Call it beginner’s luck, but last year in my very first year of gardening, I managed to go the entire spring, summer, and fall seasons without ever encountering powdery mildew on my zucchini plant. This year I’m growing pumpkins, and apparently powdery mildew comes more easily among the vine-y squash varieties, because there’s been a breakout, and it spread quickly. It not only covered quite a few of the pumpkin leaves, it’s on the zucchini, the purple kale, the collards, and even the artichoke. It might even be responsible for the failed sugar snap crop, but since it’s already gone, I have no way to know.
Reconnaissance in the Neighborhood
On my walk around the neighborhood the other day, I noticed quite a few cucurbits covered in powdery mildew. A butternut squash vine had quite a few fully formed (gigantic actually) squash that didn’t seem affected at all by the white speckled leaves, but just one block down a watermelon vine and a whole patch of pumpkins were devastated — completely white and no decent fruit at all.
This stuff travels through the air (and quickly) so I’m crossing my fingers that it stays away from the tomatoes in the back yard, because after last year’s dreary little crop, we have a lot of emotional investment riding on this year’s tomatoes!
What’s Powdery Mildew?
Powdery mildew is a fungus that creates little white powdery dots all over the leaves of a very large number of garden and wild plants. It eventually overtakes the leaves and prevents photosynthesis from taking place, thereby suffocating the plant if left untreated. It can become a problem in warm, humid weather, and it’s exacerbated when leaves are overly wet without drying adequately in the sun (creating a steam bath between the leaves and the ground). It can result from improper spacing and pruning, but often occurs when the leaves get wet during watering. It can be spread through the air and contaminated gardening tools used in other areas of the garden without proper washing. Watering the soil at the base of the plant without wetting the leaves either early in the morning or after sunset in the evening is a good preventive measure for this disease, but once a plant has it, there doesn’t seem to be a sure-fire way to get rid of it organically.
Reconnaissance on the Web
Just like most things in gardening, surfing the web brought up as many solutions as there are websites talking about powdery mildew, so we started with the suggestion to dilute skim milk in water and spray it on both sides of every leaf. I grossly underestimated how much milk we’d need — twice. Started with a pint (30% milk, 70% water) and didn’t even cover one bed in the front yard. Then moved to a 1/2 gallon, which I promptly ran out of before reaching the back yard (closer to 40% milk, 60% water). The following afternoon, I mixed 1 gallon milk with 1 gallon water and went to town on everything, no holds barred. I repeated this exercise 3 times over the course of a week.
The milk did nothing.
Some people say it works great, but for us, nada.
Our second line of defense was a product that contains copper, called Bonide 811 (affiliate link). It’s approved for organic gardening and includes powdery mildew in the list of fungi it can destroy, so we went for it. We’ve applied it three times after severely cutting back all the affected leaves during the failed milk phase. It’s arrested the problem but not totally cured it on the pumpkin plants. I have already pruned the heck out of them and am hesitant to take any more leaves, so at this point, containing it is good enough for me. One plant hasn’t produced flowers since I (over)pruned a few weeks back. (sad) All the other plants seem cured as of today. I’d recommend this product over the milk any day, but it remains to be seen if it will actually completely eradicate the problem through multiple applications. With the amount of milk I used, it wasn’t much of a price difference either, to be honest. We sprung for the heavy-duty concentrate and diluted it in a big garden sprayer thing like this (affiliate link – this is exactly the one we have).
Timing is Everything
Lucky for us, we already have 14 fully-formed pumpkins ripening on the vines that won’t be affected by the mildew. My over-pruning has had some consequences though, because my zucchini plants have had trouble getting pollinated ever since. One zuc plant hasn’t made a male flower since I started hacking. I had to hand-pollinate for the first time last week after losing 3 baby grey zucchini to the shrivels of not being properly fertilized.
8 Tips for Preventing Powdery Mildew
(or at least keeping it manageable if you get it)
- Water early in the morning or after sunset, and try to keep the water on the soil, not the leaves.
- Follow spacing guidelines for your plants (especially squash) and prune as you go to keep the air circulating between the leaves and the ground
- Don’t over-water
- Strike early if you start to see signs of powdery mildew by removing the infected leaves and sealing them in plastic for disposal (do NOT use them in compost). Don’t overdo it like I did though!
- Clean your tools thoroughly with disinfecting soap if you have used them on infected plants.
- Rotate your crops to prevent reinfection each year.
- Condition your soil between seasons with rich mulch that will maintain proper biodiversity and naturally combat invaders.
- Be judicious about products you use to contain the problem in order to maintain your own organic standards.
Surprises at Every Turn!
The lesson I keep learning in gardening is that nothing is predictable. The success of last year’s garden has basically nothing to do with how things might go this year or next. Last year’s tomatoes were thick-skinned, mealy, and not great. The plants were MONSTROUS; the fruit not so much. We over-watered, had too much nitrogen in the soil, and didn’t space the plants well (or so I’m guessing). We adjusted, and this year, the plants are full of big, beautiful fruit that WON’T TURN RED. Still crossing my fingers that we’ll get a heat wave soon. There are just so many variables. But that’s what makes it fun!
Gardening is a lesson in releasing control and riding in the passenger seat to find out what nature has in store for you each season.
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