Plant Problem Diagnosis Key / Growing conditions
Southwest injury (winter sunscald and frost cracks)
Winter sun warms the south and southwest side of a thin-barked trunk during the day and the bark freezes again at night, killing it or splitting the trunk. Young maple, linden, honeylocust, ash and fruit trees are most at risk.
Signs
- A long, sunken or cracked strip of dead bark on the south or southwest side of the trunk.
- Vertical cracks that reopen and lengthen in later winters.
- Mostly on young or newly planted trees.
What favors it
Thin bark, young trees, and bright winter sun on clear days after cold nights.
Prevention
- Wrap the trunks of young, thin-barked trees with white tree wrap or a light-colored guard from November to April, then remove it.
- Paint the trunk of fruit trees with white interior latex paint diluted half with water.
Crops it shows up on
Shade & ornamental trees; Apple, pear & stone fruit.
Often confused with
Sources
- Frost CrackMontana State University Extension
- Preventing Sunscald on Tree TrunksColorado State University Extension
- Whitewashing TrunksUC IPM
Treatment by crop
Cultural, biological and chemical options in the order to use them, and notes written for each crop.
Identification is free. Treatment is on the Home and Pro plans.
Questions in the key that lead here
- Look the plant over, leaf undersides included. Are insects, mites, slugs, eggs, webbing or droppings on it?
No, only damage or discoloration - Where is the problem?
A tree or shrub - Which part of the tree or shrub shows the problem?
The trunk or bark - What is in or on the bark?
Sunken, discolored or dead patches of bark - Where is the dead bark, and what is with it?
On the south or southwest side, with long cracks or bark falling away
Not a match? Start the key or describe what you see.
More photos
More from university Extension: search Extension pages on southwest injury, or find a plant diagnostic lab through your state's Extension.
Other growing conditions
- Blossom drop
- Blossom-end rot
- Cold and frost injury
- Construction and root damage
- Drought stress (underwatering)
- Edema (oedema)
- Fruit cracking
- Girdling roots and a buried root flare
- Heat and light stress
- Herbicide injury
- Leaf scorch and drought stress
- Light bleaching
- Mower, trimmer and animal injury
- Normal fall needle drop
- Not enough light (stretching)
- Overwatering (low root oxygen)
- Road salt injury
- Sunscald
- Transplant shock
- Winter burn of evergreens