Cherry Growers Now have a new Option for Managing Leafrollers and Spotted Wing Drosophila – Emamectin Benzoate

Author – Katie Chriest

By now, the legend of young George Washington confessing that he’d chopped down a prized cherry tree is widely accepted as myth. Nonetheless, cherries remain a cherished part of our country’s heritage. From u-pick orchards to cherry festivals, these delightful red orbs are beloved symbols of summer.

Despite this popularity, life isn’t always “just a bowl of cherries” for growers. Pests like the obliquebanded leafroller (OBLR), a native which is resistant to pyrethroids and organophosphates, have proven hard to manage. But thanks to IR-4, growers now have the use of emamectin benzoate to control this troublesome pest.

“For most of my 28 years at Michigan State University (MSU), obliquebanded leafrollers were considered an important pest in apples, but not in cherries. It was really in the last decade that they began to be a problem as a contaminant pest,” explains John Wise, a professor in the MSU Department of Entomology, and Research and Extension Coordinator of the MSU Trevor Nichols Research Center.

“OBLR can be an important pest in sweet cherries as well as tart cherries, but there’s a unique situation in tart cherries that causes a different type of risk to tart cherry growers,” Wise continues. “Tart cherries go into a cold water washing and cooling procedure after they’re mechanically harvested. And because of the marketing order associated with tart cherries that demands a USDA inspection for pests in those tanks, any leafrollers that are detected are considered a contaminant.”

He adds that while sweet cherry growers are certainly concerned if there is significant injury to their fruit from leafrollers, “that can be handled more readily in an IPM scouting mechanism, where the insect can be monitored with pheromone traps, and/or visual sampling, and then action can be taken.”

But for tart cherry growers, the presence of OBLR can lead to substantial loss. “It’s an unintended consequence of a policy that was designed to keep this food product safe and healthy for consumers,” Wise says. “But in the end, it drives growers to have a very high concern over the condition of their crop at the time of harvest.”

And it doesn’t take many leafrollers to ruin a harvest, Wise adds. “Theoretically the leafrollers might not even be feeding on the fruit, but if they fall into the tank, or if they’re shaken from the tree by the mechanical harvesters and end up in the cold water tank, detection leads to an automatic rejection of that load.”

USDA figures from 2017 rank the US as the world’s second largest cherry producer overall, and tart cherry production remains a vital part of specialty crop production industries in the Great Lakes states, Wise explains. “However, it’s fair to say that there have recently been a number of challenging pressures,” he says, and “OBLRs were very high on the radar. The spotted wing drosophila (SWD) has also become a real burden on the industry, because it has been quite difficult to handle. That, and global markets – the influx of cheap subsidized cherries from Turkey – have been another problem for US tart cherry producers.”

Machine designed to harvest cherries. It has arms holding heavy cloth that surround the base of the cherry trees. The bottom part is in contact with the base of the tree and shakes it to dislodge the ripe fruit. Not all the fruit ripen exactly at the same time, so they can return to each tree and shake it again. The cloth catcher softens the drop so less bruising occurs. Photo courtesy of Cristi Palmer, IR-4 Headquarters.

At least now there’s one less hurdle for growers to clear. Still, the pressure to control SWDs has greatly affected cherry IPM.

“Growers’ use of certain compounds to manage SWDs may result in OBLR becoming a bigger problem in the future. Even if leafrollers aren’t being targeted, they will be exposed to the same compounds if they’re in the canopy at the time near harvest when SWDs are being managed,” Wise explains.

He notes that the synthetic pyrethroids, and the spinosads and organophosphates being used against SWDs could result in an OBLR flare-up, “which makes it important that a very different chemistry in emamectin benzoate will be available.” This is especially true in early season, since spinosyns and diamides, while also effective on OBLR, are generally held for late-season SWD control.

“OBLR tend to develop resistance very quickly,” Wise adds. “The patterns that growers were using were disruptive to biological control agents and natural enemies, and the leafroller broke through the materials being used. They can be explosive in that way.”

Wise says that “a number of parasitoids are quite effective. You rarely see OBLR in a noncommercial setting, because they tend to be balanced and suppressed in more natural environments. It’s in commercial systems where products are knocking out biological control—that’s where we see them.”

Previously registered products were inadvertently eliminating natural predators, when we needed selective pesticides to—ahem—“cherry-pick” the OBLR.

“Those were mostly what I would call ‘20th-century chemistries,’ and many of the newer compounds that are registered through the IR-4 Project like emamectin benzoate are important tools to have in the toolbox,” Wise explains.

He emphasizes IR-4’s ability to usher those better tools into growers’ hands as a critical complement to the work of land grant entomologists and other pest management scientists.

“Groups of researchers are able to retain grants to address big new problems like SWDs or brown marmorated stinkbug. But once they understand the biology of these new pests and how to monitor them, and they’ve identified two or three compounds that are really important—that group of scientists doesn’t have any way to bring those compounds to the farmers.”

Through reaching out to IR-4, however, “scientists or farmers can submit a request and say, ‘We really need this product in tart cherries,’ and then IR-4 can get the packet together and submit it to the EPA to provide a legal use.”

Wise emphasizes that “all of the new chemistries or compounds are much safer for the environment and for workers and consumers than the products that were available in the 20th century.” He adds that research packets submitted to the EPA include substantial field data that demonstrate each product’s lack of substantive risk to consumers, when used as directed.

“It’s really a robust, research-based process that we should have confidence in if we use the products correctly,” he states.

That’s great news for growers and consumers—with a cherry on top.

PR# 10685 Cherry (Obliquebanded leafroller)

Katie Chriest is a freelance technical writer in Erie, Pennsylvania; kmc503@psu.edu.