Crape Myrtle Scale

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December 3, 2016

I really appreciated your article in the paper about crape myrtle bark scale.  In your article you recommend 3 treatments:  1. Wash with warm soapy water (I have already done this) 2. After the leaves fall, treat with dormant oil (I purchased “All Seasons Horticultural & Dormant Spray Oil” and I am just waiting for the leaves to fall to do this step.)  This may be somewhat difficult since my Crape Myrtle is very tall and I am not sure how to reach the top branches, but I will do my best.3. It is the third step that I am unclear on.  It says in late March through early May; treat with a systemic insecticide containing imidacloprid (Merit or Bayer Advanced Tree and Shrub Insect Control), thiomethoxam (Meridian) and dinotefuran (Greenlight Tree and Shrub Insect Control with Safari).  Are you saying that we need to use any one of these three products, or are you saying that we need to use all three?

Do your best when it comes to spraying with the dormant oil, but coverage is greatly improved after the leaves have fallen, so there is nothing to get in the way.  As for the systemic insecticides in step 3, use only one of the products, not all three. 

October 3, 2015

I have had success with the soil drench in the spring for controlling the crape myrtle bark scale. What about that type of treatment later in the year (summer and fall)? Is it still effective?  I am seeing it on some of my other crape myrtle trees now, and I don’t want to wait until spring to take action.  Is the dormant oil as effective as the drench? Also, you mentioned in your article to not treat the trees preventively. Is that an environmental issue? What if there are several trees and only one has damage? 

The way the drenches work is through movement via the sap. In the fall and winter there is not much movement upwards. They tend to be preparing for winter and storing reserves in the root system, therefore the product is not as effective as it is in the spring when we get strong upward flow. Preventative is in my opinion overkill, since we don't know if all plants will be affected. There is still a lot of debate about the effects of the neonicotinoids and the bees and beneficial insects, so using it as needed versus blanketing the landscape is my preference. We have seen a rash of attacks in the past two months, and we aren’t sure if it was due to drier conditions or what.  The dormant oil is not as effective, but it gives you the beginning of control, and should keep them in check until you treat in the spring. 

(September 26, 2015)

 I live in Nashville AR and wrote a couple of years back, and sent a photo, of an infected tree. You recommend dormant oil, but that tree went on to die. We have 3 young crape myrtles (Natchez I think), planted two years ago that are infected. The nursery sent a worker out to spray the tree and apply an insecticide to the soil. It is too early to tell if the treatment will be therapeutic. From your article, I need to aggressively prune late winter, wash, and use dormant oil. Or should I start over with a different variety? I noted it was first detected in Dallas and spread over the south. Our first tree and these 3 above all came from the same nursery in Texas. Do the trees come into a nursery already infected or do they become contaminated at the nursery? Or where does this pest come from? You mentioned several insecticides applied to the soil. Which, in your opinion, is the best?  

all good questions and unfortunately no definitive answers.  We have seen that some varieties tend to get it more than others, but we don’t have enough data over a long enough period of time to know for sure.  Where I did the photo shoot for the story two trees were totally infested and the dwarf crape myrtle beside them, had no damage.   The insects could travel from tree to tree in a nursery situation, or be transferred by pruning one tree and then another without cleaning off the pruners.  Putting damaged branches out on the curb and then loaded into an open truck could allow for spread too.  I do not think your crape myrtle would have died at least that quickly from crape myrtle scale.  I have seen trees literally covered with them and still living.  It does affect the size and amount of flowers, but I think it would take years growing unchecked to out and out kill a tree.  We have seen excellent results with the systemic insecticides containing Imidacloprid (Merit, Bayer Advanced Tree and Shrub, etc.—all same chemical just different brand names)  Only prune out heavily infested small branches, clean the main trunk and then spray with a dormant oil this late fall to early winter.  Systemic insecticides would be best applied as the trees begin growth in the spring. I would not give up on planting crape myrtles, just stay on top of things.