Update on Late Blight Outbreak in Allegany County

We have important updates regarding the current late blight outbreak in Allegany County:

• Laboratory Tests Confirm US-23 Strain. After collecting samples from affected tomato plants, recent laboratory tests have identified the late blight strain as US-23. This finding is significant because the risk of the blight overwintering is greatly reduced. Overwintering requires the presence of oospores, which are sexual spores of this pathogen (P. infestans), and to produce these spores it’s necessary to have two different strains at the same time in the same location, so having only the US-23 strain present lowers this risk of overwintering.
• Equal risk to potatoes and tomatoes. As expected, both potato and tomato crops are equally susceptible to the US-23 strain. Growers should take proactive measures to protect their crops and prevent the spread of the disease such as buying disease-resistant plants, preventive fungicide applications, monitoring crops to have early detection of late blight, rotating crops, and reporting late blight findings.
• Mefenoxam has proven effective. In more positive news, testing has confirmed that systemic fungicides containing mefenoxam (also known as metalaxyl-M), can be used to protect crops from this strain of late blight. Commercially you can find it under different names, for example: Ridomil, but the important part is to check that the main ingredient is mefenoxam (a.k.a. metalaxyl-M). This is an unrestricted chemical treatment and, as an older product, it may offer a more cost-effective solution for growers, and so far no resistance to this fungicide has been observed, making it a reliable option to combat this strain of late blight. Applying mefenoxam, or any fungicide, for late blight control should be based on several factors, including disease pressure, weather conditions, crop growth stage, and local extension recommendations. Always read the labels, follow the instructions, and use protective equipment.
• Stay informed and report to your local cooperative extension office. Late blight remains a significant threat, and it can continue to spread. Stay vigilant and take all necessary precautions to protect your crops. If you suspect you have late blight, please take pictures of your affected tomato and/or potato plants and send them by email to Cristian Acosta (CCE Allegany Ag educator) at cfa34@cornell.edu or call 585-268-7644 ext. 14.

Stay safe and protect your crops!

Last updated August 27, 2024