Source: Pennsylvania Department of Conservation and Natural Resources - Forestry, Bugwood.org
Pear thrips can be a severe pest of sugar maple. Thrips feeding in nectarine blossoms and fruitlets in areas of the state where sugar maples are common has caused scarring injury on the fruit.
Pear thrips produce just one generation per year. Adults are dark brown and occur only as females in North America. Adult emergence occurs around the time of leaf flush of sugar maple. In outbreak years pear thrips may infest many deciduous hosts that are in bloom at this time, including most tree fruits.
Adult and larvae feeding on developing nectarine fruit can cause scarring injury that expands as the fruit matures. Pear thrips injury to apple blossoms has occurred in New England but is not known in Pennsylvania.
Monitoring should begin at bloom in areas at risk for pear thrips. Sample blooms from 10 to 12 trees at each of three to four sites per orchard. Blooms should be slapped against a light yellow surface to determine abundance of adults. The presence of larvae is determined by dissecting at least 50 blooms per orchard. The threshold is adult infestation of more than 5 per 50 blooms or presence of larvae. Specific chemical recommendations for home gardeners are in Fruit Production for the Home Gardener , and recommendations for commercial growers are in the Penn State Tree Fruit Production Guide .