Orchard growers in many regions of the nation face serious pest challenges throughout the growing season. Spray programs can include various control agents from dormant oils to organophosphates and carbamate pesticides. Although all offer control of insect populations, their modes of action can affect other organisms. In the short term, these pesticides can be effective in controlling serious insect pests in the orchard; however, their nondiscriminatory nature means potentially harming populations of beneficial insects, pollinators, wildlife and microbes that contribute to a healthy orchard ecosystem.
One project dedicated to the study of biocontrols is called “Enhancing Western Orchard Biological Control”, a collaborative project led by Washington State University. Its multipronged mission involves research on the effects of pesticide use on the natural pest enemies found in orchards, and methods to improve integrated pest management (IPM) programs in orchards through enhanced biocontrols.
On the East Coast, Penn State University Tree Fruit Research Entomologist David Biddinger’s research focuses on IPM in the orchard and minimizing the impact of pesticides to “preserve the good bugs” via conservation biocontrol methods. Biddinger has been working for decades to assist orchard growers in the proper timing of pesticides to best control pests that results in the least impact on beneficial insects. Another important component of his work is in conserving the natural wild pollinator population, which thrives in the fence rows and woodlots commonly found bordering the region’s orchards.
“Only one insect out of 100 is a pest,” Biddinger said. “There are a lot of others that could be beneficial,” and all farmers can benefit from the natural biocontrols present in the orchard if they work to “conserve what’s already in the system.”
Primary orchard pests – those that feed on the fruit, rendering it unmarketable – require more control than natural enemies can provide. Secondary pests can be controlled with biocontrols “if you don’t disturb their natural enemies,” he said.
A common misconception is that biocontrols are products that are purchased – an example is Trichogramma egg parasitoid – and released into the orchard. Although this is one route for implementing biocontrols, Biddinger prefers to focus on providing habitat and protecting those predatory bugs that already call the orchard home, or would if they could survive there.
Biocontrols are methods of controlling pests using their natural enemies. These enemies fall into four categories, with differing modes of action. Parasitoids, parasites, predators and pathogens are all part of the biocontrols arsenal; all work differently, and often in conjunction, to keep pest thresholds low.
Many growers are familiar with the use of the pathogen Bacillus thuringiensis (Bt). In apple orchards, Bt combats leaf rollers that feed on and damage apples. Today, leaf rollers are no longer major pests of concern to growers in the eastern region of the U.S. Bt toxins are somewhat host-specific, and none work on codling moth, one of the primary pests causing damage in the Northeast, so they’ve fallen out of favor here, Biddinger said.
Predators are not prey-specific. They are generalists, eating whatever is most available to them. Parasitoids are host-specific for at least one stage of their lifecycles, typically immature stages, and will kill the host. Parasites don’t kill their hosts, but can weaken it. Pathogens – such as the Bt – can be fungal, bacterial or viral in nature, and attack the host.
Using biocontrols effectively often requires combining them with other methods of pest control. But this must be done carefully when products toxic to the beneficial insects are used.
Although good bugs can develop resistance to pesticides, they generally do so over a much longer time period than the pests, Biddinger said. Growers can use IPM guidelines to apply pesticides when they are most likely to harm the pest, yet still allow beneficials to thrive.
Mating disruption, particularly for codling moth and Western peach tree borer, is one less lethal control method. Mating disruption works best on a large scale. If one orchard is using mating disruption – using pheromones to confuse the male insects – but neighboring growers are not, its effectiveness declines. Biocontrols can enhance the effectiveness.
Pyrethroids should not be used in apples, Biddinger said, due to their extreme toxicity to the good bugs. With the recent brown marmorated stink bug (BMSB) concerns, many growers returned to using these to combat this new pest, disrupting the populations of orchard beneficials. Rebuilding of the biocontrol populations is now happening, as the BMSB is less of an issue and appears to have found a biocontrol of its own: the ladybird beetle, which will eat its eggs.
Success in orchard biocontrols includes use of the parasitoid Aphelinus mali, which solely targets the wooly apple aphid when colonies are small. In conjunction with a combination of syrphid fly species, plus the predatory brown and green lacewings, control is augmented.
There has been a 90 percent decrease in miticide use in Eastern region apple orchards, thanks to “the most successful biocontrol program on the East Coast,” Biddinger said. The program involves conservation of the native populations of mite predator, such as Typhlodromus pyri, to control the European red mite and the twospotted spider mite – serious pests.
The “Enhancing Western Orchard Biological Control” short course is available for viewing
Penn State Extension, “Natural Enemies/ Biological Control in Orchards,” by David Biddinger
Promoting orchard beneficials
Biocontrol programs use organisms, harmless to the crop, to keep a crop pest in check, preventing it from reaching damaging population levels. But beneficial organisms aren’t always readily available to do their jobs. Often, orchard practices can harm beneficial microbes and insects, rendering them ineffective. The orchard environment may not provide a place for these insects to thrive, or offer them an alternative food source or a safe place to overwinter.
Ground cover often provides habitat where natural enemies can thrive and remain in the orchard throughout their lifecycles, enhancing their ability to provide pest protection. Planting nectar sources for adult stages of parasitoids increases longevity and reproduction, as many feed on nectar, for example.
One problem with orchard ground covers is the bloom time. With most annuals and perennials blooming after the apples, they aren’t attracting pollinators at the right time. Biddinger has found that the woodlots and fence rows, where a variety of earlier-blooming trees and shrubs are found, work best for native bee habitat. By providing this natural habitat, farmers are able to take advantage of the pollination services of over 40 species of wild bees, saving costs of renting or maintaining honeybee hives, Biddinger said.
In a natural system, a complex mix of biocontrols often occurs. But without all the players doing their jobs, that balance can be upset and pests can thrive. Conservation biocontrol promotes orchard habitats where a natural mix of insects keeps the pest controlled, wild bees can provide pollination and farmers can produce a crop while spending less money on orchard sprays, without any reduction in yields or quality.