Why Are My Cucumber Leaves Curling Up?

Cucumbers (Cucumis sativus) are members of the squash family that can be grown in the home garden as vines or bushes. Cucumber leaves curling can be a symptom of a disease or can indicate the presence of a pest, which can affect crop production. Proper sanitation and cultural practices can help prevent this condition.

If the leaves of your cucumber plant are curling inward, Alternaria leaf blight might be to blame. Caused by the fungus Alternaria cucumerina​,​ the disease starts as brown spots on the leaves near the plant's crown, gradually becoming bigger. Leaves that are severely infected turn brown, curl and die. Alternaria leaf blight tends to be a problem when the weather is warm and humid. It is often spread by infected garden tools.

A cucumber plant's leaves may curl downward if it is infected with cucumber mosaic virus. This virus is often transmitted by aphids, which are small, soft-bodied insects that suck sap from the underside of leaves. In fact, the feeding of aphids alone can cause the leaves to curl.

The striped cucumber beetle can also spread the cucumber mosaic virus as well as bacterial wilt, a disease that also causes leaves to become distorted. Plants infected with any diseases should be removed to keep the pathogens from spreading in the garden.

Keeping the leaves dry when watering your cucumbers can go a long way when it comes to preventing fungal diseases, like Alternaria leaf blight. You should also avoid handling cucumber plants when they are wet. In addition, you can save yourself a lot of trouble by choosing cucumber cultivars that are resistant to the diseases that can cause leaf curling.

Many types of plant fungi, including the species that causes Alternaria leaf blight, can overwinter on plant debris, which is why removing all dead vegetation after the growing season is key. Many of the pathogens that can cause cucumber leaves to curl can also linger in the soil for a long time. Therefore, you should wait at least three years before growing cucumbers in the same soil where related vegetables were planted, such as watermelons, squash and pumpkins.

In the case of Alternaria leaf blight, you may need to apply a fungicide as a preventative, like chlorothalonil and mancozeb. If you do use one of these fungicides on your cucumber plants, wait at least five days before harvesting fruit. Copper fungicides are also an option.

If aphids are causing your cucumber leaves to curl, you can try to eliminate them with soapy water. Make sure to rinse the leaves with clean water afterward. You can also use insecticidal soap to get rid of them. Beneficial insects, like ladybugs, help to keep aphids in check, so avoid using pesticides that can harm these predators, which can make an aphid infestation worse.

To keep striped cucumber beetles from feeding on your cucumber plants, cover them with netting. Like fungi, beetles can overwinter in plant debris, so good sanitary practices are crucial to preventing these insects from becoming a long-term problem.