Crape Myrtle Pest and Disease Control

But like anything, they're not immune to everything. And some varieties have been bred (or are naturally), more resistant to certain pests and diseases than others. Here we will go over some of the more common (and some not so common), issues you might run into.

Don't Panic!

Although the following list may seem daunting at first, it's really not much compared to other plants, such as roses. And a little prevention goes a long way.

The most common issues you may encounter are:

• Crape Myrtle Aphids
• Sooty Mold
• Powdery Mold

Some uncommon issues may be:

• Caterpillars & Grasshoppers
• Ants
• Cercospora Leaf Spot
• Bark Scale

Aphids are tiny little critters that effect many different varieties of plant. In fact, there are over 5,000 different kinds of aphid in the world! And you guessed it, Crape Myrtles have their very own species.

The scientific name for these little buggers is Tinocallis kahawaluokalani. They lay eggs in the fall right before the leaves drop. Those eggs hatch the following spring. During the summer they can reproduce every 14 days so immediate and ongoing treatment is critical to keep them under control. In the case of aphids, an ounce of PREVENTION is worth a pound of cure. In their nymph stage they will be tiny, smaller than 1mm in length and shades of light green in color. They appear under the leaves and feed by sucking out all of the plant's vital, delicious (evidently), juices. It only takes a few days for a nymph to become an adult. As adults, they develop wings, can fly to other crape myrtles and feed in the same manner as the nymphs. They can live up to 14 days, and in that time can lay over 150+ eggs. By the time you notice a problem, there can thousands of those little buggers slurping up your crape myrtles.

Aphid Identification

The first thing you'll notice is that the tops of some of the leaves will appear shiny and the upper leaves will have a yellowish tinge to them. Flip over some leaves and you'll see them. They may be adults, just nymphs or a combination of both. You can rinse them off with water or remove them with your finger (gross). The shiny residue you'll see on the leaves is "honey dew," a fancy word for aphid poop. Honey dew itself isn't harmful to your plant, but it does cause other problems, which we'll cover soon.

Control and Prevention

Prevention is easier than control, obviously. Taking the right steps at the right time of year is going to save you grief in the long run.

1. Application of Dormant Oil. Apply any number of dormant oils (most are mineral oil based), in late fall when the plants are beginning to lose their leaves, and again in spring just as soon as you see tiny new buds appear. This is when the eggs are most active, making the dormant oil much more effective. This step alone goes a long way.
2. Apply a systemic insecticide containing imidacloprid. A systemic chemical is absorbed by the roots and then travels through the plants system. Any brand is fine as long as it says systemic. In spring, after you see a few inches of new growth, apply the systemic following the instructions on the bottle. Don't worry if you go a little heavy on the concentration, you're not going to hurt the plant one bit. Most brands will claim this offers year-round protection, but we find that's not the case. Be prepared to apply the systemic again in mid-summer and have a foliar spray on hand for flare ups. And remember, adult aphids fly, so if your neighbor has an aphid problem expect those little buggers to fly over to your trees for their next feast.
3. Use a foliar spray for heavy infestations. We've found the best foliar sprays contain acesphate (make sure the water you mix in has a pH of 6.5 or lower), pymetrozine, or imdicloprid. Mix up a batch following the instructions on the bottle. APPLY IN THE EVENING WHEN YOU'RE NOT EXPECTING RAIN. This way you will not harm pollinators such as bees, nor will you harm beneficial predatory insects like lady bugs. Try to spray the underside of the leaves as much as possible as that's where these critters hang out. Spray every seven days at the most to prevent toxicity to your plants. But with the above-mentioned chemicals, you shouldn't have to spray that often, if at all.
4. Organic Options. There are all sorts of tricks out there that will help control the aphids. Mixing dish soap and water, then spraying the plant works well. Wash them off with water. Neem oil, or other horticultural oils work well. Make sure you're NOT applying them when the temperature is expected to get OVER 85 degrees as you will chemically burn the leaves. The only issue you'll find with most organic options is that you'll need to reapply every seven days, or even more frequently. You can find a number of organic dormant oils, so make sure you take advantage of that option. Don't forget the good ole predatory insects. There are numerous wasps, flies, spiders, beetles and even some species of ants that love to eat aphids. A single Lady Bug can eat over 1,000 aphids a day. Although you can mail order these predatory insects (they're not cheap), and let them loose on your crape myrtles, you may find that most have flown away in a day or two.

