I recently moved into a new home in Florida. The first day, I walked outside and noticed that the relatively large cycad in my front yard was covered in scale insects.
I went back to check them out yesterday and it turns out it is in much worse shape than I originally thought. The undersides of the leaves are completely white with scale insects. Upon closer look, I determined they are cycad aulacaspis scale, Aulacaspis yasumatsui.
This armored scale insect, native to Thailand, is a major insect pest of cycads in Florida. These insects were introduced to Florida in 1996 and have since become an established pest of cycads throughout the state. Leaves of cycads with heavy infestations begin to yellow, brown, and eventually die. In the photo below, I lined up branches in order from least to most damaged to illustrate the progression of yellowing to death.
You may also notice some black patches on the surface of the leaves. This is sooty mold, which suggests there is another insect pest getting in on the action. Armored scale insects (like the cycad aulacaspis scale) do not excrete honeydew, which facilitates the growth of sooty mold. Insects like aphids, whiteflies, mealybugs, and soft scale insects do secrete honeydew. Upon closer inspection, I found some soft scale insects and a mealybug feeding amongst the A. yasumatsui. Double the trouble for my cycad.
Managing scale insects can be tricky and requires persistence and patience. Regularly inspect your plants so that infestations don’t get to the level of the cycad in my yard. Check the undersides of leaves for scales, but be careful because the leaves of some cycad species will draw blood.
Keep an eye out for evidence of biological control. In 1998, two natural enemies were introduced to Florida to control this pest, a predacious beetle (Cybocephalus binotatus) and a parasitoid wasp (Coccobius fulvus). These natural enemies provide moderate control but have not prevented the spread of this scale. I did find a lone lady beetle larva snacking on the scales, but it was severely outnumbered. If scale insect populations are low enough, these beneficials may be enough. However, they may need assistance if populations become too extreme.
Comparison of a heavily scale-infested leaf (top) to a relatively clean leaf (bottom) Photo: A.G. Dale
If you need to treat your plants, horticultural oils have shown good control with little impact on the natural enemy community. However, you’ve got to make applications pretty frequently. Some people have reported good control with high pressure water sprays to wash off the insects. Other systemic products may provide control but results are mixed. The trick to good control when making foliar applications is good coverage. Make sure you’re spraying underneath the foliage where the insects are hiding. If your plant is as heavily infested as mine, pruning the most heavily-infested leaves off and disposing of them before spraying may be the best remedy. Keep in mind this adds stress to the plant. For more information on the biology and management of cycad aulacaspis scale, see the links below.