There are some things in our gardens that we have, at least, some control over, and there are others that we do not. We may think that we have control over insect pests and diseases. In reality, our actual control is probably quite limited. We can maintain good cultural gardening practices and be quite diligent, but sometimes things occur suddenly that our control over is very minimal.
A good example of this is the fungal disease powdery mildew. It spreads by spores, which are spread by wind. Obviously, it is rather difficult to control the wind that is blowing through a garden. There are many plants, both ornamental and edible, that are susceptible to powdery mildew. If you have lived and gardened in the Willamette Valley, you most likely have experienced damage on some of your plants from powdery mildew. Plants that seem to be the most susceptible are grapes, squash, cucumbers, and roses.
Squash and cucumbers often get powdery mildew toward the end of the summer and if the entire plant is not infected, simply removing the diseased leaves can give some control. Be sure to cut the leaves at the bottom of the stem because the stem can be infested as well.
Are you also battling blossom end rot on your squash? Find out what you can do about it here.
Contrary to popular belief that mildew is most prevalent in rainy weather, the ideal conditions for powdery mildew to grow and spread is when we have warm days and cool nights, Powdery mildew spores thrive in high humidity. As the spores grow on leaves, they sap nutrients from the plant which can sometimes cause death of the leaf. A severe infestation may cause death of the plant, although this is uncommon in home garden situations. Powdery mildew is easier to prevent than to control once it has infected a plant. If you have plants that are susceptible, a preventative program might be best.
Wilco has a wide selection of disease control products that specifically list powdery mildew as one of the diseases controlled. There are both inorganic and organic controls available. Always read and follow label directions including the precautionary statements. For example, Bayer Bio-Advanced Insect, Disease & Mite Control is for ornamentals only. This comes in a concentrate that is mixed with water and then sprayed on plants. As per the precautionary statements, this is toxic to bees and should not be used on flowers when they are flowering. This is very important information to be aware of.
For many years, an organic solution to powdery mildew has been sulfur. Bonide Sulfur Plant Fungicide Dust can be used as a dust or spray on a wide range of plants including many ornamentals and edibles. Wilco Category Marketer, Brian Coons, told me that he has been using sulfur dust as a spray-on his grapevines and it has been doing a good job. Two other organic Bonide products for powdery mildew are Bonide Liquid Copper Fungicide and Bonide Rose RX 3 in 1 Ready to Use, which contains neem oil.
Bonide, Captain Jack's Copper Fungicide Spray, 32 oz
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When powdery mildew attacks roses, it usually will first appear on the new growth and flower buds. Roses vary greatly in their susceptibility with some roses rarely getting it and others that are mildew prone.
It is very visually unattractive on roses which are grown for their flowers and glossy foliage. Many newer roses are being bred for disease resistance and their plant tags will note this. A cultural practice of removing some of the rose canes to open up the bush for more air circulation can be helpful.
Be diligent in your garden and get control of diseases like powdery mildew before they get the upper hand. Keeping your plants healthy is a positive step as a healthy plant is less likely to suffer the damage that an unhealthy one will.
Photos courtesy Rich Baer
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