Chemical Thinning--Pear

contributed by Dr. Kathleen Willemsen
WSU-Tree Fruit Research & Extension Center

The chemical thinning of pears is not as common or as generally satisfactory as with apples. Problems with inadequate fruit set are more common. Delay application of thinning sprays until fruit set can be adequately appraised. During cool season, when the bloom period has been prolonged, delay application until 21 days from bloom or when fruit are 10 to 15 mm in diameter.

Both NAD (Amid-Thin W) and NAA have been used successfully to thin Bartlett pears. Inadequate thinning is more likely to be a problem than overthinning. NAA may not thin Bartlett pears in some seasons.

Apply NAD or NAA 15 to 21 days after bloom. Use a wetting agent to improve their effectiveness. Use higher rates on vigorous trees. Avoid spraying weak trees.

Note: Not all formulations of NAA are registered for use as thinning materials on pear. NAD may cause a "flattening" of leaves, but does not adversely affect tree performance. Rates of NAD or NAA that thin Bartlett pears are likely to overthin other varieties.

POSTBLOOM THINNING: Bartlett

Apply 15 to 21 days after full bloom. NAD may overthin varieties other than Bartlett. NAA may not adequately thin Bartlett some seasons.

Washington State University
Tree Fruit Research and Extension Center
1100 N. Western Ave.
Wenatchee WA 98801

phone: 509-663-8181
fax: 509-662-8714

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May 2, 2000