Margaret McGrath

The goal of my applied research program was to improve the management of important diseases of vegetable crops grown on Long Island within both conventional and organic production systems. Diseases of herbs, in particular basil downy mildew, became an additional focus following detection of this new disease in NY in 2008. Typically, these diseases have been important elsewhere in the northeastern United States. To reach this goal, I conducted research to increase our understanding of these diseases and to develop effective components for integrated pest management (IPM) programs. Specifically, I identified the sources of the disease-causing organisms, determined how these organisms survive between crops, developed scouting protocols and action thresholds for timing the initiation of fungicide applications after disease detection, investigated factors that favor disease development and used this information for timing fungicide applications, and evaluated new control tactics including new resistant varieties and mustard biofumigation. Management practices for improving soil health, including reduced-tillage production systems and compost soil amendments, were examined for their impact on plant diseases. Fungicide resistance can be an important consideration in managing diseases; therefore, effort was devoted to studying its occurrence, its impact on disease control and its management. Diseases studied include basil downy mildew; powdery mildew, downy mildew, bacterial wilt and Phytophthora blight of cucurbit crops; late blight, Septoria leaf spot, tospoviruses, and powdery mildew of tomato; white rust of spinach; bacterial leaf spot of pepper; and black rot of crucifers. Research was conducted to determine the impact on plant productivity of ambient ozone, which reaches concentrations that cause acute foliar injury to many crops each summer on Long Island.

