Phytophthora infestans is a water mold that causes the disease known as late blight, primarily affecting potatoes and tomatoes. It thrives in cool, moist conditions and can spread rapidly, leading to significant crop losses. The organism produces spores that can be carried by wind or water, making it highly contagious. This pathogen was responsible for the infamous Irish Potato Famine in the mid-19th century, which resulted in widespread starvation and emigration. Farmers can manage late blight through resistant crop varieties, proper field management, and timely fungicide applications to protect their plants from infection.