Common Reasons for Tree Decline & Mortality
Trees, like people, have a lifespan, but due to certain climatic events, site conditions, or human related actions, a trees lifespan can be cut short. Using integrated pest management (IPM) homeowners and landowners can use multiple techniques (ie: cultural, mechanical, biological, & chemical) to manage pests or disease problems, while minimizing the negative impacts to the environment.
In order to protect your trees from pests or disease, start by selecting tree species that are well adapted to the climate fluctuations (SEE CF pubs) and site conditions of your area. A simple soil test can provide you with valuable information on the soil characteristics of your planting area. Also, choosing a diversity of tree genera instead of several of the same species will also help minimize problems that affect a certain tree type.
Preventing and reducing stress is the next most important thing you can do for your tree(s). Making sure to water properly and reduce mechanical or pest damage will keep your tree healthy.
If you are in need of a proper diagnosis of you tree problem, it can be completed by your local K-State horticulture extension agent, Kansas Forest Service community forester or rural district forester. This may require some monitoring of your tree(s) to understand the problem. The professional that is able to look at your tree(s) will assess your concerns and identify the windows of opportunity to target the concern and determine the best management practices for the situation.
Drought stress can lead to an increased risk of invasion by otherwise “weak” pathogens or native insect pests. Trees that are under stress reduce the production of defensive chemical compounds that keep these secondary agents at bay. To identify drought stress over a particular disease or insect, the damage pattern will manifest itself over the entire tree canopy.
- Armillaria root rot, due to physiological changes in the stressed tree which stimulate the Armillaria fungus to shift into aggressive growth mode, and hasten death of the tree.
- Dutch elm disease, because drought stressed trees become much more attractive to elm bark beetles (the vector for the fungus), actually attracting them to lay eggs in the tree.
- Pine wilt nematode, because drought stressed pines cannot make resin which may protect from “beetle maturation feeding” infection; and because drought stressed trees attract the long horned pine sawyer beetle vector to lay eggs in the tree (another opportunity for infection).
- Verticillium wilt, because drought stress inhibits the tree’s ability to “wall off” the fungus. This allows the fungus to invade more of the wood. Drought stress increases symptom expression. Infected trees will exhibit much more severe symptoms following drought stress.
- Many canker fungi appear to require that the tree be stressed in order for disease to occur. In many cases this is a complex situation where both drought stress as a predisposer and wet conditions to allow infection are required. Some example include Botryosphaeria cankers (redbud, apple, rhododendron, many others); Cytospora canker of conifers (spruce); Cytospora canker of Prunus, willow and maple; Hypoxylon canker of oaks; Nectria cankers in many hardwoods; Fusarium cankers (especially following late spring frost injury); Diplodia (Sphaeropsis) canker on two needle pines. If plants have a root disease (fungal or nematode) they will be more rapidly and severely damaged by drought.
To understand how important supplemental watering is to a tree, a large mature tree can transpire (water movement through the tree and its evaporation from leaves, stems, and flowers) up to 80 gallons or more of water during a hot summer day.
Helpful guidelines to follow during the year for watering your trees:
- Remove grass and weeds under and around trees and shrubs.
It is important to reduce competition for water and nutrients in stressful situations because the majority of tree roots are in the upper 18 inches of the soil profile.
Grass is more efficient at taking up water and nutrients than woody plants, so it is important to remove grass from around trees and shrubs as a general practice.
- Mulch all bare soil under trees and shrubs with 2 inches of coarse arborist chips, bark, or leaves near several inches away from the trunk and as increase the mulch depth to 4 inches as you go out towards the drip line. Coarse mulch will allow water to soak through, but will shade the root zone and keep moisture in the soil. It is best to avoid fine bark mulches have a tendency to matt up and will not allow water to soak through as easily.
- Learn to only water trees according to their needs. Newly planted trees may need water where established plants may not. The easiest way to check if your tree needs water is to stick a 12 inch screwdriver into the ground. If the screwdriver cannot be pushed into the soil at least 6 inches, it is time to water. A slow, deep, infrequent watering is best for your trees. Using a soaker hose for several hours during dry and hot conditions will allow moisture to soak into the soil and into roots. Remember that young trees may need more tender loving care than large established trees. Do not wait for moisture stress symptoms to emerge before watering.
Links & Resources
- Directory of Common Plant Problems in Kansas - Kansas State University
- Identifying the Problem: Decline & Dieback of Trees - University of Illinois Extension
- Tree Damaging Mistakes / 24 Ways to Kill a Tree - Virginia Cooperative Extension
- Abiotic Problems of Trees - Nebraska Forest Service
- How to Plant a Tree - Clemson Extension
- Drought Resources - UNL Extension
- Caring for Trees in a Dry Climate - CSU Cooperative Extension
- How Drought Stress Predisposes Trees and Shrubs to Diseases - University of Maryland
- Drought Damage to Trees - University of Georgia
- Drought and Landscape Plants - Bartlett Tree Research Laboratories
- Irrigating Trees and Shrubs During Summer Drought - MU Extension
- Tree Watering Tips - Texas Forest Service
- Rainwater Harvesting in Residential-Scale Landscapes - UNL Extension
- Texas Manual on Rainwater Harvesting - Texas Water Development Board
- Tree Root Problems - The Morton Arboretum
- Mechanical Damage - Missouri Botanical Garden
- Protecting Trees from Construction Damage: A Homeowners Guide - University of Minnesota Extension
- Reducing Damage Caused by Tree Roots - Michigan State University Extension