How to Prevent Squash Vine Borer and Powdery Mildew on Squash, Organically

Many organic gardeners who have grown squash in the southeast US will think this must be a practical joke. It’s not! There are chemical-free ways to grow as much squash as your “conventional” neighbors. Then you can finally participate in Sneak Some Zucchini Onto Your Neighbor’s Porch Day. No really, that’s an honest-to-goodness national holiday on August 8th every year.

The best solution for powdery mildew is a spray of 1 part milk to 9 parts water coating the leaves every 1 – 2 weeks. Use the spray when there is full sun (morning is best) before the disease sets in and you’ll have a 90% prevention rate. I’ve already written an extensive article on this remedy (siting the scientific studies backing it). Here it is:

How to Spray Milk to Prevent Powdery Mildew Disease

Photo Caption: This is the perfect size to pick a ‘Tromboncino’ summer squash (C. moschata), though it is edible at any size or stage. If left on the vine it will harden into a butternut winter squash. We love the funny “spoon” shape.

Squash Vine Borer (SVB) is one of the most difficult pests for organic gardeners to control. As diurnal moths, they are active in the daytime instead of at night. SVBs are also a wasp mimic, but can’t sting you.

What they can do is decimate a squash plant almost overnight, leaving many gardeners confused about the culprit. SVB adults lay their eggs on the base of the plant and then the maggot-like caterpillars burrow inside the stems to eat. Symptoms of SVB include leaves wilting even though the soil is moist and wet brown frass (caterpillar poop) collecting at the base of the stems. SVB damaged plants are much more susceptible to other problems like Powdery Mildew.

SVB larva spend their time eating the plant from the inside out, which means they are notoriously difficult to remove. Sprays, powders, and other traditional methods are largely ineffective. Hand-picking can only be done by slitting open the squash stem and finding the tunneling caterpillar. This can have some success, especially if the damaged stems are then covered with soil so the squash can put out new roots.

However, it’s a pain! I don’t do it anymore.

Instead, I plant my summer squash and zucchini as early as possible each season. SVBs show up late enough in the summer that I can get a decent harvest before my plants start succumbing. I’ve already gotten enough squash and zucchini this year to make me feel like my handful of plants were worth it.

But I don’t give up on having squash all season, either. Squashes are in the genus Cucurbita and most of the summer squashes & zucchini humans have bred for the garden are from the species C. pepo. SVB moths prefer this species above all other squashes. They also like squash, pumpkins, and gourds bred from C. maxima. There isn’t much hope keeping SVBs away from these two, so I also grow summer squash and pumpkins bred from C. moschata to take over for me later in the season. C. moschata varieties have tight, narrow stems that the SVBs don’t seem interested in.

They also have some yummy fruits! Any unripe C. moschata variety can be eaten like a summer squash when it is young enough that the skin can be pricked with your fingernail. They tend to be pale green like a zucchini and have a nearly identical flavor and texture. If you’re more interested in winter squash, wait until the fruit hardens and the stem connecting it to the vine starts to turn tan.

My favorite C. moschata variety is an Italian heirloom that was actually bred to be eaten like a zucchini. I buy it from Pinetree Garden Seeds under the name ‘Zucchetta Rampicante Tromboncino.’ I’ve also seen it sold at places like Territorial Seeds under the simplified name of ‘Tromboncino.’ The flavor is fantastic and the vines produce like… a zucchini! They don’t have a bush habit, though — make sure to use a sturdy trellis for their long vines. Near the end of the season I leave some of the fruits to mature into giant, 4′ long butternut squashes.

Photo Caption: This mature ‘Tromboncino’ from last year is almost as long as me! At this stage it can be stored as a winter butternut squash.

I also have a favorite pumpkin. It is slightly flat and a beautiful muted pink, like something out of a fairy tale.

Photo Caption: This harvest from last year shows a mature (butternut) ‘Tromboncino’ squash on the left and a ripe, round ‘Long Island Cheese’ pumpkin toward the upper middle of the photo.

Even better is the pumpkin’s name of ‘Long Island Cheese.’ Perhaps it isn’t romantic to be named for looking like a wheel of coagulated milk, but it is certainly memorable. They’re delicious! I’d consider ‘Long Island Cheese’ to be one of the best flavored heirloom pumpkins. We especially love them in pies and curries.