Recent Publications

• Shishkoff, N and McGrath, M. T. 2026. In vitro testing of organic spinach seed for viable oospores of Peronospora effuse and germination of seeds to determine any possible seedling infection. https://doi/10.1094/PDIS-05-25-0983-RE
• McGrath, M. T.  2024.  Sweet basil cultivars resistant to downy mildew evaluated under open field conditions.  Crop Protection 184:106815.  https://doi.org/10.1016/j.cropro.2024.106815
• Klosterman, S. J., Clark, K. J., Anchieta, A. G., Kandei, S. L., Mou, B., McGrath, M. T., Correll, J. C., Shishkoff, N. 2024. Transmission of spinach downy mildew via seed and infested leaf debris. Plant Disease 108:951-959. https://doi.org/10.1094/PDIS-06-23-1225-RE
• McGrath, M. T. and Homa, K.  2023.  Biopesticides in Vegetable and Herb Disease Management. In: Elmer, W. H., McGrath, M., and McGovern, R. J. (eds) Handbook of Vegetable and Herb Diseases. Handbook of Plant Disease Management. Springer, Cham. https://doi.org/10.1007/978-3-030-35512-8_4-1
• McGrath, M. T.  2023.  Efficacy of organic fungicides for downy mildew in field-grown sweet basil.  Plant Disease 107:2467-2473. https://doi.org/10.1094/PDIS-10-22-2424-RE
• Sanogo, S., Lamour, K., Kousik, S., Lozada, D. N., Parada-Rojas, C. H., Quesada-Ocampo, L., Wyenandt, C. A., Babadoost, M., Hausbeck, M. K., Hansen, Z., Ali, E., McGrath, M. T. , Hu, J., Crosby, K., and Miller, S. A.  2023. Phytophthora capsici, 100 Years Later: Research Mile Markers from 1922 to 2022.  Phytopathology 113:921-930.  https://doi.org/10.1094/PHYTO-08-22-0297-RVW.  
• Saville, A. C., McGrath, M. T., Jones, C., Polo, J., and Ristaino, J. B.  2023.  Understanding the genotypic and phenotypic structure and impact of climate on Phytophthora nicotianae outbreaks on potato and tomato in the eastern US. Phytopathology 113:1506-1514. https://doi.org/10.1094/PHYTO-11-22-0411-R
• Patel, J. S., Wyenandt, C. A., and McGrath, M. T.  (2021). Effective downy mildew management in basil using resistant varieties, environment modifications, and fungicides. 30 Aug 2021 Plant Health Progress 22: 226–234. Published Online: 30 Aug 2021 https://doi.org/10.1094/PHP-02-21-0041-FI
• Parada-Rojas , C. H., Granke , L. L., Naegele, R. P., Hansen, Z., Hausbeck, M. K., Kousik, C. S., McGrath, M. T., Smart, C., and Quesada-Ocampo, L. M.  (2021).  A diagnostic guide for Phytophthora capsici infecting vegetable crops. Plant Health Progress 22:404-414. Published Online: 30 Aug 2021 https://doi.org/10.1094/PHP-02-21-0027-FI
• Jones, J., Everts, K. L., McGrath, M. T., and Gugino, B. K.  2021.  Efficacy of fungicides for Pseudoperonospora cubensis determined using bioassays over multiple years in the Mid-Atlantic and Northeastern United States.  Plant Health Progress 22: 355–361. Published Online: 30 Aug 2021 https://doi.org/10.1094/PHP-10-20-0086-FI
• McGrath, M. T.  (2020).  Efficacy of conventional fungicides for downy mildew in field-grown sweet basil in the US.  Plant Disease 104:2967-2972.  https://doi.org/10.1094/PDIS-11-19-2382-RE
• McGrath, M. T.  (2020).  Fungicide resistance in Podosphaera xanthii and impact on managing cucurbit powdery mildew.  Phytopathology 110:S2.205. https://doi.org/10.1094/PHYTO-110-12-S2.205.
• Spawton, K. A., McGrath, M. and du Toit, L. J.  (2020).  First report of Stemphylium leaf spot caused by Stemphylium beticola in New York State.  Plant Disease 104:3068. https://doi.org/10.1094/PDIS-02-20-0343-PDN
• Xiang, Y., Miller, A. N., McGrath, M. T. and Babadoost, M.  (2020).  Genotyping-by-sequencing for analysis of the genetic variation of Podosphaera xanthii, incitant of cucurbit powdery mildew.  Plant Disease 104:951-957.
• Leadbeater, A., McGrath, M. T., Wyenandt, C.A., and Stevenson, K. L.  (2019).  An Overview of Fungicide Resistance and Resistance Management – History and Future Trends.  Chapter 1.  Pages 3-19.  In Fungicide Resistance in North America, Second Edition.  APS Press, St Paul.
• McGrath, M. T., Scheufele, S. B., and Gugino, B. K.  (2019).  Evaluation of fungicides and resistant cultivars to reduce use of chlorothalonil for powdery mildew in pumpkin and winter squash. Phytopathology 108:S2.97.
• McGrath, M. T., Wyenandt, C.A., and Stevenson, K. L.  (2019).  Occurrence of fungicide resistance in pathogens of non-solanaceous vegetable crops.  Chapter 23.  Pages 309-332.  In Fungicide Resistance in North America, Second Edition.  APS Press, St Paul.
• McGrath, M. T. and Sexton, Z. F.  (2018).  Poor control of cucurbit powdery mildew associated with first detection of resistance to cyflufenamid in the causal agent, Podosphaera xanthii, in the United States. Plant Health Progress 19:222-223.  https://doi.org/10.1094/PHP-06-18-0029-BR (doi: 10.1094/PHP-06-18-0029-BR).
• McGrath, M. T.  (2017).  First report of resistance to quinoxyfen in Podosphaera xanthii, causal agent of cucurbit powdery mildew, in the United States.  Plant Health Progress 18:94.  http://dx.doi.org/10.1094/PHP-03-17-0018-BR
• McGrath, M. T. and Wyenandt, C. A.  (2017).  First detection of boscalid resistance in Podosphaera xanthii in the United States associated with failure to control cucurbit powdery mildew in New York and New Jersey in 2009.  Plant Health Progress 18:93.  http://dx.doi.org/10.1094/PHP-03-17-0014-BR
• Neufeld, K.N., Keinath, A.P., Gugino, B.K., McGrath, M. T., Sikora E. J., Miller S. A., Ivey M. L., Langston D. B., Dutta B., Keever T., Sims A., Ojiambo P. S.  (2017).  Predicting the risk of cucurbit downy mildew in the eastern United States using an integrated aerobiological model.  Int J Biometeorol. 62:1-14.  https://doi.org/10.1007/s00484-017-1474-2