Here at the nursery, we certainly get aphids. There's no way around it. Healthy crape myrtles = delicious feast for aphids. But we very rarely spray our mother plants. If we see an aphid here and there, we'll most certainly find hungry lady bugs and wasps, so we let Mother Nature Take its course. We do, however, use systemic imidacloprid twice a year on all our plants and keep some acesphate on hand for flare ups. This is our home and our farm, so we strive to minimize the use of chemicals as much as possible.

Sooty mold is mold that looks like black soot on the leaves, trunk and mulch under your crape myrtle. It's black and can easily be wiped off with your finger. Although it does not directly feed on the plant, it does decrease or prevent photosynthesis from the effected leaves.

The fungal genus Capnodium is exclusively symbiotic with the crape myrtle aphid. It feeds only on aphid "honey dew." So as the aphids "eject" their "honey dew," it lands on anything below them including leaves, the trunk, mulch, grass or even lawn furniture. Those surfaces will initially look shiny and sticky to the touch. The natural occurring fungus will find this projectile poop and dig right in.

Control and Prevention

Prevent the aphids and the sooty mold won't grow. It's that simple. No aphids = no sooty mold. So simply follow the above guidelines outlined above to prevent and control aphids.

*Note: There is no fungal spray that will remove the black sooty mold form the tree or its surroundings. Even if killed with fungicide (not necessary), it will remain until the plant drops it's leaves and sheds its bark. You'll need to replace any discolored mulch over winter and clean outdoor furniture with white vinegar or bleach. But don't worry, it WILL go away on its own. With no "honey dew" on which to feed, it will not grow. *

Of all potential problems you may have, powdery mildew/mold is by far the easiest to remedy. It's extremely easy to identify. It's a white, powder-like substance that grows on leaf tips and new flower clusters.

The fungus Erysiphe lagerstroemiae is responsible for powdery mildew, and it affects a wide variety of plants, not just crape myrtles. It normally occurs during humid summers and moist conditions. Powdery mildew will not only be obviously white mold, but it will also mutate the tips, stems and flower buds preventing them from blooming. So, let's get this taken care of.

Although any number of systemic fungicides can be used twice a year to prevent powdery mildew, it's just as easy to treat with a foliar spray.

1. If you choose to prevent powdery mildew altogether, make sure your crape myrtle gets plenty of sunlight and has plenty of air circulation. Powdery mildew loves warm, moist, partially shaded spots.
2. Use a systemic containing any number of fungicides for powdery mildew/mold. For example, Bayer BioAdvance makes a great 3 in 1 for roses that controls disease, mites and insects. Although it's for roses, it great for all ornamental flowering hardwoods. And we've had great success with it over the years.
3. Use any number of foliar sprays rated for powdery mold/mildew. Just about any fungicide will work. We like myclobutanil (Immunox Full Spectrum) or Chlorothalonil (Daconil). Apply following the instructions on the bottle every seven days until it's gone. It normally takes one application, two if the infestation is bad. The flower buds normally recover enough to bloom, but the leaves usually drop. Don't worry, they'll grow back healthy in short order.
4. Organic Options. The best is a copper fungicide, or even a sulfur based one. Both work equally as well as the above-mentioned chemicals and will actually provide trace minerals to the oil. BUT try to mix them exactly as the bottle instructs. Too much of either of these can act as an herbicide (albeit it would take a huge amount of either one to damage your plants). Neem oil is also a good option, just be careful not to apply it in the heat of summer as it can burn the leaves. Neem is also a great natural insecticide. Copper and Sulfur will normally need be used once a week for a couple weeks while neem will need to be used for a longer period of time.

Note: Powdery mildew/mold isn't going to kill your plant. But if left unchecked to run rampant, it will certainly damage any potential flowering and may kill the small branches on which the flower clusters form.

Caterpillars and grasshoppers are seasonal critters, normally appearing in spring to munch on the new crape myrtle leaves. And they can do quite a bit of damage. Don't panic, they are seasonal after all, and your plants will recover.

Caterpillars and Grasshopper Identification

There are numerous kinds of caterpillars and grasshoppers all over the country that like munching on crape myrtle leaves. Too many to mention here. But they all seem to have one thing in common: one day your tree will be emerging for dormancy, covered in perfect leaves and the next day it will be eaten down to almost nothing. Worst part is that you more than likely won't find the culprit. So, if you see your leaves eaten down to the main leaf vein or large circular areas missing, chances are its caterpillars and/or grasshoppers.

You may see a guilty grasshopper leaving the scene of the crime, but the caterpillars are tougher to spot. Normally they can be seen when they make cocoons with the leaves of your plant.

