Common cucumber diseases: identification & treatment
Cucumber plant problems can be tricky to identify, as they can succumb to a number of different diseases that can destroy the entire harvest if they take hold. However, there are preventative measures that can help keep cucumber plants healthy and producing their delicious fruits.
Cucumbers (Cucumis sativus) are part of the Cucurbitaceae family, along with other squash, gourds and melons. Unfortunately, if disease strikes, there is often limited or no treatment available for the home gardener, so preventative measures are crucial for maintaining plant health.
The most common cucumber diseases
Cucumber diseases are caused by bacteria, fungi or viruses. Cucumber plants are more susceptible when grown in a humid greenhouse, as the airflow is restricted. This is unfortunate for UK gardeners, as our climate favours growing cucumbers undercover.
Some of the most common cucumber diseases in the UK include:
- Cucumber wilt
- Cucumber rot
- Cucumber anthracnose
- Powdery mildew
- Cucumber mosaic virus (CSV)
- Grey mould
Thankfully, new cucumber varieties have been bred with better resistance to these diseases, which should help you decide which cucumbers to grow.
Perhaps the most common problem when growing cucumbers is the occurrence of mildews. Read our dedicated article on treating and preventing mildew on cucumber leaves.
There are several different types of wilts that can affect the cucumber. Luckily, they are relatively rare here in the UK. The most likely to occur is verticillium wilt (Verticillium albo-atrum). Verticillium wilt is a soil-borne fungal disease that can affect certain fruit, vegetable and ornamental plants, including cucumbers. It enters via their root systems.
Often occurring suddenly and without warning, verticillium fungi physically block the channels that carry water within the plant and release toxins. This causes cucumber leaves to yellow, dry, wilt and eventually dieback. Verticillium wilt often affects the lower leaves of cucumber plants first, which, if spotted, is a good indication that the disease is present.
Currently, there is no way to treat this fungal cucumber disease. If wilt is suspected, any diseased plants and the soil they were grown in need to be removed and destroyed, rather than added to a home compost system.
Preventative measures against cucumber wilt can include growing cucumber varieties with good resistance and practising good tool hygiene. Clean and disinfect your garden tools regularly. Another effective way to prevent cucumber wilt is grafting cucumbers on resistant rootstocks, such as fig-leaf gourd (Cucurbita ficifolia).
Cucumber rot can affect different parts of the cucumber plant from the roots (root rot) to the stem (basal stem rot).
Root rot encompasses several fungal diseases that target the roots of cucumber plants with the worst being black root rot (Phomopsis sclerotioides). It often occurs later in the growing season, clear signs on inspection are rapid wilting as well as brown and black lesions on the roots.
With no control measures currently available, the infected plants must be removed and destroyed along with the soil they were grown in. Preventative measures include growing cucumbers in new compost each year, practising crop rotation if growing outdoors and watering correctly throughout the season.
Anthracnose is a fungal disease that not only affects cucumbers but also other cucurbits and beans (Phaseolus). Caused by Colletotrichum fungi, symptoms include small brown spots and marks on the foliage, which rapidly grow in size and develop a yellow edge, as well as pink mould developing on the stems and stalks. Anthracnose can be spread by contaminated seed and airborne spores and is encouraged by warm and moist conditions, such as when grown in glasshouses, but it can affect outdoor grown plants as well.
As with most cucumber diseases, there is no treatment and, if identified, the plants need to be destroyed. To prevent anthracnose, it is recommended to practise crop rotation, good plant hygiene and to increase ventilation for indoor grown plants.
Cucumber sclerotinia disease
Sclerotinia disease is another fungal disease that can cause problems when growing cucumbers. Affecting both vegetable and ornamental plants, Sclerotinia fungi can unfortunately live for a long time in the soil.
Sclerotinia disease may cause cucumber plants to deteriorate rapidly with symptoms including yellowing foliage, wilting, rotting stems and a white fluffy substance forming on the stems and fruit. To prevent cucumber sclerotinia disease, grow cucumbers in new compost each year, as currently, there is no remedy and infected plants must be destroyed.
Cucumber mosaic virus
Cucumber mosaic virus is a common viral disease that can affect not only cucumbers and cucurbits but also spinach (Spinacia oleracea), lettuce (Lactuca sativa) and some ornamental plants. Symptoms include distorted and yellowing cucumber leaves with a mosaic pattern and reduced plant growth, resulting in reduced yields and misshaped fruits.
Mosaic virus is most often spread by insects, especially aphids. However, it can also be transmitted by infected garden tools and after handling other cucumber plants with the virus.
With no chemical controls available to treat mosaic virus, any infected plants have to be destroyed entirely. Ways to prevent cucumber mosaic virus include growing resistant cultivars, controlling aphid populations, watering to the base of the plants and practising good garden hygiene.
Cucumber grey mould
Grey mould (Botrytis cinerea) is a common fungal disease that can affect numerous plants, including cucumbers. It normally affects already struggling plants or gets in through wounds, but the high humidity in a greenhouse or rainy season can increase its likelihood.
The main symptoms include grey-brown mould on the stems, stalks and fruit, which often occurs after pruning cucumbers and causes dieback above the infected area. With no fungicides approved for home gardener use against cucumber mould, the only option is to remove and destroy affected plants.
Prevention is key in the fight with grey mould, especially for indoor grown plants. To prevent grey mould remove all dead and rotting material and feed cucumber plants regularly to keep them well-nourished and healthy. Also, improve air circulation, reduce humidity and avoid wetting the foliage when watering.
Cucumber diseases, if they take hold, can wipe out an entire crop, so carrying out the preventative measures is a key part in keeping cucumber plants healthy. Choosing the right location to plant cucumbers can also help prevent disease. Find out all about planting cucumbers, including which soil type is best as well as where to grow them.