Farmers are getting anxious for the 2008 cropping season to start. This spring's cool temperatures and rain have prevented them from starting their field preparation activity. The last Illinois Crop and Weather report listed the current soil moisture conditions in Central and Eastern Illinois as 87 and 55 percent in the surplus moisture category. The weather forecast is still calling for periodic rain showers which may limit significant soil drying. Hopefully, the upward temperature trends will help.

We often start April with some corn already planted and we normally end April with about 60 percent of the corn planted, based upon the 5-year average published by the National Agricultural Statistics Service. The slowest corn planting start in the last 10 years was in 1999 when only 8 percent of the crop had been planted by May 1. Even with the slow start back in 1999 yields ended up about average. So while it is still too early to worry, there is real concern that delayed planting could take another year of bumper crops out of the picture.

Even if fields were dry, soil temperatures have bee too low to foster corn germination and growth. A soil temperature of 50 degrees has often been used as the threshold and considered to be the minimum for corn planting. Corn will germinate at such temperatures and with temperatures later in the day rising by 10 to 15 degrees in sunny weather, seeds will take in water and begin to germinate slowly. Even so, we would probably not want to plant into such soils if we knew that soil temperatures were not going to move upward.

The expectation is, however, that soil temperatures will warm during April, if not steadily, at least as a trend. Observations have shown that it generally takes about 110 growing degree-days for corn to emerge, though the fact that soil temperatures do not always correlate well with air temperatures makes the GDD amount vary considerably. With uncertain future conditions it could take as long as three weeks to accumulate 110 GDD. Three weeks is a long time for corn seed and seedlings to live underground; in that time insects, diseases, soil crusting, flooding, and other factors can decrease emergence and vigor.

Research that we conducted a few years ago showed that, even with the same established plant population, corn planted in early April did not yield as well as corn planted in late April. This yield loss was not large, but planting as early as April 10 resulted in yields about 5 bushels per acre less than corn plant April 25. There are several possible reasons for this, but the most likely is that temperatures are too low at some critical early stages in the corn plant's life. Very early-planted corn tends to be short, leaves tend to be slightly smaller, and may have lower kernel number than corn planted later. First-generation corn borer, herbicide injury, and some other diseases and pests may also affect early-planted corn more than later-planted corn.