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Gardening in a Changing Climate, Part II: A Horde of Locusts

By: Sierra Laverty, Assistant Horticulture Director | 12/04/2018

In the final days of October, we transplanted more than 100 vegetable seedlings into our raised beds and cold frame. Tucked under row-cover and a little plastic, we’ve overwintered broccoli, kale, cauliflower and other cold-season crops in our Vegetable Garden in the past. These seedlings were a little smaller—their leaves were deliciously sweet, and would’ve been perfect in a salad. Apparently, our resident mice population thought so, too. The mischievous little pests ate the entire crop within a week.

Last winter was mild and warm. This year we’ve seen more mice than in recent memory, which is perhaps the product of a toasty winter. While gently increasing winter minimum temperatures isn’t thrilling enough to be the focus of A Day After Tomorrow, a 2004 sci-fi disaster film on global warming, it may have a remarkable impact on backyard gardens and agricultural crops. Plant pests and diseases are already a source of anxiety and heartache for home gardeners, horticulturists and farmers. Climate change may further complicate those interactions in subtle ways, worsening some infestations while culling others.

A summer drive up to Bogus Basin in the Boise National Forest is all that is needed to witness the destructive abilities of insects firsthand. Bark beetles have killed billions of trees in Idaho forests, destroying more trees than wildfires in recent years. Frigid winters control some bark beetle populations, but often do so less frequently as warming trends persist.

Pesky bark beetles can wreak havoc on local trees. If you start seeing intricate patterns like the ones pictured here, you may have a bark beetle infestation.

Hotter spring and fall average temperatures could enable some insects like bark beetles to increase their reproductive ability. Extended warm seasons can also cause migratory insects like the potato leafhopper, which cannot survive Idaho winters, to arrive earlier or remain longer throughout the year.

The effects of climate change on pest populations are impossible to generalize, given that every creature has its own unique biology. Insects are among the most vulnerable living beings to climatic shifts because, like snakes and lizards, they are ectothermic and can’t regulate their body heat. An insect’s coloration can even influence its distribution—lighter insects may be more abundant in hotter regions and darker insects more common in colder ones. Will warming trends change these patterns? Again, nature’s ways are hard to predict.

Let’s use aphids as an example. The success of this sticky pest may be attributed to their reproductive abilities. An aphid can give birth to 80 babies a week, spawning over 20 generations in a single growing season. What if that growing season was longer? More aphids, one would think. Aphids may actually give birth less during hotter summer temperatures. The business of understanding the consequences of climate change is messy at best.

Facing such uncertainty, what is a gardener to do? Similar to the advice of Part I, get outside and observe!

•Educate yourself on the basic groups of insects and signs of damage
•Keep notes when you suspect pest or disease problems
•Learn the principles of integrated pest management (IPM)
•Practice the mantra “right plant, right place”
•Ask your local nursery about disease-resistant cultivars
•Contribute to citizen science with Bumble Bee Watch, iNaturalist, or Monarch Watch

This is the second article of a three-part series. Next month look for Gardening in a Changing Climate, Part III: A World Without Water.