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Cucumber leaves turning yellow? Here’s why and what to do!

Why Cucumber Leaves Turning Yellow

Are you worried and frustrated after seeing your cucumber leaves turn yellow? If you want to know what’s happening with your plant, you’re on the right page!

The good news is that yellowing cucumber leaves is a common problem. In this article, we’ll explore the different causes of this dilemma and provide simple solutions so your plants can get back on track to producing cucumbers.

Why are my cucumber leaves turning yellow?

Why are my cucumber leaves turning yellow
Image: The Plant Bible

Cucumber leaves turn yellow because of inconsistent watering, insufficient sunlight, pest infestation, cucumber mosaic virus, fusarium wilt, downy mildew, and nutrient deficiency.

Read on to know how these causes turn cucumber leaves yellow and how to fix them.

1. Inconsistent Watering

Inconsistent Watering
Image: Growing Happy Plants

How To Fix:
Allow the soil to dry out before watering again.

Cucumbers are 96% water – the highest water content for any vegetable – so they need about 1 to 2 inches a week to thrive. Too much or too little water could lead to oxygen-deprived roots that can cause the leaves to turn yellow or wilt. 

Overwatered cucumber plants are most vulnerable to root rot. It starts with the top leaves wilting, turning yellow, and falling off the plant.

Similarly, underwatering cucumber plants causes yellow leaves. The leaves first curl, turn brown at the edges, fade from green to yellow, and droop off.

Solution: Allow the soil to dry out before watering again.

DifficultyEasy ●●●○○
Things You NeedWatering can
Organic matter
Mulch (straw, wood chips.)

It’s essential to deep-water cucumber plants once or twice a week. Once you see the symptoms of over or underwatering, give your cucumber plants, and they’ll bounce back quickly after drying out. 

How To Do:
1. Stick your finger into the first 1 to 2 inches of the soil.
2. If the soil feels wet, don’t water it, but if it feels dry, water the cucumber plant deeply.
3. Water the soil around the base of the plant and avoid splashing water onto the bottom leaves.
4. It’s best to Water the plant early in the morning or in the evening to reduce evaporation.
5. If the soil is still wet after 24 hours, improve drainage by adding organic matter.
6. Apply a layer of mulch around the base of the cucumber plant to retain soil moisture.

2. Insufficient Sunlight

Insufficient Sunlight
Image: Gardener Basics

How To Fix:
Relocate the cucumber plant.

Cucumbers love the sun and need at least 8 hours of full sun every day. When cucumber plants don’t get enough sunlight, their leaves droopy and turn yellow. 

Still, balance is key. Too much direct sunlight also causes leaves to turn yellow and die, exposing fruits and reducing flavor and yield. 

Solution: Relocate the cucumber plant.

DifficultyAverage ●●●○○
Things You NeedAccess to a sunny location
Pot or planter Gardening gloves 

Cucumbers are sun-loving plants requiring at least 8 hours of direct sunlight daily for optimal growth and productivity. To achieve this, consider moving your plant to the sunniest spot in your yard or removing objects that block their exposure to sunlight.

How To Do:
1. If the plant is not receiving at least 6 to 8 hours of direct sunlight, relocate it to a sunnier spot, preferably in a south-facing area.
2. If natural sunlight is limited, you can use supplemental grow lights to hang the grow lights above the plant.
3. Make sure they emit the appropriate spectrum of light for cucumber plants.
4. During the hot summer, provide shade during the hottest part of the day to prevent heat stress on cucumber plants.

3. Pest Infestation

Pest Infestation
Image: The Reid Homestead

How To Fix:
Identify the pest and apply the appropriate pest control method.

Aphids, whiteflies, leafhoppers, and spider mites are common causes of leaf discoloration. They suck nutrients and sap out of cucumber leaves and leave small, yellow patches behind. 

For instance, potato leafhoppers feed on the sap in the leaves, injecting a watery saliva that damages them and causes them to turn yellow until they wilt and fall off the plant.

Solution: Identify the pest and apply the appropriate pest control method.

DifficultyAverage ●●●○○
Things You NeedInsecticidal soap
Neem oil
Row covers
Sticky traps

Regularly inspect your cucumber plants for signs of pests and repeat control methods as needed. Early detection and intervention are crucial to preventing pest infestations from causing significant damage.

After identifying the pest species, decide on the most appropriate control method. You can choose from using sticky traps, applying insecticidal soap or neem oil, or practicing companion planting in your garden.

How To Do:
1. Insecticidal Soap
Use insecticidal soap to control soft-bodied pests like aphids and spider mites. Mix insecticidal soap with water and spray the affected areas of the cucumber plant.
2. Neem Oil
Apply neem oil to control beetles, borers, and caterpillars. Mix neem oil with water and spray the entire plant, including the undersides of the leaves.
3. Row Covers
Use row covers to protect young cucumber plants from pests. After planting, install row covers over the plants and remove them once they have grown too large to fit under the blanket.
4. Sticky Traps
Place sticky traps around the cucumber plants to capture flying pests like aphids and whiteflies. Monitor the traps regularly and replace them as needed.
5. Handpicking
For small infestations, handpick pests from the cucumber plants. Drop them into a bucket of soapy water to kill them.
6. Companion Planting
If you prefer organic pest control methods, you can try companion planting, where you plant herbs or flowers near your cucumber plants to repel pests.
Some good companion plants for cucumber plants are peas, corn, beans, radishes, beets, carrots, onions, oregano, dill, marigolds and sunflowers.