Right now we have summer squash, ‘Tromboncino’ squash, and ‘Long Island Cheese’ pumpkins producing in the garden (though the pumpkins are far from ripe). I know I can count on the ‘Tromboncino’ variety to take my summer squash’s place when the SVBs really get going.

Now if anyone knows of some surefire solutions for squash bugs and pickleworms, we’ll be all set! (My great-uncle tells me that squash bugs are easier to hand pick early in the morning when the dew is still on the leaves). If you have any other suggestions please leave them in the comments.

Eliza Lord

I'm a Greenville, SC native (the Appalachian foothills) who wears the hats of Greenville Master Gardener & Upstate Master Naturalist. I love to write about food and sustainability.

25 thoughts on “How to Prevent Squash Vine Borer and Powdery Mildew on Squash, Organically”

  1. Diana - June 22, 2011 9:09 am

    Planting the squash early seems to help before those bad guys started to make trouble.
    Diana´s last blog post ..White sweet potatoes and shoots with coconut milk dish

    1. Sustainahillbilly
      Twitter: appalachianfeet
      - June 23, 2011 12:36 pm

      I agree! I’ve experimented with planting them after the SVBs peak, but no luck with that method so far. Maybe I should try again with a row cover until the plants are large enough to produce flowers.
      Sustainahillbilly´s last blog post ..How to Identify Fusarium Wilt and Septoria Leaf Spot in Tomatoes

  2. Pam's English Garden - June 22, 2011 9:45 am

    Dear Eliza, I am definitely going to try the milk and water thing. But I guess I planted my zucchini too late — oh, well — next year … Thanks for the tips. P. x
    Pam’s English Garden´s last blog post ..My ‘Bloomers’ on June Garden Bloggers’ Bloom Day

    1. Sustainahillbilly
      Twitter: appalachianfeet
      - June 23, 2011 12:37 pm

      Is it already getting borers? Good luck with the milk spray!

  3. Zoe / pearled earth - June 22, 2011 6:00 pm

    Great information, Eliza! I did not know that the borers don’t much like moschata… But we have grown the troboncinos with success before, and will try again, with this new info. I HATE squash borers, which we do have up here in northeast PA, but I LOVE finding them inside a stem and squishing them with a piece of wire. I’m sick like that.
    Zoe / pearled earth´s last blog post ..How to Cool Off on a Hot Day

    1. Sustainahillbilly
      Twitter: appalachianfeet
      - June 23, 2011 12:38 pm

      Haha, well I get a therapeutic enjoyment out of feeding Japanese beetles to the chickens… I understand!

  4. Anna - June 22, 2011 7:09 pm

    We’ve had great luck with succession planting — just keep planting squash and cucumbers every two weeks until the end of July and we’re eating the results all summer. That said, this year we’re trying out yellow crookneck squash because we’d read that it’s one of the least vine borer friendly of the traditional summer squash. And even though I saw the vine borers pass through the garden, we’ve yet to see any wilting!

    The trouble is that I paired the succession planting and the variety selection, assuming one would work if the other didn’t. Since both seem to have worked, we might finally be giving away summer squash this year. After all, five beds worth is a *lot* of squash when the plants don’t die young.
    Anna´s last blog post ..mark: Unwrapping a roll of chicken wire

    1. Sustainahillbilly
      Twitter: appalachianfeet
      - June 23, 2011 12:41 pm

      That sounds awesome… I wish I had room for 5 beds of squash!!! Although yesterday we had a storm come through and blow over a row of our tomatoes so I might unintentionally have some room for succession plants.

      I hope you end up with more squash than you know what to do with!

  5. Karin/Southern Meadows - June 23, 2011 6:28 am

    Thank you so much for this post! I will be trying this! I won’t use chemicals so this may be a lifesaver for me if I am to grow squash in my garden!
    Karin/Southern Meadows´s last blog post ..Wordless Wednesday: Incognito

    1. Sustainahillbilly
      Twitter: appalachianfeet
      - June 23, 2011 12:41 pm

      Great! I hope it works for you.

