WSU Scientists Use Flower Power to Combat Orchard Menace
Apple orchards are intricate webs involving a delicate balance between trees, soils, water, insects, and more. To manage the pests that can potentially damage a crop of apples, growers often apply pesticides. There are several problems associated with pesticide use, though, including risks to environmental and human health, the costs of the chemicals, and the equipment and labor needed to apply them. That’s why Washington State University researchers have been pioneering alternatives to pesticide use for managing pests.
One of the most promising pesticide alternatives is biocontrol, in which a beneficial insect is encouraged by various means to prey upon the insects that cause damage to trees and fruit. WSU researchers decided to pursue this approach when they received reports from Washington apple growers of an expanding wooly aphid population lowering crop yields. The scientists started with the working knowledge that the sensitive balance of orchard ecology can easily be disrupted from a changed pest-control regime reducing the proportion of bad pests to their good natural enemies.
“Growers began noticing an increase in the number of woolly aphids in apple orchards starting in the early 2000s,” said WSU entomologist Betsy Beers. Beers is based at WSU’s Tree Fruit Research and Extension Center in Wenatchee. “There is some evidence that suggests it was a change in pesticide programs that led to an increase in woolly aphids. The question became, what could we do about it?”
Beers said that woolly aphid debilitates trees over the long term by sucking the sugar out of plants. “They are pernicious little beasts. They use the plant’s sap (phloem) as food. They not only suck sap from leaves, but also from the plant’s woody parts. They also infect the roots, reducing the plant’s ability to take in nutrients and water. In addition, they cause hypertrophic galls, which are tumor-like protuberances that can kill fruit buds. Dead fruit buds mean lowered productivity, a serious concern for apple growers. “This is one of the meaner aphids.”
Beers said that a survey of woolly aphid’s natural enemies indicated that syrphids are the most commonly seen predator in woolly apple aphid colonies. “We predicted syrphids could control the aphids–the trick is getting more syrphids into the orchard, and making sure they are happy there.”
Syrphids are more commonly known as flower flies or hoverflies. As their name suggests, they like to hang out among flowers, as the adult syrphid’s primary food is nectar. The syrphid larvae, however, grow and thrive on a diet of aphids–and woolly aphids are just dandy for maturing syrphid larvae. “It’s wonderful to watch them chew their way through an aphid colony,” said Beers.
Enter doctoral student Lessando Gontijo, who came to WSU from his native Brazil to study biocontrol. Working with his mentors, Beers and WSU biocontrol expert Bill Snyder, Gontijo set up a series of experiments to test the idea that syrphids could be used to control woolly aphid populations. The team first examined six different flowering plants for attractiveness to syrphids, and sweet alyssum won hands down. This plant is low-growing and flowers from a few weeks after planting until frost, making it ideal for use in orchards. The next step was to plant small plots in orchards, in the lanes between rows of apple trees (normally occupied by grass sod). While all the details aren’t sorted out, the aphids disappeared faster next to the alyssum plots than they did in the grassy control plots. Gontijo used a sophisticated method known as “immunomarking” to prove that the syrphids found in the apple trees had visited the alyssum flowers, further evidence that alyssum could promote biocontrol.
The results of the small-scale experiments are promising. “These experiments are the first steps in a much longer process,” Beers said. “We needed to pass the initial proof-of-concept tests: do these flowers attract beneficial insects, are they manageable in an orchard, and do we see a decrease in the pest populations? We passed all those tests.”
The next phase of the project will be to run experiments in commercial orchards. Beers said she is looking for funding to expand the work, adding “It’ll be a great opportunity for future graduate students to do good science that has a real-world impact on the way apple growers manage pests.”
–Brian Clark
Photos courtesy Betsy Beers/Washington State University. Learn more about WSU’s world-class leadership role in tree fruit research and extension by visiting the tree fruit web portal »
WSU Plant Pathology Professor to Lead Center for Clean Plants
Ken Eastwell, a professor in the Washington State University Department of Plant Pathology based at WSU’s Irrigated Agriculture Research and Extension Center in Prosser, has been appointed director of the Clean Plant Center of the Northwest. As director of one of the most comprehensive branches of the National Clean Plant Network, Eastwell provides leadership for the development and distribution of regionally grown deciduous fruit trees, grapevines, and hops that are free of viruses and virus-like agents.
