What conditions limited the spread of Phytophthora infestans?

The primary environmental condition that limits the spread of Phytophthora infestans—the water mold responsible for late blight—is hot, dry weather.1

While the pathogen thrives in humid regions with temperatures between 4 and 29 °C (40 and 80 °F), these warmer, arid conditions effectively check its development and transmission. Conversely, the disease is most active during periods of cool, moist weather, which facilitate the germination of spores and the continued cycle of infection.1

Beyond environmental factors, other management strategies can help limit the impact of the disease, such as:

• Handling practices: Delaying harvest until foliage has been killed by frost or mechanical means, and avoiding physical damage to tubers during digging and packing, can reduce disease incidence.2
• Resistant varieties: The development and use of potato and tomato varieties resistant to the pathogen serve as a critical defense against the disease.1
• Chemical control: The timely application of fungicide can be used to manage the spread of the blight.1