Encouraging Native Pollinators in Apple Orchards
Bee balm, a perennial that blooms from early to midsummer, is a great attractant for most bee species.
Photos courtesy of Jim Gillis, NRCS, Adams County , Pa.
Despite the challenges that come with creating habitat for native pollinators, the bottom line is that establishing such habitat may improve apple blossom pollination.
Is possible improvement enough of an incentive?
Growers are frustrated with the increasing difficulty of keeping bees, the rising cost of hive rental, and the disappearance of feral colonies. Establishing wildflowers and native woody species to attract native pollinators sounds like a great idea, but it isn't easy.
Penn State tree fruit entomologist Dr. David Biddinger is working to help growers solve the pollinator dilemma by monitoring pollinator populations and noting how they change over time. He acknowledges the decline in honeybees, but says there are numerous reasons for it, including the use of insecticides for mite treatment, pesticide applications to crops, and loss of natural habitat.
Even if honeybee colonies weren't declining, the species is far from being the perfect pollinator. For example, Biddinger says that honeybees prefer multiple food sources, and if a hive is placed in the middle of an apple orchard, the bees might choose to visit nearby dandelions instead of apple blossoms. Research has shown that as little as 10 to 20 percent of the pollen from a honeybee hive in an apple orchard is from apples, while Japanese orchard bees (Osmia cornifrons) tend to carry at least 95 percent of the pollen of the orchard they're in.
A midsummer blooming meadow draws bees, but not in time for apple pollination.
To help growers meet the challenge of securing reliable pollination for orchard crops, Biddinger is part of a team working on developing habitat for native pollinators. The project, which started in the fall of 2010, is a cooperative effort between the U.S. Department of Agriculture Natural Resources Conservation Service (USDA NRCS) and about 25 growers in Adams County, Pa., who have established a total of about 150 acres of pollinator habitat.
"We helped plan the mix [of plants]," Biddinger says. "The original idea was that it would help bees - there were flowers that bloomed all season long - but it hasn't helped us identify bees that pollinate apples."
One problem is that the flowers in the pollinator mix bloom in early summer, which is too late for apples. There's also the issue of which bees are active at the ideal time. "There's a core group of about 40 to 50 bee [species] that we know help with apple pollination in spring. Most of those are in a group that comes out early in spring and has only one generation," Biddinger explains. He adds that the plantings help bumblebees, which build multiple generations through summer, but those colonies usually die back to a single queen in winter.
Osmia species nest in existing holes and can be encouraged to nest in man-made boxes such as this one.
Once established, a pollinator habitat, or meadow, lasts for up to five years. However, planting requires special drills that can handle the tiny seeds. The seed is expensive, up to $100 per pound, and seeded at a rate of 4 to 8 pounds per acre.
Biddinger suggests that growers figure out what crop they want to have pollinated and aim for pollinator habitat suitable for the bee species that will be active at the critical time. "Tailor the NRCS mix to the crop you want," he says. "For apples, we've planted more woody perennials, such as red maple and redbuds, that bloom early but not at the same time as apples. Those species will help the [pollinator] populations that come out real early in spring with some extra food, then when apples bloom they'll do a much better job pollinating apples."
Issues in establishing habitat include weed control and seedbed preparation. "We used Roundup in the fall, and a lot of the fields turned out to be very weedy," Biddinger notes. "We have to do a lot more preparation before we plant." He adds that although different drills were tried, a push-type fertilizer spreader designed for use on home lawns worked best, and mixing kitty litter with the seed helps distribute the seed more evenly.
Although new pollinator habitat plantings sometimes followed cover crops, many of the plantings were in old orchards that were mostly grass and dandelions. Biddinger says, "There's so much wild habitat surrounding orchards that weed seeds enter the prepared fields no matter what kind of preparation is done, and we have to use no-till because turning the soil brings up new seeds."
Many of the varieties used for pollinator habitat require cold stratification, so spring planting means that seeds lay dormant all summer and weeds get ahead before the flower seeds germinate. To minimize the weed issue, seeding should be done in the fall.
Biddinger and the team are still trying to determine the ideal placement for habitat strips. "Ideally, strips should be 'stepping stones' from the woods, where there are wild populations," he says. "If a bee flies 200 yards, you want the pollinator strip within that 200 yards so they can fly in from the woods and get established there. Osmia tend to live in dead trees and hollow cavities. We can enhance flower strips for Osmia by putting in wooden blocks so they have places to nest. They have food and a shelter away from pesticides."
Which pollinator species seem to work best? Biddinger found nine species of Osmia, eight of which are native, in apple orchards. Of those, O. cornifrons is the most abundant. "We've put them in wooden blocks or straws, cleaned out the parasites, and moved them from site to site when they go into a cocoon in winter," Biddinger says. "We can hold them in the refrigerator to fool them into thinking it's a long winter, and bring them out at apple bloom. Normally, they come out about three weeks earlier, at apricot bloom."
Biddinger notes that work he has done at the Penn State Fruit Research & Extension Center has shown that the ingredients in tank mixes can have a negative synergistic effect on pollinators. "We know what each one does by itself, but we don't always know what happens when they're in combination," he states. "There's also a possibility that certain adjuvants may have a negative effect."
Another finding is that certain pesticides are much more toxic to honeybees than to wild bees, and vice versa. "It's on a case-by-case basis, so you have to do the work to be able to say what's really going on," says Biddinger.
For more information on pollinator conservation efforts, visit the Xerces Society website at http://www.xerces.org/pollinator-conservation.
The author is a frequent contributor and freelance writer who farms and raises Great Pyrenees in south-central Pennsylvania. Comment or question? Visit http://www.farmingforumsite.com and join in the discussions.