12 Zucchini Plant Diseases And How To Fix Them

It is little wonder that zucchini is a favorite home-grow vegetable. They’re easy to germinate and grow, and if you achieve the ideal growing conditions, you will be rewarded with a large harvest of zucchinis. But when things go wrong and your zucchini plant is affected by disease, you will want to find a solution. So here we look at zucchini plant growing problems and how to fix common zucchini plant diseases.

Zucchini Plant Disease and How to Fix Them - zucchini growing problems

But before you ask yourself: what’s wrong with my zucchini plant? It’s a good idea to be aware that when a zucchini plant is coming towards the end of its lifecycle, it is far more likely to be susceptible to disease and attack by pests. So do keep this in mind when it comes to your zucchini plants because after producing a great crop, they can succumb to different growing problems, naturally. However, if you haven’t had a crop yet, but your zucchini plant is struggling to thrive then you will definitely want to identify any disease and find a solution.

Related: 11 Zucchini Pests (And How to Get Rid of Them!)

A Note On Covering Plants During Prolonged Rain

A few preventative methods for reducing disease in the below list include covering plants during extended rainfall.

First of all, this is entirely up to the individual gardener and the effort you are willing to go to as well as the climate you garden in. Prolonged heavy rain fall may mean you need to protect your plants.

Personally, I have never covered my plants but if you want to try it because you’ve experienced disease in previous growing seasons, or if you have young plants or seedlings to protect, then it would be worth a go.

For covering to be effective, the material you use should be waterproof, so in the case of a mature zucchini plant that could extend 40 inches (1 meter), a tarpaulin such as this one, could be used. I would suggest the covering doesn’t touch the plant and for it to be secured in place to prevent it from blowing away. Also, make sure any covering is positioned so the rain runs off away from the garden bed.

Now on to identifying zucchini plant disease and their solutions.

Zucchini Alternaria Leaf Blight

A fungus causes yellowish-brown spots with a yellow or green halo that begins on older leaves of the zucchini plant. The older leaves are attacked first before spreading to the younger ones. If the disease is left untreated, the fungus spreads and joins before the leaves curl, then rot and die. Lesions may also appear on the fruits.

Prevention: Avoid watering the zucchini plant from above. Water the plant only at the roots. During prolonged rainfall, you could consider covering zucchini plants.

Treatment: Trim the infected leaves by cutting them from the plant close to the stem.

Zucchini Bacterial Leaf Spot

It begins as small yellow spots on the leaves of the zucchini plant. If the disease is left untreated, they grow and merge and can lead to small beige indented spots on the zucchini fruit.  Bacterial leaf Spot thrives in hot, humid conditions.

Prevention: Rotate crops every two years.  Buy disease-resistant zucchini seed varieties.

Treatment: Copper-based fungicidal treatment spray.

Zucchini Bacterial Wilt

Causes the whole zucchini plant to wilt, and the leaves might turn a dark green, dull-looking color. This disease tends to begin with a few wilting leaves or runners for no other apparent reason; it then quickly takes over the whole zucchini plant. The disease is spread by both spotted and striped cucumber beetles.

Prevention: Keeping weeds away from the zucchini plants may help as they could be a host for the cucumber beetle larvae. You could lay some dark landscaping fabric around zucchini plants to keep weeds at bay and prevent the adult beetles from laying eggs. When you have space, the squash variety Blue Hubbard works as a sacrificial trap crop to attract the bugs away from the zucchini.  

Treatment: Once a zucchini plant is infected, there is nothing to be done.  Pull up the plant and dispose of it without adding it to compost to avoid spreading the disease.

Zucchini Blossom End Rot

Light brown spots appear at the ends of young zucchini fruit.  It expands and may take on a leathery appearance.  

This can be caused by insufficient calcium in the soil or by erratic watering.

Prevention: Check the soil for calcium levels; if there is a deficiency, then adding calcium sulphate or calcium chloride to the soil before planting ensures there is sufficient calcium to support the plant.

Water frequently not allowing more than the top 1 inch of soil to dry out between watering zucchini.

Treatment: Pick and destroy all affected zucchini fruits off the plant and water the plant consistently.

Feed the zucchini plant monthly to ensure the plant is receiving enough soil nutrients to support healthy fruit development. Try this organic fertilizer here.

Zucchini Choanenphora Wet Rot 

This disease begins on the zucchini flowers and will show up as a powdery white substance. These are the fungal spores that will cause the zucchini fruit to rot at the flower end leaving a purple-like or white powder.

Prevention: The best form of prevention is to ensure you start your garden with healthy soil and practice crop rotation.

Treatment: This disease spreads quickly and unfortunately there is no treatment. It’s best to remove and destroy the plant without composting it. Some gardeners claim success with fungicide, however, because it is the flowers that pass the disease, it is only effective on each treated flower. Because new flowers are forming daily, it is not a long-term solution for the health of the plant or the developing fruit, and therefore not recommended.

