Warty zucchinis with skinny leaves may mean the zucchini yellow mosaic virus has infected your plants.
No garden would be complete without the versatile, fast-growing zucchini. A favorite in stir-fry, breads, and the ever popular chocolate zucchini cake, zucchini can be very productive plant, as long as it stays healthy.
Zucchini yellow mosaic symptoms
Whitened leaf veins, mottled, abnormally small leaves with alternating light and dark areas, and deformed, warty fruit are all signs of zucchini yellow mosaic. These are also symptoms of watermelon mosaic and papaya ringspot virus, two viral diseases that often occur at the same time as zucchini yellow mosaic. Watermelon mosaic infections tend to include blistered leaves, while zucchini yellow mosaic has the added symptom of leaf lobes becoming long and narrow, creating a ‘shoestring’ or ferny appearance.
Zucchini yellow mosaic host plants
In addition to infecting zucchini, zucchini yellow mosaic also infects other members of the cucurbit family, including melons, squash, pumpkins, some gourds, cucumbers, cantaloupe, and watermelon. The disease is transmitted by aphids.
Zucchini yellow mosaic management
As anyone who gardens knows, controlling aphids is difficult. These pests seem to appear overnight, in huge numbers. And all it takes is one aphid to get the whole process started. Unfortunately, insecticides are rarely useful in managing zucchini yellow mosaic, because the disease has often been transmitted before you even know the aphids are there. Reflective mulches can be used to discourage aphids, just be sure to remove the reflective material before it gets too hot. Row covers can also be used to reduce access to susceptible plants.
This disease can also be spread on infected garden tools and seeds, so be sure to sanitize your tools regularly and get your seeds from a reputable source (and not that zucchini from the grocery store).
Infected plants should be destroyed and replaced with resistant cultivars.
Since this virus is only viable for a few hours within their aphid carriers, creating a physical barrier of tall, non-host plants around your cucurbits can be enough to prevent the aphids from getting to the plants while the virus is still active.
Zucchini is a summer squash that can sneak up you. Large, prickly (edible) leaves shade the ground and defend against insects. They also hide the occasional zucchini, allowing it to reach horse leg proportions. In Britain, they call these epic squash ‘marrows’, but zucchini are generally harvested when much smaller and younger. According to Guinness World Records, the longest zucchini on record was over 8 feet long and the heaviest weighed in at over 64 pounds! Holy smokes! Imagine stuffing one of those monsters!
Before our zucchini ever reach those proportions, let’s learn more about how they grow and how we can help them be flavorful and productive.
How zucchini plants grow
Zucchini are members of the squash family, making them cousin to pumpkins and melons. Botanically, zucchini are berries - isn’t science fun? Adding zucchini to the garden or landscape is an excellent way to grow your own food. Like other gourds, zucchini have both male and female flowers. Both flowers are edible, with the pistil and stamen removed. Zucchini flowers can be deep fried, baked, sautéed, or added to soups or salads. Personally, I’d rather have the more substantial produce, so I leave the flowers alone. Honey bees and other pollinators are needed, so avoid using broad-spectrum pesticides near zucchini plants. If there are not enough pollinators, you can always hand-pollinate.
Zucchini is a very forgiving and productive plant and it loves our California weather. You can grow zucchini in large containers, straw bales, towers, raised beds, or in the ground. Seeds germinate best at 70° to 95°F and should be planted one inch deep. You can plant seeds individually or in hills. Individual plants should be spaced 3 feet apart. Hills (6-8” high and 12-24” wide) can support two or three plants. Zucchini plants do not handle being transplanted very well and they will benefit from a layer of mulch. Be sure to irrigate regularly. Water-stressed zucchini, and other squash, will taste bitter. This bitterness is caused by toxins that can be potentially dangerous. Don’t let this scare you off, just be sure to water your zucchini plants regularly. This will also help prevent blossom end rot.
Zucchini pests and diseases
Sporadic watering and insufficient calcium can cause blossom end rot in zucchini. Overhead watering can cause powdery mildew, downy mildews, and white mold, so irrigate regularly with soaker hoses. Other diseases include curly top, damping-off, fusarium crown and foot rot, verticillium wilt, and various viruses. Aphids (isn’t it always aphids?), earwigs, cutworms, cucumber beetles, crickets and grasshoppers, slugs and snails, flea beetles, armyworms, nematodes, loopers, leafminers, leafhoppers, thrips, squash bugs, squash vine borers, spider mites, wireworms, and whiteflies will all want some of your zucchini. The good news: you’ll still probably end up with more zucchini than you know what to do with!
Too much zucchini?
Zucchini plants are very productive. While harvested zucchini are very mild and can be adapted to many different dishes, sometimes you just need a change. After you have sautéed, stir-fried, baked, grilled, spiralized, and broiled all the zucchini you can handle, try my family’s recipe for Chocolate Zucchini Cake. This particular recipe has been responsible for transforming the opinions of toddlers, teens, and skeptics for generations. Zucchini can also be pickled, and you can puree it and freeze it for later use. Don’t bother trying to freeze cubed zucchini - it doesn’t end well.
Zucchini and the cross-pollination rumor
Many gardeners worry about cross-pollination between members of the gourd family, but this worry is unnecessary. Natural cross-pollination can only occur within a species (we will not discuss genetic manipulation at the nano surgery level). This means that zucchini plants can cross-pollinate with other zucchini and summer squash varieties, but not with melons or cucumbers. This is actually how we get many new cultivars. When cross-pollination does occur, it has no affect on the current season’s fruit or vegetable. It does alter the DNA within next year’s seeds.
Even if you are a card-carrying Brown Thumb, give zucchini a try this year. It is a very rewarding plant and you can never have too much Chocolate Zucchini Cake!
Cucurbits are members of the squash family.
This family is a thick-skinned group that grows on vines and keeps its seeds in a line down the center of their fruit. The squash, or cucurbit, family is made up of cucumbers, gourds, luffas, melons, pumpkins, squash, watermelons, and the inevitable zucchini. These plants love hot weather and many of them have protective bristles.
Most of the 975 cucurbit species are susceptible to frost and many are trailing annual vines with tendrils. They tend to have large bristle-haired leaves and both male and female flowers (monoecious).
Cucurbits have relatively large seeds and they do not transplant well after the first 3 weeks. It is best to directly sow seeds in the ground. As a group, cucurbits grow fast. They need very little nitrogen, but they use a lot of potassium and phosphorus. Side dressing plants with aged compost goes a long way toward creating a big harvest.
Cucurbits prefer full sun and deep, infrequent watering. During the hottest days of summer, it is a good idea to keep an eye out for wilting leaves, a sure sign that you waited too long to water!
These semi-climbing plants benefit from the use of trellises, stock panels, or ladders. Heavier fruits can be supported using hammocks or net bags. This keeps the fruit off the ground, preventing fungal disease, rot, and pest damage.
Cucurbit pests and diseases
Regularly watering in the early morning allows cucurbit leaves to dry out before evening, preventing powdery mildew and other fungal diseases. Because of the wide leaf coverage of most cucurbits, weeds are seldom a problem. Cucurbits are frequently attacked by cucumber beetles, flea beetles, squash vine borers, and squash bugs, so squash those bugs whenever you see them!
Be sure to harvest fruits regularly, to ensure continuous production. Once plants believe they have completed their reproductive cycle, you generally won't get any more fruit.
You can grow a surprising amount of food in your own yard. Ask me how!