Check berry crops for winter injury

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black raspberry
Black raspberry.

By Kathy Demchak

Some growers are noticing that their berry crops are breaking dormancy a bit ahead of schedule, prompting several emails and phone calls about what to do with them.

Even if plants still appear to be on schedule, they could move along quickly with some warmth, so it makes sense to pay attention to them now.

Winter injury

One concern is winter injury with fluctuating spring temperatures. There doesn’t appear to be any injury at all on our brambles or blueberries at the research farm in central Pennsylvania, perhaps because we never had any truly cold temperatures this winter. Also, because the soil never froze more than a couple of inches deep, roots would have been able to pull up water all winter long, reducing any desiccation injury.

Strawberries

Strawberries grow anytime the soil temperature is above 40 degrees at about 4 inches deep, so you might want to take a peek under the row covers or straw if you haven’t yet. It may be a good idea to take row covers off to keep the plants from blooming too early, and then put the row covers back on as needed to protect from nighttime cold or stagger row cover removal to stagger bloom time.

If plants are mulched with straw, keep the plants covered until they start to grow, but don’t try to hold them much past this point. If you want to check the soil temperature and don’t have a soil thermometer on hand, various household thermometers with a metal probe work well as long as they specify measuring in this range, and you check them in ice water to make sure they are accurate at colder temperatures.

Blueberries

Blueberry buds are swelling, so you should be able to easily differentiate flower buds from leaf buds at this point. The best time to apply lime sulfur is when the buds are swelling and bud scales are separating. You can apply lime sulfur even if you are seeing the tips of some flower buds emerging, but check the label to see if the rates need to be reduced.

To check buds for winter injury, you can slice flower buds either across or lengthwise with a razor blade, sharp utility knife or a craft knife. If the tissue is green all the way through, then the buds are healthy.

You can use a hand lens or magnifying glass to check; most smartphone cameras also take good enough quality close-ups to allow you to tell whether any buds are damaged or not.

Cut the bud and lay it on a flat background material like a piece of cardboard so your camera can focus on it. You can expand the photo or upload to a computer and enlarge it on the screen to see what is going on.

You can use this information to determine whether you need to make any adjustments to your pruning techniques, which you may want to be making some good progress on now.

Raspberries and blackberries

Raspberry and blackberry plants are at about the same stage of dormancy as blueberries, so delayed dormant lime sulfur applications should be happening now or very soon.

To check bramble buds for winter injury, it works best to cut through the buds lengthwise. The flower tissue will be damaged first and appears as a blackened area within the bud tissue.

If you are seeing some winter injury, you can leave a few extra canes within the row that you can remove later. All of the buds I’ve checked look good so far, even on our thornless blackberries, so hopefully, we’ll continue on this path for the remainder of the spring.

(Kathy Demchak is a Pennsylvania State extension senior associate.)

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