Your cucumber leaves are most likely turning white because of powdery mildew (a fungal disease). They could also be turning white because of excess moisture or blanching.
In this post, you will learn everything important about these things that can make cucumber leaves turn white and how to deal with them.
The Things That Can Make Cucumber Leaves Turn White And How To Fix Them
When you see your cucumber leaves turning white, ninety percent of the time the cause is powdery mildew. This is because it is one of the most common fungal diseases. Virtually all crops, shrubs, ornamental trees, and plants can be affected by it. The only good thing about the disease is that you can easily identify it and there are several ways to fix it.
Signs To Look Out For
To know if the white in your cucumber leaves is caused by this disease, you should look at for certain signs.
First, you should look out for white powdery spots covering entire leaves. The spots also usually appear on other parts of the affected plants including flowers, fruits, and stems. So check if your cucumbers have white powdery spots all over them to confirm if they have been attacked by this disease.
Second, you should look out for signs such as leaf browning and curling. This often occurs at an advanced stage of the disease.
Lastly, you should also look out for early bud drop, which is another characteristic sign of this disease.
Luckily, the signs of powdery mildew often look worse than the real damage the disease causes. So you do not need to panic when you discover them. Moreover, the disease is rarely fatal.
What To Do After Identifying The Disease
Once you are very positive that the white spots on your cucumbers are caused by powdery mildew, you need to act immediately. Your first action should be to remove the conditions that increase the likelihood of mildew formation. The conditions include poor air circulation, over-fertilization, and poor lighting.
By improving air circulation through spacing your cucumbers better, preventing over-fertilization by using a slow-release fertilizer, and addressing poor lighting by trimming overhead trees/plants, you will make the conditions less favorable for mildew formation.
The second action you should take should be to address the disease. There are several ways you can do this. See the section below.
How To Fight Powdery Mildew In Cucumbers
Once you have detected powdery mildew in your cucumber plants, you should act immediately to stop the disease. If you do not act immediately, the disease could spread and negatively affect your entire cucumber crop.
1. Commercial Fungicide Product
The easiest way to fight powdery mildew is to purchase and use a commercial fungicide product. Make sure the product is natural and it is not going to make your cucumbers toxic.
While using commercial fungicide products to fight powdery mildew is easy, eliminating the disease is not a given. You have to continue being on the lookout for signs of the disease and to take action the moment you discover something.
2. Baking Soda
Baking soda is a popular safe and organic solution for mildew. When combined with liquid soap, it can easily prevent a mildew outbreak because it kills the fungi responsible for powdery mildew. To make a baking soda solution for mildew, mix a tablespoon of the chemical with liquid soap in 3.5 liters of water. Spray the solution extensively on your plants especially on the white spots to end the disease.
3. Potassium Bicarbonate
This is also a solution for ending powdery mildew. The best thing about this chemical is that it kills mildew fungi on contact. The second best thing about it is that it can be used in organic farming. So it is certainly a wonderful option for fighting powdery mildew.
Vinegar can fight powdery mildew because it has acetic acid in it. To make a vinegar-based solution for controlling mildew, you should add 3 tablespoons of vinegar to 3.5 liters of water. When using vinegar, be careful not to burn your cucumbers by putting too much of it in your solution.
Milk is believed to contain compounds that kill powdery mildew. It is also believed to contain compounds that improve the immune system of plants. Several experiments have shown that applying a solution made of 33 percent water and 66 percent water, can have devastating outcomes for the fungi responsible for powdery mildew.
6. Neem Oil
If you are not new to the gardening world then you surely know that neem oil is the panacea for many plant pests and diseases. Neem oil is gotten from the neem tree that is found in East Africa and India. It is an effective killer of many pests and diseases and at the same time, it does not bear any harm for humans, animals, plants, and many beneficial insects. When applied, this solution can control and even eliminate powdery mildew.
As you can see above, you can control mildew in several ways. However, while the disease is controllable, you are better off taking action to prevent it than to try and control it.
Excessive moisture can also make cucumber leaves to turn white. This is because when there is too much water in the ground, the nutrients quickly leach out making it difficult for leaves to maintain their normal color. The leaching of nutrients often turns green leaves white or pale yellow.
To correct the lack of nutrients in the soil, you need to first improve the soil and/or reduce watering to ensure nutrients do not leach quickly. And then you need to apply a phosphorus-rich fertilizer to correct the situation.
A good example of a phosphorus-rich fertilizer that you can use is the Espoma TP6 Triple Phosphate Fertilizer that is found on Amazon.
In horticulture, blanching is a method used to produce vegetables that are pale in color. The method involves covering shoots to block sunlight, prevent photosynthesis, and stop chlorophyll production (hence the pale color).
When you accidentally position your cucumbers in such a way that some of the leaves or the cucumbers themselves do not receive enough sunlight, they will turn pale/white with time. The foliage of your cucumbers and/or neighboring plants can also block sunlight from reaching your cucumber leaves resulting in pale/white leaves.
To undo blanching, you should make sure light hits all the leaves on your cucumbers. You can do this by moving your cucumbers, trimming them, or trimming neighboring plants or trees.
The Final Note
As you can see, three things can make cucumber leaves turn white – powdery mildew, horticultural blanching, and excess moisture. By implementing the solution or solutions I have presented under each cause of cucumber leaf whitening, you can save your cucumbers.