CHAMPAIGN- URBANA, ILLINOIS - "If it rains on Easter Sunday – it will rain the next seven Sundays."

That saying comes to mind every spring if you are involved in row crop agriculture. Many would term that saying "questionable" and would place it in the same genre as "deaths coming in threes," "brown woolyworms heralding a cold winter," and "shaving causing facial hair."

Those with agronomy degrees tend to chuckle and laugh off the saying. Yet should the spring rain tap turn to "on" - the most stoic agronomist will reluctantly admit a primeval fear that "overcast holy days mean ominous planting delays." What does a planting delay mean for crop development and does a planting delay encourage or discourage additional in-season problems?

The corn planting "window" is a wide one. We know, for instance, that the best time to plant corn rests somewhere in the back half of April, but we also know that we can "get by" with planting corn in early April (not that long ago – before getting burned by two to three spring frosts – some producers even flirted with late March).

The window is equally broad on the reverse side with insignificant potential yield losses until after the first full week of May. From that point into the middle part of May, potential yield losses only hit a half-bushel per day when planters are kept out of the field. Those losses accelerate once we pass that point and press toward the "June threshold" with potential yield slashed in half by early to mid June. That said, some producers in the area will testify that they have limped to the finish line with June planted corn. They will often state that it was "nothing to write home about" but also will note that it was not "a complete loss." In other words, our area has about two and a half "comfortable" weeks to work with once corn planting is delayed into late April. Past mid-May, planting delays increasingly feel painful at harvest.

Additional trouble for late planted corn comes in a few different forms. Late planted corn – as noted in past growing seasons – tends to be the preferred egg-laying site for the first generation of European corn borer. It also tends to expose a much more immature plant to a much more developed foliar disease complex. In other words, many young (disease prone) leaves are exposed to fungi that have been around and "feeding" for a while. Because of this, plant pathologists tend to project an increased likelihood of yield loss from foliar diseases when corn is planted very late. Late planting also means bad news for ear rots such as Diplodia. Late planting means delayed dry down and that equates to an ear that is much more susceptible to infection (ISU Integrated Crop Management – May 3, 1999).

Beans can be planted into mid-summer. Planting delays have little to no effect on soybean yield until late May or early June. Losses incurred after that point are difficult to categorize but often range between 5 to 10 percent. By mid-June, losses to potential yield may hit 15-20 percent with yields slashed in half by late June/early July.

Late planted beans see more mid to late season moisture stress. This increases the likelihood of charcoal rot, which prefers hot, dry weather. The U of I often cites increased yield losses associated with the Soybean Cyst Nematode when planting is delayed – although that prediction is not universally accepted (U of I Report on Plant Disease No. 507). The development of insect populations and the exposure of those insects to various plants also tend to increase exposure to yield and/or quality reducing viruses – viruses which are vectored/ transported by insects (ISU Integrated Crop Management – May 3, 1999).

On the bright side, planting delays reduce the likelihood of Sudden Death Syndrome (SDS) in beans and reduce the likelihood of corn/bean stands being hammered by seedling disease. That said –all of us would really prefer to get into the field, plant some corn, and forget "rainy Easter sayings"….for another year.

SOURCE: University of Illinois Extension