If Your Cucumber Leaves Have Brown Spots, Act Fast With One of These 5 Easy Fixes

You had a bumper crop of cucumbers all season long, but now, as the dog days of summer begin to wind down, your cucumber plants are looking less than vibrant. The weather is still warm, yet your cucumber leaves are riddled with brown spots as if they’re dying off for the winter.

Want to revive your cucumber plants and stop the blight of brown? Here’s how to diagnose the brown spots on your cucumber leaves and fix them, fast.

5 Reasons Your Cucumber Leaves Could Have Brown Spots

Cucumbers should be able to keep producing until the first frost, as long as they don’t fall victim to pests or disease. Unfortunately, the brown spots can be an early indicator that there’s an issue.

Jason Skipton, executive director of Growing Gardens, explains that these brown spots often occur around the change of seasons.

“This is normal, and at this time, this happens to a lot of plants, especially in the Cucurbitaceae family, including cucumbers and squash,” he says. “Don’t be too hard on yourself, but there are steps to take to keep your plants healthy and producing long into the fall months.”

Here are five reasons your cucumber leaves could have brown spots, and what you can do to reverse course and restore their healthy green color.

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Mildew

Powdery mildew and downy mildew can both afflict cucumbers, particularly when the weather has been particularly wet or the plants have been overwatered.

“These mildews are spread from plant to plant through the air, overhead watering, not disinfecting pruners, and from plant material contacting other leaves,” says Skipton.

To fight mildew, Skipton recommends pruning out any infected leaves and throwing them away in the garbage, far from the plant. Make sure to sanitize your pruning shears after removing any afflicted sections.

Apply a powdery mildew spray to prevent the mildew from coming back.

Cucumber Beetles

Cucumber beetles can launch a multi-pronged attack on your cucumber leaves. First, they’ll eat holes in the leaves, drying them out and causing brittle spots. Then, they run the risk of transmitting bacterial wilt to the cucumber plant, which will cause the leaves to brown, then wilt, Skipton shares.

“Look underneath the leaves as you will find the cucumber and or squash beetle eggs,” he says. “If you find these, prune out the leaves with the cluster of eggs and throw them away in the trash.”

Lack of Nutrients

“At this point, the plants are nearing the end of their lifecycle and will need a boost of energy,” says Skipton, who notes that a lack of nutrients can lead to brown spots on leaves.

He suggests using a fish fertilizer and adding potassium to a watering can before your next morning watering.

“The added nutrients should give them a leg-up in this battle of the summer,” adds Skipton. 

Spider Mites

Spider mites are a tiny but terrible pest to have in your garden, and cucumbers are fair game when it comes to their preferred places to feed. If you see small spots on your cucumber leaves, then it could be due to spider mites.

While the initial spots may be yellow, heavy infestations can eventually lead to brown sections on the leaves.

Luckily, as long as you catch them early, they’re easy to get rid of. Spray your plants with a blast of water, then apply an insecticidal soap or oil.

Fungal Disease

Cucumbers are also susceptible to fungal issues, including cucurbit anthracnose, which can cause brown spots on the leaves of cucumbers. While the issue may start small, it can spread, eventually damaging the entire plant.

Avoid the spread of fungal diseases by giving your cucumbers enough space to allow for air circulation between plants and watering them only as often as necessary.

If you see leaves that look as if they have fungal issues, prune them immediately