Let natural enemies play a role
IPM means managing pests, not eliminating them.
Growers today tend to think that integrated pest management has to do primarily with monitoring pests and scheduling pesticide applications.
But that’s not what IPM was envisioned to be at the outset, Dr. Nick Mills, entomologist with the University of California, Berkeley, told growers during the Washington State Horticultural Association’s annual meeting.
Twice during the past 20 years, the National Academy of Sciences has revisited the idea of what IPM is and what growers should be thinking about in implementing IPM, he said. They see IPM as an ecologically based system that seeks to manage, rather than eliminate pests.
“I think that’s a really important concept,” Mills said. “We still think
of using insecticides to eliminate pests, but what you really need to do is not eliminate them, but manage them in an ecological way so that natural enemies and biological control can play a greater role. This needs to be done in a profitable, safe, and durable way.”
In 2010, the National Academy issued a publication entitled “Toward Sustainable Agricultural Systems for the 21st Century,” which emphasizes the need to reduce pesticide use through a greater focus on cultural techniques, resistant varieties, and biological control.
“So, the way we think about IPM is changing, and it’s something that we should be considering more and more as we move towards the future,” Mills said.
Mills said there are several reasons why it’s in the grower’s interest to enhance biological control. It’s a natural pest control system that’s available at no cost. Natural enemies reduce the need for pesticide applications, which are an additional cost. By allowing growers to minimize the use of pesticides, they reduce risks to human health and the environment and help preserve food, water, and air quality—all of which will become more important in the future.
Sixty years ago, University of California scientists introduced the concept of integrated control as a system that combines and integrates biological and chemical pest control, with chemical control used as necessary and in a manner that’s the least disruptive of biological control.
The failure to recognize that the control of pest populations is a complex ecological problem has led to the error of imposing insecticides on the system rather than fitting them into it, they wrote. The ideal pesticide is not one that eliminates all individuals of a pest species. It's the one that shifts the balance back in favor of natural enemies.
“I think that really captures a lot about what we need to know about IPM,” Mills said. “We’re not looking to eliminate pests from the system. If we did that, we lose our biological controls forever. We’re looking to redress
the balance, the shift between the numbers of natural enemies there relative to the number of pests.”
Mills said those scientists recognized the important role of biological control in IPM, but growers still struggle to come to terms with that concept today.
During the past 15 years, the tree fruit industry has made increasing use of mating disruption for key pests, which has led to a reduction in pesticide use and consequently allowed natural enemies to provide much more effective biological control of secondary pests.
There are no natural enemies in place for the new invasive pests spotted wing drosophila and the brown marmorated stinkbug yet, so growers will need to resort to pesticides, Mills said.
“What we have to bear in mind as we manage these new invaders is the insecticides are going to impact all the natural enemies that are doing such a good job in managing the secondary pests in our orchards, and if we’re not careful, we will disrupt that biological control. The choice of insecticides is going to be really important in how much biological control you may retain in your orchards when you’re managing a new invasive pest.”
As use of standard organophosphates, such as Guthion (azinphos-methyl), ends, growers will need to understand the potential consequences of the alternative pesticides they use, he said. “Natural enemies can be very sensitive to pesticide use, and if we have incompatible insecticides in our system, those natural enemies will struggle,” he said.
Many of the pesticides from new classes of chemistry are interesting to growers because they have lower mammalian toxicity than the older pesticides and so are safer for workers, but in many cases it’s not known how compatible they are with natural enemies.
Natural enemies tend to be more exposed to pesticide residues than pests because they’re more active and are searching across the leaves all the time, looking for hosts to attack, whereas the pests sit still and feed, he said.
“We have complex orchard systems, and we have to realize that pest management is not just throwing pesticides at a pest,” Mills said. “Those pesticides are affecting the system in complex ways. Biological control can play a much greater role for us if we have sound information to work from and if we implement that information effectively. It’s too late to appreciate the value of biological control when you’ve lost it.”