Last week was another week of slightly cool days with scattered storms. "As we begin July, many fields in Iowa have uneven corn stands, but the weather is warming this week and hopefully crop growth will begin to catch up," says Rich Pope, an Iowa State University Extension specialist who keeps track of degree day accumulation.
Cumulative heat units during the week of June 23 to 30 lagged behind long-term averages by 10 to 25 degree days in Iowa. Flooding, cool temperatures and wet soil in June provided stress to struggling crops, and those stresses are showing up in poor growth. "As we get more heat the corn and soybeans should recover, but the weather we've had has set the crops up for future stresses," says Pope.
First report of soybean aphids
Crops in much of eastern and southeast Iowa generally don't look very good. "However, across the state, the fields that got planted by mid-May that have escaped the onslaught of flooding and ponding are doing quite well," says Pope. "Northwest Iowa is the garden spot in the state this summer. But they too are behind because of lack of growing degree days and cloudy weather in June."
The first 2008 report of soybean aphid in Iowa was on June 28, by ISU field agronomist Brian Lang in Winneshiek County. The infestation was scattered clusters of small aphids, 5 to 30 aphids per soybean plant. Lang lives at Decorah and the field where he found the aphids is in that far northeast corner of Iowa.
Many fields of yellow, uneven corn
How do ISU crop specialists around the state rate the 2008 corn and soybean crops in Iowa? Here's the general summary from their weekly telephone conference June 30. There are many reports of uneven stands of corn, and it is yellow-looking. These fields are especially common in central and eastern Iowa. With all the rain in May and June, this year's corn crop is shallow-rooted.
John Sawyer, ISU Extension soil fertility specialist, says "We aren't sure how much nitrogen is still out there in these fields. With all the rain, we know there have been nitrogen losses. But it's variable. When the corn root systems really start to grow and get down to where we hope the nitrogen is, we'll know."
Soybean diseases are beginning to show up. ISU plant pathologist X.B. Yang is looking at brown spot and bacterial blight as potential problems this summer.
Even northwest Iowa is lagging
In central, southern, eastern and southeast Iowa, crops are uneven and mostly range in fair to good shape. In some fields, corn and soybeans are rated fair to poor. Because of the flooding in many areas, farmers with these fields won't harvest much—or very little from a number of these fields that were flooded in June and then replanted in late June.
While northwest, western and north central Iowa have some of the better looking crops this year, they have some river bottom ground that experienced flooding and also some fields where heavy rains caused ponding. Many of those drowned-out spots were replanted late. Some were not replanted.
In northwest Iowa, crops are in pretty good shape—the best looking crops in the state. "Our corn is greening up nicely and growing, but it's not as far along as last year at this time," reports Joel DeJong, ISU Extension agronomist in northwest Iowa. Corn in his area at the end of June this year is in the V-9 growth stage. Last year at this time, it was V-14 or higher—almost tasseling by July 1.
So the best crops in Iowa as we enter July this year are in northwest Iowa. But they too, like crops in the rest of the state, are behind normal because of lack of growing degree days and cloudy days in June.