Iowa State University

Freeze Injury Versus Drift Damage on Trees   
by Bob Hartzler

May 02, 2007 - The hard-freeze in early April caused significant damage to many early-emerging, herbacious plants across the state. However, it appears that the buds on many of the woody species (oaks, maples, green ash, etc.) were sufficiently dormant to protect the enclosed leaf tissue from the freezing temperatures. However, damage is evident on some of the species that leaf out early in the spring. Here in central Iowa, minor damage was visible on most crabapples, with deformed leaves and necrotic lesions on leaf margins. The most severe damage I observed was on willow, with tip branches being killed by the low temperatures. It is possible that freeze damage may be more widespread in southern Iowa since plants in this area would have been further along in development than trees in central and northern Iowa.

Although the freezing termperatures occurred well before herbicide applications on farm fields swung into full gear, it is likely that some people may mistakingly attribute this damage to herbicide drift. The following factors can be used to help differentiate between the two sources of damage: 1) Freeze damage will be more species specific than most cases of herbicide drift. 2) Freeze damage usually is characterized by randomly distorted leaves and necrotic margins on leaves. Herbicide damage varies with herbicide type, but often involves chlorosis. Growth regulator herbicides (2,4-D, dicamba, etc.) cause distorted leaves with parallel veins. 3) Symptoms due to herbicide drift typically become less severe as distance from the treated field increases, whereas symptoms of freeze damage on the same species should be fairly uniform across the landscape.

Freeze injury images: Left - dieback on willow branches; Right - malformed crabapple leaves

Distorted crabapple leaves

Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University