Lookabaugh, E. C. and Ivors, K. L. and Shew, B. B.}, year={2015}, month={Nov}, pages={1550–1558} }