The Cause of and Fix for Cucumber Leaves Turning White

It’s summer, yet your cucumbers’ green leaves suddenly look like they’ve been dusted with snowflakes. Powdery mildew has found your cuke patch. It’s a stubborn problem, but with these tips you can send it packing.


The Fungi

Two strains of powdery mildew disease fungus target cucumbers. Although unrelated, they progress the same way:

  • Light yellow spots surface on the older leaves and stems.
  • As the spots grow, powdery white spores start to spread over them.
  • Infected leaves grow dull and often wilt in the heat of the day.
  • Finally, they turn grayish-brown, dry up and fall off.

Powdery mildew doesn’t directly affect cuke fruit. But if a vine loses too many leaves, decreased photosynthesis may affect the size of your harvest.

Mildew-Favoring Conditions

Powdery mildew thrives in:

  • Temperatures between 75°F and 85°F (23.9°C and 29.4°C)
  • Humidity between 80 and 90 percent
  • Dry weather
  • Inadequate sun — less than the 5 hours of daily sun cukes need.

Powdery Mildew Prevention

Powdery mildew can be difficult to eradicate. Your best course is to remove and dispose of the infected plants and debris. Then follow these preventive practices:

Choose Mildew-Resistant Cukes

Replacing infected plants with with mildew-resistant varieties significantly reduce the chances of a repeat attack. Some popular choices:

  • ‘Eureka’ produces table-ready, deep-green fruit in 57 days. Pic at 1.5 to 5 inches for pickles and at 8 inches for slicing.
  • ‘Straight Eight,’ a vining cuke ready to harvest in 60 days. Pick the fruit at 2 to 4 inches for pickles, or at 8 inches for slicing.
  • ‘Jackson Supreme,’ a compact, 20-inch pickling cuke produces two cukes from every node. It’s ready for picking in 52 days.

Provide Sun and Space

Select a replanting site with 5 or more hours of daily sun.Space sprawling cukes 6 feet apart. Allow 3 feet between link u=cucumber-trellis]trellised[/link] ones.

Remove Excess Foliage

As your plants grow, remove just enough foliage to let sunlight reach the lower leaves; shade from the upper ones makes them more prone to mildew.

The Baking Soda Solution

As soon as the humidity and temperature favor mildew, spray your cukes with an organic solution of 1 part milk to 9 parts water. Apply it on a sunny day and repeat every two weeks until the conditions subside.