by Courtney Llewellyn
With autumn ending, greenhouse growers are now in the planning stages for their next season. They’re choosing which varieties they want to plant again and which ones they may want to experiment with. They’re also preparing for another year of battling harmful insects, mites and other pests.
There are a lot of tools in the toolbox for managing pests these days. Dr. Raymond Cloyd, a professor and Extension specialist in horticultural entomology and plant protection in the Department of Entomology at Kansas State University, pondered two big ones in his presentation, “Using Biological Control and Pesticides Together to Manage Greenhouse Insect and Mite Pests: Can It Be Done?”
“Greenhouse-grown horticultural crops are susceptible to a wide range of insect and mite pests, often simultaneously,” Cloyd explained. “The primary means of dealing with them are pesticides and miticides. With them, you get the psychological feeling you’ve wiped them all out, even though that’s not true.”
Another strategy is biological control: using good insects or mites to kill bad insects or mites. Biological control agents will not eradicate a pest, Cloyd said; their success is contingent on maintaining pest numbers at low levels. Using them is a preventative strategy for regular pest populations. Parasitoids, predators and beneficial nematodes are all considered biological controls, and many are commercially available.
Interest in using both control methods simultaneously is out there, according to Cloyd – and there is a lot of information about the integration of biological and chemical control available, dating back to the 1960s. The issue isn’t whether they’ll work together or not, but what the benefits are of using them together – and if doing so is cost effective.
Two things to consider are the direct and indirect effects chemical controls can have on biological controls. Directly, pesticides can result in mortality of your “good bugs.” The effects depend on the pesticide type, formulation, rate, the biological control agent type (Cloyd noted parasitoids are generally more sensitive to pesticides, and predators less so), the life stage of the biological control (egg, larva, pupa or adult) and length of exposure.
Indirectly, pesticides could impact the physiology and behavior of biological controls, such as their development time (and survival), their prey consumption, parasitism, mobility, sex ratio, foraging behavior and reproduction.
“The labels will state if they will have direct effects on biological agents,” Cloyd said. “Look at the active and inactive/inert ingredients.”
Cloyd listed the following as potential benefits of integrating biological control agents with pesticides:
- Reduced pesticide inputs, which may lower the risk of pesticide resistance developing in insect and mite populations
- Less risk of phytotoxicity or harm to plants
- A safer work environment for employees
- Less pesticide residue on plant material
Ultimately, though, the success of integrating biological and chemical agents depends on spatial and temporal interactions, Cloyd said. To avoid problems, growers must focus on the timing of chemical application and the timing of biologicals’ release.
Makes the Dream Work?
There are some potential downsides, though. Changes in pest population numbers due to pesticide application may reduce the availability of food sources for your biological controls. Predatory insects may avoid consuming prey infected by a pesticide as well. In both situations, prey search time increases, predation rates decrease and efficacy is reduced.
Additionally, parasitoids may avoid laying eggs in prey that’s been affected by pesticides. Parasitoids may also be negatively affected by a pesticide when they’re already developing inside an infected host. Both predators and parasitoids could also fall victim to the pesticide applications.
“So can they be used together? It depends,” Cloyd said. “It’s not a yes or no answer. You need to ask what would be the most appropriate for your operation.” He said there are two major questions that need to be addressed: 1) Is a pesticide needed or will the biological control agents regulate pest populations enough to avoid noticeable plant damage? and 2) Will the pesticide application enhance or disrupt the normal regulatory process?
“Think – what is practical and cost-effective?” Cloyd asked. He recommended those interested in finding the answers to these questions check out a four-hour online course called “Biological Control for Greenhouse Growers,” available at canr.msu.edu/online-college-of-knowledge/biological-control.