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Diseases of Crape Myrtles

July 23, 2018

Written by Dave G.

Crape Myrtles (Lagerstroemia) are very popular shrubs for warmer areas, and no wonder. They have spectacular blooms for an extended period, grow well in poor soil, and are heat and drought resistant. They also come in many sizes, so there is a plant for every purpose around the garden, from specimen tree to low shrub or container plant. If you grow Crape Myrtles in your garden, you may see some damage to the leaves, and this is often the result of two diseases that attack Crape Myrtles. The good news is that if you choose the right varieties, and don’t settle for cheap plants simply sold as ‘Pink Crape Myrtle’, without giving a proper variety name, you can usually avoid these diseases. If you already have Crape Myrtle bushes, and see symptoms of disease, here are the two most likely causes.

Powdery Mildew

This is the most common disease seen on Crape Myrtles, and it is easily recognized. In summer you will see the foliage start to look ‘dusty’, as a whitish powder builds up on the leaves. It begins as patches, and soon spreads until it may cover the leaves almost completely. These white or beige spots also appear on the new shoots, and on the outside parts of the flower buds. Often the new shoots and flower buds become twisted and deformed, so that flowering suffers, and only the first spring flush of flowers is attractive. Shoots can even wither and die back, adding to the unsightly look of your plants, and stunting their growth.

This disease – caused by a fungus called Erysiphe – is also seen on other garden shrubs, including lilacs and roses, but each plant has a specific form that only attack it, so powdery mildew on Crape Myrtle cannot spread to lilacs, or vice-versa, although they may appear simultaneously during suitable weather conditions. Powdery Mildew of Crape Myrtle can be seen as early as mid-April, but it is much more common in June, when the dryer weather, warm days and cool nights create the perfect conditions for its spread. Once the mildew spreads across the plant it cannot be removed, so even if killed it remains unsightly. It does not however normally kill the plant, and heavily-infected plants will sprout the following year with fresh, healthy, clean growth. The disease passes through the winter sitting on the leaf buds, so as soon as the weather becomes favorable, back it comes.

This disease has been a problem since Crape Myrtles were first introduced into the USA, and in the 1960s plant breeders at the National Arboretum in Washington, D.C. began breeding new varieties, with the specific goal of finding plants that would not get Powdery Mildew – plants that were resistant, and that would stay attractive all summer long. They bred over 20 new varieties, all with the names of Native American tribes, and most show good levels of resistance to this disease. Rather than trying to control it with chemical sprays, plant newer varieties, and take advantage of their resistance. Names like ‘Natchez’, ‘Tonto’, or ‘Cherokee’ all indicate varieties that will resist Powdery Mildew well.

If you do have plants of old varieties you treasure, there are steps you can take to reduce the risk of this disease developing. Removing diseased leaves as they fall, keeping plants watered, using low-nitrogen fertilizers to reduce soft growth, eliminating heavy pruning, and spacing plants for better air-circulation, are all methods that will reduce, even if not eliminate, the disease. Milk, diluted 50%, has been proven to reduce or prevent powdery mildew, but it must be sprayed frequently from early in the season, and certainly after any rain has fallen. This could see you spraying every few days. Otherwise your local garden center can advise you on chemical controls, but these too must be applied every couple of weeks. It makes sense to instead look for and plant resistant varieties.

Cercospora Leaf Spot

This disease is not as well known as Powdery Mildew among gardeners, but it is a serious disease of Crape Myrtles, and one that has become more widespread in recent years. Perhaps because it occurs later in the year, it is seen as ‘natural’ and not as the damaging disease it is. Cercospora Leaf Spot begins on the lower foliage of a Crape Myrtle bush, and the leaves develop irregular brown circles, about ¼ of an inch across. As these spots spread and multiply the leaves may take on ‘fall’ colors, turning yellow or red before dropping to the ground. You might start to see spots on the lowest leaves as early as late-June, but it is more usual from early July, increasing through August, so that by mid-September 50% of the leaves may be gone. If this sounds like your plants, it is not fall coming early, but Cercospora Leaf Spot.

