Dr. Terence Robinson, Cornell University
- apple fruit thinning should be driven primarily be economic considerations
- the carbohydrate balance of trees from bloom through about 15-20 mm fruit size is important to understand the potential effect of a chemical thinning spray
- temperature and light during the same period described above primarily determines carbohydrate balance
- carbohydrate balance can be modeled, and thus some form of numerical 'thinning index' can be developed as a tool to assist growers in making chemical thinning decisions
- the 'Darwin' mechanical thinner has proven useful (with modification) in bloom thinning peaches to consistently reduce amount of time hand thinning and improving peach fruit size. More...
- the Darwin thinner was also used in apples, and may have particular utility in organic apple orchards; but, there is increased risk of transmitting fire blight because of it shreds foliage; more research is needed in apples
- Greene covered timing (bloom to 25 mm), chemicals (NAA, NAD, carbaryl, 6-BA, and ethrel) and the impact of light and temperature on the activity of chemical thinners
- Honeycrisp has a strong capacity to overset
- crop load of Honeycrisp should be no more than 4 to 6 apples per sq. cm. trunk/limb cross-sectional area to get adequate return bloom
- young Honeycrisp trees should probably be hand-thinned only to achieve desired results (chemical thining too risky because of ease of over-thinning)
- mature trees can be thinned with a combination of carbary (1 pt) + BA (100 ppm) or NAA (8-10 ppm) to reduce crop load to <>
- summer NAA treatments can improve return bloom
- Clarke gave an excellent overview of the theory behind fruit thinning and talked about how Valent is looking at ABA (abscissic acid) and AVG (ReTain) as potential additions to the thinning/crop load management toolbox
