Q: Iโve got a previously healthy stand of Mexican fence post cactus that has been infested with a white scale pest of some kind. Can you tell me what it is โ and how I might get rid of it?
A:Your scale insect was identified asย Diaspis echinocacti. They are found on a variety of cacti and other plants. The recommended management strategy for scale insects is a combination of integrated pest management tactics including natural enemies, physical removal, and applications of horticultural oil or insecticide. Because their outer covering protects scale insects, the ideal time to spray them is during the time in their life cycle when the young have recently emerged from their eggs and are crawling about unprotected. The timing is not always easy to determine but you have options to figure it out. Late winter is a good time to start watching. Carefully examine the infested plant to see if crawlers are present. A magnifying glass or loupe will come in handy when looking for these tiny insects. Alternatively, place double-sided tape around the cacti in affected areas of the plant when crawlers are expected. The tiny insect bodies get stuck in the adhesive. Once you see them you will have a general idea when they emerge. The next trick is to notice what else is happening nearby with your other plants. For example, what is recently blooming in your landscape? Year to year variation in insect development can be estimated by the use of phenology (the known influences of weather variations on plant and animal life cycles). By watching known phenological indicator plants you can accurately predict when particular scale insect eggs will hatch in your area in following years and thus you will be better prepared to manage the scale insects.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email questions to tucsongardensage@gmail.com