As with Powdery Mildew, the best approach is to choose varieties that are resistant to the disease. Resistant plants may still show a few spots, and a few leaves may drop, but these will only be the lowest leaves, and the effect is almost unnoticeable. Many of the National Arboretum Crape Myrtle varieties are resistant to this disease, as well as to Powdery Mildew, and the ones already mentioned above are good choices. Others may not be. For example, ‘Hopi’ and ‘Comanche’ are varieties that resist Powdery Mildew well, but they do not resist Cercospora Leaf Spot at all. So choose carefully. Many more modern varieties, such as the ‘Magic’ series developed more recently by the plant breeder Dr. Michael Dirr, all have good resistance to both diseases. Names like ‘Purple Magic’ are ones to look for. As well, in this range are varieties like ‘Plum Magic’ and ‘Sunset Magic’, that have purple foliage as well as attractive blooms.

Again, if you have old plants that you can’t bear to part with, you can control this disease by the same methods mentioned above for Powdery Mildew. There is no evidence that milk works against this disease, but it might. Most of the chemical controls for Cercospora Leaf Spot also work on Powdery Mildew, so a single spray, repeated as recommended, will give you control over both diseases. Over several years, if you can successfully control these diseases, the rate of natural infection may fall, and less control will be needed. In any case, only use chemicals when you begin to see the first symptoms, not as a ‘just in case’ measure, where you could be spreading chemicals around your garden needlessly.

In Conclusion…

Neither of these diseases will kill your Crape Myrtles, but they are definitely unsightly, and the gradual loss of leaves from Cercospora Leaf Spot means you lose most of the wonderful fall display these plants give. When choosing new varieties, look for resistance to both diseases, and you will have beautiful, trouble-free plants that look great from early spring right into winter. Enjoy!

Comments 20 comments

  1. April 21, 2020 by Tracy Buice

    Please, please help me…I am desperate to learn what is happening to my crepe myrtles. I have 2 crepe myrtles that bloom pink blooms located in the front of my home in Little Elm, Tx. They are approx 3 yrs old, and we’re planted in the ground, directly where rose bushes had previously been but died of the strange thorny rose bush disease. Over the last 3 years, these 2 crepe myrtles have grown a weblike material across half of the leaves of the plant, which almost looks like they are being choked out. Additionally, and even more alarming to me, is that last year I noticed a white, cream-cheese type substance appearing on the bark of the entire tree…most specifically in small tear drop size spots at the knots where limbs had once been growing, as well as at an axis where limbs are currently growing. When I touch the spots, they smear like butter or cream cheese, and there is a smaller bit of a red color underneath…that when smeared together, looks like blood or that the tree is bleeding.

    Does anyone know what this might be or moreover, how I can rid my poor crepe myrtles of this disgust?

    Thank you in advance

    tracylbuice@gmail.com

    1. April 21, 2020 by Dave G

      I am not familiar with Texas insects, but the white sounds like mealy bugs or scale insects. The webbing is perhaps tent caterpillars. Try spraying with dormant oil or neem oil.

  2. May 19, 2020 by MARTIE WINTER

    The branches are falling off my crepe myrtles! The leaves are still green but the branches are falling off on the trunk . I live in Huntsville, AL…..

    1. May 20, 2020 by Dave G

      Have you had strong winds, or an obstruction taken down? That could do it by changing wind patterns. Is it very dry? Hard to say what the problem is, otherwise.

  3. May 20, 2020 by DeLores L. Jones

    I planted a Crape Myrtle bush (Lagerstroemia Hybrid) in my front yard Dumfries, VA, last Spring (2019) and it appeared to be doing quite well. I’ve now noticed white milky looking spots on the very tips of many of the leaves. Wondering if it is a disease. If so, how to treat it. Please advise.

