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4 Worst Causes For White Spots on Crepe Myrtles

4 Worst Causes For White Spots on Crepe Myrtles

I love my crepe myrtles. These hardy shrubs are great for pruning, and they make a lovely vegetative barrier between property lines.

So when I planted my living wall of crepe myrtles, I wasn’t impressed by the white spots that appeared on them a few months later.

Concerned, I spoke to a horticulturist specialist. They gave me a few possible reasons why my crepe myrtles had suddenly started looking like reverse Dalmatians with white spots all over.

Once I knew what the white spots could be, it was a process of elimination to determine the probable cause and find a solution.

If you have a living hedge of myrtles that suddenly becomes all spotty, you can find all the answers right here.

 

What Causes White Spots on Crepe Myrtles?

The usual suspect why a crepe myrtle develops white spots is powdery mildew on the shrub’s bark and leaves from poor ventilation. Another more recent cause is the bark scale on a poorly pruned tree. A white aphid infection and hard water can also cause white spots to appear on your crepe myrtle.

White Spots on Crepe Myrtles
White Spots on Crepe Myrtles

 

4 Common Causes of White Spots on Crepe Myrtles and What to Do

I wasn’t sure which cause was responsible for my crepe myrtles’ white spots, so I decided to look closer and first see what might be the cause of the unsightly white spots.

 

1. Powdery Mildew on Crepe Myrtles

Powdery mildew is a fungus that spreads through spores carried by wind and water. When your crepe myrtle is planted in an area that’s not well-ventilated, chances are the shrubs will become susceptible to fungal infection.

The powdery mildew can appear on your crepe myrtles in patches or spots, or it can also cover the leaves, flowers, and bark in a dense layer in an advanced infection.

A crepe myrtle infected with powdery mildew not only affects the tree's leaves but may include the bark as well in advanced stages
A crepe myrtle infected with powdery mildew not only affects the tree’s leaves but may include the bark as well in advanced stages

 

What to Do With Powdery Mildew Causing White Spots on Crepe Myrtles

If your crepe myrtles have a coating of pale white to light gray spots or a dense film of white mold, you can save your plant by trimming away branches that have been severely infected.

Like this apple tree, you can trim off the crepe myrtle branches and leaves severely affected by the powdery mildew
Like this apple tree, you can trim off the crepe myrtle branches and leaves severely affected by the powdery mildew

Increase sun exposure by trimming away myrtles that have grown dense and bushy.

Water your myrtles during the first half of the day to ensure the leaves have time to dry off, as wet leaves and bark will create a natural breeding ground for the powdery mildew spores.

 

2. Bark Scale on Crepe Myrtles

Early in 2004, a new pest species called Lagerstroemia spp was identified in Texas on crepe myrtles. From there, this invasive pest that originated in China has spread throughout many parts of the U.S.

While it may look like regular powder mold, this is a living microorganism that will ooze pink-red liquid when crushed.

The bark scale will infest a crepe myrtle plant, forming colonies on the leaves, bark, and even roots. Often, this organism will be accompanied by a black powdery mold that seems to be a companion to the bark scale organism.

Crepe myrtles will eventually weaken and die if the bark scale is left unchecked as this organism drains the sap and vital nutrients from the crepe myrtle.

 

What to Do With Bark Scale Causing White Spots on Crepe Myrtle

To remove the bark scale, you can mix a weak solution of water and dishwashing detergent in a spray bottle and thoroughly douse your crepe myrtles with the solution.

You can mix water and dishwashing liquid in a spray bottle to douse your crepe myrtle's bark in it and eradicate the bark scale infecting it
You can mix water and dishwashing liquid in a spray bottle to douse your crepe myrtle’s bark in it and eradicate the bark scale infecting it

Within a few days, the bark scale will be dead, and you can brush the dried scales from the shrub. If necessary, you can repeat the treatment as the water and dishwashing liquid is safe for the plant.

 

3. Aphids on Crepe Myrtles

Aphids can also gather in colonies on your crepe myrtles. When enough aphids are gathered together in a colony, the coloring becomes white and fluffy, almost resembling mealybugs.

Aphids can gather together in colonies that appear as white and fluffy spots on the crepe myrtle's leaves that resemble mealybugs
Aphids can gather together in colonies that appear as white and fluffy spots on the crepe myrtle’s leaves that resemble mealybugs

The aphids suck the sap of the crepe myrtles, which can weaken the plant and cause slower growth and eventually death.

 

What to Do With Aphids Causing White Spots on Crepe Myrtles

To get rid of aphids, the most natural way is to encourage ladybugs to come to your garden. Ladybugs naturally feed on aphids.

One natural way to treat aphids on your crepe myrtle is to introduce ladybugs to it
One natural way to treat aphids on your crepe myrtle is to introduce ladybugs to it

However, posting a sign isn’t enough. It’s possible you have to take the situation into your own hands and spray your crepe myrtles with a weak soapy water solution.

The aphids will suffocate in the soapy residue and die.

 

4. Hard Water Deposits

While it may not even occur to you to think of the water in your taps, hard water can cause mineral deposits to form on your crepe myrtles, which can resemble some sort of bacterial or fungal problem.

Many states in the U.S. have limescale that forms as a result of the high mineral content of the tap water. When your crepe myrtles are constantly receiving the same pattern of water spray such as from an irrigation system, it can leave a white spotted deposit.

 

What to Do With Hard Water Deposits Causing White Spots on Crepe Myrtles

While these deposits aren’t really harmful to your crepe myrtles, the deposits aren’t pretty.

You can fit a filter to your irrigation pump so your tap water gets cleaned up, or you can use an irrigation tank that has a filter fitted so you can use clean and low mineral water.

If you're using an irrigation pump to water your crepe myrtles, you can fit a filter on it to filter out the limescale causing white spots on the tree
If you’re using an irrigation pump to water your crepe myrtles, you can fit a filter on it to filter out the limescale causing white spots on the tree

 

Frequently Asked Questions about White Spots on Crepe Myrtles

 

What are the white dots on my crepe myrtles?

Most likely, the white dots are a fungus known as powdery mildew or white mold. The dots form when your crepe myrtles have poor ventilation and are often damp from top-down watering.

 

What will kill the fungus on crepe myrtles?

Treatment with a weak soapy water solution is effective, but you can also use a spray with neem oil, dust it with bicarbonate soda, and mix a spray with flowers of sulfur to kill off the fungus. An antifungal spray can also be purchased to do the job.


 

Conclusion on White Spots on Crepe Myrtles

White spots on crepe myrtles are caused for the following reasons:

  • Poor ventilation
  • Bark scale
  • White aphid infestation
  • Hard water

Author Bio

Daniel Iseli

Taking care of houseplants and gardening are my greatest passions. I am transforming my apartment into an urban jungle and am growing veggies in my indoor and outdoor garden year-round.

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