Pear psylla is not an individual orchardist’s problem—it is a neighborhood issue.
The pest disperses in the winter and flies back into orchards in the spring. No matter how well growers have controlled pear psylla the previous year, they start the following season with the same problem as every other grower in the neighborhood, Tim Smith, Washington State University Extension educator, reminded growers at the North Central Washington Pear Day.
“Psylla are flying up and down the valley,” he said. “Whether you’re a good manager, or a bad manager, you will have the same number in March.”
That’s why an areawide approach is recommended with prebloom applications of Surround (kaolin), which is designed to chase adult psylla out of orchards and deter them from laying eggs.
“If you’re the only one in your neighborhood that doesn’t use Surround, you’re a refugee site,” Smith said. “We probably should be going fence to fence. Everybody should be using it. It’s more effective than anything we have used before.”
Surround should be applied in the dormant or delayed-dormant period, so that it’s covering the tree before a significant number of eggs have been laid. It does not kill eggs. It just deters females from laying eggs on the tree.
In hilly sites, where it’s difficult to get a tractor into the orchard in early spring to make the first application, Surround can be applied in the fall instead, as long as the weather is still good enough after leaf drop, Smith said. The residue doesn’t break down and will still be effective in the spring.
“The real purpose of Surround is to keep adults out of the orchard and stop them laying eggs, so you have flexibility in timing,” he said.
However, if an application can’t be made until cluster bud, it will chase the adults out, but they will already have laid eggs. An insecticide will need to be applied at cluster bud to control the eggs and nymphs that are already there and reduce the pressure later.
Smith recommends layering applications of Surround at a rate of 50 pounds per acre to keep the foliage covered as it grows. Applications are recommended at two-week intervals.
“You’re going to get some egg lay, even with Surround, but you’ll drastically reduce the number of nymphs you have to target with insecticides,” Smith said.
Pear growers start out each season with confidence and faith that they will be able to control pear psylla, Smith said. The pest develops through five or six generations in Washington.
In May and June, they’re still confident and feeling a sense of accomplishment because they made it through the first generation of the pest. By July, they’re overconfident and dismay begins to dawn, along with renewed determination to tackle increasing populations of pear psylla. By the end of the season, they’re angry, frustrated, and perhaps in denial.
Growers are prepared to tackle the first generation of the pest, but tend to let down their guard during the second generation, Smith said. Those who continue their efforts to control psylla during the second generation, even though they don’t see many of the insects, are likely to have a more successful summer.
A number of pesticides are available to control the pest during the spring and summer.