Cycad scale: a threat to wild and cultivated cycads
Armored scales are small insect pests that use a straw-like mouthpart to suck out plant juices, have a hard exterior like a shell, and in high numbers can cause serious problems or kill the plant. The cycad scale (Aulacaspis yasumatsui) is a new pest that was first introduced to Miami in 1996 from the importation of infected plant material and quickly spread. Hosts include plants from three different families: Cycadaceae, Zamiaceae, and Stangeriaceae. When the cycad scale was brought to the US, it left any natural enemies behind – which allows for a population explosion due to a lack of predators. This pest can be damaging to both ornamental and wild cycads, and can have a significant impact on the nursery trade in South Florida where cycads are commonly grown and shipped around the US and the world.
The cycad scale is often seen on king sago (Cycas revoluta), which is an endangered plant and the genus is preferred by the pest and susceptible to the scale. The symptoms of feeding will somewhat depend on the location of the infestation. If the scales are feeding on a bud or growing point for the plant the area will dieback, whereas feeding on the leaves will just cause discoloration.
Similar species – the false oleander scale
The cycad scale will most frequently infest the underside of the leaves first, which can help distinguish it from the false oleander scale (Pseudaulacaspis cockerelli) which feeds on the upper surface of the leaves. In addition to the location, false oleander scale can be differentiated from the cycad scale by removing the white armored cover of the scale, revealing the body. False oleander scale will have a yellow body while the cycad scale has an orange body.
Chemical management options for this pest may be necessary due to the lack of natural predators. Many natural predators that already occur in the US will not attack this pest, possibly due to the absorption of defensive chemicals from the cycad host that makes the pest undesirable. The most effective treatment for this pest is a fish oil emulsion or petroleum horticultural oil. Target crawlers (the first life stage) because they do not have a cover and are very susceptible to chemical sprays. The scales can still pose a problem after they die because the body stays on the plant and can disrupt photosynthesis and be unsightly.
To learn more about this scale read please visit the Featured Creatures. If you need help managing this pest, please see the UF extension publication by G. S. Hodges, F. W. Howard, and E. A. Buss, Update on Management Methods for Cycad Aulacaspis Scale.