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Can Cold Winters Knock Out Corn Rootworm?
There’s a glimmer of good
news in the brutal cold snaps that have occurred so far this winter. The
Arctic-type cold temperatures could dent corn rootworm populations for 2014.
Put a lot of emphasis on the
word “could”, though. If you’re counting on cold temperatures to replace
rootworm management steps like crop rotation or rootworm-resistant trait
rotation, don’t. Rootworm egg survival over winter hinges on several factors.
“Cold winters with no snow aids rootworm
mortality,” says Ken Ostlie, University of Minnesota Extension entomologist. Ostlie
discussed rootworm issues at last month’s University of Illinois AgMasters
That scenario may apply to
today’s sub-zero cold that’s embracing central Iowa. Last weekend’s
temperatures that zoomed into the 40s burned off lots of the snow cover that
blanketed fields. Today’s sub-zero temperatures flanked by sundogs are better
for killing rootworm eggs than snow-covered fields, says Ostlie. Even if temperatures dip to
-20 lows, deep snow cover can keep soil temperatures balmy for rootworm eggs to
Much also depends on rootworm
species. Northern corn rootworm can survive cold temperatures better than
western corn rootworm. The bad news is western corn rootworm has expanded its
range to where it’s now prolific in northern states like Minnesota, says
Tillage is another factor
that can positively or negatively impact rootworm survival.
Research cited in a 1995 entomology
journal paper authored by University of Nebraska entomologists cited 1967
research that showed tillage could bury about one-third of rootworm eggs below
15 centimeters (about 5.9 inches). This help shelter eggs from cold soil
temperatures for hatching later in the year.
Conversely, though, tillage raised
some eggs closer to soil temperatures where they were more prone to freezing.
Tillage also removed insulating soil cover that sheltered eggs from freezing