The crape myrtles all over town are showing their remarkable colors once again, as they do every summer. Valued for their useful qualities – moderate size, drought tolerance, sidewalk-friendliness and ease of care – they are now, arguably, over-used. Quoting myself in this space a few weeks ago: “Enough with the crape myrtles already!”
In our region they are generally thought of as pest-free trees, but that is a relative term. Every tree, as far as I know, has associated organisms with the potential to harm them.
In the mid 1970s, when I first learned of crape myrtles in the nursery trade, the only ones available at the time were Lagerstroemia indica varieties. These are susceptible to powdery mildew in our region except in the hotter climate zones with low humidity.
Then the hybrids were introduced. These are, mostly, the ones we see lined up in curb strips all over town. The most common are ‘Natchez’ (white flowers), ‘Muskogee’ (lavender), and ‘Tuscarora’ (red). Disease resistance is one of the reasons they have become so popular and successful. Hybridizing L. indica with L. faurei – Japanese crape myrtle – yielded Lagerstroemia X faurei varieties. They are faster and larger growing with larger, showier flowers and strong resistance to powdery mildew.
After thinking of them for many years as pretty much invulnerable, I was surprised to learn, after closely inspecting one a couple weeks ago, they have their own special insect pest: the crapemyrtle aphid (Sarucallis (Tinocallis) kahawaluokalani. An article from North Carolina State University says it was first described in Hawaii and named for Queen Kahawaluokalani. Big name for an aphid that measures only about 1/16th of an inch in length. This was the first time I had seen it. It took a strong hand lens for me to see it and a macro lens on my phone to capture a photo of it.
Reading up on crape myrtles, I gathered that this and several other pests tend to be of more significance where the climate is conducive to the pest.
Stepping back a bit to look at the misconception of pest-free trees, I found this in “Insects That Feed on Trees and Shrubs”: “A list of aphid species that attack shade trees alone would be extensive and would include at least one species for each of most of our common trees.”
Here are some examples of what I have seen and what can be found around town, depending on the season:
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— On Deodar cedar, a tree we generally consider pest free: bowl legged fir aphid (Cinara curvipes). In my experience it is very rare here.
— On Chinese hackberry, a very sturdy street tree, now showing a sticky mess on the sidewalks and streets under the canopy: Sticky honeydew secretion form hackberry wooly aphids.
— On Eastern Tulip Poplar (Liriodendron tulipifera): Sticky mess under the tree from tuliptree aphid.
Management of these pests is a huge subject. There can be many options depending on the tree, the pest, and circumstances. Aphids and other insect damage can range from insignificant, to nuisance, aesthetic damage, vector for lethal disease, to severe economic losses.
Depending on the situation, control methods can range form no action, to rinsing with plain water, to low-toxicity insecticides, biological control, toxic spray applications, and systemic insecticide soil drenches or direct injections.
When you are looking into a tree pest problem, UC IPM Online is great place to get started. It is a product of the Statewide Integrated Pest Management Program. Just go to it online, select a category, like “Home, Garden, Turf and Landscape Pests” and follow the links to your subject of interest.
I have been pleased to see, over the years, most homeowners I meet with seem to reject the use of toxic sprays in favor of the least toxic approach as long as it works.