Degree Days - Cool July With Good Crop Conditions

July 28, 2009
ICM News

By Rich Pope, Department of Plant Pathology

Iowa corn is tasseling and silking this week. We think of the silk date as a marker for the final 60 to 65 days in which the corn reaches physiological maturity. That means we might expect dry down to extend into October across the state. Soybeans are setting pods, and with timely August rainfall, pods should fill nicely. Last week we lost approximately 50 degree days to average across Iowa, making July 2009 as one of the ten coolest in history.  

Degree day accumulation map for July 26

Scouting for pests now has the potential to  influence yield profits. Soybean aphids are present in many areas, particularly central and northern Iowa, but most populations are below the economic threshold. Corn diseases like eyespot (especially in north central and central Iowa) and gray leaf spot (especially in southwest and south central Iowa) should be monitored.  For soybean, we are seeing a few fields with sudden death syndrome symptoms being expressed. 


Rich Pope is a program specialist with responsibilities with Integrated Pest Management. Pope can be contacted by email at or by calling (515) 294-5899.

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