How to Remove Yellow Spots On Cucumber Leaves

Cucumbers are refreshing.

They taste great in salad, give your water a unique taste and can be turned into pickles. If you are a cucumber fan, why not grow them in your backyard. Fair Warning: They can be a little challenging to maintain but not impossible.

One of the biggest problems most people face when growing cucumbers is the yellow spots that appear on the leaves. Finding out the “why” behind them can be difficult because there is a number of causes. However, we can help you solve the mystery with the information we are about to provide.

Sometimes, it can be a little difficult to identify the type of disease your cucumber plant has. So, before we begin, let’s take a look at the most common cucumber diseases:

  • Alternaria Leaf Blight (Alternaria cucumerina)

Small flecks that turn into brown spots.

  • Anthracnose (Colletotrichum orbiculare)

Dry brown spots that form near the veins and then turn into tiny holes.

  • Bacterial Leaf Spots (Septoria cucurbitacearum, Pseudomonas syringae, or Xanthomonas campestris)

Angular, brown, small spots that have a yellow halo. They dry out the leaves from the middle and leave holes in them.

  • Powdery Mildew (Erysiphe cichoracearum or Podosphaera xanthii )

Starts with pale yellow spots on old leaves and turns to white powder.

  • Downy Mildew (Pseudoperonospora cubensis)

Starts with yellow spots on leaves that later turn brown.

  • Bacterial Wilt (Erwinia tracheiphila)

Leaves start to wilt.

  • Cucumber Mosaic (Cucumber Mosaic Virus)

Leaves become stunted and malformed. The virus spreads quickly and can affect other plants as well.

  • Belly Rot (Rhizoctonia solani)

Causes wilting and stunting.

Now that you have the complete picture of the diseases that can destroy your cucumber plants, let’s move on to our main topic of discussion.

Why Are My Cucumber Leaves Turning Yellow?

We now know that the disease “Downy Mildew” (Pseudoperonospora cubensis) is responsible for turning your leaves yellow. Let’s take a look at it in detail.

The technical term used for your plant’s condition is “chlorosis.” It occurs when the level of chlorophyll, an ingredient used for photosynthesis, falls low. Since the plant is no longer able to produce sugar, it starts to die slowly. 

However, this is not the only cause of the yellow spots. A few others include:

  • Pests
  • Insufficient lighting 
  • Improper watering 
  • Poor nutrition 

The Culprits of Downy Mildew


First up are deficiencies, which are a result of chlorosis. One of the most important steps of gardening is to ensure that you are giving your plants nutrient-rich soil. This helps your plant thrive. Start by doing a soil test to find out what nutrient the plant is lacking. You can then buy a fertilizer accordingly to amend the deficiency.

  • Nitrogen Deficiency

Nitrogen is the most common nutrient, the lack of which causes yellow spots on cucumber leaves. You need to immediately balance the soil, or your plant might die.

The best way to fix nitrogen deficiency is to give your plant a fertilizer with a ratio of 5-10-10. The amount needs to be exactly right because overdoing it will harm your plant. Once the plant begins to flower, add a tablespoon of ammonium nitrate into the soil and repeat this three weeks later.

  • Potassium Deficiency

Cucumber plants need more potassium in the initial growth stage. If you see the leaves turning yellow from the tips and edges, your plant has a low level of potassium. This can be easily fixed with a balanced fertilizer.

  • Iron Deficiency

Take a hard look at the leaves of your cucumber plant. If the new leaves grow out yellow, but with green veins, the plant is low in iron. There are two ways to fix this: You can either sprinkle granular iron on the roots or spray the plant with liquid iron.

  • Zinc Deficiency

If the cucumber leaves look droopy, their zinc level is low. If you don’t fix this deficiency, yellow spots will slowly start to appear on the leaves and block the plant’s growth. You can fix this by spraying the leaves with a zinc sulfate solution.

  • Calcium Deficiency

Cucumber plants growing in humid conditions can develop yellow spots due to calcium deficiency. A few other factors that cause this deficiency include:

  • Water-logging
  • Soil salinity
  • Root diseases
  • High-level ammonium or potassium

Calcium deficiency makes the leaves distorted. They also cause the vegetable to become tasteless. You can fix this by limiting the use of fertilizers with ammonia or applying lime to the soil.

  • Magnesium Deficiency

This deficiency causes the veins in cucumber leaves to pop out. As the level drops lower, the leaves develop a light tan that makes them look burnt. Magnesium deficiency also reduces the growth of the vegetable.

You can fix this by spraying the leaves with a solution of magnesium nitrate or sprinkling some Epsom salt on them.


Whitefly, Aphids, and Mites

Pests can wreak havoc on your cucumber plants. They pierce the leaves and drink sap through the holes. Aphids happen to be the largest threat, and they cause the Mosaic Virus. When the sap is sucked out of the leaves, those spots turn yellow and cause blotching.

When the damage goes untreated, it becomes extensive to the point that pests completely drain the plant and leave it to die.

Moving on to mites, heavy infestation can make your plant look completely yellow. It’s actually the spots merging that gives this illusion. The problem with mites is that you don’t find out about the infestation until it’s too late because the yellows spots appear under the leaves.

The easiest way to remove mites is to blast your plant with water. However, this won’t stop them from appearing again. The next thing you need to do is spray neem oil or a solution of water and insecticidal soap on it twice a week.

