How to Manage Pests

Mechanical injury

Mechanical injury occurs when plant parts are crushed, cut, punctured, rubbed, or struck due to accidental or deliberate physical actions.

Identification

Other causes of symptoms resembling mechanical injury include

• aeration deficit
• canker-disease pathogens
• gas injury
• herbicide phytotoxicity
• other chemical phytotoxicity
• root-decay pathogens
• thermal injury, or high temperatures
• vascular wilt fungi
• vertebrate pest chewing
• water deficit
• wind
• wood-boring insects

Causes of mechanical injury include

• changing soil grade in the root zone
• chewing, rubbing, or scratching by animals
• cutting roots or trunks during excavation or trenching
• cutting trunks or root crowns with mowers or string trimmers
• girdling from stakes or ties
• impact from vehicle bumpers
• operating heavy equipment or laying pavement over roots
• pruning
• vandalism

Sometimes the cause of injury is evident, such as ties or wires embedded in bark due to improper staking. A mature tree that lacks basal trunk flaring indicates that the soil grade has been raised. If deer, gophers, mice, rabbits, or other vertebrate pests gnawed bark and wood, chewing marks, excrement, footprints, or nesting sites characteristic of the species, or the pests themselves, may be observed on site.

Historical knowledge can help you diagnose the cause. For example, learn the local history of construction or development and whether potentially phytotoxic chemicals were applied.

Mechanical injury to roots can be especially difficult to diagnose because wounds are hidden underground and aboveground symptoms may not become obvious until months or years after root injury. Use a pneumatic excavator (e.g., Air Knife or Air Spade) to remove soil around roots or carefully excavate or wash soil away and inspect roots to help determine whether they have been injured.

Damage

Mechanical injury to aboveground parts often produces obvi­ous wounds, such as broken limbs and gouged or stripped bark. Injuries above or below ground can cause a wide range of decline symptoms, such as discolored foliage, limb dieback, premature leaf drop, slow growth, and wilting. Injury wounds can attract boring insects, serve as entry sites for disease-causing pathogens, and lead to limb, root, or trunk failure and plant death.

Solutions

Prevent wounds to trunks and roots through appropriate site design, proper planting, and good landscape maintenance. Protect trees by installing protective barriers and screens and keeping other vegetation back from trunks. Properly stake young trees and promptly remove support when no longer needed. Avoid injecting root crowns and trunks. Minimize soil disturbance, at least within the drip line of canopies.

Consult Abiotic Disorders of Landscape Plants, Living among the Oaks: A Management Guide for Landowners and Managers, and Oaks in Urban Landscapes for more information.

Trees killed by root cutting

Poor pruning (topping)

Trunk girdled by a tie

Unprotected tree trunk