Symptoms of Late Frost Injury

By Gail Ruhl, Sr. Plant Disease Diagnostician, Purdue University

This week we have received samples and images exhibiting symptoms of late frost injury from the low temperatures experienced around the state the past few weeks.

Late spring frost injury is a type of cold injury that results from low temperatures in late spring or when a plant has broken dormancy too early. Cold temperatures damage young tissue as leaves are emerging from their buds. Many species of plants may be affected by frost injury including trees, shrubs, flowers and vegetable plants. Shoot dieback from frost in conifer species including Norway and Colorado blue spruce, white pine and fir, has been reported in several counties throughout Indiana.

Symptoms of a late spring frost on trees, shrubs and herbaceous plants often appear as brown, black, curled, and shriveled leaves and stems on new plant growth. Often small pockets of leaf cells on developing leaves (maple, hackberry, oak) are killed by frost. As the leaf matures, these pockets do not grow and become holes that appear more prominent (tatters) as the leaf reaches mature size. This tattered appearance often resembles insect feeding damage.

Variation in the amount of damage from tree to tree is likely a result of a number of factors including variability in genetic vigor, sensitivity of newly emerged growth (leaves and candles), and microclimate around each growing site.

Although symptoms from frost injury can look alarming, most plants will grow out of the injury. If the frost injury is severe, the plant may drop the damaged leaves, replacing them with new ones. Pruning frost injured tissue will improve the appearance of the plant, however, do not be too quick to prune out growth as many plants will put out new buds just below the point of dieback.

Note, if similar symptoms appear more randomly on the foliage of trees such as maple, ash, oak, walnut and sycamore, then a fungal disease known as anthracnose  (pdf file) may be responsible for the leaf blight. This fungal disease can cause darkened, necrotic areas on leaves, particularly in the lower canopy, following wet, springtime conditions. Another typical symptom of anthracnose on sycamores is the dieback of new shoots.

Click image to enlarge

Spruce; injury from late frost
Image courtesy of Ed Sheldon

Spruce; injury from late frost

Yew; injury from late frost
Image courtesy of B. Erickson

Acer japonicum (Full Moon Maple); frost damage

Ash; look-alike injury caused by
anthracnose, a fungal disease.