Developing Augmented Biocontrol Recommendations for Tree Fruit Growers
When growers use a pesticide to control insects, they have a lot of information at their fingertips. The product’s label tells them what crops and pests the product can be used for, as well as the rate to apply and any temperature limits to be aware of.
Biological control insects, like lacewings, don’t come with such labels.
So for growers trying to incorporate lacewings or other natural insect enemies into their pest-control strategy – especially those buying biocontrol insects and adding them to their fields or orchards – it’s pretty much been trial-and-error.
Rebecca Schmidt-Jeffris is working to change that.
With funding from the Western IPM Center, Schmidt-Jeffris, a research entomologist with the U.S. Department of Agriculture’s Agricultural Research Service stationed in Wapato, Washington, is working to develop augmented biocontrol recommendations for the state’s tree fruit growers.
The goal is to provide growers with the same kind of information they can get for a chemical pesticide for biocontrol insects – which species work against which pests, the rate to apply, the best methods to apply them, the right time to apply them and, perhaps most importantly, how not to apply them.
“We’re asking all the same questions you would ask about applying a chemical pesticide but with living things,” she said. “It gets so much more complicated because they interact with their environment and with each other.”
Schmidt-Jeffris is focused on the tree-fruit-growing region of central Washington which produces apples – including about 90 percent of the country’s organic production – as well as pears and cherries. Codling moth is the biggest pest of apples and controlled through an area-wide mating disruption program and careful management. Pear psylla is the major insect pest of pears.
Her biocontrol research targets secondary pests like aphids, mealybugs and various mites – arthropods that can be controlled by natural predators but can also flare up and damage trees and fruit when those predators aren’t around.
The region has hot, arid summers and cold winters, so the first question is which biocontrol insects can thrive there. There are, for example, two different species of commercially available lacewings and one may be better adapted than the other. Knowing which to order matters.
“The next question is that lacewings, when you order them, come packaged in a variety of ways,” Schmidt-Jeffris said.
Growers can buy lacewing eggs or lacewing larvae, and they can be packaged loose in a material like rice hulls or vermiculite to make them easy to shake out and apply, or eggs can be attached to small cards which are hung on individual trees.
“The grower questions we have are which life-stage to release and dispersal method to use,” Schmidt-Jeffris said. “The larvae are more expensive because they take longer for the insectary to produce, but they’re probably a little hardier and a bit better able to defend themselves from predators in the orchard, like ants.”
So are larvae better despite the additional cost, or is there an application rate for eggs that is just as good?
The ideal application method is another open question. Sprinkling eggs or larvae every so often in an orchard isn’t very precise – “humans are not great metering devices,” Schmidt-Jeffris notes – but hanging cards with 200 unhatched eggs has its own potential downsides.
“With cards, you’ve got all these eggs concentrated together,” she explained. “Are we creating a predator smorgasbord? If an ant finds them, do they all basically get wiped out? And baby lacewings are cannibals. Do the first couple of lacewings that hatch just end up with a really good meal?”
The team has cameras trained on hanging cards to try to answer that question.
Ring the Dinner Bell, Provide a Snack
Timing a biocontrol insect release is another decision growers have to get right. Deploy them too early, before the pest species has emerged, they won’t have anything to eat and will leave the orchard looking for food. (Or they can all be killed by a late frost; farming is hard.) Deploy them too late and the pest insects can cause unacceptable levels of damage before the natural enemies knock down their numbers.
To try to thread that needle, Schmidt-Jeffris’ team is trying a tactic she calls “ringing the dinner bell and providing a snack.”
Plants under attack give off distress odors which have been synthesized and put into lures to attract predator insects, who believe there will be plant-eating pest insects to be found. Putting these chemical lures in an orchard is the dinner bell.
The snack is tying strips of plastic tape coated with brine shrimp eggs (sea monkey eggs for those old enough to remember sea monkeys), throughout the orchard.
“That basically provides the predators something to eat when pest levels are low, hopefully keeping them around a bit longer or encouraging them to stay put,” Schmidt-Jeffris said. “They’re getting all the signals that there’s something good here and they should stay in the orchard.”
Make the Mistakes Now So Growers Don’t Later
While many of the research questions could take years to answer, Schmidt-Jeffris’ team already has some recommendations about things that just don’t work. Here are a few:
Daylight releases of winged insects – If you’re releasing winged insects like ladybeetles, do it after dark. Daylight releases, especially the really cool-looking releases from drones overflying an orchard, just lead to the insects flying off toward the sun and scattering in your neighbors’ fields.
Remember your box of biocontrol bugs are living things. Growers new to ordering insects through the mail sometimes forget to check to see if the right insects arrived or if they arrived alive, and a few have forgotten to keep them cool until they’re dispersed.
Don’t spray – pretty much anything – right after an insect release. Even if the chemicals in the spray don’t harm the insects, the airblast application blows the beneficial insects out of the trees.
“One challenge our growers are facing is that they’re doing releases right around the same time they’re doing their fire blight chemical applications,” Schmidt-Jeffris said. “And those sprays are definitely not optional because you run the risk with fire blight of a disease that can kill the tree. So we need to know how long these sprays might be harmful to the beneficial insects. Can they do a release two or three days after spraying? Do they wait a week? It’s an important question.”
And it’s just one of many.
“The questions are fairly infinite,” Schmidt-Jeffris said. “I will never be bored.”