Insect Pests and Plant Diseases in the Winter Garden

During unusually cold winters I often hear comments from gardeners like, “well, at least the bugs are being killed off.” It’s fun to think that suffering through extraordinarily cold weather might at least mean fewer problems come spring. It would make it worth it, right? But can colder-than-usual weather mean fewer insects or plant diseases the following spring? And what about those years when winter weather is fleeting, or spring seems to come super early? Does warmer-than-usual weather mean more pests and diseases earlier than usual? Let’s look closer at both of these things.

Unfortunately, most plant pathogens that attack plants in colder climates are not fazed by especially cold winters. These organisms have adapted to survive extreme winter temperatures and wait until the weather conditions are right to start a new life cycle each spring. Fungi, bacteria, viruses, and nematodes in more temperate regions can survive the winter inside insects, plant debris, and soil. So, even if the temperatures are colder than usual, these organisms have all found a way to survive. It would take very long periods of very colder-than-usual weather for the region to have any significant impact on plant diseases.

So, what happens when the winter temperatures are warmer or increase earlier than usual? Well, we have to consider that temperature is just one of the environmental cues to which plant pathogens react to. The other major cue is moisture. If there is significant enough levels of rain combined with warmer temperatures, you might see plant diseases show up earlier than normal. Infections can also be more severe in this instance, too.

Insects also play a role in plant disease cycles each year. Disease cycles in which the plant pathogens are overwintered and then transmitted by the insects will be closely linked to that insect’s activity. If the weather turns warmer earlier and the insects subsequently also become active earlier, then the plant diseases will be active earlier, too.

Speaking of insects, what about insects as plant pests? How do colder or warmer temperatures over the winter affect those?

Insects are more sensitive to cold and may be killed over the winter if they get too cold for too long. So, in the most extreme situations of unusually cold weather for an extended period of time, you might see a decrease in those insect pests. But most insects spend the winter in or on the ground, protected by the soil or by plant debris. Snow can act as an insulator, keeping the ground sufficiently warmer than the air above it. So, even if there are long periods of frigid temperatures, if it’s accompanied by snow cover most insects will be protected from the cold.

Levels of rainfall and humidity, temperature, and other weather factors all greatly affect plants, pathogens, and insects, and the way they interact with each other. Weather patterns during the growing season generally have much more influence on this activity in our garden than the winter temperatures do.  The best way to prevent insects and diseases from becoming a problem in the garden is to be proactive. Remove dead and diseased plant debris immediately and clean up the garden area at the end of the season. This helps prevent diseases and insects from overwintering where they have ample opportunity to move into your garden the next spring when the timing is right.

Be sure to clean garden tools, too, to prevent transmitting diseases and transporting insect pests and their eggs from one area of your property to the other. Finally, if plant diseases and insects are targeting specific families of plants, consider skipping a year and planting something those pests aren’t attracted to. All of these activities are much more effective than hoping for an unusually cold winter to kill off pests and will protect you if the weather warms up earlier than usual, too.

Your Friend in the Garden,