Is Moisture Killing My Bees?

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Is Moisture Killing My Bees?

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Dan Donahue writes:

In Portland, it is damp all winter. Even with hives wrapped from the cold, moisture is a real problem and ventilation. I put a black groundcover cloth down and then build a stand on top of that, raised about 14 inches.

Some of my hives have a screened bottom board with a closeable sliding plastic sheet. A couple have solid bottom boards. In my backyard, the grass in the winter holds water; I sink in a couple of inches almost every year. Sometimes my hives get a light blue mold-fungus growth on the honey or inner cover, even with about a 1/3 open on the landing board and inner cover venting at the top.

I lost two hives this month when the temps got down to 27-29 degrees F for a couple of days. All the bees seemed to freeze in place on the frame in their nucleus. We had freezing weather in January, and they lived through it, but in March, it finished them off. So I am guessing high humidity and freezing weather was too much for them. Humidity can go over 80% here. I saw no mites or other viruses. The bees were working, bringing in pollen in the week before the last freeze. They had honey and a tad of pollen two weeks ago. I was giving them 1 ½ – 1 syrup. They also had a small about of brood in all stages. They are down to about one frame of bees.


Rusty Burlew replies:

As long as they are dry, honey bees are wizards at staying warm. But a moist hive can be a death sentence because evaporation is a cooling process that steals the heat from a bee’s body. Living in a damp hive is like standing in a cold room while dripping wet from a shower.

I live in the same lowland trough as you do, just further north. My overwintering protocol focuses not on warmth but on dryness. It doesn’t get cold enough in the Puget-Willamette lowlands to worry about cold, so concentrate on the wet. At every wintering decision, ask yourself how to reduce moisture in the hive.

If your ground cloth is nonporous, start by getting rid of that. Plastic can hold moisture in the ground and promote the growth of mold spores close to the hive, so if your hives are in the mud, try layers of small rocks or gravel instead. Also, get rid of the wrap. Wrapping is ideal for dry places with cold temperatures — like North Dakota or Vermont — but it’s not suitable in a wet environment. That wrap is holding moisture in.

Then I would replace all solid bottom boards with screened ones. This allows the hive to breathe, and if it ever gets down into the 20s for more than a day or two, you can slip the plastic drawers back in until the weather warms back into the 30s.

Above the brood box, I would use a solid candy board or a shallow super with hard candy for winter feed. Do not feed syrup in the winter because it adds too much moisture to the inside of the hive. Also, use a moisture quilt to absorb all the water that condenses from the bees’ respiration. I also like to use an upper entrance. Since warm, moist air rises, it’s easier to vent it from the top than the bottom. However, if your moisture quilt is well ventilated, an upper entrance is not crucial.

However, all the drying protocols won’t work if your bees have varroa mites, which is what your description sounds like to me. So in addition to keeping your bees dry, test for varroa mites on a regular schedule.


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