  4. June 3, 2020 by Stacey Matheny

    I am having a problem with one of my crepe myrtles I planted last year. About half of the leaves look lacey and ruffled. I have not seen any insects and my other crepe myrtles are not affected. It has been rather moist this year with a lot of rainfall. 

    1. June 3, 2020 by Dave G

      It does sound like an insect problem – some are very small! Try an organic pesticide like pyrethroids or neem oil.

  5. June 8, 2020 by lawrence corvino

    i just planted a small crepe myrtle tree about a month ago and the tips of the leaves are turning brown what should i do. thank you lj

    1. June 9, 2020 by Dave G

      Hard to say for sure, but it could be dryness. Water about twice a week, making sure you get the water into the soil close to the stem, where the rootball is. Is it in full sun, which it needs? If the weather has been dry it will need deep watering until the roots are established.

  6. June 9, 2020 by Patricia Winslow

    Help I have three watermelon Red crepe Myrtle trees that were planted almost four years go. They are twelve to fifteen feet . The leaves have turned fall colors and are falling off. Others around town are blooming but mine are not. I have also had three Altheas in the same flower bed that were almost four years old that have died. They were healthy growing and blooming one day dropping leaves the next. Thanks

    1. June 9, 2020 by Dave G

      Really not sure what that problem could be. It sounds like something cultural – drought, or soil contamination – rather than disease.

  7. June 16, 2020 by Linda Suits

    The tpo of the tree the branhes are not turning green and looks like it is dying what can i do for it please help

    1. June 16, 2020 by Dave G

      I can’t really tell from this what the problem is. If it is just the upper branches it could be they died in winter. Cut them off just above the point where there are new shoots – they will soon grow back.

  8. June 24, 2020 by Margie Fluitt

    gray stuff is sitting on the branches and growing on my crepe myrtle to where I have flowers but branches are bare and to get rid of this I must cut the branches to detach this growing fungus. What is it as you never have mentioned it attacking trees. I have one single tree trunk coming out of the ground…and then branches coming from that. I got rid of this growth on the trunk but would have to cut branches to get rid of it on the rest of the tree. Can nothing be done about this growth on the branches of my crepe myrtle?

    1. June 24, 2020 by Dave G

      This sounds like powdery mildew, which is mentioned in this blog. Don’t start cutting branches to get rid of it – it’s not necessary, and only destroys your trees. This is a harmless hot weather disease that disappears in winter and the plant comes back clean the next spring. Try growing resistant varieties – most of the modern ones are – or spray several times, starting just before the hot weather arrives. You can use chemical controls from your garden center, or a solution of milk in water. Try 3 parts milk to 7 parts water, but you have to spray again every time it rains, as the coating is washed off easily.
      Alternatively, if this is mostly on the branches, and not the leaves, it could be scale insects – check out these images and see what you think. If it is, again there are chemical controls, but a strong jet of water – a power wash with soapy water is ideal – will get rid of it. But stop cutting branches off your trees – you soon won’t have anything left!

  9. June 25, 2020 by Nancy S

    Thanks so very much for this article and blog. It’s a real lifesaver! For me and my crape myrtle

  10. June 25, 2020 by Bonnie Jackson

    I have branches that look healthy until the last foot or so. The branch turns red and the leaves start splotchy then towards the end they curl up…. It is only one of my crape myrtles, I have 7 in the yard.

    1. June 26, 2020 by Dave G

      It sounds like cold damage from the winter – trim them back to the healthy sections – they will soon re-sprout and bloom.

  11. July 4, 2020 by Ruth

    I think I have a problem with Japanese Beetles, they are yellow and a lot of my leaves are turning almost a black color. Is there anything I can do to save the tree

    1. July 6, 2020 by Dave G

      Japanese Beetles are more greenish-brown – check that you have the right identification. If they are, you can buy traps to catch them. They work well, but you need to put the traps in areas where there are no beetles, otherwise the traps will just attract more beetles to your trees.