Crop Update

Corn

The corn looks very good where the water did not stand on it, or it did not suffer greensnap, or other stand issues. Due to the weather we’ve had this year, there are more of these problem areas than in most years at NWRC. There are more spots in fields showing N deficient symptoms, primarily where water stood, even for only a day or so at a time. Many of these spots had water standing several times during the early season. Compaction in these wet areas may have compounded the problem by not letting the water get away sooner and limiting root growth. Either of these could have reduced the amount of N available to the crop, and together they compounded the N deficiency problem.

The unusual weather we are seeing has resulted in some symptoms in the corn that are not typical to this part of Illinois. Corn with symptoms of crazy top have shown up in some areas where water ponded for a short period. The symptoms are a proliferation of small leaflets just under the tassel and no ear developed. These are caused by an infection by a downy mildew fungus during the ponding. The fungus produces zoospores which can swim in the water and infect the corn plant. According to the Compendium of Corn Diseases, soil saturation of 24 to 48 hours is sufficient for infection.

Another disease preliminarily diagnosed on corn leaves at NWRC is eye spot. Typically this disease is primarily a problem in states like Wisconsin, which have cooler growing seasons. This fungus survives in corn residue and a causes small round lesion (less than 1/8") with a yellow halo. These symptoms were only observed on one hybrid in a field that has been in continuous corn for 6 years. Inoculum may have been building over time.

There are more gray leaf spot (GLS) lesions visible on the corn than has been seen for several years. The differences between hybrids in susceptibility to GLS is easily seen. There are several fungicide studies being conducted on corn at NWRC this season, so it will be interesting to see the yield results this fall.

The greensnapped plants that revived and sent up a new shoot will not make much contribution to yield. Some are producing silks, but most do not have leaves or tassels above the ear leaf. At least these plants are helping keep the weeds down by filling in the canopy. Most of the plants around the greensnapped plants have compensated to a degree by producing 2 good sized ears.

The lack of sunshine to accumulate growing degree days (GDD) continues to be a concern. How far we are behind really depends on your perspective. We are 86 GDD behind last year for the period May 1 to July 31, 126 GDD behind a 11 yr average (IL Water Survey), or 332 GDD behind the 1971-2000 average. This would mean the corn planted on May 1 is ~4 days behind last year, 6 days behind the 11 yr average, or 16 days behind the 30 yr average; take your pick. Of course, you could also factor in a later planting date for this year. However, it has been reported that later planted corn doesn’t need as many GDD’s to get through the grow stages as corn planted earlier; the corn plant has some ability to adjust to the season. The bottom line is that yes, the corn is behind, but the corn that hasn’t had stress issues (e.g. water) looks very good. The rest of the season will determine how good it is, and whether it is good enough to compensate for problems areas in the field to keep yields at or above average.