“Ken Eastwell is a seasoned professional with areas of specialty that exactly match the focus of the Clean Plant Network. He has already built a strong foundation for the future expansion and refinement of the Center,” said Ralph Cavalieri in announcing the appointment. Cavalieri is associate dean for research and director of the Agricultural Research Center.
“Ken Eastwell is a world-renowned expert on graft and vector-transmitted viruses and virus-like agents. He is the architect of the Clean Plant Center and is a driving force behind making it a reality,” added Hanu Pappu, chair of the Department of Plant Pathology and Samuel Smith Distinguished Professor of Plant Virology. “His advice and expertise are sought by researchers and industry professionals in all corners of the globe. His research has greatly contributed to the sustainability of a diverse range of crops.The National Clean Plant Network is an industry-driven program designed to provide virus-tested propagation material to improve crop yield and quality and help growers and nurseries be more competitive in global markets. In response to uncertain and diminishing funding to operate specialized programs established in the 1950s and 1960s, producers of perennial specialty crops united to create the National Clean Plant Network in 2009 with initial funding through the 2008 Farm Bill. The National Clean Plant Network now supports 15 centers across the United States representing five perennial specialty crops.”
“Viruses are particularly devastating to specialty crops such as tree fruits, grapes, and hops,” said Eastwell. “Because these crops are perennial, annual losses to production caused by viruses occur every year and can ruin the economic outlook of a farming operation. The National Clean Plant Network has provided a critical focal point for researchers, regulatory agencies, and industry to share ideas and advance the production of virus-tested foundation planting stock to meet the nation’s needs.”
–Brian Clark
Learn more by visiting the Center’s web site at http://healthyplants.wsu.edu/.
WSU Study Examines Forest Fire Suppression Effects on Bighorn Sheep Habitat
Bighorn sheep in northern Washington are not thriving the way they should, and WSU scientists are working to figure out why. Bighorn sheep were reintroduced into the Sinlahekin Wildlife Area in the 1950s; today there are about 100, according to Mark Swanson, an ecosystem analyst and associate professor of landscape ecology and silviculture in WSU’s new School of the Environment. His question is, “what really is preventing these animals from achieving historic populations?”
While poaching and exposure to domestic ovine diseases have played a role, another key factor is how suppression of natural fires on the wildlife area has changed its landscape. Prior to intervention by new settlers, a natural cycle of forest fires as well as Native American burning practices in the area kept smaller trees and shrubs at bay. That preserved prime sheep habitat–wide-open spaces with lots of room to graze and, perhaps more importantly, lots of room to see approaching predators and escape, Swanson said. When that historic fire cycle was interrupted, smaller trees and shrubs filled in the open spaces between larger trees and encroached on open grazing spaces. “If you look at historic photos of the Sinlahekin and then look at current shots of those same places, there is a dramatic difference,” Swanson said. “You can see the grazing areas getting smaller and smaller.”
The effect of that encroachment is three-fold, Swanson said. In addition to reducing grazing areas, a closed forest canopy shades out many of the grasses, shrubs, and herbs that are staples of the sheep diet. In addition, closed forests provide much better cover for predators such as mountain lions. “That, obviously, makes the sheep much more vulnerable,” Swanson said.
Over the past two years, Swanson, WSU wildlife ecologist Lisa Shipley, and their research teams have worked with state fish and wildlife biologists to capture and tag a sample of sheep with GPS radio collars to track their movements and use of habitats in the wildlife area and adjacent lands. That information has helped focus research on the prime habitat that remains. “We can now assess the demographic consequences of fire suppression on the trees in the wildlife area and how bighorn sheep respond to those changes,” Swanson said.
Swanson and graduate student Tiffany Baker will next make recommendations on how to restore lost habitat, including the use of strategic forest thinning and prescribed low-severity fires. “We need to consider putting low-severity fires back into the forest management mix,” Swanson said, “enough to kill the seedlings and saplings filling in between the larger trees.” Both he and Baker acknowledge that recommendation could meet with concern from adjacent landowners and others. “Another component of our work will be educating the public that prescribed burning and thinning is really good for the landscape,” Baker said.
–Kathy Barnard
Learn more about the new WSU School of the Environment at http://environment.wsu.edu/.