Orchardists face two new invasive pests

Insect pests are in U.S. orchards in every part of the country and have a long history of wreaking havoc. Some pests are persistent and have required decades of work before control has been obtained. With each new wave of pests, researchers and growers must focus on the most serious problems at hand while continuing to control previously established pests. The brown marmorated stinkbug (BMSB) in the mid-Atlantic states and the spotted wing drosophila in western states are two of the newest invaders that warrant concern as orchard threats across the country.

Damage caused by the brown marmorated stinkbug.

Brown marmorated stinkbug moves to orchards

Although identified in 35 states, damage to orchards by brown marmorated stinkbugs to date has been primarily to apple crops in the mid-Atlantic states, where an estimated $37 million in damage was caused in 2010, according to the U.S. Apple Association. The damage was primarily in lowering fruit quality, which required fruit to be diverted from fresh markets to processing or juice production.

“Pesticides are a temporary stop for a growing problem,” said Dr. Greg Krawczyk. “But as more scientists across the country begin to bring attention to the brown marmorated stinkbug, I am optimistic that within a few years, a longer-term solution will be found and utilized.” Krawczyk, a tree fruit entomologist at Pennsylvania State University, is one of about 50 researchers across the country intensely looking for answers to control this new orchard pest.

Currently, there’s a joint BMSB working group operating within the Northeast IPM Center that includes researchers from around the U.S. Krawczyk said, “These researchers have applied for federally funded research grants to cope with this growing challenge.”

A longer-term solution is what growers and scientists are banking on, but in the meantime, growers are utilizing all the tools at hand to combat this latest pest as they have previous invaders into their orchards. Krawczyk has begun immediate research partially funded by a $50,000 grant from the Pennsylvania Apple Marketing Board and the State Horticultural Association of Pennsylvania. While this two-year research project is but one of numerous approaches around the country, its goal is to offer some early insight into management options.

A healthy shoot contrasts with one showing bronzing that accompanies European red mite feeding.

Krawczyk noted that the BMSB was officially identified in Pennsylvania in 2001, with significant detectable orchard, vegetable and row crop damage occurring in 2009. “We think it has probably been here since the mid-1990s, but it was misidentified,” Krawczyk said. A number of native stinkbugs are common in the mid-Atlantic region, with the invasive brown marmorated stinkbug arriving from Asia, where it had been active in Japan, Korea and China. More than 300 wild and cultivated plant hosts have been identified that the brown marmorated stinkbug feeds upon. “They don’t need fruit or vegetables to survive,” Krawczyk said. The high number of diverse hosts is an important point in the ability of the BMSB to survive and multiply. The pest overwinters in protected areas such as homes, mini storage units and protected undergrowth.

Current control procedures

While no currently existing control for the BMSB completely conforms to most IPM standards, orchard managers are looking at products that will help alleviate their immediate problems. Dan Sherrod, DuPont product development manager for insecticides, noted the importance of trying to maintain the IPM standards in managing orchard pests.

The brown marmorated stinkbug is a new invasive pest.

Most effective insecticides for BMSB are broad-spectrum and may not be IPM=compatible. Products such as Vydate L and Lannate LV and SP may be used for management in some states. Timing for any control approach is crucial. Sherrod cited four approaches that must be taken in managing this new problem. “Growers should seek advice from state cooperative extension entomologists, professional consultants or other qualified authorities to determine appropriate action in developing a management approach,” he said.

Sherrod suggested that after reaching a consensus, growers should follow these recommendations in carrying out the approach to management:

  • Monitor the pest to know exactly what is in the crop
  • Select the appropriate application insecticide that fits the need
  • Set the rate and timing
  • Manage applications and apply only where the problem actually has been identified, in some cases including the surrounding vegetation

Sherrod emphasized the importance of following good IPM practices, particularly in rotating chemicals with differing modes of action to help in resistance management.

