Mar 12, 2015

Winter damage likely to Pennsylvania berries

The question that seems to be on every berry grower’s mind is how much winter injury occurred this winter. This, of course, depends on the crop.

Strawberries

I expect that we will see injury in some locations, but not necessarily because of our low winter-time temperatures. Plants should have been protected under snow, straw or row covers by the time the really cold temperatures hit. However, last November we reached some lows in the lower teens and upper single digits during the third week of the month, and many plantings were not yet mulched or covered for the winter at that point. So, some injury could have taken place then especially on exposed sites. You can cut through crowns lengthwise to check for damage. Healthy crowns will be creamy white throughout, while slightly injured crowns will have some brown discoloration, and very severely injured crowns will be dark brown.

Raspberries and blackberries

At least partial injury of canes is likely, either from cold or desiccation, since not only was it cold in January and February, it was also very windy. With blackberries, exposed canes are very likely to have been killed from cold temperatures.

It’s very difficult to see the symptoms of winter injury in the buds when they are still tightly closed unless you have a microscope. However, you can cut some canes and put them in a vase of water and see whether they leaf out. You can also tell if the canes became desiccated by looking for striations (narrow grooves) in the surface of the cane tips while you are pruning. If you see these, it means that the tissue dried out too much. Of course, you can also check canes for a layer of green tissue under the bark as a sign of life, though color alone is not always a clear indicator as dead canes sometimes retain some green color. However, dead canes often feel lighter, and the cut ends feel totally dry. Live canes contain some moisture that you can usually feel if you place the cut end of the cane against more sensitive skin such as your cheek or lips (assuming they aren’t so frozen that you can’t feel anything).

This coming summer, if you notice canes failing to leaf out and are wondering whether the problem is winter injury or a disease, remember that if winter injury is the culprit new canes will grow normally, whereas if you have a root rot problem primocane growth will be weak or nonexistent.

Blueberries

Even though it got cold, it didn’t get cold enough to kill canes of most varieties, as blueberries can generally take temperatures down to minus 20˚ F or even lower. Injury from desiccation is a concern, however. You may be able to see browning in buds if you cut through them, or as with raspberries and blackberries, you can cut some canes and put them in a vase of water to see whether they bud out. Cane color is a trickier indicator with blueberries than it is with raspberries and blackberries, though moisture and weight can be an indicator of survival if you are sufficiently experienced to be able to tell a difference. A brown or tan color to the wood can be an indication of a disease issue.

More to come?

With brambles and blueberries, exposure to fluctuating temperatures this spring can still cause additional damage, as the plant tissue is more susceptible to damage as it becomes less dormant and less capable of tolerating cold temperatures.

The one bright spot in these cold temperatures is that hopefully spotted wing drosophila populations will be “slow out of the gate” as happened last year, buying us a few additional weeks of harvest before populations rise to damaging levels.

– Kathleen Demchak, Penn State University