Chemical Fruit Thinning in Apple

Greetings,

I just wanted to share with you some of the slides and information I presented this past Tuesday via zoom in case you haven’t had a chance to attend the meeting. You may also consider reading my previous blog post on blossom thinning (https://treefruithorticulturevaes.wp.prod.es.cloud.vt.edu/2020/03/28/apple-blossom-thinning-general-overview-and-updates/) and the factsheet on the Virginia Cooperative Extension webpage (https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/spes/spes-134/SPES-134.pdf) if you want to get a better idea about the science and application of chemical thinners, e.g. 6-BA, NAA and ethephon.

Table 1: Chemicals and plant growth regulators labeled for fruit thinning in Virginia

Notes: Exilis 9.5 SC contains 9.51% of 6-BA, compared to 1.9% in Maxcel and 2% in Exilis Plus.
There are two forms of Refine, Refine 3.5 and Refine 6.25. The later contains a higher concentration of NAA.

Table 2: Thinning chemicals and rates recommended for petal fall-5 mm fruit diameter

Notes: NAD and NAA cause pygmy fruits when applied to Red Delicious and Fuji.
Carbaryl can be applied as a carbaryl only thinning spray between petal fall and 5 mm fruit diameter, but it will be less effective as fruits are getting bigger.

Table 3: Thinning chemicals and rates recommended for 6 mm-15 mm fruit diameter

Table 4: Chemicals and rates recommended for rescue thinning applications (at 16-25 mm fruit diameter)

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
Tel. 540-232-6035, Email: ssherif@vt.edu


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About S. Sherif

Dr. Sherif M. Sherif is an Associate Professor of Horticulture at the School of Plant and Environmental Sciences at Virginia Tech, USA. He received both his bachelor's and master's degrees in horticulture from Alexandria University, Egypt, and his doctorate in plant agriculture from the University of Guelph, Canada. Dr. Sherif's broad research experience in molecular biology, plant development, and tree physiology has led him to lead several research projects focusing on the biotic and abiotic factors affecting fruit trees' production, sustainability, and competitiveness. Sherif's current research program at Virginia Tech focuses on frost mitigation strategies, precision crop load management, high-density production systems, molecular regulation of critical horticultural traits, and germplasm development.