Many questions have been asked this last week about top die-back and leaf yellowing that everyone sees while driving the country side. There are several things going on in each field that are not easy to diagnose unless you get out and go for a walk.
1. Maturity and Planting Date.
Corn planted in May is maturing fast and what we see in some fields is the normal drying down phase of the crop. We have received enough heat for 28-2900 heat unit hybrids to reach blacklayer. Silage harvest is getting underway which tells us that it is normal for corn to begin drying up as the plant consumes its reserves to finish the grain fill period.
The June planted corn is coming along quickly too.
This corn is on schedule to black layer the first week of October. The one thing we notice in the later planting dates is northern corn leaf blight.
Norther Leaf Blight expresses itself as cigar shaped lesions on the leaf. Most hybrids have some resistance to NLB, but these lesions will continue to spread consuming valuable leaf area.
2. Diseases and Stress
This plant is infected by anthracnose stalk rot. It causes the top of the plant to turn red and die. If you peel the leaf you will see the black colour on the stalk, right at the node.
Cut the stalk open and you see the dead pith in the middle.
This type of disease is worse in the stressed pockets of the field. We now see the accumulated stress from a wet spring, a wicked blast of heat at pollination time and a week of cloudy wet weather in early September. A weak plant is not able to fight off disease infections, just as a weak person is more susceptible to pneumonia.
The weak plants are also showing signs of infection by my old friend, gibberella ear rot.
This is the centre of a cob infected by gibberella.
I am a little surprised how easy it is to find gibberella in corn this year. I do believe it is the result of accumulated stresses during the growing season because it is easier to find in the weakest part of the field.
3. Hybrid differences are also responsible for some of the things we notice. We know late season health differs from hybrid to hybrid. Will this impact yield performance? We will know in a few weeks.
If I asked you which hybrid is earlier in maturity, you might say P9623HR, because it is drying down quicker than P9519HR. In reality, P9519HR is the earlier hybrid of the two. It is demonstrating better late season plant health.