How to assess cold damage | WSU Tree Fruit | Washington State University

Written by Matthew Whiting and Bernardita Sallato, April 11, 2021

As reproductive buds move towards flowering, the tissues become increasingly susceptible to cold damage. While fully dormant buds can withstand temperatures well below freezing, most buds at the current stage of flowering across Washington’s orchards are sensitive to temperatures in the mid- to upper-20s. Just how hardy buds/flowers are in your orchard will depend primarily on the stage of development, and cultivar, but several other minor factors will play a role.

Following a cold night like this past Saturday/Sunday, many growers are concerned about damage to their crops. Here is a brief tutorial for assessing damage in your blocks:

Open flowers: look to the middle of open flowers and find the pistil (Fig. 1). If it is missing, there was likely damage at an earlier stage of development. If it is present, emasculate the flower and look for any darkened/discolored regions on the style, or the ovary; these are indicative of damage (Fig. 2).

healthy pistils in sweet cherry blossoms — Figure 1. A cluster of sweet cherry flowers at full bloom. The arrows indicate green, healthy pistils

Healthy green pistil and brown pistil damaged by cold — Figure 2. Two emasculated sweet cherry flowers. The pistil on the left is healthy, the pistil on the right is damaged by cold.

Closed flowers: emasculate the flowers, or cut through the lower region of the flower to reveal the pistil. Again, find the pistil and look for discolored regions – these are indicative of cold damage (Fig. 3)

green pistil in the top and brown pistil in the bottom — Figure 3. A partially emasculated cherry flower revealing a green, healthy pistil (above), and a fully emasculated cherry flower revealing a pistil killed by cold damage (below)

green bud top and brown flower bottom — Figure 4. Transverse dissection of apple flowers to reveal healthy flowers (above), and a flower damaged by frost (arrow below).

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