4. Cucumber Mosaic Virus

Cucumber Mosaic Virus
Image: My Garden Life

How To Fix:
Remove the infected plant immediately.

If your cucumber plant is showing yellowish patches or green and yellow mottling on leaves, then unfortunately, this is a sign it has contracted the cucumber mosaic virus. 

This virus also causes stunted growth and mottled fruits, significantly reducing crop yield on cucumber plants.

Aphids usually spread the cucumber mosaic virus, which, unfortunately, will apply quickly in cucumber plants, soil, and other nearby plants.

Solution: Remove the infected plant immediately.

DifficultyAverage ●●●○○
Things You NeedGarbage bag

Cucumber mosaic virus can’t be cured, and you can only isolate the infected plant and prevent it from spreading in your garden.

How To Do:
1. When you notice signs of cucumber mosaic virus, isolate and destroy infected plants to prevent further spread. 
2. Place the infected plant in a garbage bag and dispose of it entirely.
3. Disinfect tools and equipment that have come into contact with infected plants.
4. Regularly inspect your cucumber plants for signs of cucumber mosaic virus.

5. Fusarium Wilt

Fusarium Wilt
Image: Positive Bloom

How To Fix:
Remove the infected plant and solarize the soil.

The fungus that causes Fusarium wilt is Fusarium oxysporum f. sp. cucumerinum, which may persist for long periods in the soil as durable spores or in plant debris.

It affects the vascular system and causes the yellowing, stunting, and wilting of cucumber leaves. If your cucumber plant begins to wilt, the plant will usually die in 3 to 5 days. 

Solution: Remove the infected plant and solarize the soil.

DifficultyAverage ●●●○○
Things You NeedGarden gloves
Shovel or trowel
Clear polyethylene plastic Tape
Stakes or weights
Water hose

Remove and destroy the infected plants to prevent further spread when you notice signs of fusarium wilt. 

Then, solarize soil where infected plants were grown to kill fusarium spores. This will kill the fungus, which is vital given that the spores can survive in the soil for 5 to 10 years.

How To Do:
1. Remove the infected plant.
Put on your gloves and carefully dig around the infected plant’s base. Loosen the soil and lift the plant, including as much of the root system as possible.
2. Dispose of the infected plant in a sealed bag.
Do not compost it, as this can spread the disease.
3. Prepare the soil.
Level the area where the infected plant was removed and break up any large clods of soil.
4. Water the soil deeply.
This will help to conduct the heat and kill more pests and diseases.
5. Cover the soil with plastic.
Cut a piece of clear plastic large enough to cover the entire area you want to solarize. Lay the plastic over the prepared soil.
6. Secure the edges of the plastic.
Use tape, stakes, or weights to secure the edges. Ensure the plastic is sealed tightly to trap the heat and leave the plastic in place for 4 to 6 weeks.
7. Remove the plastic.
Allow the soil to cool down for a few days, and the soil will be ready for planting.

6. Downy Mildew

Downy Mildew
Image: University of Minnesota Extension

How To Fix:
Remove the affected leaves and apply fungicide.

Downy mildew is a pathogen caused by Pseudoperonospora cubensis, which thrives in wet or humid conditions. It causes angular yellow spots and is bounded by leaf veins, eventually turning all the leaves brown. 

Solution: Remove the affected leaves and apply fungicide.

DifficultyAverage ●●●○○
Things You NeedGarbage bag
Potassium bicarbonate Water

Removing affected leaves and spraying with an appropriate fungicide can help slow the spread. The good news is that downy mildew can’t survive on plant debris as it can only grow on living plant tissue.

How To Do:
1. Remove the affected leaves.
Remove and dispose of the infected leaves completely.
2. Mix the fungicide.
Mix one tablespoon of potassium bicarbonate powder with 1 gallon of water.
3. Spray the plants.
Spray the potassium bicarbonate solution on the cucumber leaves, ensuring thorough coverage.
4. Repeat application as needed.
Reapply the fungicide every 7 to 10 days or as needed.

7. Nutrient Deficiency

Nutrient Deficiency
Image: Geeky Greenhouse

How To Fix:
Feed the soil with the lacking nutrients.

Inadequate amounts of nutrients in the soil also cause cucumber leaves to yellow. For instance, on an immature plant, vines grow slowly, and other leaves uniformly turn yellow and drop when the plant lacks nitrogen.

New leaves become chlorotic, turning a pale yellow-green, then completely yellow if they lack iron, while the lowest leaf on a shoot turns bright yellow when the plant doesn’t get enough phosphorus.

Solution: Feed the soil with the lacking nutrients.

DifficultyAverage ●●●○○
Things You NeedSoil test kit Organic matter Balanced fertilizer for cucumbers
Foliar sprays Soil pH adjustment amendments (lime for acidic soil, sulfur for alkaline soil)

The best way to solve nutrient deficiency is to amend the soil during the spring or fall season. We recommend using organic and slow-release types to avoid over-feeding or burning your cucumber plants.

How To Do:
1. Perform a soil test to determine your soil’s nutrient levels and pH.
2. Add organic matter into the soil to improve its nutrient content and water retention capacity.
3. Apply a balanced fertilizer formulated for cucumbers.
4. If nutrient deficiencies are severe, use foliar sprays containing the deficient nutrients.
5. Observe the plant’s response to the applied nutrients and adjust the nutrient application program accordingly.

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