The Powdery mildew problem can be found on many garden plants. It is easy to spot, the whitish powder like covering spreads all over the leaves of the plant. It blocks the sunlight available to the leaves and can prevent the photosynthesis process from working efficiently. Resulting in the plant struggling to survive.
Powdery mildew produces a light powder like covering on the leaves and stems normally white at first but overtime turning darker as the spores are produced. The leaves may distort, some may show yellowing patches and drop prematurely. Often the infected buds may not grow out.
Powdery mildew is more prevalent in warmer climates. It is often found when poor air circulation is present. Plants placed together in close proximity and with no air circulation are most at risk. So this makes it imperative if your area is prone to Powdery Mildew to make sure you divide and re-plant your bulbs and other plants that produce thick clumps.
There are many things you can try out to reduce the likelihood of a powdery mildew attack. Always remove plants showing any signs or at the very least remove any affected foliage by either picking the leaves or pruning the stem. Never compost these plants or any discarded foliage or branches.
Careful, thoughtful pruning of shrubs, the trees and any sturdy perennials allowing adequate air circulation will help prevent an outbreak. Powdery mildew likes the warm, higher humidity areas that often surround plants. If you can reduce the relative humidity then you will undoubtedly reduce the spread of the powdery mildew spores.
A common mistake at the end of summer is to give high nitrogen feeds to plants, resulting in lots of soft, succulent and more importantly, susceptible to powdery mildew growth. Always apply fertilizer in the earlier part of the year.
Even taking the precautions listed above you may still find an outbreak of powdery mildew, if you are unlucky enough to have tried everything you may still need to resort to chemicals. Fungicide is needed for powdery mildew and there are plenty on the market and a quick trip to your local garden center should enable you to find a suitable product. Make sure that the fungicide you are purchasing is suitable for the plant and or plants you want to use it on. Chemicals are very often different for Vegetable and Ornamental plants.
Before applying any chemical control I always try to eliminate in problems by pruning or stripping off the affected leaves, this applies to many garden pest problems, not just powdery mildew. Always apply fungicide strictly adhering to the manufactures instructions that should be clearly shown on the product label. One thing to bear in mind, powdery mildew spreads out in the plant and may require more than one application of the fungicide to eliminate it.
There are many plants that are susceptible to this issue but on the other hand within these particular plants groups the breeders have been busy and in many cases, roses in particular you will find varieties that are disease resistant. Always enquire at your local Plant Nursery or Garden Centre.