Powdery mildew is a
fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of fungi in the order
Erysiphales. It is one of the easier diseases to spot, as its symptoms are quite distinctive. Infected plants display white powder-like spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any part of the plant that shows above the ground. As the disease progresses, the spots get larger and thicker as massive numbers of
spores form, and the mildew spreads up and down the length of the plant.
The fungus causing powdery mildew of onions is Leveillula taurica (also known by its anamorph name, Oidiopsis taurica). It also attacks the artichoke.
Left untreated, powdery mildew will kill your plant. Common fungicides bought at a local garden store will help by either killing the fungus or by not allowing the fungus to make spores and reproduce. When applying, be sure to spray the leaf, the underside of the leaf, the stem connecting the leaf to the vine, and the vine itself. These fungicides, though, are not cheap and there are some natural ways to treat the powdery mildew. Baking Soda is a very versatile, readily available, and relatively inexpensive; it also can help control and even cure Powdery Mildew. A mixture of one tablespoon Baking Soda, 2.5 tablespoons vegetable oil, and 4-5 drops of liquid soap added to a gallon of water will act as a fine, natural, and inexpensive fungicide (be sure to agitate spray bottle regularly while applying to keep the ingredients from separating). Another natural cure for this mildew is a mixture of one part milk (any kind or brand) to three parts water.
Powdery Mildew reproduces through what is known as cleistothesium. This structure is circular in shape and is a totally enclosed ascocarp. This is a dense, hard, fungal mass created from fungal tissues. The ascocarp cracks open and releases bodies called asci (singular Ascus). These asci hold the ascospores the 'seed' of the fungus.
