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FIMBY: A squash plant has mosaic virus, and it's not pretty

Mottled fruit, skinny leaves are symptoms of disease

Sacramento Digs Gardening
BY Kathy Morrison PUBLISHED JUL 22, 2025

See the difference between one normal zucchini, top, and two squash picked from a plant with mosaic virus. Kathy Morrison

This is the latest installment in our weekly Food in My Back Yard series, focused on edible gardening.

It showed up seemingly overnight. One of three healthy zucchini plants on a hill was suddenly looking weird. The newer leaves were skinny, curled versions of their lusher colleagues.

Sick zucchini leaf — This is one sick zucchini leaf.

And the newest green squash growing on the plant had a mottled, somewhat bumpy appearance.

Uh, oh, it looks like a case of mosaic virus.

Sure enough, after I checked sources on the UC IPM (integrated pest management) website, the symptoms confirmed the virus. The only possible action: Pull that plant now before the virus spreads to the others on the hill (a gamble, to be sure) and to the two hills of zucchini in the next raised bed over.

Mosaic viruses are fairly common problems for cucurbit plants: Squash, pumpkins, melons, watermelons and cucumbers can all suffer from them. In the case of squash mosaic virus, it is spread by cucumber beetles feeding on the plants or by infected seed. Other strains can be spread by aphids. The various viruses are not, apparently, limited to the plant they're named for; the UC IPM site has a photo of a summer squash infected with watermelon mosaic virus.

My plant had early symptoms of whichever strain this was; a severe case would limit fruit production and stunt the plant, eventually killing it.

In a community garden like mine, viruses can spread fast and far. One year it seemed everyone growing summer squash was getting mottled, mishapen and weirdly colored squash. It's particularly strange-looking on yellow squash, which develops blotchy green abstract art on the skin.

The squash still is edible, fortunately, but there is no cure for the virus.

With gloved hands, I carefully removed my plant, gently pulling out as much of the long root that I could, then bagged the plant and tossed it in the trash, not the green waste.

Healthy leaf — For comparison, a healthy zucchini leaf.

And believe me, I'm on close watch for symptoms in my other plants. I'm not ready to be done with zucchini just yet this summer.

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Keywords:

FIMBY Food in My Back Yard squash zucchini plant diseases mosaic virus pests vegetables cucurbits pumpkins cucumbers melons summer July Sacramento gardening

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Flowers in My Back Yard Series

May 12: Know your coreopsis from your bidens

May 5: Mums the word on Mother's Day weekend

April 28: Majestic Matilija poppy is worth a look

April 21: Celebrate roses, America's favorite flower

April 14: Small flowers with outsized impact

April 7: Calendulas do double duty

April 3: Make Easter lilies last for years to come

March 31: In praise of a pollinator magnet (small-leaf salvias)

March 24: Azaleas brighten shady spots

March 17: The perfect flower for beginners? Try zonal geraniums

March 10: Keep camellias happy for years to come

March 3: Fruit tree blossoms are a fleeting joy

Feb. 27: Are your roses looking rusty?

Feb. 24: Treasure spring daffodils now and for years to come

Feb. 17: How and why to grow wildflowers

Feb. 10: Let's talk Valentine's Day roses

Feb. 3: Why grow flowers?

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Garden checklist for week of May 10

Take it easy during that high heat – then get to work! Your garden is calling.

* Remember to irrigate your tender transplants. Seedlings need consistent moisture. Deep watering will help build strong roots and healthy plants. Water early in the morning for best results.

* Plant, plant, plant! It’s prime planting season in the Sacramento area. Time to set out those tomato transplants along with peppers and eggplants. Pinch off any flowers on new transplants to make them concentrate on establishing roots instead of setting premature fruit.

* Direct-seed melons, cucumbers, summer squash, corn, radishes, pumpkins and annual herbs such as basil.

* Harvest cabbage, lettuce, peas and green onions.

* In the flower garden, direct-seed sunflowers, cosmos, salvia, zinnias, marigolds, celosia and asters. (You also can transplant seedlings for many of the same flowers.)

* Plant dahlia tubers. Other perennials to set out include verbena, coreopsis, coneflower and astilbe.

* Transplant petunias, marigolds and perennial flowers such as astilbe, columbine, coneflowers, coreopsis, dahlias, rudbeckia and verbena.

* Keep an eye out for slugs, snails, earwigs and aphids that want to dine on tender new growth.

* Feed summer bloomers with a balanced fertilizer.

* For continued bloom, cut off spent flowers on roses as well as other flowering plants.

* Put your veggie garden on a regular diet. Set up a monthly feeding program, and keep track on your calendar. Make sure to water your garden before applying any fertilizer to prevent “burning” your plants.

* As spring-flowering shrubs finish blooming, give them a little pruning to shape them, removing old and dead wood. Lightly trim azaleas, fuchsias and marguerites for bushier plants.

* Don’t forget to weed! Those invaders are growing fast.

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