Winter Burn of Evergreens

Mike Mickelbart, Horticulture & Landscape Architecture, Purdue University

Janna Beckerman, Botany & Plant Pathology, Purdue University

Winter burn is a common occurrence to boxwood, holly, rhododendron, and most conifers. Winter burn symptoms often develop when temperatures warm up in late winter and early spring. This type of winter damage is often misdiagnosed as an infectious disease or damage from excessively cold temperatures.

To understand winter injury, it is important to understand that while a plant is creating its food by photosynthesis, it is releasing large amounts of water through the process of transpiration (the evaporation of water from the plant). Over the course of a day, a large tree can lose hundreds of gallons of water. When plants are unable to obtain the water they need (due to drought or frozen soil), the water lost through transpiration cannot be replenished, resulting in dehydration, foliar damage, and even death.

The pines in the picture are showing damage on the road side of the trees. This is most likely a combination of three factors: 1) this is south-facing, so heat from solar radiation will cause the needs on that side of the tree to lose water more rapidly, 2) salt spray from the road during winter can burn the foliage, and 3) increased wind (relative to the north side) from traffic can lead to needles drying out.

Symptoms. Winter burn causes the scorching of leaf tips or outer leaf margins, complete browning of needles or browning from the needle tips downward, or death of terminal buds and/ or twigs.

Management. Several techniques to minimize or prevent winter burn can be implemented, with varying degrees of success:

• Carefully choose plant material, avoiding trees and shrubs that are known to suffer from winter burn (including, but not limited to Sitka spruce, English holly, and Colorado blue spruce).
• Avoid planting broadleaved evergreens like rhododendron in areas of high wind exposure.
• In the Fall, deeply water plants before the ground freezes, and continue to water during winter months when temperatures are above freezing but there is little precipitation
• Erect physical windbreaks
• Wrap problem plants with burlap or other material to protect from wind and subsequent moisture loss to evergreen shrubs and small trees.

Varying types of antitranspirants are available, but there is no data that these products limit winter damage.

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