WSU--Tree Fruit Research & Extension Center

Research Summaries

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E-mail to Kathleen M. Willemsen: willemsen@wsu.edu

Tree fruit production and management

Kathleen M. Willemsen, Extension Horticulturist, WSU

High density orchard systems are appealing to growers because the trees come into production much earlier than those planted in conventional systems. This shortens the orchard payback period, i.e., the time it takes for the orchard to become profitable. Early production also allows growers to plant new varieties, such as Fuji, Gala or Braeburn, which are currently more profitable than Delicious or Golden Delicious. One method of educating growers about these new orchard systems is to plant demonstration trials at research stations and grower locations. Formal educational meetings, such as fruit schools, shortcourses and the Washington State Horticultural Association's annual meeting, are excellent means of transferring technology to the tree fruit industry. Articles in trade magazines such as the Good Fruit Grower and Western Fruit Grower are also important for keeping the industry current on research developments.

As the tree fruit production specialist, one of my important roles is to serve as a liaison between industry and research personnel. By working with these two groups, research needs are identified. I am a faculty member of the Department of Horticulture and Landscape Architecture at Washington State University and thus serve as a representative of the university. I coordinate and develop programs with other extension personnel at the state, regional and county levels. I work with extension and research faculty in other departments, such as plant pathology and entomology, to ensure a balanced program and successful dissemination of information.

Additionally, I have an applied research program focusing on plant growth regulators in apple production. The use of plant growth regulators for chemical fruit thinning of apple is an important production practice for regulating crop size and maintaining consistent annual production. Bloom thinning materials which are either acids or salts are being tested for potential federal registration. Bloom thinning of apple is critical for assuring consistent cropping in varieties such as Fuji. The bloom thinning compounds under test are considered environmentally safe and have no residues that could harm wildlife or insects. These materials fit very well into an integrated fruit production system, with the goal of reducing harmful or potentially harmful compounds in the apple production system. Postbloom thinning programs that are based on synthetic bioregulators and that eliminate the use of insecticides such as carbaryl are being developed for several apple varieties. These synthetic bioregulators affect fruit growth and development by mimicking naturally occurring materials. There are no harmful environmental effects of these compounds. The challenge is to develop a program which is consistent and effective on Delicious and the other major varieties grown in Washington.

Growth regulators are also used to retain apples on the tree. Prevention of premature fruit drop allows for more orderly harvesting of the fruit and can increase fruit quality in terms of size and color. One material, AVG, can delay harvest up to two weeks. This delay allows for increased fruit size, enhanced color and improved fruit flesh pressure. Fruits treated with AVG maintain firmness in regular and controlled atmosphere storage regimes. A chemical growth retardant, prohexadione calcium, that controls growth with no deleterious effect on fruit quality is being tested under Washington conditions. Combination sprays of postbloom thinning materials and prohexadione calcium are being evaluated in commercial orchard blocks.

Other aspects of my applied research and extension program involve developing enterprise budgets with agricultural economics faculty, and providing technical support on irrigation, evaporative cooling systems, pear production, nursery stock quality and horticultural ("summer") oils.