J-root planting damage on Virginia Pine. Courtesy of Bill Murray, University of Georgia, Bugwood.org (#0485015)
Equipment used in a new tree block generally passes trouble free down the straight rows. As the trees grow, causing the rows to narrow, it becomes harder for the equipment to travel down the rows without causing damage. Equipment damage results from the tractor and its tires and implements.
Equipment used for mowing and spraying can also cause damage to the trees. Entire small trees can be crushed and lower branches of larger trees can be broken or pulled from the trunk by equipment tires. The spray boom can scrape branches as well as damage bark and buds. Mowers are known to scrape the base of trees. Trees at the ends of the rows are more susceptible to damage because of turning-radius requirements by the tractor and implements. It may take several weeks after the damage occurs for symptoms to appear, but they are most quickly noticeable around bud break. Equipment damage is often permanent and disfiguring.
Some growers have modified their equipment by adding guards to prevent branches of trees from being pulled into the path of the tires or implements. Damage can also be reduced by widening the distance between rows. Where the current standard is 5 feet by 5 feet (1.52 by 1.52 m), some farms are going to 5 feet by 6 feet (1.52 by 1.83 m) or even 6 feet by 6 feet (1.83 by 1.83 m). It is important to provide ample turning area at the end of rows when planting.
Heat and fumes from equipment exhaust can damage trees. Exposure time does not have to be long, especially with new growth. Symptoms include discolored or browned needles and dying shoots (Figure 1). The damaged area is generally about one square foot. Exhaust damage can be diagnosed by looking down the rows. If exhaust damage is likely, the burned spots will be at the same height on numerous trees in the row. Narrow rows are most susceptible.
Figure 1. Exhaust burn at the bottom of a tree. Courtesy of PDA
A few solutions for reducing this type of damage include directing exhaust away from trees, keeping hot engine parts away from trees, using a catalytic converter, and keeping equipment speeds increased rather than decreased.
String trimmers cause serious damage to trees by damaging the bark at the base of the tree. This is especially true when trees are larger and the operator has difficulty seeing into the trunk. The cuts and gouges in the bark offer entrance sites for several insect pests and diseases. To prevent string trimmer damage, maintain good weed control in the rows and avoid use of string trimmers under trees.
Planting equipment may also lead to tree injury. If the planting depth is not correct, the taproot may curve upward instead of straight down. The tree roots will continue to grow upward—a condition known as J-rooting—and the trees will become stunted and eventually die (Figure 2). To avoid J-rooting, adjust mechanical planters for each use with the proper planting depth required for the size of transplants being used.
Figure 2. A J-rooted tree. Courtesy of PDA
Shearing can damage trees. If a shearing knife is not used properly or is not sharp, branches will not be cut cleanly and partial cuts or broken branches may result. This results in dead or “flagged” branches. To reduce damage when using a shearing knife, always use a sharp blade and swing with enough force to ensure minimal uncut branch ends (Figure 3).
Figure 3. Clean, sharpened, 16-inch shearing knife. Courtesy of Sarah Pickel, PDA
Improper machine shearing can also harm trees. If the branches move away from the moving teeth, they will be left with a “chewed off” look. The end result is yellow, unattractive, or dead branch ends. Trees can be damaged by excess lubricating oil and will appear burned. Avoid using too much when lubricating the blades. When machine shearing, keeping the equipment at the proper angle and speed while cutting into the branches will reduce the “chewed off” look of branch ends.
Shearing is dangerous, so use all recommended safety equipment and provide training to those working on this activity.