Enhancing Orchard Sustainability and Product Consistency through Improved Crop Load Management Practices

During the first several weeks after bloom, fruit tissues grow by cell division.  This is referred to as the exponential phase of growth, with many cells dividing simultaneously.  As the number of cells increase, fruit growth occurs at increasingly faster rates.  Near the completion of cell division, cells that are no longer dividing begin to expand.  Cell expansion continues for the remainder of the season and accounts for the majority of fruit growth.

Several factors can limit fruit growth.  Unless freezing spring temperatures reduce the number of viable fruit blossoms, fruit trees tend to set many more fruit than they can grow to optimum size.  The overabundant number of fruitlets compete for limited plant resources—most likely carbohydrates or nitrogen.  This competition inhibits fruit growth, especially during cell division.  For this reason, an essential cultural practice in a commercial orchard is to reduce fruit numbers early in the season through a process known as fruit thinning.  Small-scale orchardists also find that fruit size improves following the hand removal of fruit early in the growing season. 

Many environmental factors similarly influence fruit growth.  Cool temperatures during cell division result in reduced growth rates.  Additionally, periods of cloudy weather early in the season limit the availability of carbohydrates, which restricts fruit growth.  In cases where the growth rate of some fruit is severely limited, they will drop prematurely.  Drought stress, nutrient deficiencies and heavy insect or disease damage may likewise reduce fruit growth.

On-farm research is one of the best ways a grower can explore ways to improve crop load management in a given fruit variety and orchard location.  During the past several growing seasons, local growers cooperated in Penn State extension trials designed to test new strategies for improving fruit size in fourteen commercial apple, peach, plum or Asian pear plantings.  New thinning strategies applied during bloom generally resulted in an improved distribution of fruit in higher packout size categories.  Another benefit was increased management efficiency.  In stone fruit orchards, follow-up hand thinning times were reduced by 20 to 50 percent.  Economic analyses indicated that the combined effects of reduced costs and higher profits significantly improved net returns.

Individuals who grow fruit for a hobby will also find that it is helpful to experiment with numbers of fruit removed and thinning timings.  A “rule of thumb” is to space peaches six inches apart and apples six to eight inches apart, leaving only one apple per spur.  Since an apple tree can develop an alternate bearing habit (a heavy crop of small fruit one year followed by no or few fruit the next), it is important to thin within a month after bloom.  With experience, you will learn to balance crop load to tree growth.

For more information on fruit thinning and other home orchard management practices, home gardeners may request a Home Orchard Calendar from the Extension Office in Adams County.  Commercial growers are invited to register for an in-depth workshop on crop load management to be held at the Adams County Agricultural and Natural Resources Center, 670 Old Harrisburg Rd., on Tuesday, December 20^th.  You may register on line at http://extension.psu.edu/fruit-times (click on events) or call 717-334-6271. 

Dr. Tara Baugher is the Penn State Extension Tree Fruit Educator serving Adams County and the fruit belt region.  Penn State is committed to affirmative action, equal opportunity, and the diversity of its workforce.  Penn State Extension in Adams County is located at 670 Old Harrisburg Road, Suite 204, Gettysburg, PA   17325, phone 717-334-6271 or e-mail AdamsExt@psu.edu.