Scientists use flower power to combat orchard menace

 

 

 

Integrating strategies to contend with pests   WSU researchers seek alternatives to pesticides because of several problems associated with pesticide use, including: risks to environmental and human health; cost of the chemicals; equipment, labor and expense needed for application.   Another ill effect is that, in addition to controlling a target insect, a pesticide also may kill insects beneficial to crop health. WSU researchers work to counter that problem by developing and advocating for a broad group of strategies called integrated pest management.   IPM minimizes use of harsh chemicals in favor of those that are highly selective for target pests. It also employs biocontrol, in which good insects are encouraged by various means to prey upon bad insects that cause agricultural damage.

WENATCHEE, Wash. – Washington State University researchers pioneer alternatives to pesticides for managing agricultural pests. Recent experiments to plant flowers in orchards to attract beneficial predator insects show promise, and funding is being sought to expand testing to commercial orchards.

 

Doctoral student Lessando Gontijo worked with his mentors, WSU entomologist Betsy Beers and WSU biological control expert Bill Snyder, to set up the experiments. Gontijo came to WSU from his native Brazil to study biocontrol, the control of destructive organisms by use of natural predators, parasites and pathogens.

 

The team tested the idea that syrphids – more commonly known as flower flies or hoverflies – could be used to control woolly aphids that prey on apple trees. The experiments were funded in part by a grant from WSU’s BioAg program.

 

 

“Growers began noticing an increase in the number of woolly aphids in apple orchards starting in the early 2000s,” said Beers, who 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?’ ”

 

Woolly aphids debilitate trees over the long term by sucking the sugar out of plants.

 

“They are pernicious little beasts,” Beers said. “This is one of the meaner aphids.”

 

A beneficial syrphid on alyssum.

A survey of woolly aphid’s natural enemies indicated that syrphids are the most commonly seen predator. Syrphid larvae thrive on a diet of aphids.

 

“It’s wonderful to watch them chew their way through an aphid colony,” Beers said, adding, “The trick is getting more syrphids into the orchard and making sure they are happy there.”

 

The adult syrphid’s primary food is nectar, so the team first examined six different flowering plants for attractiveness to syrphids. Sweet alyssum won hands down.

 

The 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 the lanes between rows of apple trees (normally occupied by grass sod).

 

Sweet alyssum is grown in the lane between rows of apple trees.

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 located in the apple trees had visited the alyssum flowers, further evidence that alyssum could promote this biocontrol.

 

 

The results of the small-scale experiments are promising, Beers said.

 

“These experiments are the first steps in a much longer process,” she 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 step will be to run experiments in commercial orchards. Beers said she is looking for funding to expand the project.

 

“It will 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,” she said.