Powdery Mildew on a leaf in the early stages of the infection. The best time to diagnose powdery mildew is in the early stage on mostly green leaves. It starts as irregular pale yellow blotches that combine until the whole leaf is yellow.
Powdery mildew is a troublesome plant disease but, thankfully, never lethal. It’s largely a Spring disease because it thrives in cool, damp weather, so it’s the first disease you will see in the mirliton growth cycle. The good news is that there’s an effective organic fungicide that manages the disease.
The most visible signs of advanced powdery mildew are bright yellow leaves. But chlorotic (yellowing) leaves can be also caused by overwatering or anthracnose. The most accurate way to identify powdery mildew is to examine the seemingly healthy green leaves near yellowing ones. Look for the early signs of mildew are irregular faded yellow blotches like in the photo above. That is the fungus forming little colonies that will eventually into bright yellow leaves.
If you find signs of the disease, there is a highly effective organic fungicide that can control it: potassium bicarbonate. It can completely eradicate the disease in three weeks and works on downy mildew as well.
We recommend L.D. Carlson’s potassium bicarbonate because the manufacturer has verified with a Certificate of Authority (COA) that it is at least 99.5% pure. It’s generally sold in one-pound quantities, which is more than you will need, but it has a long shelf life, and you can share it with other growers. Click here to order online.
L.D. Carlson’s potassium bicarbonate.
If you are using a 99.5% pure potassium bicarbonate product, mix one tablespoon with a gallon of water and shake vigorously. Then spray only in the evening and thoroughly wet the tops and bottoms of all leaves. Apply once a week for three weeks until there are no signs of early infection (faded yellow blotches on green leaves).
For a more thorough article on powdery mildew and mirlitons, see my paper here.