Crape Myrtle disease - Ask Extension
Hello
I have two Crape Myrtles. This spring the trees have a black crust with white spots that when smashed are gooie..
I used a pressure washed on...
Knowledgebase
Crape Myrtle disease #879619
Asked July 31, 2024, 2:39 PM EDT
Hello
I have two Crape Myrtles. This spring the trees have a black crust with white spots that when smashed are gooie..
I used a pressure washed on the front tree and removed most of the black crust from the large branches. The trees are not producing many blooms. The Rocket Crape Myrtle 20 ft tall is in the back yard and the branches also have the same problem.
I have two on the south west side of the house and they are ok. The old bark is shedding but it has sap under the bark.
I have sprayed them the best I can with Funguiside 3. Nothing happened. The only way I see using the pressure washed in the fall.
Anne Arundel County Maryland
Expert Response
We are glad that you contacted us.
For the last couple of years, we have been dealing with a new pest on crapemyrtle called Crapemyrtle bark scale.
You can learn more about them here:
https://extension.umd.edu/resource/crapemyrtle-bark-scale-home-gardens/
Scale are sucking insects that feed on sap and then excrete a sticky substance called honeydew. They stay still, settled in place and covered with a white waxy, protective film for most of their life cycle, other than an active, bare stage called crawlers.
The black you are seeing is a mold that grows on the honeydew. It will wear away with time.
Your use of the powerwasher may have gotten rid of a bunch which is great, but be careful not to damage the bark. A soft brush with soapy water on the branches you can reach may suffice.
You could also consider a dormant oil application as well.
Before you treat though, know that we got some really good news from our researchers a couple of weeks ago that many populations are being collapsed or seriously reduced, seemingly by natural beneficial predator insects, primarily by the larval/young life stage of a couple types of ladybeetle that feed on them.
You should look closely for them. They look very much like the scale and can be easily confused with it, but they are larger, move faster, and have fluffy filaments similar to a fleece blanket or sheep. If you look closely, you may see their legs beneath the fluff as well.
Your fungicide use was not useful, and we generally don't recommend using them in home gardens as they are not curative and need to be repeated at intervals.
Christine
For the last couple of years, we have been dealing with a new pest on crapemyrtle called Crapemyrtle bark scale.
You can learn more about them here:
https://extension.umd.edu/resource/crapemyrtle-bark-scale-home-gardens/
Scale are sucking insects that feed on sap and then excrete a sticky substance called honeydew. They stay still, settled in place and covered with a white waxy, protective film for most of their life cycle, other than an active, bare stage called crawlers.
The black you are seeing is a mold that grows on the honeydew. It will wear away with time.
Your use of the powerwasher may have gotten rid of a bunch which is great, but be careful not to damage the bark. A soft brush with soapy water on the branches you can reach may suffice.
You could also consider a dormant oil application as well.
Before you treat though, know that we got some really good news from our researchers a couple of weeks ago that many populations are being collapsed or seriously reduced, seemingly by natural beneficial predator insects, primarily by the larval/young life stage of a couple types of ladybeetle that feed on them.
You should look closely for them. They look very much like the scale and can be easily confused with it, but they are larger, move faster, and have fluffy filaments similar to a fleece blanket or sheep. If you look closely, you may see their legs beneath the fluff as well.
Your fungicide use was not useful, and we generally don't recommend using them in home gardens as they are not curative and need to be repeated at intervals.
Christine
