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Published February 24, 2014, 09:25 AM

Extreme cold winters influences insects and disease

In general, insect populations are highly influenced by the weather, both during the growing season and winter. Most of the insects that inhabit North Dakota are known as “cold hardy insects,” which means they have the capacity to survive cold winters.

By: Venkataramana Chapara, NDSU Extension Service

In general, insect populations are highly influenced by the weather, both during the growing season and winter. Most of the insects that inhabit North Dakota are known as “cold hardy insects,” which means they have the capacity to survive cold winters.

The successful survival of an insect depends on its overwintering, or diapause, ability.

They break their diapause on the arrival of sufficient growing degree days in the spring.

Insects prepare themselves in the fall by eating a lot in a short amount of time when the temperatures are dropping before they get into diapause stage. They build enough body reserves to reach the appropriate stage of development and start traveling to overwintering sites, which could be deep in the soil, seed, stubble, plant debris and even houses.

Insect pests of north-central North Dakota that normally cause significant damage to crops include: grasshoppers, wheat stem saw flies, wheat midges, army worms, root worms, aphids, thrips, banded sunflower moths, red sunflower seed weevils, European corn borers and alfalfa weevils. They overwinter as a full grown larva or as an egg or pupa. Stubbles will be hit particularly hard if extreme cold conditions prevail longer than usual.

Prolonged wet conditions can lead to drowning or exposure of these overwintering stages to diseases that might affect insect population levels in the spring. The same is true for beneficial insects such as pollinators, predators and parasitoids.

Extreme cold winters might have a detrimental effect on overwintering insects locally, but do not overlook the migratory insects that cause significant damage, such as sunflower head moth and Aster Yellow leafhopper, which do not have the ability to overwinter in North Dakota but migrate every year from southern states. Keep an eye on these migrating insects, as they do not have competition from local insects or natural enemies.

Keep in mind there will be a certain percentage of insects that always survive the odds and contribute to the buildup of the spring populations.

Most plant pathogens that cause plant disease require a particular temperature and relative humidity before they sporulate or initiate infection. But they have the capacity to produce dormant structures — special survival structures that are thick walled and can survive extended cold periods or extremely dry conditions.

Plant pathogens can tolerate the range of temperatures that typically occur in the place they have adapted to, so many plant disease pathogens that have made a home in North Dakota generally can tolerate cold winter temperatures.

Editor’s note: Chapara is a North Dakota State University Extension crop protectionist at the North Central Research Extension Center in Minot, N.D.

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