Control and Prevention

We have to make the plants taste terrible to be unappealing. Prevention is going to be much easier than control. Once the guilty parties leave the scene of the crime the application of a foliar spray isn't going to be of much use.

1. Make your plants unappealing to insects. Do this by using a systemic insecticide (as mentioned above: systemic imidacloprid). Apply when you see the first new leaves and your plants will be fairly well protected. You might see a bite or two as a taste test, but they're definitely going to move on to more tasty plants in the area.
2. If you happen to see a hatch of grasshoppers or caterpillars, you can use a foliar spray directly on them. Imidacloprid and acephate (just to name a couple), work fine. If you see your plant has already been damaged and there's no sign of the culprit, using a foliar spray typically won't work. The caterpillars and grashoppers will give it a couple days for the chemical to wash off or become inactive, then back to the plant they go.
3. Organic Options: There's always good ole fashion neem oil again, or you can mix up some dish liquid with water. Apply a few times a week to the plants and hope for the best. Or you could care for the plant like normal, let the caterpillars have their yearly short-lived feast, and let your plant recover naturally.

Note: Caterpillars and Grasshoppers aren't going to kill your plant. They'll take their share and be on their way in a week or two.

Ants can also be a seasonal problem for crape myrtles. In spring, the new leaves of a crape myrtle are filled with sugars. Sometimes these leaves can produce so much sugar it will form crystals at the tips of the leaves, a phenomenon called "guttation." And we all know how much ants love sugar.

Ant Identification

We're pretty sure everyone has seen an ant. Be it a bull ant, crazy ant, red ant or carpenter ant. Ants are ants and are a pain. So, we're not going to focus on the type of ant, we're going to focus on their home base. You'll first notice ants crawling up your crape myrtle to the very tips of the top leaves, this is where the most sugar is located. They will nibble on the leaves a bit (not nearly as bad as caterpillars and grasshoppers), and take the sugar back to their nest. it's the way home we want to follow. Once the nest is found, the treatment can begin.

Control and Prevention

1. The most effective way to destroy a pesky ant hill is to mix up a batch of bifen (Bifenthrin). Mix a gallon or two following the directions on the bottle and apply as a drench to the ant hill. This will kill the ants.
2. If you don't want to kill the nest, you can apply any number of granular ant killer, such as Sevin. It won't kill the queen, and they'll just move to another spot. Keep in mind, even if they move, they may still go back to your crape myrtle for lunch.
3. Organic Options: The sugars present in the new leaves won't be there for very long as the crape myrtle puts on new green growth. After a week or two the ants will move on to more calorie rich foods. In this case you don't need to do a thing. But if you want to try to get rid of them there are a myriad of natural options from diatomaceous earth, Twenty Mule Team Borax, coffee grounds, baking soda and vinegar just to name a few.

*Note: Ants will not kill your crape myrtle. They'll damage a few leaves in spring, but typically aren't a big deal. In fact, some species of ants actually eat aphids. In that case it may be beneficial to determine the exact variety of ant you have. You can contact your local Agricultural Extension Office for help.*

Cercospora leaf spot is a pathogenic fungus that affects the leaves of crape myrtles. Cercospora affects countless species of plants all around the world in one way or another. It's extremely common and can found in one form or another in most gardens.

Cecospora Leaf Spot Identification

Cercospora occurs in moist, humid climates with poor air circulation. It manifests by small brown and black spots under the leaves that will eventually show through the tops. In crape myrtles the leaves will change fall colors, normally reds, oranges and yellows (depending on the variety of course). The plant will naturally drop these leaves and regrow new ones. However, if the fallen leaves, or a nearby plant is infected, the new leaves will also exhibit the first signs of cercospora infection. The first signs of cercospora will appear on the lower leaves of the plant (where humidity is normally the highest). Defoliation and regrowth from cercospora can happen up to 5 times per year.

The good news is that it will NOT kill your plants. It's an aesthetic nuisance.

Control and Prevention

Prevention is best with cercospora leaf spot. It can easily spread by the wind, rain, plants next to each other and fallen leaves or mulch from the previous year.