  6. Carolyn @ Carolyn's Shade Gardens - June 23, 2011 9:01 am

    Eliza, I just had a customer ask me about powdery mildew on garden phlox. I sent her your post. You didn’t mention garden phlox P. paniculata but I am assuming it will work. Thanks, Carolyn
    Carolyn @ Carolyn’s Shade Gardens´s last blog post ..Supporting Sustainable Living: Part Two

    1. Sustainahillbilly
      Twitter: appalachianfeet
      - June 23, 2011 12:43 pm

      Basically there aren’t studies showing if it works on plants other than cucurbits and grapes. However, it worked on my zinnias last year so I think it could potentially work on any powdery mildew strain. Thanks for sending your customers to my site!
      Sustainahillbilly´s last blog post ..How to Identify Fusarium Wilt and Septoria Leaf Spot in Tomatoes

  7. Mark Willis
    Twitter: marksvegplot
    - June 23, 2011 2:34 pm

    Interesting post. I had heard about the Milk remedy, but not actually come across anyone who had successfully used it.
    BTW: Are you not going ahead with the How to Find Great Plants link-up?
    Mark Willis´s last blog post ..Chilli babies

  8. Casa Mariposa - June 26, 2011 9:27 am

    I don’t grow many veggies but did have corn stalk borers damage some of my flowers. It was really frustrating! I have yet to find an organic solution for getting rid of them.
    Casa Mariposa´s last blog post ..The Final Lesson

  9. Bill Brikiatis
    Twitter: hobby_farmer
    - August 20, 2011 8:40 am

    In New Hampshire, it’s better to plant late than plant early if you want to prevent squash borer. There is only one generation of SVB, so you can wait it out. In your area, I bet there are multiple generations.
    Bill Brikiatis´s last blog post ..Controlling Squash Borer, Part II

  10. Linda - December 2, 2011 4:44 pm

    SVB is seen in my area, Tybee Island GA, by mid May, so early planting has helped. I also wrap sections of old pantyhose around approx 4″ of the base of the stalk right to the ground. Its acts as a barrier as the SVB can’t pierce it. And as the plant grows the pantyhose stretches with it. Later, I cut away the oldest leaves nearest the base and wrap aluminum foil another 6″ or so up the stalk. Last year I planted 11 hills, 4 zucchini, 3 yellow, and 4 patty pan, a total of 34 plants. Only 6 plants succumbed to the SVB. Unfortuneately, by July 1st, most of the plants became infected with powdery mildew before I learned about the milk fungicide.

    Thank you for the recommendation of using the Moschata varieties. I’ve purchased several, including an heirloom Long Island Cheese, Trombochino, and a Seminole.

    We first see that nasty pickleworm in September here, so I refrain from planting a fall crop of curcurbits.

  11. Pingback: Powdery Mildew on My Squash | Lettuce Share

  12. hoo-boy - July 9, 2012 9:49 am

    I have a friend that has a commercial vegetable garden in south Georgia, His squash bears untill fall tempertures arrive. He uses NO Chemicals to controll vine borers just a common household kitchen item!
    I will ask him if its ok with him before I reveal the item if any are intersted, he was kind enough to share his secret with me AND IT WORKS! I owe it to him TO not if he objects.

    1. Sustainahillbilly
      Twitter: appalachianfeet
      - July 25, 2012 2:44 pm

      Sounds good! Hope you can tell us. :)

  13. Dano - August 1, 2012 9:07 am

    We are pretty new to gardening and really learning a lot. We have been devastated by the SVB. We have 2 beautiful pumpkin plants that will not turn a bud into a pumpkin (and multiple other squash plants infected). The buds just fall off after they are pollinated. My question is this: Will my garden become “infected” with SVB if I don’t get rid of them (pull out and throw away the plants) or will I see the same attack next year regardless of how I manage them this year?

    1. Sustainahillbilly
      Twitter: appalachianfeet
      - January 16, 2013 10:23 am

      In my experience it doesn’t matter how much you manage them, you’ll still see them next year. Although I suppose poor garden sanitation could definitely increase their numbers.

  14. Joseph - August 5, 2012 11:31 am

    Those squash vine borers are the worst. I planted punkins this year and it is my first time dealing with them. I use Neem now but next year I’m going to use Neem and BT injections also I’m going to plant some dummy crops. Check out my homemade seaweed fertilizing mulch formula video.

  15. Bernadette - February 6, 2013 7:52 am

    Instead of hand picking squash bugs, cucumber bettles or any small bugs; I use a hand held vacumn with a long extension cord. It gets the job done quickly. Best if all, you become much faster than the bugs can run. Usually, within a week all bugs and their eggs are gone.

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