MILDEW (Isn't that an enticing title??)
Not so exciting, however, were the various mildews we discovered this week. While harvesting some of our abundant basil, we found a dark, fuzzy substance on the undersides of many leaves. It easily rubs off, but we were unsure of its origin or if it was still safe to consume. After some research, we found that our basil plants have been afflicted with downy mildew. Downy mildew is a new problem in the US, with the first reported cases in 2007. Since then, the pathogen has spread quite rapidly, especially as more people are recognizing the signs. One of the main signs of an infestation is a yellowing of the leaves, which resembles a nutritional deficiency. The other main sign of downy mildew is a sporulation of the fungus on the lower leaf surface, which is the dark fuzzy stuff we had observed. The pathogen, Peronospora belbahrii, can be transmitted through the air, or also through unknowingly contaminated seeds, which is likely responsible for the rapid spread of the pathogen throughout the world. It appears that sweet basil may be more susceptible to downy mildew than other more ornamental varieties. The pathogen is not toxic to humans, so the basil may still be safely consumed, however it will soon kill our basil plants and we will be forced to destroy them to limit its spread.
In addition to the downy mildew, we also discovered powdery mildew on the zucchini, some squash, and a few pumpkin plants. Powdery mildew shows up every year around this time. It first appears as small white circles on the upper surface of the leaves, and then spreads to cover the entire leaf surface with what looks like a powdery substance (hence, the name). Powdery mildew can be controlled by spraying weekly with solution of 1 Tablespoon of baking soda and 1 teaspoon liquid soap dissolved in 1 gallon of water. This solution works best if it is used even before the powdery mildew appears, but we are hoping it will still produce results for us now.