Cucumber Leaves Turning White | How to Fix It

Cucumbers are a wonderful addition to any edible garden. Their fruit is delicious and nutritious, and the plants are generally low maintenance to grow. If conditions are ideal, cucumber plants will produce bountiful harvests all season long. But, if you find your cucumber leaves turning white, then something is going wrong with your plants that could lead to diminished yields or plant death.

This article covers all you need to know about why your cucumber plant’s leaves are turning white and what to do about it. 

Why Does My Cucumber Plant Have White Leaves?

There are several environmental factors that can naturally turn the green leaves of cucumber plants white. These include issues with water levels in the soil, a lack of sunlight, sun scalding, nutrient deficiencies, transplant shock, pests, and diseases.

Diseases in Cucumber Plants

There are numerous diseases that can infect cucumber plants at any stage of growth. Many of them will cause enough harm to the plant that it cannot produce a proper harvest. While leaf spot diseases are common with cucumber plants, the most common diseases that can turn a cucumber’s leaves white are cucumber mosaic virus and powdery mildew. 

Powdery Mildew

Powdery mildew is the most common cause of white spots on cucumber leaves. It is caused by several different genera of fungi that are found everywhere in nature, all of which need a live host to survive and reproduce. The fungi favour high daytime temperatures and high night-time humidity, followed by low daytime humidity. These favourable conditions most often develop during the spring and fall seasons. Powdery mildew will not usually kill the cucumber plants right away, but it will likely stress them enough to diminish their yield capabilities.

cucumber leaves tuning white
Powdery mildew is the most common reason cucumber leaves turn white

Cucumber Mosaic Virus (CMV)

Cucumber mosaic virus (CMV) is a virus that has been found in over 1300 species around the world. This infection most often spreads mechanically, mainly by aphids. Symptoms include loss of colour, mottling, and overall distortion of the leaves. If left untreated, leaves will begin to narrow, and growth will be stunted. The only treatment that is effective is the removal of infected leaves and the prevention of aphid infestations.

Natural Remedies

Neem oil is a popular natural product that is well-known to treat and prevent a wide array of infections including powdery mildew, cucumber mosaic virus, and leaf spot diseases. Neem is also great as a natural insecticide for pests like spider mites, aphids, and beetles. 

A Note on Neem Oil

Neem oil is often found in pre-mixed bottles that contain other essential oils like lemongrass, eucalyptus, and lavender. These natural remedy products work great against fungal infections but are aware that neem oil causes leaves to become very photosensitive.

It should only be applied when direct sunlight is no longer on the plant for at least 12 hours. Otherwise, severe leaf damage and discolouration are likely to occur. Neem oil is frequently found in a concentrated form and must be properly diluted. 

Homemade Baking Soda Spray for Cucumber Leaves

All natural homemade baking soda remedies work by coating the plant with sodium bicarbonate, which alters the pH enough to inhibit the growth of fungal spores. Add 2 teaspoons of baking soda to 1 gallon of water and mix with a carrier oil.

The oil adheres to the baking soda mixture of the foliage. Horticultural oil is often recommended but is labelled as a pesticide due to its chemical additives, so use a mixture of cottonseed oil and soap if you want to make an effective natural alternative.

Watering Issues

Cucumber plants require a lot of water to produce their harvests. The plants need at least 1 – 2 inches of water per week during their vegetative growth cycles and twice that during fruit production. If these requirements are not met, then the cucumber plants will likely show signs of leaf discolouration and diminished growth. 

Overwatering 

Overwatering can leach the soil of valuable nutrients, leading to nutrient deficiencies, many of which cause chlorosis or discolouration of the leaves as a first sign. Overwatering can also stress the plant by suffocating the roots. This can cause the entire plant to lose its green colour and turn white. 

Irregular Watering

General stress from irregular watering can cause cucumber leaves to turn white. While you should only water when the cucumber plants need it, you should be very watchful about the moisture level of the soil. Letting the soil and the plant’s roots dry out repeatedly can cause the cucumber plant to have too much stress to flower or produce fruit. 

Lack of Sunlight

Cucumber plants need full sun, which is between 6 and 10 hours of sunlight per day. If they don’t receive enough sunlight, they will appear pale from a lack of photosynthesis. Shaded cucumber plants will have diminished growth, increased fungal growth, and a lower probability of fruit production. 

Sun Scalding

Sunscald is a physical condition that is caused by overexposure to the sun’s ultraviolet rays. Symptoms include the presence of papery white and crispy leaves, especially along the leaf edges.

Cucumber seedlings are particularly vulnerable to sun scald damage, so begin sowing your seeds outside as soon as the weather conditions allow. Planting in the early spring will give young cucumber plants time to harden before being exposed to the harshness of the summer’s sun.  

Nutrient deficiencies 

Many nutrient deficiencies cause chlorosis, which is when environmental factors cause leaves to produce an insufficient amount of chlorophyll, which is the green plant structure responsible for photosynthesis. When this happens, the green colour provided by the chlorophyll disappears and the leaves appear pale or yellow. 

Zinc Deficiencies

The nutrient zinc is necessary for the production of chloroplasts which is why the lack of zinc will cause interveinal yellowing leaves. As the zinc deficiency progresses the entire leaf colour bleaches and becomes predominantly white. 

Transplant Shock 

Cucumber seeds are often planted straight into the garden because they don’t transplant well. Cucumbers are very susceptible to the stress involved with the transplant and will often show symptoms of leaf chlorosis, wilting, and lack of growth. Many cucumber plants will not survive a transplant, but if you must move them during the growing season, then follow these suggestions to increase the odds of survival. 

  • Limit the damage to the root system by loosening the soil around the plant and gently removing its entire root ball and the soil around it to its new location. 
  • Water the cucumber plant immediately after transplanting and every day thereafter for at least a week. 
  • Cut off a few small leaves to trigger the plant to focus on growing roots.
  • Be patient and gentle with the transplant until it doubles in size. 

Pests

There are many insects that are general pests in the garden and will feed on any type of plant. These pests include many different species of caterpillars, beetles, and mites. The following cucumber-specific pests are known to cause plant leaves to turn white. 

Aphids, Leafhoppers, and Leaf Miners

Aphids, beetles, and borers are all attracted to cucumber plants. These piercing and sucking insects suck the nutrients from the foliage, leaving them white and dry. They also have the potential of depositing bacteria, fungal spores, and viruses on the plant, which can cause other major infestations to spread rapidly. Removing the infected plants is usually necessary to control the spread. 

Integrated Pest Management

Integrated Pest Management (IPM) is a scientifically proven way to control unwanted pests and diseases without using excessive insecticides. Some of the techniques implemented in IPM include the mechanical removal of invasive plant species, the establishment of native species that repel pests, companion planting, and the addition of shelter that will attract predatory insects and birds.

Cucumber Leaves Turning White – Final Thoughts 

The best treatments are those that are implemented early. There are several all-natural products and remedies, including neem oil sprays and homemade baking soda mixtures, that do a great job of preventing or treating small infestations of fungi, mildew, and pests that feed on cucumber plants.

Using integrated pest management techniques, such as invasive species removal and companion planting, will decrease your workload while increasing the immunity of your entire garden. 

FAQ White Leaves on Cucumber Plants

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Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.