Does a Hard Winter Mean Fewer Bugs?

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Berries covered in ice

Winter officially begins on the Winter Solstice, the day when the sun stops sagging ever southward, which falls on December 21 this year. Ahem. At my house we have already seen snow twice, and the look and feel of winter has people talking about what this might mean to next year's garden pests. Does a hard winter mean fewer bugs?

According to recent research, the answer depends on what we mean by a hard winter. Insects have had about 400 million years to figure out how to survive cold, and they are very good at it. Starting in fall, overwintering insects accumulate chemicals that limit the ability of ice crystals to damage the organism, whether the insect spends winter as an adult, pupae, or egg. The pupae of cabbageworms, for example, can survive temperatures to -25°C (-13°F); the eggs of bean aphids don't begin to crack until temperatures drop to -34°C (-29°F).

Weather this frigid is often accompanied by snow, which works to insects' advantage by keeping temperatures steady. Insulated from weather changes at the surface, cold-hardy insects enjoy a restful, uneventful winter in years with good snow cover.

Snowy garden

The kind of winter that is likely to take a heavy toll on garden pests is much more of an up-and-down affair, with mild periods falling in between hard freezes, and scant snow to protect places where insects like to hide. Overwintering insects that are repeatedly exposed to freezing and thawing are more likely to die, and those than survive typically lay fewer eggs. Up-and-down winters that are brutal one week and balmy the next are bad news for overwintering insects.

Changeable weather is also rough on slugs, which are so traumatized by hard freezes that they lay low for four to five days afterward, even if the cold snap is following by a mild spell. In cool maritime climates where slugs are active year round, the garden benefits most from erratic winters. In very cold climates, however, slug adults and eggs stay deep in the ground until the soil thaws in spring. Then you have slugs like the Spanish slug (Arion vulgaris), a cold-sensitive species from southern Europe that has successfully invaded northern Europe by breeding with native species, thus increasing its cold tolerance. Citizen scientists please note: The John Innes Centre is hosting the SlugWatch project, which hopes to track the Spanish slug (sometimes called the giant killer slug) in the UK.

Solstice candle

We gardeners pray for a warm spring so we can get busy planting, but a cool spring is harder on pesky insects. In fact, when spring comes so slowly that plants get a head start before pests emerge, insects tend to be easier to manage. But when mild weather causes overwintering insects to emerge ahead of schedule, their numbers can increase rapidly, so they are ready and waiting to damage tender young plants.

And so, with the Winter Solstice upon us, we must rely on our own observations as to what the effects of winter might be on our gardens and the insects that inhabit them. Why not wish for the best? Borrowing from ancient Winter Solstice rituals, you might start the day in darkness illuminated by a candle that is surrounded by stems of evergreen foliage. Symbolically, the lit candle uses fire to call for returning light, while evergreens represent the continuity of life according to Nature's rhythms. Now make your wish.

By Barbara Pleasant

Bugs, Beneficial Insects and Plant Diseases

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Show Comments


"Hi Barbara, thanks for the information you posted here... I despise chemicals for controlling bad garden bugs. I was wondering if I fired up the rototiller and tilled up the frozen soil in my garden if it would help eliminate some bugs? I understand a lot of bugs over winter in the ground and my thought was maybe by tilling up the soil I could put a dent in the population? I'm looking to control squash bugs, flea beetles and Harlequin cabbage bugs - What's your thoughts - good or bad idea? Any other suggestions?"
Jeff Mills on Tuesday 7 January 2014
"Jeff, I would not risk ruining your soil's structure to possibly impact insect pests. I get decent squash bug management by letting them find a couple of early plants (a trap crop) and gathering them up. You will need row covers to manage spring flea beetles. I run my spring cabbage crops early so they are ready to harvest just as the harlequin bugs emerge. Fall brassicas are protected with row cover until late summer, when the harlequin bugs are gone. Good luck! "
Barbara Pleasant on Wednesday 8 January 2014
"I would assume the tilling would also destroy the earthworms and other beneficial insects as well. I try to fluff up my soil in spring with potato fork or regular fork to avoid hurting as many worms as possible and to work compost in. Some say just leave compost on top but even in raised beds the soil seems to get awfully compact."
Rebecca Knight on Sunday 19 January 2014
"Rebecca, your method is quite sound. Many gardeners use a special tool called a broadfork to aerate permanent beds without causing excessive upheaval among the soil's inhabitants. "
Barbara Pleasant on Sunday 19 January 2014
"Disturbing the soil is your problem in a nut shell. Healthy soil consists of countless micro organism including mycorrhizal fungi which symbiotically work with the plants to create ideal growing conditions. By tilling, your destroying this micro ecosystem leaving your plants to fend for themselves. Healthy plants are less prone to insect damage and disease. I'm not saying you wont have damage, a healthy Eco-system will have pests. It will also have predatory insects to keep them in check. I have squash bugs every year. They're gross! I call them legion for they are many (to coin a phrase) but Ive never lost a squash plant because of them, have you? It also has never effected my plants productivity. I strongly urge you to look into the techniques of no dig gardening and the benefits it can bestow. "
AFarmerFromPennsylvania on Sunday 26 January 2014

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