The common question floating through a corn growers mind is what impact will this low temperature trend have on the crop in the field. The fact that corn responds to heat makes us inherently nervous when the thermometer dips below average in the middle of summer.
I am here to relieve some of that nervous anxiety. In Ontario we are growing corn on the northern edge of the adaptability zone for this crop. We are well equipped with drying and storage systems that allow us to harvest the crop at high moisture levels. We had to invest in this equipment because our growing season is not long enough to allow the crop to dry naturally in the field. That being said, from a plant development point of view, early tasseling is a major contributing factor to good yields. An early tasseling crop provides a safety margin against late season problems. Early tasseling is defined as completing the pollination process by August 1. Normal tasseling extends the period into Aug 7.
Heat plays an important role in getting corn to tassel, but it plays less of a role after tasseling and during grain fill. In the pre-tassel stage more heat means faster development which is good, less heat means slower development which is bad. Once pollination commences the relationship between heat and yield reverses. Excessive heat adds stress to a plant that is already at maximum load shedding pollen and fertilizing all the new embryos that become kernels. After pollination the grain fill period of corn is broken down into 5 stages, each stage being about 12 days long.
Day 1-12. Milky embryo or blister stage
Day 12-24. Young sweet corn stage
Day 24-36. Beginning dent stage
Day 36-48. Half milk line stage
Day 48-60. Hard dent stage and black layer formation
Heat and drought stress shortens the stages, which we saw last year. In 2012, we went from pollination to black layer in 50-55 days. This year the stages will return to normal and with the cooler temperatures they may even lengthen a bit. However, the 60 day estimate will remain fairly accurate. High yields are built during years when plants make use of the long sunshine hours in August AND take the full advantage of the 60 day grain fill period. Bright sunny days and average temperatures are ideal. My buddy Pat Lynch has always argued that September weather determines the corn crop and he is at least partially correct.
The average killing frost date for this part of Ontario is October 7. Given that our crops pollinated during the last week of July and 1st week of August, we are looking at black layer maturity on or about October 1.
This is why the corn market has been losing its value the last month. Moisture and cool weather do not cause much stress to the crop once it is pollinated. The market is responding by trying to buy new crop corn as cheaply as possible. An early September frost will upset this trend, but that is a discussion for another day.
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