Outreach and Extension Focus

Applied research was conducted on managing vegetable diseases during summer. Farms were visited to determine disease occurrence and to diagnosis problems. Disease samples were also submitted to the laboratory by growers and IPM scouts. Field Days and Twilight Meetings were hosted annually to permit growers an opportunity to see research results for themselves. Findings were shared with growers predominantly in the northeastern US through newsletter articles, web postings, and presentations at grower meetings during winter. Growers were also provided with general information on diseases and their management, especially new developments. Materials for outside NY often need to be adjusted due to differences in fungicide registration. Phone calls and e-mail requests for information from growers and extension specialists were answered throughout the year. Content of the Cornell Integrated Crop and Pest Management Guidelines for Vegetables was updated each fall with other Cornell University extension faculty. When needed, requests were prepared and submitted for emergency registration of new fungicides and for fungicide label amendments (eg 2(ee) requests for adding diseases) for NY. Comments from growers and other stakeholders and survey results were the primary means used to assess program success. Two-hour session on “Plant diseases and their management” was presented most years for the annual Master Gardener Training Program.

Recent Presentations

• Fungicides A to Z.  2022 Giant Pumpkin Commonwealth International Growers Convention.  3/12/22.
• Incorporating Biopesticides into IPM.  Ontario Fruit and Vegetable Convention.  Niagara Falls, Canada.  2/23/22.
• Recommendations on Managing Diseases of Cucurbits Based on Recent Research.  Long Island Vegetable Growers Meeting.  Virtual.  2/15/22.
• The Lowdown on Basil Downy Mildew. Virtual Winter Greenhouse School 2022.  2/9/22.
• Downy Mildew Management on Cucumber and Cantaloupe.  2022 Mid-Atlantic Fruit and Vegetable Convention. Vine Crops Session.  Hershey, PA.  2/1/22.
• Managing Powdery Mildew and Bacterial Diseases on Pumpkins.  2022 Mid-Atlantic Fruit and Vegetable Convention. Pumpkins/Winter Squash Session.  Hershey, PA.  2/1/22.
• Keys to Success in Disease Management.  NOFA-NY 20220 Winter Conference.  Virtual meeting.  1/21/22.
• Phytophthora Update.  NEVBGA Winter meeting.  1/7/22.
• Research Guides Management Recommendations for Cucurbit Mildews.  New England Vegetable and Fruit Conference.  Virtual meeting.  12/15/21.
• Biopesticides for Managing Diseases of Vegetable Crops.  Les Vendredis Horticoles de la Montérégie – 2e édition.  Quebec, Canada.  Virtual meeting.  12/10/21.
• Refining Your Disease Management Program for Pumpkin and Winter Squash.  New Jersey Vegetable Growers Virtual Convention.  2/25/21.
• Managing Diseases with an Integrated Mindset.  2021 Empire State Producers Expo.  IPM School.  Virtual meeting.  1/13/21.
• Thirty Years of Research Helping Farmers Manage Diseases of Cucurbits.  Watermelon and Melon Training.  Zhengzhou, China.  9/26/18.
• Options for Organic Management of Diseases in Vegetable Crops.  3rd International Congress on Plant Protection in Vegetables.  Guadalajara, Mexico.  8/17/18.
• Resistance to Fungicides in Vegetable Pathogens: Current Situation and Strategies for Managing.  3rd International Congress on Plant Protection in Vegetables.  Guadalajara, Mexico.  8/16/18.