Blueberries and Winter Injury Concerns

Posted: March 31, 2017

Fluctuating temperatures can cause as much or more crop loss than cold winter temperatures or spring frosts.
Blueberry buds breaking. Photo: Erutuon on (CC BY-SA 2.0)

Blueberry buds breaking. Photo: Erutuon on (CC BY-SA 2.0)

Unfortunately, our ‘Bluecrop’ blueberry field at the Horticulture Research Farm has more flower bud damage this year than I’ve ever seen before. While our site makes winter damage especially likely, I’m afraid we won’t be alone.

Our planting is right on the valley floor where we’ve never been able to overwinter blackberry plants without tunnels. We get really cold temperatures overnight, and it warms up nicely during the day, so the temperatures tend to fluctuate anyway. But the fluctuations this year were extreme.

From February 18 through March 1, highs were in the 60’s or 70’s on 6 out of 11 days. Then we had highs only in the 20’s on March 3 and 4 and a low of 7 on March 5. This was followed by highs in the 50’s on March 7, 8, and 9, a high of only 22 on March 11, and a low of 7 on March 13.

The flower buds were still perfectly fine at the end of February. However, out of 36 ‘Bluecrop’ buds collected 2 days ago (March 28) from various parts of the plants, 33 were nearly completely killed, 2 had a small amount of green tissue, and about half the tissue in one was still green. ‘Bluecrop’ is supposed to be one of the more hardy varieties. Our ‘Patriot’, a very hardy variety higher up on a slope, has only a slight amount of injury despite being at a more advanced stage of bloom, so both site location and variety likely had an effect.

One of our local growers had asked, when checking for winter injury, whether it was better to cut the buds lengthwise or across. I guess I’d say that’s personal preference. Information online and in the literature says that the most tender tissue is that which connects the buds to the stem. Cutting lengthwise allows one to see injury in this area, though I must admit, that’s a little tricky. I find it easier to hold the bud lengthwise when cutting it, though maybe that’s not a good reason for doing so. Eric Hanson at Michigan State University, who has a lot more experience with this than me, tells me he cuts the bud crosswise about a third of the way from the tip, and then a second time about a 2/3’s of the way down, checking each time for injured tissue. So, to be safe, I guess you could do both.

Here are several images with varying degrees of injury, and with buds cut both cross-wise and length-wise. These are greatly magnified, so it won’t be as easy for you to see the damage, and you might need to use your imagination a bit when looking at the blossoms. It helps a lot to have a single-edge razor blade, fresh utility knife blade, or an exacto-knife for making the cuts. Also make sure that any brown you see isn’t just a loose piece of bud scale that got stuck to your knife when you were cutting.

Note in the photos below that the little bar on the right is only 1 mm, so you’re seeing a lot of magnification here.

uninjured blueberry blossom

Photo 1 'Patriot' uninjured. Photo: Kathy Demchak, Penn State

Photo 1 shows a ‘Patriot’ blueberry bud that appears to be uninjured when cut crosswise.

uninjured blueberry blossom2

Photo 2 'Patriot' uninjured side view. Photo: Kathy Demchak, Penn State

However, you can see in Photo 2 that when the same bud is cut lengthwise, one of the would-be blossoms (lower left) is partially injured.

partly injured blueberry blossom

Photo 3 'Patriot' partly injured. Photo: Kathy Demchak, Penn State

Photo 3 shows a flower bud in which one of the would-be blossoms is completely killed.

injured blueberry blossom

Photo 4 'Patriot' base injury. Photo: Kathy Demchak, Penn State

Photo 4 shows a ‘Patriot’ blossom where it appears that the tissue at the base of the bud that would connect it to the plant is water-soaked in appearance, so probably is injured. If this is the case, the bud may not be able to survive past bloom.

blueberry blossom center injuryPhoto 5 'Bluecrop' center injury. Photo: Kathy Demchak, Penn State

Photo 5 shows a ‘Bluecrop’ bud where tissue in the center of the bud is injured.

blueberry blossom dead connecting tissuePhoto 6 'Bluecrop' dead connecting tissue. Photo: Kathy Demchak, Penn State

In Photo 6 where the bud is cut lengthwise, the tissue that would have formed the pedicel and the individual blossoms has been killed.

blueberry blossom dead

Photo 7 'Bluecrop' very dead. Photo: Kathy Demchak, Penn State

Our final image, Photo 7, is what nearly all of our Bluecrop blossoms look like. This shows a flower bud in which all of the blossoms have been killed. The tissue that is still creamy-tan is what would have been the anthers. If you look closely, in the upper left quadrant, to the lower right of the anthers, you can see tiny white spherical structures. These are the ovules which, after pollination, would have eventually become the seeds in the berries.

Hopefully these images will help folks with sorting out what might similar situations with some of their flower buds. It certainly is starting out to be an interesting year.

Thanks to Don Smith and the NEWA network for making on-site weather data available, and to Eric Hanson at Michigan State University for his for input and review of this article.

Contact Information

Kathy Demchak
  • Senior Extension Associate
Phone: 814-863-2303