Programs to Increase Fruit Size and Yields In Stone Fruit

The most important determinant of profitability for soft fruit growers in Washington is consistent cropping of large target fruit. The Washington Tree Fruit Research Commission (WTFRC) has tested programs to adjust crop load and improve light distribution in the canopy over the past eight seasons in commercial stone fruit orchards in Washington. Our results indicate that chemical blossom thinning of stone fruit can be achieved by a variety of chemicals. Ammonium thiosulfate (ATS) has been the most consistent performer and individual fruit size is frequently increased with effective chemical thinning. Reflective ground covers, such as Extenday™ or Daybright™, increase light available for photosynthesis, especially in lower, shaded portions of tree canopies. We have found this technology consistently increases individual fruit size, as well as frequently improving overall yields in apple, cherry, pear, peach, and nectarine orchards.  Improved fruit color and quality due to reflective ground covers have facilitated fewer picks in some instances. Best results are typically obtained by season-long application. We continue to explore impacts of partial season placement and carryover effects from year to year on vegetative and reproductive vigor.