New Mealybugs Showing up in Woody Cut Stems

As imports continue their impacts on North America and the rest of the world, an influx of new plant pests goes right along with them. One of these is a South American mealybug now showing up on roses and other woody plant material. Cut flower growers growing and selling heirloom roses, and ornamental trees and shrubs must be on the lookout for the obscure mealybug, Pseudococcus virburni.

In November of 2017, a garden center manager in Maryland noticed that rose plants shipped from Florida sported clusters of mealybugs at each of the branch axils. Samples were sent to mealybug specialist Dr. Douglass Miller of the USDA, who identified it as the obscure mealybug, and noted that it has turned up in several locations in the U.S. It was found years ago on California grape vines, and has now moved onto almond trees. Both grapes and almonds are important economic crops.

The obscure mealybug is a polyphagous feeder, meaning it feeds on a wide range of plants—over 295 species—including annuals, herbaceous perennials, evergreens, and deciduous species. When you purchase plants, inspect them closely to be sure you do not bring this mealybug into your operation.

What to Look For

The body of the female varies from pink to light purple with white filaments projecting from the body. A mature adult female is about 3 millimeters in length. There are two long anal filaments arising from the abdomen. If you cut a female in half, the blood that comes out is clear to white in color. The eggs are light gray to yellow, and laid in an ovisac much like citrus mealybug. If you see something that looks like this, contact your department of agriculture or get a sample to your university extension office for definitive identification.

Control Options

If you develop a problem with mealybug I suggest trying the insect growth regulator (IGR) called Enstar II. When applied to immature mealybugs, it prevents them from shedding their skins and progressing into the next life stage, which leads to death.

Two other materials that work well are Endeavor and Aria. Both stop up the insects’ feeding stylets, starving them to death. In 2017 we tested Mainspring, a relatively new systemic insecticide, applied as soil drench at 8 oz/100 gallon for citrus mealybug on coleus. It took almost a month to show efficacy, but we obtained a very high level of control with this material 30 days after treatment.

Stanton Gill

Extension Specialist

Stanton Gill is an extension specialist (professor rank-principal agent) in IPM and entomology with the University of Maryland Extension based at the Central Maryland Research and Education Center in Ellicott City. He is also a professor in the Landscape Technology Program at the Germantown Campus of Montgomery College. Contact him at [email protected]