The calendar may now say we are in the month of May, but it certainly doesn’t feel that way with the weather and with planting progress across Iowa.
Soil temp. Ideally we want soil temps at the 4” depth to be 50oF or warmer prior to planting corn. While we did surpass the 50oF mark, soil temps dropped after the recent weather over the past weekend (April 26 to April 28). Soil temps in northern Iowa are currently in the mid to upper 40's oF and in southern Iowa are in the 50’s oF.
Precipitation. In addition to the cooler conditions, most of the state saw 1” or more of rainfall with some areas in east central Iowa receiving closer to 3” of rain. The forecast for this week is calling for some more precipitation events with the southeast part of the state looking like it could get the most rainfall.
Outlook. Unfortunately, the 2 week forecast doesn’t show much for a change in current conditions. The outlook shows the cool and wet conditions lasting until mid-May.
Implications. So what does this mean for the crop that has been planted and for the crop that still needs to go in the ground?
For the crop already planted, evaluating stand establishment will be important. Imbibititional chilling/cold injury could be one potential concern in corn. With the current cool temperatures and Growing Degree Day (GDD) accumulation of less than 10 GDD/day based on the current forecast, it could take 2 or more weeks for emergence to occur. With the longer time to emergence and exposure to cool, wet soils, seedling diseases, dampening-off, and herbicide injury could all be potential concerns.
For the crop that needs to be planted, the window to achieve 95% yield potential in corn goes from April 15 to May 13 (Baum et al. (2019), while the soybean planting window goes until May 20 (Kessler et al., in prep). While field operations are at a standstill, there is still time to get the corn and soybean crop planted timely. Changing crop maturity and seeding rate is not recommended until planting dates are delayed past June 1.
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- Field Agronomist in EC/SE Iowa
- Field Agronomist in Central Iowa
- Associate Professor
- Extension Cropping Systems Specialist