Issue link: https://read.dmtmag.com/i/275392
www.goodfruit.com GOOD FRUIT GROWER MARCH 15, 2014 39 The aphidlike nymphs that hatch from the eggs develop through five instars. Typically, in Washington, there are two or three generations of sum- merform psylla. By August or September, nymphs destined to be winter- form adults start to develop. They leave the orchard in late September and October. Historical studies suggest that psylla can move up to six kilometers (3.75 miles) over the course of leaving and returning to orchards, Unruh said. Their dispersal ability can promote the spread of resistance to pesticides among orchards. Unruh and Horton from the USDA and Vince Jones from Washington State University in Wenatchee con- ducted a study to find out if biological control of pear psylla could be improved by planting a ground cover that would provide habitat and other food sources for preda- tors of psylla, such as Anthocoris and Deraeocoris bugs, ladybugs, green lacewings, and spiders. The study was conducted in an experimental Bartlett pear orchard with alfalfa planted in the alleys and com- pared to trees with traditional orchard grass understory. The scientists monitored the movement of the predators and analyzed their gut contents to find out what they had been feeding on. The alfalfa cover crop had significantly more predators than did the orchard grass ground cover. On trees above alfalfa ground cover, there were slightly more preda- tors than on trees with grass ground cover, but the number of pear psylla also increased in trees in the alfalfa plots, resulting in a similar preda- tor-to-prey ratio in the trees in both ground cover treat- ments. The increase in psylla in trees with the alfalfa ground cover may be explained by an increase in leaf nitrogen in those trees. Thus, while there was some movement of predators, particularly lacewings and ladybeetles, between the orchard floor and the trees, there were no striking differences between alleys with the alfalfa cover crops or grass. When the concept was tested in commercial organic orchards, there was minimal build-up of natural enemies in the alfalfa, probably because frequent mowing kept alfalfa plants small and increases in leaf nitrogen did not consistently occur. Densities of both pests and predators in the trees were low. "These results were not what we expected," Unruh told the meeting. "We didn't increase biocontrol enough to make a difference. What we did do is become determined to try again someday." • "Savings in hand thinning time and/or increases in fruit sizes resulted in a net positive impact of $123/ha to $1368/ha compared with hand thinning alone." - Baugher, Schupp, et al. Mechanical string thinner reduces crop load in various stages of bloom development in peach and nectarine trees. HORTSCIENCE 45(9): 1327-1331, 2010 Manufactured by; Beamsville, Ontario | 905.563.8261 www.provideag.ca Contact us directly or one of these dealers; Scotian Gold Co-op - 902.679.2191 Blueline Equipment - 800.827.0972 Crown Orchards - 434.979.0619 Louis Gelder and Sons - 269.934.9900 Fifth instar pear psylla nymphs, like this one, are called hardshells. All stages of psylla have distinctive red eyes. PHOTO BY ELIZABETH BEERS, WSU