New Detection of Phytophthora Infestans Genotype US-23 Highlights Increased Risk and Calls for Immediate Action
Potato late blight has been confirmed in an additional commercial field in St. Joseph County, Michigan. The confirmation, reported on August 5, 2024, follows the detection of the disease over the weekend. The pathogen identified is Phytophthora infestans, specifically the genotype US-23, which was observed on several plants along the northern edge of the affected field.
In response to this outbreak, sanitation and management measures are being implemented, with plans to commence vine-kill of the entire field as soon as weather conditions allow. This approach is crucial in preventing further spread of the disease and protecting remaining crops.
The US-23 genotype can generally be managed effectively using phenylamide fungicides, such as mefenoxam and metalaxyl. The timely report by Rob Schafer of Mid-Michigan Agronomy has been instrumental in enabling producers to take necessary precautions and manage the disease effectively. It is advised that growers maintain preventative foliar programs and conduct diligent crop monitoring to mitigate the risk of late blight.
Currently, the late blight risk in Michigan is categorized as medium. This risk level reflects recent conditions marked by frequent and heavy rainfall, which have created an environment conducive to the development of the disease. For detailed late blight forecasting, growers can refer to the UW-Madison Vegetable Disease & Insect Forecasting Network.
The situation is mirrored by recent reports from other regions. On July 10, Dr. Eugenia Banks confirmed an additional case in Alliston, Simcoe County, Ontario, following earlier detections in Elgin and Kent Counties. In New Brunswick, Dr. Kutay Ozturk reported the molecular detection of P. infestans sporangia on July 29, with a single spore identified in a trap, though no foliar infection was noted as of yet. Growers in Maine and surrounding areas are advised to remain vigilant, particularly in fields near Grand Falls, and adhere to a 5-day spray schedule to ensure comprehensive coverage.
No Phytophthora infestans DNA has been detected in experimental spore samplers managed by the MSU Potato and Sugar Beet Pathology program in Montcalm County. Results from recent samples will be available shortly.
