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.”

Pesticides (insecticides, miticides, fungicides and bactericides) are used to manage arthropod (insect and mite) pests and diseases (fungi and bacteria) in greenhouse production systems. Pesticides, in general, are easy and convenient to apply, and effective in terms of control, suppression or management. There are several factors related to greenhouses that favor pest population growth including environment (e.g., temperature, relative humidity and photoperiod); cultural practices (e.g., watering and fertility); and plants provide a continuous food source (many plants grown in the greenhouse and spaced close together). Consequently, greenhouse producers routinely apply pesticides to prevent or minimize plant damage. However, continually relying on pesticides promotes the development of resistance in arthropod pests and plant pathogen populations.

This is the fifth article in a series of six scheduled for publication in Greenhouse Management associated with pesticide resistance and resistance management of arthropod pests and diseases. Three articles were published in 2019 and the fourth article was published in the 2020 March issue of Greenhouse Management. In this article, we discuss how pesticide mixtures may help in resistance management.

Arthropod pests

A pesticide mixture is associated with mixing (tank-mixing) or combining two or more pesticides (in this case, insecticides and/or miticides) into a single spray solution. The mixture, when applied to greenhouse-grown horticultural crops, exposes individuals in an arthropod-pest population to each pesticide simultaneously. The mixing of pesticides together is designed to manage multiple concurrent insect and mite pests, and reduce labor.

So, how can pesticide mixtures be used in resistance management programs? The issue of pesticide mixtures and resistance management is not well understood. In fact, applying two or more pesticides at different intervals is thought to have the same advantages as a pesticide mixture. However, this is not correct; each individual insect or mite in a population has not been exposed to a lethal dose or concentration of each pesticide. Consequently, resistance can evolve more rapidly than what might occur with a pesticide mixture. Therefore, mixing pesticides with different modes of action (MOAs) can delay resistance within an arthropod-pest population because the mechanism(s) required to resist the pesticide mixture (e.g., metabolic detoxification or target site insensitivity) may not be widespread or present throughout the arthropod pest population. Furthermore, it may be more difficult for individuals in the arthropod-pest population to develop resistance to several MOAs simultaneously. In addition, individuals in the population resistant to one or more pesticides in all likelihood would succumb to the other pesticide in the mixture, as long as agents with different MOAs are mixed together.

Pesticide mixtures may be helpful for mitigating the potential for resistance developing in an arthropod-pest population. For instance, developing pesticide mixtures that include agents with site-specific (narrow-spectrum) MOAs with pesticides that have non-specific (broad-spectrum) MOAs such as insecticidal soap, horticultural oils, and beneficial fungi and bacteria, may mitigate the development of resistance. Tank-mixing pesticides with different but specific MOAs can potentially lead to multiple resistance or resistance to two different pesticides, although this depends on the specific insect or mite pest.

It is important to note that continued use of the same pesticide mixtures in succession may result in resistance developing in an arthropod-pest population to both modes of activity. Therefore, greenhouse producers must use different products with distinct MOAs to mitigate the potential for resistance. Insect and mite pest populations that have acquired resistance to two different pesticides with different modes of activity are extremely difficult to manage, which will limit pesticide options.

The effects of pesticide mixtures on arthropod-pest populations can vary depending on differences related to species, strain and biotype associated with physiology and the resistance mechanisms present in the population. Moreover, using pesticide mixtures to avoid resistance will only be successful if there is no cross-resistance among individuals in the pest population (based on a single resistance mechanism that confers resistance to pesticides in the same chemical class and/or having similar MOAs) to any of the pesticides in the mixture.

Plant pathogens

The use of pesticide mixtures (tank mixes) to reduce the possibility of resistance developing in fungal and bacterial plant pathogen populations is well established in ornamental disease control. In the early days, research associated with large-scale agriculture demonstrated equal benefits from using pesticide mixtures or rotating products to mitigate resistance developing in disease-causing agents. We have moved from relatively few broad-spectrum products that were available in the early 1980s to at least 10 times the number of products. Consequently, the question of tank-mixing has taken on a new meaning. Many products from the 80’s had broad and multiple effects on plant pathogens, making development of resistance less likely. In the early 1980s, several large agrichemical companies got together and started the Fungicide Resistance Action Committee (FRAC), with the purpose of providing fungicide-resistance-management guidelines to “prolong the effectiveness of at risk fungicides and reduce crop losses should resistance occur.” Today, products are much more environmentally safe and have targeted MOAs representing more than 30 different FRAC groups; thus making tank-mixing very targeted but quite complex.

The reason tank-mixing works in our industry is due to the complexity of our product mix and the fact that we have overlapping crop cycles in our operations, which results in the need to protect crops from damage. Prevention is much more important for ornamental crops than agricultural ones such as vegetables, fruits and grains where only a portion of the plant is harvested. Furthermore, we have to focus on certain market targets, which means that delaying crop regrowth can mean a loss of the market window, and therefore a loss in profits.

