A few weeks ago, we discussed Gloomy Scale, which is a real threat to maple trees. In that post, I mentioned Cottony Cushion Scale and that will be our topic for today. Cottony Cushion Scale’s latin name is Icerya purchasi and resembles cotton of all things. It is known as a soft scale, meaning that its protective outer covering is soft and squishy instead of being hard and virtually impenetrable like armored scale.
When the scale are young, they are mobile and crawl around the plant seeking out a place where they will spend the rest of their existence. As crawlers, they are reddish-brown in color and don’t have the cottony appearance of the adults. Once they have declared squatter’s rights on a particular stem, they start to exude a white waxy covering that will later protect them from predators. As is the case with armored scales, the best time to attack them is during the crawler stage. And as with armored scale, an application of dormant horticultural oil can all but eliminate your Cottony Cushion Scale problems.
Some of you may know that Cottony Cushion Scale was imported into the U.S. in the late 1800′s by accident and that it nearly wiped out the citrus crop in California and later Florida. Entire citrus groves had to be destroyed as a result. Thankfully, the Vedalia beetle was tried as a biological control and it had great success in bringing the scale population down to manageable levels. Cottony Cushion Scale is often thought of as a southern insect but I have personally encountered it overwintering on Chinese Holly (Ilex cornuta) and Skypencil Holly in Richmond, VA. Some of my Zone 5 and 6 readers may not have to concern themselves with this particular scale but it is alive and well in Zone 7.
Thankfully, Cottony Cushion Scales are easy to spot as they are generally around 1/2″ long when they are covered with their protective coating. You may notice a black coating on the stems and leaves near the scale…this is sooty mold. While the scale are literally sucking the life out of your plants, they are also excreting honeydew which sooty mold thrives on. Don’t be too concerned with the sooty mold; if you eliminate the scale, you’ll eliminate the sooty mold too. I hope that you’ve learned something today about another pest that we gardeners have to deal with. If there is a particular pest or disease that is wreaking havoc in your garden and you’d like me to address it, feel free to leave me a comment below or e-mail me at firstname.lastname@example.org. Happy gardening!