Home & Garden: Adieu, Powdery Mildew

Grapes, pumpkins give a safe and swift heave-ho to fungal diseases.

If ignorance is bliss, I was happily entranced. In 2002 with all the enthusiasm of the truly naïve, my husband and I decided to plant grape vines.

We were encouraged by our friend John in wine making. He’s a skilled vintner, and even won some prize last year, somewhere, from some committee.  In other words, the Pied Piper.

John is a busy scenic designer and a very handy guy who can build just about anything from dinner table scraps and twigs. So, of course, why wouldn’t we follow along? 

I imagined tending vines as carefully as we did our children, then pooling the enormous harvest with saintly John, who began to take on mythic proportions in my mind. I wondered if he could walk on water. I hoped he could at least walk across Lake to get to our house if there was a wine emergency. 

John said he would do the pressing, fermenting, bottling. All the science. Yecchh, be my guest!  I had only to dig some holes, plant my dormant Sonoma vines and wait. On the horizon I could see flirtatious bottles of liquid gold preening for my corkscrew.

Our winemaking history went back to 1999.  My husband bought vintner’s grape juice and made wine in our basement that year. In this example, I use the word “wine” casually. Our beverage produced a puff of smoke when uncorked. It was a pale yellow color with a curving ribbon of red coloring inside. In reality, our wine looked like blood-tinged urine. My husband still says it was very decent table vinegar.  Last Christmas I tried one of the last bottles, and it had in fact become a nice sherry. Huzzah.

Never the slacker, I did some research after my vines arrived.  We were not going to harvest any grapes for four years or so.  Give the vines a chance to settle in and mature. I am good, no, excellent at forgetting things. This was going to be too easy.

By 2007, I remembered we had Cabernet and Shiraz vines growing in the front and back yards.  During harvest time, in September, I was pleased to have saved a small fortune on chicken feed as the girls had been eating slugs, snails and all our grapes for the past three months.  Early in 2008, after winter pruning, plantsman and diligent gardener Reynaldo fenced in the back yard grapes.  Our son graduated from high school in the spring and we took him to New York instead of enjoying harvest season. 

In 2009, we harvested five laundry baskets of grapes! This was a lot of work over two blistering hot days.  But boy, was I proud! We delivered them to John and waited for his praise. Patiently, I waited. For weeks. Eventually he answered my phone call. He said my grapes, oh yes, hm, how to put this? They weren’t very good. After seven years of my life? Are you kidding me? I bit my tongue, thanked him and did some private eye rolling in my kitchen. I slammed doors till I felt better.  I pruned the bejesus out of the grape vines in January.

Now it’s 2011. Last harvest season was a blur, what with a month for me in New York with our son’s pulverized heel, and our daughter’s bittersweet departure for UCLA. The chickens did their eye rolling and slamming of nesting boxes as wild birds ate all the grapes that weren’t fenced in. 

This past week I called Saint John to ask for help.

After all this time, I admitted I’m not sure how to prune grapes correctly. Plus, I have rampant powdery mildew in front. In the back, where the microclimate seems to be perfect, the vines are overcrowded. Bottom line: I’d like to have a grape harvest this year, if it’s not too late.

Christ-like as ever, John said, “I’m the wrong guy to talk to,” about vine care. So consider this a research exercise.

John offered these pointers:

-Grapes need no additional summer water.

-Likewise, no fertilizer. But add lime.

“If I have a sack of lime lying around, I’ll throw it on the grapes.”  Why?  “Vines like lime.  Sweetens the soil.”

Dolomite lime lowers the acidity or the pH level of the soil. Most Southern California soils are pH neutral, within the 6.0 to 8.0 range. Raising the alkalinity or lowering the acidity of the soil shouldn’t be a concern.

-Clean up! Keep litter off the ground under the grapes.

-Prune any low branches that touch the ground.

-Train the cane. Find 3 canes from each vine during winter/March pruning. One cane is tied to a left-running wire, one is tied to a right-running wire. The third cane is a spare in case one of the other two fail to develop.

-Combat powdery mildew.  Some use a sulfur spray. Take care not to inhale the mixture, as sulfur may inflame mucous membranes. 

Summer is a fine time for eliminating powdery mildew from grapes, pumpkins, squash, melons and other cucurbits. Petroleum-free products, like Neem oil, are the good choices for the task.

Neem oil is extracted from the East Indian Azadirachta indica or Neem tree.  The seeds of the tree provide oil and azadirachta, a concentrated form of neem essence. Neem oil products may contain both neem seed oil and azadirachta concentrate.

Fun Facts: Neem oil is a botanical pesticide meaning it is derived from a plant.

Neem oil qualifies as an organic treatment when used for agriculture or food plants.  It can be applied up to the day of harvest. 

According to our friends at Wikipedia, neem oil repels a wide variety of pests including  mealy bugs, aphids, cabbage worm, thrips, whiteflies, beetles, leaf miners, various moths and caterpillars. And for our purposes, it also controls black spot, anthracnose,rust and powdery mildew.  Fungal pathogens all.  

Neem oil is preferred (by John) over sulfur treatment.  While sulfur was first used in the 1870s as a pesticide, neem oil has been used in India for hundreds of years in soap making and cosmetics. 

Neem oil can knock out powdery mildew in 24 hours. More likely, one or two repeat applications at seven day intervals will follow. It’s very easy for powdery mildew to overwinter in wet soils infested with fungus, so tackling it in summer aids winter maintenance. 

Neem oil may smother about 200 species of immature soft-bodied insects on contact, and acts as a grown regulator, preventing juvenile insects from reaching the next stage of development. 

Neem oil has little or no effect on adult beneficial insects.

Neem oil breaks down quickly. It lasts 100 hours in sunlight or during rain over overhead sprinkler exposure.

It works best when temperatures are between 60 and 85 degrees.  Do not apply during especially hot days.  Leaf burn are likely when it’s too hot.  If elevated temperatures are anticipated, spray early in the morning, before sunrise, if possible.  Allow product to evaporate on leaves and stems for several hours before brutal heat sets in.

Do not use when plants are stressed, either from heat or drought.

Read application label carefully, as with all pesticides and herbicides.

Buy only what you will use. In case of leftovers, dispose of unused oils.  Do not store as pesticides of all stripes expire. Take extra containers to nearest haz-mat site.

Test small section of plant in advance.  Check plant each day for one week; if no adverse reaction, treat remainder of plant.  Continue to monitor daily.

Make sure you understand the application rate of any product used in your garden.  Minimize the use of pesticides and magically, their hazards will be minimized. Store out of reach of children and pets.


Leslie Aitken July 11, 2011 at 02:03 PM
This is an excellent, informative article......thank you!
John Stephens July 11, 2011 at 06:41 PM
Glad you liked it, Leslie!


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