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Cool temps stoke frost concerns

Though growing degree days (GDDs) are still ahead of the normal pace in some areas of corn and soybean country, they're still running on the short side in other areas where the corn crop is already behind its normal developmental pace. And, as July winds down, some farmers are starting to wonder if the cooler temps will keep the already-behind-schedule crop from reaching its full potential before frost hits this fall.

"Now it's all about how much time this crop is going to have in the northern tier," says Marketing Talk senior contributor jennys_mn. "I can tell you right now that the advantage of the hot weather has now been lost. We are back to where we were -- a late-planted crop that is in jeopardy."

The discrepancy in GDDs isn't on the same side of normal everywhere. South-central Minnesota, for example, is 10 to 20 GDDs behind normal, while areas of central Iowa remain about 40 GDDs ahead of the normal pace. Alhough things will likely gradually warm up in the next two weeks, many key locations have seen record or near-record low temperatures in the last few days, according to Harvey Freese of Freese-Notis Weather, Inc.

"It was a chilly weekend over the north-central Corn Belt states. Rockford, Illinois, reported an average temperature of 60.5 degrees Fahrenheit over the weekend on the 27th and 28th of July. This is the coldest July weekend on record for Rockford and ranks as one of the top 10 coldest for Chicago," Freese says. "Both cities reported a record low-maximum temperature on Saturday of 65. This week temperatures will slowly begin to warm toward normal conditions. No excessive heat is forecast for the next two weeks."


This map shows percentages of GDD accumulation for the Corn Belt in the week of July 29. Numbers represent percentages of normal, showing the entire region is expected to fall short of normal GDD accumulation for the week (map courtesy Don Keeney, MDA Weather Services).

And, it wasn't just in the Corn Belt; conditions were just as cool farther west, exacerbating the existing yield worries in an area that still has a way to go before it's climbed out of last year's drought.

"The last three days in western Nebraska have seen highs in the 60s and lows in the 40s... Those temps don't make a crop!" says Marketing Talk contributor westnefarmer. "The Corn Belt put most of the corn in the ground under stressed circumstances, and in my experience, when you make a below-average start, you never end up with a bumper crop."

Though the recent temps have slowed development now, the threat of an early frost is the biggest issue. Though just tardy now, the lateness of the crop could mean trouble as harvest nears. The good news is that's yet to make its way into the forecast just yet, says MDA Weather Services senior ag meteorologist Don Keeney.

"Since this will push the crops further behind, this does raise the concerns for the crops to be hit with frost prior to maturity," Keeney says. "Right now we're not expecting a very early frost, but even with a normal frost, this would still cause concerns."

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