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Fruit thinning, branching, and stop-drop

Written by: 
Win Cowgill, Win Enterprises LLC

Fruit thinning, branching, and stop-drop of Pears

Chemical fruit thinning

Some general comments on chemical fruit thinning of pears, including Asian pears:

  • use/calculate diltue tree volume, which is typically 100 to 200 gallons per acre for pears; then
  • when applying chemical thinners, use the table rate below per 100 gallons (dilute TRV)
  • dilute (1X), up to 2X concentration works best with chemical thinners, do not exceed 4X concentration
  • if spraying concentrate, also concentrate the thinning chemical as you would any other pesticide application
  • apply chemical thinners when the temperature is rising into the 70's or low 80's and will remain there for 3 to 4 days
  • for Aian pears, apply chemical thinners when largest fruits are 10 to 14 mm in size; 6-BA (Maxcel, Riteway, Refine) at 200 ppm (high rate) has worked good on Hosui and Kosui Asian pears in trials, however, Asian pear varieties differ in their sensitivity to chemical thinners
  • for more detailed information, see the following publications




Chemical thinners

timing product concentration rate comments
5-7 days after petal fall Amid-Thin W (NAD) 10 to 50 ppm 1.6 to 8 oz per 100 gal Label specific for use on Bartlett and Bosc.
14-21 days after full bloom Fruitone-L, PoMaxa, Refine 3.5 WSG 10 ppm 4 to 8 oz per acre Apply as soon as fruit set is apparent and weather favors chemical thinning efficacy. Late applications may result in pygmy fruit. Apply when temperature is 70 to 75 F. Thinning efficacy depends on variety.
fruit size 8-14 mm (7-28 days after bloom) Maxcel, RiteWay 75 to 200 ppm 80 to 128 fl oz per 100 gal Start with 150 ppm for Bartlett, 75 ppm for Bosc. Apply when temperature is 60 to 85 F. See comments.
fruit size 8-14 mm (7-28 days after bloom) exilis Plus 75 to 200 ppm 46 to 122 fl oz per 100 gal See comments 
fruit size 8-14 mm (7-28 days after bloom) exilis 9.5 SC 75 to 200 ppm 9.6 to 25.6 fl oz per 100 gal See comments
fruit size 5-20 mm Protone® 100 to 500 ppm 6.6 to 33.1 oz per acres Make 1-2 application, but one application during a period of carbohydrate deficit is usually sufficient. Protone® may be a particularly good pear thinner.


Branching young trees

Timing product concentration rate comments
BEFORE buds break in spring on 1-year old wood Maxcel, Promalin; exilis plus, exilis 9.5 SC 5,000 ppm see label If dormant buds are present on one-year-old wood only. DO NOT apply after bud break. See product labels for more details and instructions.
AFTER bud break in spring on 1-year old wood Maxcel, Promalin; exilis plus, exilis 9.5 SC 500 ppm see label If buds have broken, and the leaf tissue is showing on one-year-old wood. Apply by spraying with a back-pack sprayer. Works best when temperatures are warm and there is enough tissue to absorb the PGR. Note: Never add surfactant to a solution of MaxCel as it is already included in the formulated product. Promalin should be combined with a NIS following the label instructions.

For more information on branching young trees, see the UMass Fact Sheet F-140 Branching Young Apple Trees with Plant Growth Regulators

Pre-harvest fruit drop control

tming product concentration rate comments
7-14 days before anticipated harvest ReTain NA 333 g per acre (one pouch) Apply in sufficient water for good coverage. Add organosilicone surfactant at 12 oz per 100 gallons.
5-7 days before harvest Frutone-L, PoMaxa, Refine 3.5 WSG 10 to 15 ppm 4 to 6 oz per 100 gal Apply 7 days before harvest to D'Anjou, Bosc, Bartlett. Make separate sprays to early, mid, and late varieties.
5-7 days before harvest Refine 24.2L NA 2 to 4 fl oz per acre Bartlett, Bosc only. Effective in 3-4 days after application and controls drop for 2 weeks.