Spotted wing drosophila

The spotted wing drosophila originated in East Asia and was discovered in California in 2008. It has been established in Hawaii since the 1980s and is widespread, with identification in Oregon, Washington, Utah and Michigan. Dr. Douglas Walsh, entomologist at Washington State University, said, “We didn’t expect this level of damage from it.”

While sweet cherries are a major concern, berries are significant hosts for the spotted wing drosophila, which attacks soft-skinned fruit. Drosophila flies, also known as vinegar flies, have been in the Northwest for years, but a primary difference is that the new spotted wing drosophila attacks ripening fruit rather than mostly rotting fruit as the traditional drosophila flies have done. In addition to compromising the marketability of the crop, the spotted wing drosophila greatly increases opportunities for other pests.

The spotted wing drosophila poses a major threat, but growers may get two major breaks. The cold winter of 2010 may have helped in mitigating the damage to some degree. Walsh said, “We had a very cold snap in November 2010, and this spring and summer have been very cool. These are factors that we speculate have led to the slow development of large populations in 2011.”

A second break for growers is the timing that the spotted wing drosophila reached its major population development. Walsh said, “We basically can detect spotted wing drosophila at low population densities about anywhere we look. Populations have been low to date, and if we have a repeat of what we observed last year, we will get our greatest abundance in mid to late fall. Fortunately, this is after most commercial fruit have been harvested and marketed. We speculate that these late populations are developing in wild host plants like Himalayan blackberries.”

The brown marmorated stinkbug.

Control approaches

As the pest has moved north from California into Oregon and Washington, a regional approach has been developed to evaluate pesticides, management guidelines and monitoring. While long-term management has not been determined, a successful IPM strategy will need to focus on reducing breeding sites and controlling adult flies.

Control recommendations emphasize that knockdown controls be applied quickly, since no registered insecticides will control larva that develop within the fruit. Chemicals must target adult populations to eliminate the adult flies before they mate and lay eggs.

Promptly removing any infested fruit and destroying by burning, bagging or freezing is urged. Any ripe, overripe or rotten fruit should be removed promptly to avoid increased feeding opportunities for the spotted wing drosophila.

Codling moth larva feeds internally on fruit.

Traditional orchard pests

Along with the BMSB and spotted wing drosophila, traditionally established pests continue to pose concerns. Scientists emphasize that careful balancing of controls is important to avoid damaging beneficial predator populations that are helping to keep other pests under control. All entomologists emphasize the importance of rotating chemicals with differing modes of action.

Whether it’s New York, California or Georgia, and midwestern states along the way, traditionally established orchard pests continue to pose significant concerns and control strategies are a must. Dr. Art Agnello, Cornell University, noted that while the BMSB is not yet an issue in New York, it will be widespread. He cited the codling moth, obliquebanded leaf roller, European red mite and apple maggots as ongoing concerns.

Navel orangeworm remains a primary pest in almond orchards.

In California, which produces 100 percent of U.S. and 70 percent of the world’s almonds, the navel orangeworm continues to be a significant concern. Dr. Frank Zalom, UC-Davis, noted that sanitation techniques of removing old fruit and the use of broad-spectrum chemicals once or twice yearly are required. He noted that California has a major environmental focus, and work on mating disruptions is a primary focus for control.

Peaches are a major economic contributor in the state of Georgia. Dr. Dan Horton, University of Georgia entomologist, said “Plum curculio is the key fruit insect pest of the southeastern U.S. Management is difficult because we do not have a trap that is sensitive enough to direct as-needed sprays for growers who pack and ship to distant markets. Chain store markets have essentially a zero tolerance for wormy fruit.” In the South, plum curculio has time to complete two generations annually, adding to the problem.

“The biggest problem in the South is the longer growing season,” Horton said. “What might work well for Michigan won’t hold the line down here. We had good suppression with older organic chemicals, but with their removal we have to spray new materials at higher rates.” Horton cited long-term management through mating disruption techniques.

“The big difference in orchards is that growers will be living with any mistakes made in 2011 for a long time to come. In vegetables, we don’t have that issue.”

Nancy Riggs is a freelance writer. She resides in Mount Zion, Ill.