We finally received some warm weather! However, warm weather sprouts fungus, especially after a period of rain. One in particular that always rears its ugly head is powdery mildew. It can destroy squash and cucumber crops, annihilate asters, and we have been seeing a ton on roses this year. With powdery mildew, it is important to prevent it or identify it quickly before it becomes untreatable.
How do you identify powdery mildew? It is a white fungus that appears on leaves and looks like a fuzzy powder. If you look at the picture below, you will see two different white marks on the leaves. One is water spotting; this can be wiped of easily with a finger, has a smooth border and does not look as fuzzy. Powdery mildew, as seen towards the tip of the leaf, has a blurred border, is harder to wipe off, and often reveals damaged leaf underneath the fungus.
For powdery mildew, the best treatment is prevention. It can be a nasty fungus that quickly develops resistance and may never truly leave you alone until the plant is dead. The good news is that each type of powdery mildew species is specific to its plant host, so it shouldn't wipe out your entire garden unless you get multiple species of fungus. A copper fungicide works the best to prevent and treat powdery mildew and is generally considered organic. We have several different types of copper soaps and sprays that come in a variety of application methods. If the copper sulfate is not working, your next step would be a systemic, broad-spectrum fungicide. Some people have had good luck with bicarb powder, which is similar to baking soda, on fungus that has developed resistance to other fungicides. As always, our staff can help you pick out the product that works best for you.