Plum curculio continues to pose a threat to fruit growers. But with research being conducted across the fruit-growing realm, plum curculio might face more focused resistance in coming seasons.
Andrea Coombs, a research technician at Michigan State University (MSU), is working with Dr. Mark Whalon and other researchers to trap, monitor and better understand the habits of plum curculio.
“Plum curculio is a native beetle that occurs east of the Rocky Mountains,” Coombs said. “Plum curculio has been found in backyard situations in Utah – west of the Rocky Mountains.”
Coombs said that plum curculio adults become active early in the spring and mate before bloom, and females are ready to lay eggs in the fruit at fruit set.
“Plum curculio causes two types of damage,” Coombs said. “Oviposition, or egg laying, stings cause serious economic damage to apples and cherries. Plum curculio also cause damage by feeding; however, this type of damage is less significant.”
To find plum curculio and look for its damage, growers can use monitoring traps on the borders of orchards in the early spring, Alternatively, Coombs said, growers can wait until after fruit set and look for fresh crescent-shaped oviposition scars on the fruit.
This year, the team of researchers found that plum curculio had a different path of action.
“Plum curculio populations were relatively low during the early part of the season; however, late season populations were very high,” Coombs said. “For example, peak capture in monitoring traps usually occurs at petal fall, but this year, we captured almost three times as many plum curculio after cherry harvest than we did earlier in the spring.”
Pyramid traps have been used to trap and monitor plum curculio for many years. The trap that Whalon’s team is using is a modified version made out of black, corrugated plastic with white stripes on the edges to make the black pyramid shape more apparent to the plum curculio.
“The trap exploits two fundamental plum curculio behaviors,” Coombs said. “One, they find host trees by searching for tall, dark silhouettes against the horizon. And, two, their natural behavior is to climb.”
As the plum curculio finds the dark silhouette of the pyramid traps, it lands and climbs immediately to the top. Once at the top, it enters into a cone that traps it – plum curculio cannot figure out how to escape.
The traps also include host plant attractants attached in a net bag at the top of the trap in order to lure the plum curculio.
Eric Hoffmann is a research technician whose job focuses on attracting the plum curculio to the trap.
“A lot of what we’ve done, it’s pretty much a continuing process of trying to find better chemistries to make our traps better at catching plum curculio so the growers can better time their control measures in the field,” Hoffmann said. “A lot of what we use are fruit volatiles and also some minor chemistries – plum essence and benzaldehyde, that is essentially that maraschino cherry smell that is sometimes called ‘almond essence.’”
Hoffmann said that those are the two major ways they lure the plum curculio into the trap. With effective odor combinations, Coombs can focus on when, where and how to most effectively trap the plum curculio, Hoffmann said. As these researchers learn more about optimizing these traps, they are able to enhance the decision-making process of the growers when it comes to controlling this pest. Coombs said that the trapping system they are using has proved successful in educating them on plum curculio’s actions.
“For many years, entomologists believed that plum curculio migrate into the orchard from surrounding areas early in the spring; however, we have found that plum curculio will overwinter in cherry orchards,” she said. “Using the pyramid traps, we have determined that there is a point in the season when we no longer capture reproductively mature plum curculio and we begin to capture the ‘summer generation,’ which will overwinter and cause damage the following spring.”
The research showed that plum curculio are active in the orchards in high numbers after cherry harvest, Coombs said.
“This would be an excellent opportunity for growers to control plum curculio to protect next year’s crop,” she said.
“Plum curculio is traditionally controlled by an insecticide – usually organophosphate – spray at petal fall and again later in the season if needed,” Coombs added.
The modified pyramid trap is available through Great Lakes IPM in Vestaburg, Mich., and IPM Technologies in Portland, Ore.
