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By Rich Pope, Department of Plant Pathology
Wet and cold! That is how many people will recall the 2008 growing season.
And in a general sense that is a good description, as the Iowa statewide accumulation of crop growth degree days was about 130 behind the 30 year average, and rainfall was more than 7 inches above normal. But when we examine each by crop reporting district through the season, the story gets a bit more complex, depending on where you are looking.
The graph below shows the degree day accumulations by crop reporting district. The statewide average across all regions is shown as the bold red line in the middle.
The chart can be read by looking at the slope of the line. When it is going up, that time of the season was gaining in heat (temperatures were above normal); when it is going down, heat was lost relative to the 30 year average.
Observations from the degree day graph
1. With a few oscilations, the first 10 weeks of the season (up to around August 10) in Iowa were consistently slightly cooler than average, with degree day accumulations lagging beind normal.
2. For approximately 6 weeks from August into early September we experienced remarkably cool weather, but by late September and the first week of October temperatures were above normal. Reports of corn and soybean both taking their sweet time to get to maturity can be largely attributed to the cool August and September. Considering early season planting problems, the slightly cooler temperatures were favorable because of the lack of heat stresses that contributed wonderfully to crop development.
The graph below chronicles rainfall relative to long-term averages. 2008 was a wet year in Iowa, in all districts except the Northwest. But about 85 percent of the seaon total rainfall above the average (6 of 7 inches) came by the second week of June. Delayed planting and replanting were key worries, and crops needed normal, but regular rainfall from June on through the season. And we got just that; once the heavy rains that caused the floods ended, the rest of the season was consistently and thankfully "normal" across the state.
It is interesting to note, the lines representing east central, southeast and south central Iowa just after September 4. The remants of Hurricane Ike and to a lesser extent Hurricane Gustaf tracked by Iowa to the southeast, and considerable rainfall was recorded in the southeastern third of the state. That is evidenced by the steep upslope in the lines for those crop reporting districts relative to the rest of the state.
Note: the source for these data is the Midwest Climate Information Center in Champaign, Illinois.
Rich Pope is an Extension specialist working in the Corn and Soybean Initiative