Pitting predators against pests
When the Orlando office of ValleyCrest Landscape Companies faced an outbreak of chilli thrips, they didn’t send in trucks with tanks of pesticides, they called in an army: thousands of entomopathogenic nematodes.
The result? These natural enemies of the chilli thrips are helping keep their populations in check, without the need for a strict regimen of synthetic pesticides.
Using a pyrethroid pesticide actually increased the chilli thrip population rather than decreasing it, says Barry Troutman, vice president of technical services for ValleyCrest in Orlando, Florida. So, they had to minimize traditional pesticides in this situation to maximize the beneficial insects. Florida has benefited greatly from the introduction of biological pesticides, he says, not only in the treatment of the invasive chilli thrips but also for controlling mealy bugs on hibiscus plants.
“We certainly have respect for the importance of beneficial insects,” Troutman says, “so we only treat when we have problems that they won’t treat.”
While Troutman knows first-hand that biological controls are effective, he recognizes the limitations of them, too, especially in an industry driven by results. Ultimately, says Troutman, the decision to use biological pest control must be weighed against client expectations.
“You have to be able to tolerate some pest damage, and that makes it hard for customers to accept,” he says.
From a cost perspective, he adds, biological controls target a narrow range of insects, while some synthetics cover a variety of pests. “That makes it hard to manage in high-volume landscaping. But in situations where you can focus on a single problem and allow some degree of plant damage, they do work well.”
The goal of biological pest control is to use parasitic and predatory insects to reduce undesirable and harmful insect populations, either by introducing natural enemies into the landscape or by nurturing the beneficial insects already there.
“I’ve always been more in favor of learning to recognize existing local enemies so you don’t work against them,” says Whitney Cranshaw, professor of entomology at Colorado State University. Many times, he says, landscapers will mistakenly wipe out beneficial insects in their attempt to eliminate other insect pests. “Know the key players. Identify them and work to create an environment that appeals to them.”
Common beneficial insects include lady beetles (ladybugs), green lacewings, predatory mites and parasitic nematodes (entomopathogenic nematodes). Lady beetles and green lacewings are general predators that consume a variety of insect pests; predatory mites feed on other mites and thrips; and nematodes target various soil pests including white grubs, mole crickets and caterpillars.
Food is often all the encouragement these local beneficial insects need to give them staying power, but it has to be more than a few isolated plants. You need a large area of host plant material to keep the good guys around for the long term.
In addition to making sure beneficial insects have enough food, Cranshaw recommends diversifying. “Use of certain flowering plants will provide nectar and pollen that can help supplement dietary needs. Also look for plants that can provide adult food needs.” To help conserve natural enemies, cut back on pesticide use or try using a more selective product that won’t also kill the good bugs with the bad.
Weighing the benefits
Using biological controls to reduce pest populations has its advantages and disadvantages.
Pros: They embody sustainability, offering long-term solutions and working for you when you are not there. Once established, they have the potential to keep pests in check.
There is less need for chemical control. To some clients, even the perception of fewer chemicals is enough incentive to embrace biological controls. Plus, fewer chemical treatments mean fewer man hours for you. If biological controls are established, resulting in long-term benefit, they are economical.
Cons: The process takes time. Time for establishment and sometimes time to fail (beneficial insects leave), reassess and start again with a new predator. It requires patience from you and your client.
Environment factors out of your control often determine the success of biological controls or eliminate them as options.
You and your client may have to learn to tolerate a certain threshold of pest and damage in the landscape.
Bringing in the bugs
Introducing predatory/parasitic bugs to landscapes in an effort to establish them as a means for long-term pest management falls under the classic definition of biological control. Your success will depend on timing, region and, of course, food supply and ecosystem.
“Biological pesticides should be customized to the region and weather (lady beetles, for example, don’t do well in heavy rainfall),” says Anand Persad, entomologist and regional technical advisor and lecturer at The Davey Institute in Kent, Ohio. A successful introduction requires research. “Technicians need to be proficient in the tri-trophic complex: the predatory or parasitic organism, its preferences and how it will impact the target pest.”
Applicators should know, for example, whether they will need to purchase adult bugs or their larvae, depending on timing and environment. If adult lady beetles are released, for example, without adequate food supply, they will likely fly away to the nearest food. “The larval form however, cannot fly away, so you may need that form initially,” Persad says.
While more and more grounds managers are implementing biological controls, Persad says use varies by market and region. In Canada, for example, where the use of synthetic products is heavily restricted, this method is employed often, but it’s not a strategy everyone can utilize due to regional limitations or because of the pest they are working with.
“It depends on your situation,” he says. “Biological control is not ideal for every landscape. You must have an ecosystem that will sustain and proliferate the beneficial pest. That’s step one. You must also be working in an environment that can tolerate pests at an aesthetic threshold.”
In other words, this method won’t be the best form of control for every client, particularly those who are unwilling to tolerate a certain degree of damage to the landscape. But for those clients who can accept some bad with the good it can provide a viable alternative to traditional pest control or as a strategy to moderate the need for chemical intervention.