The warm weather we experienced a couple of weeks ago accelerated the loss of cold hardiness of flower buds in many of our fruit crops, which has resulted in early bud swell in grape and bud break in apples and blueberries. Unfortunately, last week’s snow plus the cold temperatures we have experienced in the last days have resulted in damage to buds and new growth.
On Monday 4/24 I visited the West Madison research station to collect material to do an assessment of damage to wine grapes, table grapes, apples, and blueberries. I found significant damage to early wine grape cultivars such as Brianna and Marquette that were at the woolly bud stage (Picture 1), but in later cultivars, such as Petite Pearl, buds were still dormant (Picture 2) and they did not appear to be damaged. Most of the table grape cultivars in our trial also appear to have significant amount of bud damage. To determine the percentage of bud damage in the vineyard, I collected a total of 20 buds form each block and dissected them using a razor blade. When buds are damaged, the interior of the bud will be brown (Picture 3), while healthy buds are green in the inside (Picture 4). Another thing I noticed when walking through the vineyard is that buds that were damaged had a slightly red coloration and seemed “wrinkled” from the outside (Picture 5), compared to a healthy bud that has a light brown/beige color (Picture 6), and when you rub them with your fingers, they will come off very easily. At this point there isn’t much to do, but to wait and see if secondary buds will push in the next week to ten days, and hopefully we will be able to have a full crop from the secondary shoots.
Apple trees are also in advance stages, especially early cultivars such as Zestar! and Paula Red which in Southern Wisconsin are already at pink. Flower clusters had some damage to the leaves (Picture 7), but after dissecting several clusters, I did not see any damage to flowers (Picture 8).
Lastly, early blueberry cultivars such as Duke are at bud cluster stage and had significant visual damage (Picture 9). After dissecting several flower buds, cold damage expressed as browning in the interior tissues of the buds was visible in the apical flower of the cluster, while the basal flowers still remained green and healthy (Picture 10).
If you want to determine the percentage of damage to buds and/or inflorescence, you should collect separate samples for each cultivar. You should also collect separated samples depending on the topography of your vineyard, orchard, and/or farm (e.g., take separate samples for blocks located in high and low areas). Collect at least 20 buds/inflorescences in each sample. Use a sharp razor blade to cut cross-sections of the bud/inflorescence and assess if the tissue is damage (brown) or healthy (green).
Here are a couple of videos that show how to determine damage to grape buds, apple flower clusters, and blueberry inflorescence:Other News and Resources and tagged Amaya Atucha, Apples, freeze, freeze damage, freeze injury, Grapes.