Lastly, whiteflies can be killed with peppermint spray. When you are pruning your plant, spray the open wounds with peppermint. This will mask the scent of the sap, which is what pests are attracted to.

Overwatering or Underwatering

Did I water my plant? Oh, what the heck! I will do it again.

That’s how you overwater a plant, which causes the leaves to wilt. Your cucumber plant needs the right amount of water to remain hydrated and look healthy.

Overwatering prevents oxygen from reaching the roots, which turns the leaves yellow, and underwatering can dry them out, giving the same result.

Here’s what you can do to fix the watering problem:

  • Water your plants every day
  • Make sure your cucumbers grow in a raised bed to prevent the leaves from yellowing
  • If the soil happens to be the issue, mix in some soil to improve drainage
  • Regularly measure the soil moisture
  • If you don’t know whether to water your cucumber plant or not, try the two-inch method. Insert two fingers into the soil two inches deep. If the soil feels dry, water your plant

Lack of Sunlight

Cucumbers love the sun! They need at least 6 hours of sunlight per day. If your cucumbers are planted in the garden, all you need to worry about is providing them with adequate water and offering shade once they have had their fill of sunlight.

If the plant is in a pot, move it to an ideal location where sunlight falls directly. If you are growing your plant under artificial light, give it at least 16 hours of light.


Preventing Cucumber Plant Diseases

Here are a few quick tips on how to prevent your cucumber plant from getting infested with pests or wilting leaves:

  • Clean your gloves, tools, and boots after gardening
  • Use bleach to sanitize the pots before you use them
  • Buy seeds from a florist who has a good reputation
  • Irrigate underground
  • Solarize the soil
  • Separate the soil and fruit by creating a barrier with plastic mulch
  • Rotate your crops after every three years
  • Grow companion plants.
  • Keep an eye out for pests

Frequently Asked Questions

Should I Prune Cucumber Leaves That Have Yellow Spots on Them?

Just because your cucumber leaves have yellow spots on them does not mean you are dealing with an infestation or nutrient deficiency. It could be a simple case of overwatering. This is why it is important to inspect the leaves thoroughly, look for the signs mentioned earlier and then make a decision.

Should I Create a Drainage Hole in My Cucumber Plant Pot?

Yes, if the leaves have yellow spots on them. It’s possible that you might have overwatered your plant, which is causing the roots to drown in water and blocking the supply of oxygen.

Do I Need a Companion Plant for My Cucumber Plant?

Companion plants help keep pests away from your cucumbers. Some of the best companion plants include sunflower, marigold, peas, onions, carrots, radishes, corn, beans, and beets. You can also plant oregano, which repels almost every insect due to its strong smell.

Are There Any Home Remedies for Curing Downy Mildew?

One of the best DIY remedies for curing yellow spots on cucumber leaves is using baking soda. Here’s how to make the solution in different ways:

  • Mix one tablespoon vegetable oil, 1 teaspoon dish soap, one tablespoon baking soda, and one gallon of water in a bottle and spray it on the plant
  • Mix two tablespoons of Murphy’s Original Oil Soap, four tablespoons of baking soda, and one gallon of water in a bottle and spray it on the plant
  • Mix one gallon of water with three tablespoons of vinegar in a bottle and spray it on the plant. Since vinegar is acidic and can burn the plant, test it first on a leaf.

Neem is the best organic fungicide that repels insects and prevents yellow spots from appearing on cucumber leaves in the first place. Look at the label and follow instructions.

Another DIY remedy you can try is mixing ten parts of water with one-part milk.

And the last remedy that many people swear by is mouthwash. Mix three cups of water with one cup of mouthwash in a bottle and spray it on the plant.

Not all remedies are effective if you didn’t diagnose the cause correctly. So, alternate with the remedies and do a soil test every day. Do not over-fertilize when using nitrogen fertilizers. They can make the new growth soft, which is susceptible to infection.

If you are repotting your cucumber plants or changing their location in the garden, space them far apart to promote air circulation and plant companion plants nearby. Infection in cucumber leaves always starts slow so snip them off the moment you see them covered with yellow spots, wilting, or in any other bad condition.

Note: Baking soda in excess can burn plants. It can also lead to deficiencies in iron, magnesium, and calcium.

Final Thoughts

If you believe that your cucumber leaves have yellow spots due to them being diseased, remove the affected ones immediately to prevent the damage from spreading. You can also prune the leaves to improve circulation and fight fungal illnesses. The faster you act, the longer your plant’s life will be. Moreover, by making sure that your plant is healthy, you get to enjoy perfect cucumbers.

If the whole plant has yellow spots on the leaves, remove the ones that are affected the most. You might be tempted to remove them all but keep in mind that plants need leaves to make sugar, which feeds them. However, if the plant looks worse for wear, we recommend that you throw it away. It’s not worth infecting your other crops!

The journey to finding what’s causing the yellow spots on your cucumber plant leaves is an adventure. There are so many causes behind it that it’s possible you might get confused. This is why you need to carefully inspect the leaves, do a soil test and then determine what could be the probable cause.

So, what are you waiting for? Go grab your tools and inspect your cucumber plants from top to bottom. Do not leave any leaf unturned! If you are having trouble taking care of your cucumber plants, visit the Mo Plants website for more maintenance guides such as this.