Managing mealybugs

Mealybugs are one of many insect pests that are a pain in a grower’s pockets. But Aaron Palmateer, Bayer’s senior technical service representative, sheds light on making mealybugs more manageable.

As a former ornamentals specialist at the University of Florida, Palmateer has gained extensive experience in providing pest and disease management recommendations for ornamental producers and landscape professionals. His education includes a bachelor’s and master’s degree in plant and soil science from Southern Illinois University in Carbondale, Illinois, along with a doctorate in plant pathology from Auburn University in Auburn, Alabama. He also served as the director of the Tropical Research Education Center, a plant diagnostic facility at the University of Florida.

“I wanted to discuss mealybugs because that seems to be the hottest issue right now,” Palmateer says. “One of the things I’ve been doing since we’ve been grounded and not traveling is keeping in touch with growers all over the U.S., figuring out what the hottest issue is and what the biggest challenges are, and mealybugs seems to be a reoccurring issue.”

The first word Palmateer uses to describe mealybugs is “hitchhiker,” and jokes that growers tend to blame Florida because, according to him, the more “common and problematic” mealybugs are citrus mealybugs that favor warmer climates, and are often found on shipments from the state. And because they often bury themselves in the plant, they are hard to scout for.

“Mealybugs are notorious hitchhikers because they’re able to get into the nooks and crannies of the plant,” he says. “You’ve got mealybugs that are problematic and infect roots and you’ve got mealybugs that go to all portions of the plant. But of course, when they’re on the roots, it’s a really big challenge because growers may not see them and they’re easily overlooked.”

According to Palmateer, mealybugs can also migrate from roots onto other portions of plants and make homes on petiole branches and leaf axles. And in plants like hibiscus, they can get under the calyx.

“When they’re in these hard-to-see areas like the lower stems underneath the leaves or branches and leaf axles, they can just stay there and remain hidden, which is kind of one of the biggest challenges,” he says. “They’re hard to spot and when that happens, you get a small population and just before you know it, they start to explode.”

While all insect pests cause damage, a high population of mealybugs results in spot development, dieback and defoliation. But Palmateer says their notorious marks are plant stunting, tissue yellowing and mold.

“Most of these piercing sucking insects have symptoms that are pretty similar,” he says. “But I think that the biggest thing with mealybugs is that in higher populations, plant stunting and what we call chlorosis (yellowing) is often attributed to their feeding damage. In certain cases, like with other sucking insect pests such as aphids, leafhoppers and whiteflies, you oftentimes see what’s called sooty mold. That’s a black fungus that moves in because of the honeydew. Sucking insects excrete a sweet sugary substance as they ingest large quantities of sap from a plant. So in a really high population, you can also see black sooty mold develop which is not a plant pathogen; it’s just mold growing on the plant surface where honeydew deposits accumulate.”

All this reduces the aesthetic quality of the plant, and in some cases, the sugar will attract ants, he says.

While the citrus mealybug is one of the most common, Palmateer says there are other types that also like tropical conditions such as the longtailed mealybug, obscure mealybug and madeira mealybug.

“The longtailed mealybug has this long waxy filament that protrudes from the end of the abdomen, and it looks like it’s got these long tails. The obscure mealybug is really short and has these white waxy filaments around it, but it looks much smaller in size,” Palmateer says. “And then you’ve got the citrus mealybug, which lacks any of the waxy filament altogether and has a gray stripe that extends the length of the body.”

The madeira mealybug has two dark strips on the body and is about 3 millimeters long. “So, they vary in look and definitely vary in shape and size.”

Managing mealybugs can be a hassle due to the confusion surrounding their name. Palmateer says while mealybugs are a scale, not all scales are mealybugs and some insecticides are for one or the other. But Palmateer says Bayer’s newest insecticide, Altus®, is “highly active on scales, including mealybugs” and has been a “tremendous product.”

He also says the insecticide has translaminar activity, which means the product moves from the upper leaf surface, through the leaf, to the lower leaf surface, providing uniform coverage.

Another application method, according to Palmateer, is by drenching the plants, which allows the product to move upward systemically in the xylem — the water conducting tissue.

“The systemic feature of the product makes it easy for controlling mealybugs because it’s going to move throughout the entire part of the plant,” Palmateer says. “So if you’re spraying, you may not be able to actively target some of the nooks and crannies of the plant, but rest assured that product’s being taken up internally and it’s moving throughout the plant. Wherever the water is moving, that active is going to get to the feeding sites or those insects. “

Palmateer also says that Altus® is not a neonicotinoid, which is good for growers who are growing plants for big-box stores due to its pollinator-friendly approach.

Another insecticide Bayer has is Kontos®, which moves bi-directionally in the plant.

“Kontos® gets into the sieve tubes of the plant, so it can even move downward in the phloem,” he says. “For example, most systemic insecticides are xylem-systemic and the xylem tissue moves upward and outward. Whereas when you spray with Kontos, you can have a root mealybug, spray with Kontos and it’ll actually move downward and get into the roots. That’s almost unheard of when it comes to insecticides. But I think one of the really important things for growers or applicators to understand is, when they use Kontos, it works best as a preventative application because it works based on ingestion.”

Palmateer says the active has to get into the plant so the mealybugs ingest it while feeding. He also says that while Altus does have contact activity, both insecticides work best as preventatives and should be applied as such.

“It’s important that growers understand, especially with some of this newer chemistry, that they need to be more proactive and take preventative action. They’re going to have a much better experience with the product if they treat a healthy plant before the pest population comes.”

While Palmateer is an advocate for Bayer products, he says that growers should get in the habit of rotating insecticides so they do not create insecticide resistance. But the properties in Bayer’s ornamental insecticides make it easier to attack and maintain the mealybug population, he says.

“The systemic chemistry [of these products] is really nice when it comes to controlling mealybugs and these are examples of what Bayer has that does so.”