One of the most common conditions that home gardeners have to contend with when growing cucumbers are white leaves on the vines. Are your cucumber leaves turning white? No worries, there is a simple cause and I will offer an easy solution to fix it!
Plus – next garden season you can take preventive measures, so the leaves won’t turn white again!
So, why are cucumber leaves turning white?
Powdery mildew is the culprit that turns cucumber leaves white. It’s a fungus that develops on the vine leaves and looks like someone sprinkled the vine with talcum powder. You can easily treat it and save the growing cucumbers if the fungus is caught in time.
Powdery mildew is also easy to prevent so cucumbers and all other warm-season annuals that belong to the cucurbit plant family will remain free of this fungus. I will talk about prevention measures later in the post, so stay tuned!
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Why Are Cucumber Leaves Turning White Around The Edges?
Powdery mildew starts attacking the edges of cucumber leaves first. If the fungus is not stopped, the white powdery spots continue to work their way inward on the leaf until the entire leaf is covered and appears white.
The small white spots will continue to enlarge and merge until the white powdery substance covers entire leaves, stems, and stalks. The fungus will engulf the entire cucumber vine if left untreated.
Although the white fungal spores don’t spread to the cucumbers themselves, the advanced stages of the white powdery spores will prevent sunlight from reaching the foliage. The plant leaves can’t undergo photosynthesis, causing the plant to grow slowly.
Also, it will drop leaves and produce fewer, smaller, poorer-quality cucumbers. Once the leaves drop, the cucumbers will be exposed to direct sunlight and will suffer from sunburn. The exposed cucumbers are also more prone to be attacked by pests and birds looking for a free meal.
Why Are Cucumber Leaves Turning White After Transplant?
Most plants will go through a period known as ‘transplant shock’ immediately after being transplanted. This condition typically only causes a temporary slowdown in the plant’s growth but if the leaves turn white it could be caused by a bigger problem.
Cucumber leaves turning white after being transplanted may indicate root or stem damage. However, it probably indicates the seedling is being attacked by powdery mildew. This fungus remains in the soil over the winter months and awaits for new spring plants to attack.
Do you have plants growing in the same location in past years that were attacked by powdery mildew? If so, the chances are very high that white leaves on new transplants have been caused by powdery mildew spores lurking in the soil.
Why Are My Cucumber Seedlings Turning White?
If you planted cucumber seeds in the garden, make sure that everything went as planned with seed germination and seedling development. However, if everything went well and suddenly the seedlings turned white, it’s probably a fungal problem.
When the cucumber seedlings are growing and developing leaf sets normally, and the plants are a healthy green color, it appears that all is well. However, things can change almost overnight and the seedings change from healthy green to ghostly white.
The problem is powdery mildew spores that have over-wintered in the garden soil or debris left on top of the garden soil all winter. When the warm spring weather arrives, the fungus spores come out of their dormant state and attack the newly sprouted cucumber seedlings.
What Causes White Mold On Cucumber Leaves?
Sphaerotheca fuliginea and the Erysiphe cichoracearum fungi cause white mold, which is commonly known as white powdery mildew. The fungus appears as white, powdery spots on the leaves.
There are three environmental factors that promote the development of the white mold on cucumber leaves:
- Shady growing conditions
- Poor air circulation
- Soggy soil
If you have a muddy soil, then you need to add some organic matter so it absorbs excess moisture. Find out how to dry soggy soil fast here. A lot of gardeners use mulch to dry the muddy soil before planting. Keep in mind that the best mulch should also retain water after saturation.
How To Get Rid Of Powdery Mildew?
Create a DIY organic spray with baking soda and vegetable oil to get rid of powdery mildew. Here is how to do it:
1. Mix 1-teaspoon of baking soda in 2-liters of water.
2. Shake the mixture well.
3. Add 4-drops of vegetable oil – it helps the DIY organic spray stick to plant leaves.
Spray on cucumber leaves at the first appearance of white spots. Moreover, apply the mixture on the soil around the plants too.
Another DIY spray is a teaspoon of liquid dish soap mixed into a quart of water and sprayed on plant leaves and surrounding soil.
If you don’t want to use organic DIY productions, there are several commercial brands of fungicide that will work to get rid of powdery mildew. For example, I am a fan of a Ready-to-Spray fungicide that is ready to use right away and you can order it online on Amazon.
How Do you Prevent White Powdery Mildew on Cucumbers?
#1 – Plant cucumbers in a location that receives full sun for most of the day. Plants that receive too much shade are prone to develop fungus.
#2 – Space cucumbers plants further apart to promote good air circulation between plants. Cucumber vines grow 6-10 feet long and produce several runners along the main vine.
The leaves on the vine are large. Unless there is plenty of space between the vines and a sturdy trellis for the vines to climb on, they can become a twisted jungle that prevents air circulation.
#3 – Reduce the number of plants you want to grow. Cucumber vines are heavy producers and just two healthy plants can keep an average family well stocked in fresh cucumbers throughout the summer.
If you want to make pickles, 4-6 plants will supply a couple of bushels of cucumbers. A few well-spaced healthy plants are far more productive than several plants growing too close to one another.
#4 – Start with seeds or plants that are mildew-resistant varieties. It significantly reduces the chances of the fungus attacking the plants while they’re growing in your home garden.
4 Tips to Prevent Powdery Mildew Spores From Over-Wintering In Soil
Tip #1 – Clean the soil at the end of the garden season. It prevents the fungus spores from over-wintering in your garden soil and attacking seedlings. Thus, from turning cucumber leaves white.
Tip #2 – Remove the plants from the soil and toss on the compost pile. When garden plants have ended their productions for the season, remove them from the soil. Put them to compost only if they are disease and pest-free.
Make sure you know when to stop adding to compost. Moreover, rake all debris off the soil so there is nothing to trap and hold moisture. Remember that all types of fungus including white powdery mildew, thrive in warm, dark, and humid environments.
The cleaner the garden soil surface is, the less likely the mildew spores will be able to survive through the winter!
Tip #3 – Sprinkle ground cinnamon on top of soil and work it into soil. Cinnamon is an organic fungicide and will kill any remaining mildew spores in the soil and prevent new ones from growing. The cinnamon will not harm plants.
Tip #4 – Plant a winter cover crop after preparing the garden soil. It prevents soil erosion, soil compaction, and improves fertility. Cool-season crops like kale, mustard, turnips, collards, clover, or ryegrass will help keep the soil healthy.
Learn how to start cool-season crops in unheated greenhouse. Fertile soil produces strong, healthy plants that are better able to fend off an attack of powdery mildew. However, do not fertilize the winter crops! Excess fertilizer feeds and promotes the growth of fungal spores in the soil.
Having your cucumber leaves turning white is distressing, but it’s a fixable problem! Early detection and swift action with either a DIY product or commercial product are essential to kill the white powdery mildew before it kills your cucumber plants.
What do you do when your cucumber plant leaves are turning white? Let me know in the comments section down below!
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Happy Growing 🙂