Living with Powdery Mildew

Living with Powdery Mildew (PM). I’ve accepted it. I have to live with powdery mildew on my edible crops. There was a time I thought I could get a handle on it, rise above PM, win out. But, even though I used a preventative spray on my seedlings this year, my new tomato transplants still contracted the fungus. The spores are everywhere, and humid conditions don’t help. We have June gloom from May through August, in fact every morning for a week has been overcast until just after noon.

Zucchini leaf covered in spots in 2013

When I started gardening three years ago, I didn’t know anything about powdery mildew. My first experience of PM was growing zucchini (I’ve had to since abandon growing it. Zucchini takes up a lot of space and my garden is cramped.) I tried the milk sprays I read about online, which seemed to keep it at bay, but eventually, it finished off the plants. You can leave the plants untreated, but the more the spores produce, the more spores are in the soil to contend with later.

Powdery mildew rarely kills, you will read in any number of copious PM postings online, but, eventually if the leaves get enough of a coating of spores it will disrupt or prohibit photosynthesis which plants need to produce flavorful fruit and vegetables. The same results if you remove too many leaves.

There are many kinds of powdery mildew and it is host-specific (so the PM on your zucchini won’t be the same as the PM on your roses), but it’s still PM and a problem. If you live in a temperate climate where it doesn’t freeze, the spores never die off and they live in the soil and travel by wind and water splashing on plants, which is why powdery mildew usually starts at the base of the stem of tomatoes and works it’s way up. (You can also spread from plant to plant by contaminated shears or handling. Sterilize clippers with rubbing alcohol, and wash hands.) By the time you see white spots on the leaves, the plant is quite infected, and in my experience it’s just a matter of time.

Before, During & Immediately After Spraying Tomato Stem with Neem Oil

THE BEST way I’ve found to live with PM is to use Neem Oil as a preventative and as a treatment. Because Neem oil is derived from the Neem plant, it is safe for organic gardening. Use the recommended amount on the label, usually 1 tablespoon per gallon of water. I’ve used the baking soda sprays, milk sprays, and even organic soybean oil sprays but nothing works any better than Neem oil. (There is organic Neem oil, Neem oil made from different parts of the Neem plant, but the purest Neem is derived from the seeds, so do your research before buying.) BTW, buy a pump sprayer and do not attempt regular spraying with a trigger sprayer. Repeated use of a trigger sprayer will inflame your hand joints. With all the other digging, shoveling, lifting and spadework, your hands take a beating in the garden.

Late Bloomer Lessons (LBS’s): Be Observant, Be Vigilant

Prune your tomatoes, so there is plenty of airflow between plants, and if you are prone to weather conditions which promote mildew, set a regular spraying schedule and stick to it. Even if the leaves look perfect, inspect the stems, and you may find the first powdery, whitish spots indicating PM. Spray the entire plant till dripping, and I especially let a good amount drip down the stems, and spray from all sides. The white spots will be gone after spraying, but that doesn’t mean it won’t come back. (The spots may look like a bruise, or darkish spots after spraying.) Don’t get exuberant and use more than the recommended amount which can burn plants. (I did that to my lemon squash last year.) Also, take care to irrigate by drip. Water splashing up the stems can carry the spores from the soil. Even with the use of biodynamic compost, which I use in planting, the spores make a return engagement.

Neem is also a good treatment for sucking pests (like aphids and the tomato suck bug), as they ingest the Neem and it inhibits reproduction. The Neem plant is from the Indian subcontinent, and I heard Vandana Shiva, the Indian eco-warrior environmentalist, say that Monsanto at one time tried to patent Neem. Vandana maintains that you can’t patent life. Lucky for us, Neem is widely available.

Vandana Shiva speaking in Los Angeles ©Kaye Kittrell 2013

A Google+ gardener recently wrote me saying that a lot of my problems would be taken care of by regular use of compost tea. I had just begun this regimen, but, it was already too late. I will be alternating compost tea with Neem spray, as, once again, I planted quite a few tomato plants. What are your biggest garden challenges? Please let me know and please share Late Bloomer with friends. Thanks for your support! – Kaye

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Category: Pest Management, Plant Diseases, Urban Gardening