Please note the following:

• Thinning rates used at bloom (liquid lime sulfur 1.5% and 2% JMS stylet-oil) will not cause enough thinning if used as a stand-alone thinning treatment, but it will likely remove some blooms that will be tough to thin at later stages. One blossom thinning treatment at 20% open bloom is enough for this purpose.
• 6-BA applications at petal fall will serve a dual purpose: a) to improve fruit size, especially in Gala, and b) to open up fruit clusters.
• Using NAA at petal fall will also sever a dual purpose in Honeycrisp: a) to improve return bloom, and b) to open up tight clusters.
• Thinning at 6-12mm fruit size is the main fruit thinning window for most apple varieties. Thinning rates and timing at this stage should be determined based on the outputs of the apple carbohydrate thinning model available at NEWA website (http://newa.cornell.edu/index.php?page=apple-thin). I will run the model as usual and share with you the model outputs and recommendations through this blog.  
•  Using 6-BA and NAA with carbaryl at 13-18 mm can also provide satisfactory results, but the efficacy of these chemicals will also be dependent on the tree carbohydrate level. So, it’s recommended to follow the model outputs at this stage as well.
• Rescue thinning treatments (at 19-25 mm fruit size), might be necessary if earlier thinning attempts did not achieve satisfactory crop loads.
• To improve return bloom in Honeycrisp it is highly recommended to apply four applications of NAA (2 oz/100 gal) at 10 days intervals, starting from 26-35 mm fruit size. Because NAA causes pygmy fruits in Fuji, NAA should be replaced by ethephon applications at 0.5 pt/acre to improve return bloom in Fuji.
• Some varieties, e.g. Pink Lady and Ginger Gold, are easier to thin than others, and it can be easily thinned at the 6-18 mm fruit size window.
• Important: all the rates suggested in these two charts are based on 100 gal/acre.

I hope you find this information useful. Should you have any questions or comments, please don’t hesitate to call me at 540-232-6035, or email me at: ssherif@vt.edu.  You can also use the comments section below to send questions and comments.

Sherif M. Sherif, Assistant ProfessorVirginia Tech, School of Plant and Environmental Sciences,AHS Jr. Agricultural Research and Extension Center
595 Laurel Grove Road, Winchester, VA 22602