CHAMPAIGN, Ill., 3/14/22: Near-average winter soil and air temperatures are an indication that crop insect pests may have survived the cold in Illinois, according to scientists Jennie Atkins and Kelly Estes at the Prairie Research Institute (PRI) at the University of Illinois.

Four-inch soil temperatures under bare soil averaged 36 degrees from December through February, 1 degree above the long-term average. Regional temperatures ranged from 34 degrees in the north to 40 degrees in southern Illinois.

However, soil temperatures fluctuated greatly throughout the season, Atkins said. Warmer weather in December led to 4-inch bare soil temperatures that were 4 degrees higher than normal, averaging 41 degrees for the month. Even the monthly lows were above freezing for most of the state.

Colder weather in January caused 4-inch bare soil temperatures to fall 9 degrees to an average of 33 degrees, 1 degree below normal. The lack of snow to insulate soils, especially in central and southern Illinois, caused temperatures to fall as low as 15 degrees. 

Increased snow cover in February for most of the state helped to shield soils from the coldest weather. Bare soil temperatures averaged 34 degrees for the month, 1 degree below normal. Yet the daily lows were higher than previously, falling to only 24 degrees, while daily highs reached into the 50s.

Temperatures were rising as the state entered March. After the first week, 4-inch bare soil temperature averages were in the mid-40s with highs in southern Illinois in the 60s. 

The temperature averages bode well for insect survival over the winter. Insects not only overwinter in different life stages, but also in different locations. Some overwinter in the soil, while others spend the winter months in leaf debris, grass, or even under tree bark.

A few different factors can affect insect survivability during the winter months: dramatic temperature swings, snow cover, and even soil moisture. Given the averages we experienced this past winter, we expect little effects of winter temperatures on overwintering field crop insect pest populations, said Estes. 

Don’t rule out the potential impact of spring weather, though. It is important to remember that what happens in April and May weather can also have an impact on insect populations heading into the growing season, especially if we see a wet spring or a late cold snap.

The Water and Atmospheric Resources Monitoring (WARM) program at PRI provides daily and monthly weather and soil information from 19 stations across the state as well as a monthly water and climate summary.

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Media contacts: Jennie Atkins, Ph.D., (217) 333-4966, jatkins@illinois.edu; Kelly Estes, (217) 333-1005, kcook8@illinois.edu