The mixing of pesticides together is designed to manage multiple concurrent insect and mite pests, and reduce labor.

Tank-mixing for resistance management is really secondary to tank-mixing for disease management. The difficult part of disease control is knowing what the problem is. For example, most plant diseases cannot be visually diagnosed, and by the time one observes disease symptoms, damage may not be reversible. So, prevention with pesticide mixtures is often practiced.

The theories associated with pesticide mixtures or tank-mixing for resistance management in plant pathology are changing. For instance, I listened to a series of talks at our plant-pathology annual meeting last summer; researchers proved that tank-mixing two different groups of fungicides to delay resistance development to one fungicide was not working in Europe.

One of the developments that may help in mitigating resistance development is using biopesticides. Many of these agents have multiple MOAs, including excluding the plant pathogen by taking up space where a plant pathogen might reside, acting as a barrier between the plant and plant pathogen (this is usually accomplished by living organisms such as Bacillus, Ulocladium and Trichoderma), parasitizing plant pathogens, creating an environment that is inhospitable to a plant pathogens, and causing plants to use disease-fighting mechanisms against the plant pathogen. Consequently, there are many factors working against the plant pathogen, which makes resistance development less likely. So, for biopesticides, rotating products may be preferable to using pesticide mixtures as a means of resistance management.

Raymond A. Cloyd is a professor and extension specialist in horticultural entomology/plant protection at Kansas State University. Reach him at rcloyd@ksu.edu. A. R. Chase is president of Chase Agricultural Consulting. Reach her at archase@chaseresearch.net.

In late April, Greenhouse Management magazine conducted a survey to learn how growers across North America administer pest management plans, budget for insect control, scout for pests and much more. Our survey of more than 200 growers found which methods growers prefer and how they manage controls programs. Read on for more insights in insect management.

Editor’s note: Due to rounding, not all percentages add up to 100.

It is an honor to partner with Greenhouse Management and Nursery Management in supporting this “State of the Market” special report. It is an important time for ornamentals as the industry continues to embrace new solutions while adapting to the current environment.

For those readers who do not know me, I provide technical support for the greenhouse and nursery business at Bayer. I am fortunate to be a part of a small, yet highly experienced, group of ornamental specialists who strive to deliver best-in-class customer support. It is always a pleasure to interact with growers and learn more about the challenges and successes of their operations. The insights gleaned from those discussions are very often what drives innovation at Bayer as we continually work to address the evolving needs of the industry.

Pests don’t rest, even in a pandemic

During these unprecedented times, we know that our customers still have businesses to run and crops to protect. Pests aren’t deterred by social distancing. So, Bayer remains committed to providing customers with ongoing technical support, and we are adapting our approach accordingly. This includes leveraging virtual tools, like FaceTime and Microsoft Teams, to keep communication lines open. Whether for product support, technical and agronomic expertise, pest diagnoses, or just someone to talk to, you can count on us to be there when you need it most.

Adding value to minimize production costs

One of the fundamental challenges growers face is staying on budget, and to do this they must manage overall production costs. Therefore, when it comes to plant protection products, successful growers demand products that bring value to the operation and result in long-term cost savings in other areas. This includes products with broad-spectrum activity and long residual control, as well as plant and environmental safety. Bayer understands these demands and continues to deliver innovative products with these criteria in mind. We also offer value calculators for our products so that customers can calculate the broader cost-savings benefits of investing in Bayer solutions.

Complex challenges call for innovative solutions

Insects, weeds and diseases will always be factors for growers to manage. Working with customers, university researchers and our internal team of developmental scientists, we continually work to provide growers with valuable solutions, such as Broadform® fungicide, Marengo® herbicide and Altus® insecticide to help them tackle their toughest challenges. Broadform, as the name implies, is an excellent rotational tool that manages a broad spectrum of diseases and protects plants from more than 50 pathogens. For weed control, no other herbicide lasts longer than Marengo. A powerful pre-emergence herbicide, Marengo demonstrates up to eight months of residual control of more than 90 weeds with a single application. And Altus provides plant protection from piercing-sucking insects with minimal impact on beneficial insects, including pollinators, and it has an excellent track record for plant safety. Growers can learn more about these and other innovative solutions for protecting ornamentals by visiting es.bayer.us/ornamentals.

Last, but certainly not least, thank you, Greenhouse Management and Nursery Management for sharing this important “State of the Market” report. Here’s to a year of embracing new challenges, implementing innovative solutions and growing beautiful, healthy plants!

Sincerely,

Aaron Palmateer, Ph.D.

Senior Technical Service Representative, Ornamentals, Bayer

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Bayer Environmental Science, a Division of Bayer CropScience LP, 5000 CentreGreen Way, Suite 400, Cary, NC 27513. For additional product information, call toll-free 1-800-331-2867. environmentalscience.bayer.us. Not all products are registered in all states. Bayer, the Bayer Cross, Altus, Broadform and Marengo are registered trademarks of Bayer. © 2020 Bayer CropScience LP.