Issue No. 9, Article 7/May 26, 2006
Crop Development as Spring Planting Wraps Up
Almost the entire 2006 corn crop is planted in Illinois, but soybean planting slipped further behind normal over the past week, with less than half the crop planted by May 21. Soybean planting progress will gear up in most areas this week, but there are still some areas with soils too wet to plant. As I mentioned last week, yield losses are starting to accelerate as soybean planting is delayed, but it's still probably not a good idea to "mud in" the crop at this point.
Due to cool temperatures, soybeans planted two weeks ago are just now emerging, and some are struggling to emerge (or have given up struggling) where heavy rains sealed them into the soil. There could be a few cornfields that have formed a crust that is reducing emergence, but most of the planted corn crop is up and starting to grow. If it has been two weeks with no sign of emergence, it is time to dig up seeds to see what is happening and to replant if it's clear that emergence won't occur.
For both replant and first planting, the return to rapid drying conditions will increase the threat of having surface soils too dry for rapid water uptake by seeds and rapid emergence. I observed some tillage of fields not yet planted in southern Illinois on May 23, and in some cases it looked like soils were almost too dry already to germinate seeds. In some of these fields, the need for such tillage seemed questionable, especially where fields had been tilled before and then rained on. People till in such cases for different reasons, including weed control, increasing the drying rate, and perhaps a better seedbed. If the tillage isn't clearly needed and seed placement without it would be good, then it might be better to plant instead of tilling. It's not uncommon that attempts to speed up drying backfire, with soils getting too dry, too fast. It's also likely that soils worked more than necessary will be more prone to crusting if there's heavy rainfall before emergence.
Corn development has been slowed by the cool temperatures in May but is tracking the growing degree-day (GDD) predictions fairly well. May GDD accumulations are 50 to 100 behind normal, and it's likely that May's GDD total will be little if any greater than April's. Our largest corn, planted on March 30, is now at V6 and about 8 to 10 inches tall. This is the stage at which the plant is poised to take off and grow rapidly as stem elongation kicks in. Rapid growth means that the crops will need nutrients readily available and that water uptake will start to grow along with the crop. If sidedressing of nitrogen still needs to be done, it's best to do it earlier rather than later, if conditions permit.
While the Illinois wheat crop is rated at 86% good or excellent, yields are still hard to call. The appearance of the crop from the road is certainly good--there are few weeds, and head number and size are good. But leaf color is not great in many fields. Reasons for this aren't always clear, but barley yellow dwarf virus symptoms are rampant in the variety trial at Belleville and may be a factor in some fields. It is clear that aphids were present in large numbers, probably during a warm period in late winter or early spring. It probably would have been difficult to find the aphids in time to use an insecticide. Using a seed-applied insecticide was somewhat effective in reducing symptoms in our trials, though even these plants show symptoms at Belleville, and few varieties show less than severe symptoms of the disease.
Heading and flowering of wheat were at about the normal time in southern Illinois and were somewhat delayed at Urbana and farther north in Illinois. Cool temperatures during May, however, have caused slower-than-normal seed development and growth. Wheat maturity in southern Illinois appears to be on track, with the earliest fields likely ready for the combine by mid-June. That means that grain filling will need to be very rapid for the next 10 days in order to get high yields. With leaves in some fields less than healthy green during this critical yield-making stage and with temperatures starting to build, grain filling could end early, and yields might not be as high as we hope. On the bright side, wheat yields following a dry stretch of weather during grain fill are often higher than expected.--Emerson Nafziger