Although many different fungi cause powdery mildew, they are so closely related, they are indistinguishable to the naked eye, and the disease progression, symptoms and treatment is the same. Powdery mildew can attack bushes and trees as well as perennials and annuals. This white fungus does not usually kill your bush or tree but will disfigure and weaken it, making it susceptible to diseases that can kill your plant and may prevent your bush or tree from flowering or producing fruit.
Powdery mould is a white or grey powder-like fungus that grows on both sides of the leaf but can also affect the shoots and flowers. In severe cases, and in some species, leaves will curl and fall from the tree. Late spring, as the weather warms but is still moist, is the time to check your plants for signs of powdery mildew. This fungus is spread by airborne spores that infect plants when temperatures are warm but not hot. The fungus that attacks rose bushes is not always the same fungus that attacks a lilac bush or apple tree.
The best way to prevent powdery mildew is to select healthy plants and keep them that way. Make sure your plant has the sunlight and water it needs to grow and don't overcrowd your garden. Improper air circulation aids the growth of powdery mildew. During the winter months, the fungus lives in decaying and dying leaves left on the ground. In the spring, it spreads to the new growth of your plants via the wind. Remove all dead leaves and dispose of them. Grow plants resistant to powdery mildew if it becomes a problem in your garden.
Many plants are more susceptible to powdery mildew than others. Shrubs such as azaleas, roses and viburnums easily fall prey to powdery mildew, although some cultivars of rose have been developed that are resistant. Maple, apples and dogwood are some trees that are highly susceptible to powdery mildew. Dogwood leaves become discoloured and curled. Powdery mildew can stunt the fruit production of many fruit bearing trees such as apple, killing the new growth and the blossoms.
If powdery mildew is a problem in your garden, begin spraying the tops and bottoms of the leaves as soon as the first white patches of the disease are found. Fungicides such as triforine found in some commercial fungicides have been shown to be successful against powdery mildew. On fruit trees such as apple, a copper spray is recommended. Repeat applications per the instructions on the individual fungicide.
Prune diseased areas of your plant and discard. The effectiveness of ammonium, potassium and sodium bicarbonates, the ingredient in baking soda, has been found successful against powdery mildew. This treatment will not harm the environment and is safe for consumers. Although experts are still arguing whether this treatment is best to prevent powdery mildew rather than treat it, it is an alternative worth keeping in mind. Four tsp of baking soda to one gallon of water sprayed on your plant once every two weeks is recommended. Do not over spray as the bicarbonate can build up in your soil and create another problem for your bush or tree.
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