Cucumber Mosaic Virus

The leaves take on a mosaic-like pattern and may curl downwards. Zucchini plants can become severely stunted. The virus can also cause problems with the zucchini fruits; they may become distorted and discolored, with rough skins, and only grow to a small size.

Cucumber mosaic virus is spread via aphids, cucumber beetles, and contaminated garden tools.

Prevention: Clean garden tools frequently with rubbing alcohol. Companion planting onions or chives with your zucchini or the herbs lavender or rosemary can help deter cucumber beetles.

Treatment: You can eradicate aphids by a regular application of washing up liquid solution sprayed onto the zucchini plants. This is usually a ratio of 1 tablespoon of dish liquid to 1 quart (1 litre) water.

Cucumber beetles are difficult to eradicate organically once they are on the plant. A strong neem solution may help deter adults from other zucchini plants. You can purchase horticultural neem oil here.

Zucchini Downy Mildew

This is a pathogen that thrives in wet, humid conditions. Most likely to take hold towards the end of the growing season. The zucchini leaves take on the appearance of being covered in grey dust.

Prevention: Only water the roots of the plant, not the foliage. Avoid overcrowding of the zucchini plant, including the leaves. Trim lower level leaves.  And consider covering the plants during long wet weather spells.

Treatment: The sooner downy mildew it is spotted, you can try an organic fungicide. But if the disease has really taken over the plant, then it’s best to pull it up to prevent it from spreading to other plant in the garden.  Remove and destroy the entire plant. Do not compost it to avoid spreading the disease.  

Zucchini Fusarium Crown and Foot Rot

Caused by the fungus Fusarium solani. The first sign is wilting leaves, then the entire plant wilts. Frequently, if you check at or just below the soil surface, there’s a fuzzy pink growth.

Prevention: Regular watering and good air circulation around plants help prevent this, so avoiding planting too close together. Crop rotation is also key to prevention. Buying certified disease-free seeds is another route to prevention.  If you suspect this fungus attack, you shouldn’t grow any zucchini or squash family in the location for at least three years.

Zucchini Powdery Mildew

Zucchini Plant Powdery Mildew

Powdery Mildew can be caused by a variety of fungi. It thrives in warm, humid conditions and usually occurs in late summer for most zones. The leaves look as though they have been coated in flour.

Prevention: Good air circulation is vital to prevent powdery mildew, keeping the area well weeded.  Remove the lower leaves at the stalk with a sharp knife to improve circulation.  Growing vertically and removing some leaves can help.

Treatment: When you see powdery mildew, use our DIY Milk Spray recipe to create your own treatment spray and spray the solution wherever you can see powdery mildew on the affected plant every seven days.

Zucchini Septoria Leaf Spot

Small beige or white circular spots with a brown surround that are caused by the Septoria cucurbitacearum fungus, prevalent mostly in Northeast and Midwest.

Prevention: Thrives in moist, humid conditions and lower temperatures of 60-65°F (15-19°C).  When the temperature rises, it is likely to become dormant and return in the fall.

Treatment: You need to scrupulously clean up plant debris because Septoria cucurbitacearum overwinters on the fallen plant remains. Trim and dispose of infected leaves, do not compost them. Treat with organic copper spray or an organic potassium bicarbonate spray.

Zucchini Verticillium Wilt

Zucchini is just one of the many plants that the Verticillium wilt fungus may attack.  It usually appears midsummer, especially if temperatures are lower, as the fungus prefers cooler weather. Identifiable because the leaves turn yellow and then die.  Frequently the plant wilts during the day and seems to pick up overnight.  On occasions, half of a plant will wilt, and the other half looks normal.

Prevention: Seek resistant varieties by looking for seeds with a “V” after the name. Cleaning garden tools thoroughly between plants can help prevent spreading the fungus.   

Treatment: There is no treatment other than to remove and destroy infected plants.

Zucchini Yellow Mosaic

Zucchini Yellow Mosaic Virus

Leaves develop a yellow-colored mosaic pattern and can look deformed or smaller than usual.  The leaves and zucchini fruit might also rot.  Similar signs to cucumber mosaic virus.

Prevention: Because aphids spread the disease, be scrupulous about checking for them and spraying with a dish liquid and water solution at the first sign.  Welcoming insect-eating birds into your garden can also help keep aphids and other undesirable bug numbers down.

Treatment: There is no cure; remove and dispose of infected plants quickly and do not compost. Clear any aphids from other plants for a chance of saving the rest of the crop.


Many of these zucchini plant diseases can be avoided by regular ground watering only, removing lower leaves, and keeping the plants weed-free.  Healthy zucchini plants are a joy to behold in the garden and you will be rewarded with more zucchini than you know what to do with!

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12 Zucchini Plant Diseases and How to Fix Them - zucchini growing problems