In my previous post about a disease that was affecting my tomatoes, I had discovered something that was new to my garden. This time, I’m writing about a disease that has been a problem in my garden for several years. It kills the lower leaves and eventually makes its way to the fruit, leaving rough textured, firm spots. Small spots can be cut away, but eventually it’ll ruin the entire fruit. Many of the tomatoes we harvested just before the frost are infected.
I think this is the disease known as Phytophthora infestans or late blight. It is called that because it shows up late in the year. It grows best in cool, humid weather; I’ve seen it wipe out all my tomato plants in a few days when we’ve had a wet fall. It also infects potatoes and was involved in the infamous Irish potato famine.
Although this is classified as an oomycete rather than a fungus, the recommended preventative measures are similar and include crop rotation, cleaning up plant debris after the growing season has finished, and not using overhead watering. Some copper-based anti-fungal sprays will keep it from spreading. I could also plant tomato varieties that have been bred to be resistant to late blight.