FLOWERING, FRUIT-SET, AND YIELD RESPONSE OF BARTLETT PEAR TO LEAF-SCORCH DAMAGE BY 2-SPOTTED SPIDER-MITE (ACARI, TETRANYCHIDAE)

The effect of leaf scorch and defoliation caused by twospotted spider mite, Tetranychus urticae Koch, was investigated on flower production, fruit set, fruit yield, and mean fruit weight of 'Bartlett' pear. The level of leaf scorch and defoliation was estimated in autumn, and the number of flowers per flower cluster, fruit set, and fruit yield were determined in the following season. The number of flowers per flower cluster was significantly reduced (P < 0.05) by leaf scorch and defoliation in the previous summer, but the response was only slight with flower clusters having approximately five flowers per flower cluster. Fruit set per flower cluster, gross fruit yield, and the yield of fruit suitable for canning were significantly reduced (P < 0.01) by leaf scorch and defoliation in the previous year. On trees with 80% leaf scorch and defoliation in the previous summer, gross yield and the yield of fruit suitable for canning were reduced to approximately a third of the level determined for trees that experienced no leaf scorch and defoliation in the previous year. Mean fruit weight increased only marginally as fruit density per square meter of planted area decreased, indicating that leaf-scorch damage from twospotted mite may affect fruit growth of 'Bartlett' pear in the following year. Fruit set was not responsive to leaf-scorch damage in the second and third years after leaf damage had occurred. The effect of these results on a damage threshold is discussed.