DEAR READERS: My recent reporting about crape myrtle scale (in the Arkansas Democrat-Gazette's Sept. 19 Style section) generated a lot of questions and got many gardeners inspecting their crape myrtles and finding the problem. Here is one more question and a clarification.
Q I live in Nashville 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 three 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. 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 three 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?
A All good questions, and unfortunately, we have no definitive answers. We have seen that some varieties tend to get crape myrtle scale 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 but the dwarf crape myrtle beside them had no damage. The insects could travel from tree to tree in a nursery, or the insects could be transferred by pruning one tree and then another without cleaning off the pruners. Putting damaged branches out by the curb to be loaded into an open truck could allow for spread, too.
I do not think your crape myrtle would have died, at least not that quickly, from crape myrtle scale. I have seen trees literally covered and still living. An infestation will affect the size and amount of flowers, but I think it would take years of the insect growing unchecked to out and out kill a tree. We have seen excellent results with the systemic insecticides containing imidicloprid (Merit, Bayer Advanced Tree and Shrub, etc.). Only prune out heavily infested small branches; then clean the main trunk and spray with a dormant oil in late fall to early winter. Systemic insecticides would be best applied as the trees begin growth in the spring.
Q I know this question has been asked over and over, but I have to ask it again because my daughter and I are having a debate about this. When is the best time to prune crape myrtles?
A I believe this ranks as the No. 1 question I get on gardening, and yet as many times as I have answered it and written about the correct way to prune a crape myrtle, we continue to see "crape murder" practiced across the state. Late February is the normal time to prune a crape myrtle -- prior to new growth. This past late February we were under attack by snow and ice, so many people did not get around to pruning until late March. So although late February is usually ideal, the best timing will be determined by weather. If you have a standard crape myrtle, select three to five main trunks or a single trunk and prune out the rest. Let the branching begin 5 to 6 feet off the ground and prune out anything smaller than a pencil in diameter as well as any crossing or rubbing branches. Then stand back and let them grow and become trees.
Q I recently saw a large bush in my friend's yard. It had big leaves, and the flowers looked like pink carnations. She said it was a rose hibiscus and only blooms in the fall. I have never heard of this plant before but would like to buy one. Are they available at local nurseries, and where is the best place to plant one?
A I believe you are talking about the Confederate rose, Hibiscus mutabilis. This hardy hibiscus usually can withstand winter temperatures from central Arkansas south. It begins growing in the spring when the soil temperatures warm, and grows six to eight feet or more in one season. It produces woody stalks, and the flowers open white or pink before fading during the course of a day to a shade of white or pink depending on the variety. This mutation or change is the reason for the species name, "mutabilis." It is an old-fashioned plant that is probably most often obtained as a pass-along plant (rather than being bought at a garden center). Getting a piece from your friend before a frost would give you a start. Take cuttings and put them in a bucket of water. They will root, and you can plant them outside next spring. The plant dies to the ground after a killing frost and will begin the process over again next spring.
Janet B. Carson is a horticulture specialist for the University of Arkansas Cooperative Extension Service. Write to her at 2301 S. University Ave., Little Rock, Ark. 72204 or email her at
jcarson@arkansasonline.com
HomeStyle on 09/26/2015