How to Test for Bud Injury

The winter weather this year has been anything but "normal". The polar vortex that dipped into Connecticut on January 8-10 bringing subzero (^oF) temperatures was followed by a deluge of rain on January 11 and then the January thaw on the 13th-17th, brought temperatures in the mid-40's. These temperature swings can cause confusion in the vine where warming trends might signal the vine to begin the process of deacclimation.
There is a test that can be done in the vineyard to see if dormant buds have suffered winter injury. There is a lot of information on line regarding how the test should be done, but I found the photos from the Michigan State University publication Winter Injury to Grapevines and Methods of Protection by Tom Zabadal to be very helpful. They show how to evaluate the dormant buds by making the appropriate slices. The annotations A-F in the bottom photo, Figure 1, correspond to the cross-section series in the Table 1 below.¹
Figure 1

Table 1

	Photo A to the left shows the bud scales of the central primary bud.
	Photo B to the left shows the bud scales of the primary, secondary and tertiary bud scales.
	Photo C to the left shows the green tip of the primary bud which is the indication that this bud is alive. This is what you want to see when you take slices through the bud. Further cut into the bud corroborate if the rest of the bud has survived but winter cold.
	Photo D on the left shows that a deeper cut made into the bud reveals the primary bud and more of the scales of the secondary and tertiary buds.
	Photo E corresponds to the slice taken from the top photo and shows the tips of the primary, secondary and tertiary buds. The green color is a good indication that all three of the buds are alive.
	Photo F shows the green tissue at the base of the compound bud that connects it to the cane.

There are also two YouTube Videos made by Hans Walter-Peterson of the Cornell Cooperative Extension on how to do field testing for bud injury prior to pruning. Here are the links:
Bud Injury Testing Part 1
Bud Injury Testing Part 2

References:
1. Tom Zabadal, Winter Injury to Grapevines and Methods of Protection, Michigan State University, Extension Bulletin E2930, June 2007, pg. 27, 30.