1. Plant your crape myrtles in an area that receives as much sun as possible, is nice and breezy and avoid overhead watering as much as possible. Having said that, you can't help it if Mother nature decides to rain on you every day for a month. Cercospora normally isn't an issue in landscape, it occurs primarily in nursery settings where plants are close together or in very humid tropical environments.
2. Once you have determined you have cercospora leaf spot, you can let it die back on its own: the leaves will fall and regrow within a month. Or you can treat with foliar sprays. These sprays are most effective BEFORE you see the first spot. So, if your plant had cercospora last year and proper hygiene wasn't followed (removal of the fallen leaves, change the mulch, etc), then there's a good chance you'll see it again this year.
3. Foliar sprays containing myclobutanil, chlorothalonil, thiophanate-methyl and azoxystrobin will all work. If the infestation is bad, rotate the use of these chemicals (you don't have to use all of them, you can just use two like Immunox and Daconil), so the cercospora doesn't have the chance to develop an immunity. Mix these foliar sprays following the instructions on the bottle and apply in the evening when you're not expecting rain. Expect leaf drop within a day or two. Don't Panic! This is the plant's natural response to getting rid of infected leaves. Remove these fallen leaves to prevent reinfection. Repete every 7-14 days depending on severity.
4. Organic Options: Copper is going to be your best bet by far. In fact, we often mix in copper with the regular preventative fungicide rotation schedule. It's cheap, organic, provides trace minerals and works. Apply copper every 7-14 days as a foliar spray, following the mixing instructions on the bottle.

*Note: We've noticed an odd phenomenon over the years. When a perfectly healthy plant is shipped during the summer months, it can arrive at its new home with leaf spots. They're similar to cercospora in that they have dark spots, but they don't exhibit any of the color change that is expected, nor do they spread. And these leaves don't fall, they continue growing. If you receive a plant that has black spots on it, first make sure it's not soil and can be washed off. Alternatively, you can pluck it off or let it grow. Either way the plant will be just fine. *

Bark scale on crape myrtles is a relatively recent pest in the United States, having originated from Asia. It primarily affects the Southeastern United States but seems to be spreading. "Knock on wood," we have not seen it here in Florida. Of all the possible pests or problems to have, this would be the most worrisome. But Don't Panic, it is treatable.

Bark Scale Identification

Bark scale appears as small white, fuzzy flecks around the pruned parts of the tree and along the trunk and branches. These tiny white felt-like critters are the female Acanthococcus lagerstroemiae. If you want to bother to look closely, you'll see tiny pink eggs under them. Also (this is gross, but a sure-fire way to tell if you have bark scale), when you squish the white felt bugs, they bleed pink and red. Your plant will have black sooty mold, as you would see in an aphid infestation.

Control and Prevention

As bark scale is relatively new in the United States, there's no sure-fire way to ensure that you can prevent your plants from becoming infected. Most arborists in the past have elected to remove the tree. However, more recent studies have concluded that bark scale can be successfully treated.

1. Once bark scale has been identified, some good ole fashion elbow grease is our first line of defense. First, prune off the most infected branches and dispose of them (preferably via fire). Then make a solution of dish soap and water. Using the scrubby side of a dish sponge or a bristle brush, manually remove as many of those little buggers as you can. For larger jobs, using a pressure washer is not unheard of. You'll lose some leaves, but you'll certainly help save the tree in the long run.
2. Next is the use of, you guessed it, systemic insecticide. Systemic imidacloprid is not only effective for aphids, but it also helps with bark scale too. This will need to be applied as a soil drench three times a year: Early Spring when the leaves emerge, early summer and again in late summer.
3. Bark scale is persistent, so a foliar spray is also required. This spray should consist of an active ingredient that's not imidacloprid. You can use any number of insecticides such as acephate, pymetrozine, malithion, permethrin, etc. You will also need to incorporate an IGR. An (I)nsect (G)rowth (R)egulator will prevent any surviving insects from reproducing. You don't have to break the bank with an IGR, Martin's I.G. Regulator is inexpensive and works well. Mix following the instructions on the bottles and apply in the evening when you don't expect rain (to protect pollinators). Note: If you choose to use acephate as your insecticide, the final pH of the spray needs to be below 6.5, otherwise the acephate will not be effective. Apply once a month, or if/when you see any white scale.
4. Dormant oil is also required. As with aphids, use any number of dormant oils and apply in fall and early spring.
5. Organic Options: This is a tough one as bark scale has become notoriously difficult to control. Manually remove heavily infested branches, scrub with soapy water as described above and use a foliar spray such as neem oil when needed. Dormant oil is also safe to use.

*Note: If the tree is large, well established and beyond physical and/or chemical control you can still save it. When it is dormant for winter, cut it completely back to the ground. It sounds extreme because it is. You must completely remove the top growth including any fallen leaves, branches and bark. The following spring it should send up lots of new, perfectly healthy shoots. You will, however, need to treat is like it still has bark scale for the first year or two. If there are no other infected crape myrtles in the area, you can completely eradicate bark scale this way.*