This page is a short guide to identifying and treating diseases and pests that may affect your cucumber crop. Remember, you can avoid many diseases by asking for disease resistant varieties at your local nursery. There are cultivars available that are resistant to cucumber mosaic, downy mildew, powdery mildew, anthracnose, angular leaf spot, scab, etc.

Additionally, crop rotation with herbs, annuals, and other vegetables not related to cucumbers will help keep your garden disease and pest free. If your cucumbers do happen to suffer from pests or diseases, your best bet is to identify and treat the problem as quickly as possible.

 

Symptoms include a series of small, whitish dots on the upper part of the leaves. Eventually, the leaves will turn brown. Try an organic pesticide to get rid of leafhoppers.

Cucumber beetles are yellowish in color with black highlights. They go after both the leaves and the fruits of cucumbers. Look for holes in the leaves and disfiguration on the fruits. Trick picking the beetles off by hand and use an organic pesticide to keep them from coming back.

Leafminers make small tunnels in the leaves of plants. Other symptoms include discoloration of the leaves. Try out an organic pesticide to treat the problem.

Nematodes are microscopic critters that infect plants and cause swelling on the roots and stems, and small knots on the roots. When infected, the plants will begin to wilt. Try planting garlic as a companion plant to keep nematodes away. Crop rotation is also important to avoid nematodes. You can also use a technique called soil solarization. Read this information from Oklahoma Cooperative Extension Service for more information soil solarization (PDF file).

Squash bugs leave tiny yellow to brown speckles on the leaves. The vines will also begin to wilt. You can use an organic pesticide or wooden boards to trap the bugs. The bugs will accumulate under the board so you can easily trap and kill them. Try picking the bugs off by hand as well.

Look for yellowing leaves, a liquid frequently called “honeydew,” and the presence of a black or gray mold. White flies are visible to the eye and will fly off in large groups when you move the plant. You can try and treat the plant with a natural pesticide if you choose, or physically remove the leaves that have white flies on them and destroy the leaves.

This bacteria disease is quickly spread through rain or water. It leaves dead spots on leaves. The best way to avoid this disease is to keep the foliage dry. Drip irrigation and soaker hoses work great to accomplish this.

This is a fungal disease. Symptoms include yellow spots on leaves that eventually turn gray. The texture is fuzzy on the undersides of plant leaves. Ask your local nursery for disease resistant varieties, and practice cleanliness in the garden by removing garden debris. Try and keep the foliage as dry and possible.

Mosaic virus causes deformation of the cucumber plants, with small leaves and underdeveloped plants. Look for discoloration and spotting on the leaves as well. This disease is spread by aphids so make sure to control these pests. When you spot mosaic virus, go ahead and remove the infected plant and destroy it. Do not compost plants infected with the virus. The fruits from infected plants should also be destroyed.

This is a fungal disease that is spread by spores carried by the wind. Look for white to gray fungal deposits on the leaves and stems of your cucumbers. As the mildew spreads, the leaves may begin to drop off. There are varieties of cucumbers available that are resistant to this disease. You can also try a natural fungicide. Make sure to keep your garden free of debris and to destroy any infected plant parts.

This disease is caused by pythium fungus and causes the entire plant to die and wilt. Look for root rot. This disease is exacerbated by poor draining soil, so make sure to add organic compost to the soil before planting to improve drainage. Growing your cucumbers in containers and raised beds. can help this problem.

This is a fungal disease called by the Vertfcillium fungus. Symptoms include wilting leaves and brown discoloration of the stems and roots. You’ll typically have to open the stem to see the problem. Eventually, this disease will cause the entire plant to wilt and die. This problem often lingers in the soil where tomatoes, potatoes, chiles, and other members of the nightshade family have been planted. Crop rotation is important to avoid this disease.

If your cucumber vines look healthy but do not produce fruit, the plants may be suffering from a lack of pollinators in your garden. Avoid using chemicals in the garden, especially insecticides.

 

Cucumber bitterness is not uncommon. This bitterness is caused early in the plant’s development by terpenoid compounds that give a bitter flower to the entire plant. Typically, the bitterness accumulates at the stem and below the surface of the skin of the cucumber. This is unfortunately a genetic problem. Newer cucumber hybrids seem to have fewer problems with bitterness. Additionally, remember to grow your vines in the proper area, with plenty of sun. Avoid over watering and use organic compost in your soil to ensure a healthy crop. UC Davis has an interesting website (PDF file) on cucumber bitterness.