The Horrid F Word: Frost

Erika DeBrouwer, Tree Fruit Specialist, OMAFRA

With the recent weather taking a turn (cold to hot to cool) and with how fast apples have progressed, 2023 has really been testing growers. This week temperatures are dropping, making it important to review critical temperatures, frost mitigation strategies and frost damage assessments.

Critical Temperatures

Apples	Silver Tip	Green Tip	½ inch Green	Tight Cluster	First Pink	Full Pink	First Bloom	Full Bloom	Post Bloom
Old temp	-8.9	-8.9	-5.6	-2.8	-2.8	-2.2	-2.2	-1.7	-1.7
10% kill	-9.4	-7.8	-5.0	-2.8	-2.2	-2.2	-2.2	-2.2	-2.2
90% kill	-16.7	-12.2	-9.4	-6.1	-4.4	-3.9	-3.9	-3.9	-3.9

This chart also shows the temperature that will kill 10 % and 90 % of normal fruit buds. These numbers were taken from Washington (WSU), Michigan (MSU) and North Carolina (NCS) Extension Bulletins. Apple – WSU EB0913