Trees are at the mercy of their environment and subjected to associated hazards. Non-living agents can damage trees and are considered part of the disease process. And these damages can often look like insect or fungi agents until closely observed. Extremes in temperature and water supply are two common causes of abiotic disease process but chemicals in soil and water, transplant shock and mechanical injury also can harm trees. Here are the most common non-infectious tree diseases:
High Temperature Disease:
High temperature and drying winds can cause rapid loss of water. This moisture loss can cause premature leaf fall and leaf "scorch". Leaf margins turn yellow or brown and leaves fall prematurely. You absolutely should water during periods of hot weather to prevent injury, especially smaller trees and new transplants. Plant trees in locations protected from prolonged exposure to sun and wind.
Low Temperature Disease:
Frost injury can occur when a tree is growing during early fall or late spring and a freeze injures or kills stem tissue. To avoid frost damage, plant locally adapted trees, cover trees if frost is expected, avoid frost-prone sites and lay off nitrogen fertilizer at the end of the growing season. "Frost crack" can cause serious damage to trees by lengthening already existing wounds after repeated freezes.
Excess Moisture Extremes:
Roots in flooded or waterlogged soils are killed by a lack of oxygen. Trees planted in heavy clay soils with poor drainage have the same symptoms. This oxygen deficiency resembles drought injury including reduced growth, small leaves and thin crowns, twig and branch dieback, and tree death. You can avoid problems if you choose wet tolerant tree species for moist sites or prepare the site to allow for adequate drainage.
Low Moisture Extremes:
Drought symptoms can be seen when loss of water through the leaves exceeds uptake of water by the roots. This is caused by inadequate soil moisture during extended periods of abnormally low rainfall. Symptoms include wilting, off-color foliage, twig and branch dieback in the crown, and the death of fine roots. You can avoid problems by not planting shallow-rooted species in low moisture or sandy soils. Mulching the tree base retains moisture and a good weekly soaking during drought will help.
Winter Injury:
Winter burn is a common conifer problem. Rapid temperature change on the south side facing the sun can cause needles to burn. Drying is caused by warm conditions taking tree moisture while frozen ground and tissue restrict plant water flow. Planting hardy trees, mulching, wrapping and avoiding areas with sudden temperature can help. Sunscald can occur in late winter or early spring when the temperature is above freezing during the day and below freezing at night. Shading or wrapping can help.
Chemical Injury - Nutrients and Salt:
Trees need certain nutrients for vigor and health. Nitrogen, phosphorous, and potassium are the most important. Other major and minor nutrients are also essential. Lacking specific nutrients can effect tree growth and cause leaf chlorosis, yellowing, and necrosis. One sure way to avoid having deficient elements is to take a soil analysis. Salt can cause injury in areas where road deicing is necessary. It affects foliage and can harm a tree over time. Avoid planting trees near salted roadways.
Chemical Injury - Herbicides and Air Pollution:
Herbicide drift can injure trees. A deciduous tree leaf will become distorted, curled, and brown on the margins. Conifer needles will turn yellow or brown, and succulent shoots will become deformed. Trees may survive, but growth will be stunted. Always follow the label and pick windless days to apply herbicides. Air pollutants emitted into the air from manufacturing and power plants and automobiles can injure trees under certain conditions. They cause various symptoms and are hard to trace.
