By Stephen A. Hoying & Mario Miranda Sazo
Images and edits: P. Jentsch
More and more NY growers will be installing apple trellis support systems with more consistency in design and methods this year. This additional effort will decrease or eliminate the need of reengineering the following years. Today a good trellis support should (1) encourage trees to direct energy to fruiting rather than growing structural wood, (2) provide a structural framework for tree training, promoting more uniform trees, and (3) improve light interception and distribution to optimize fruit quality and uniform ripening.
Tree support is required for modern planting systems. The object is to produce as much fruit as possible as quickly as possible. Modern high density plantings with tree densities from 500 to 2000 trees/acre produce more fruit than the trees trunk and limbs can initially support, so a support system must be provided. The support system must be engineered to support the maximum potential crop as well as additional stresses that will be imposed on the support systems such as the wind, rain or snow load.
Support systems have been devised using a variety of materials and conformations with cost, availability of materials, ease of installation and strength being the major factors. Unfortunately, cost has been a major consideration and producers have tried to minimize cost by utilizing materials that were not strong enough to support the crop; especially when confronted with other unusual circumstances. 2011 provided abundant lessons of the weaknesses of tree fruit support systems. Weather, such as wind, snow load, and excess rainfall which resulted in waterlogged soils, were major factors resulting in support system failures.
A full crop of apples in a modern orchard can weigh approximately 63,000 lbs/A. Any trellis built must at least support this crop. They must also be engineered to withstand the additional stresses caused by wind, snow and rain. Engineers have calculated additional forces. An acre of Tall spindle can occupy 871,000 cubic ft or a surface area of more than 27,000 square ft. Winds at 70 mph can add approximately 2 lbs/square ft of force which adds an additional 58,000 pounds essentially doubling the load. Snow can add as much 20 lbs cubic ft additional weight. The additional weight this adds is another 871,000 lbs! It is apparent that support systems must be engineered to support more than 10 times the weight of a crop load for worse case scenarios!
Essentials to building a support system to withstand hurricane season!
Use pressure-treated or a rot-resisting wood species. Lodgepole, Southern yellow pine, Locust, and Cedar are the best. All locally sourced posts should be debarked. Avoid wood species that have whorled branches, and large knots. End posts and anchors should be at least 4-5 inches and inline posts 3-4 inches in diameter.
Match the trellis system to the planting system. Trees in tall planting systems such as the “Tall Spindle” or “Vertical Axis” should be supported to 10 feet. Use 10 foot end and in-line posts with individual tree stakes to provide tree support and use 12 foot posts when wire alone provides tree support.
Use an equilateral triangle end assembly consisting of an angled end post, high tensile steel wire, and the distance along the ground from the base of the angled post to the wire as the three sides of the triangle. The physics of this end assembly is the most stable of all end assemblies.
Drive posts – do not auger. Driven posts will not move through the soil.
“Deadmen” or screw-type anchors are not as strong as driven anchors. Rings on the ends must be securely welded to prevent straightening out under stress.
Drive the anchor post vertically 3-4 feet into the soil. This will seat the anchor below the frost line to prevent heaving and the resistances preventing the anchor from being pulled out of the ground will be maximized.
Space inline posts no more than 30 feet apart. Increasing crop load and taller systems have created more torque on the support system than before.
Pound end and inline posts at least 3 feet deep to prevent frost heaving.
Drill the post for the top wire and thread wire through. One of the major causes of trellis failure is staple pull-out. By drilling through the posts and threading the top wire, staple pull-out is eliminated. Any additional wires on each post can safely be attached with staples without the threat of pull out.
Use 1.75 inch galvanized barbed staples to minimize pull out and use two staples (1 horizontal and one vertical) at stress points where wire changes direction. This provides 3 points of contact for the wire. Be sure and drive staples so that arms flare away from each other rather than toward each other.
Use 12.5 gauge Hi-Tensile steel wire. Soft wire will stretch too much.
Use a high quality wire tightening device on each wire so that wires can be tightened and loosened as needed.
Perform annual maintenance.
Steps in Annual Maintenance
*Replace broken and weakened posts.
*Re-pound anchors and in-line posts that have heaved.
*Straighten leaning posts.
*Check and replace pulled staples especially those at stress points where wire changes direction.
*Readjust wire tension after harvest and crop has been removed.
By paying attention to these points, support systems will withstand all but the most traumatic events.
Some images taken in 2015 of system support being used in Washington State apple production.