As I've been discussing for weeks now, the last safe planting dates for corn have come and gone for some areas of the state. Corn growers in basically the northern half of Indiana should now be switching to soybean planting if possible. Considering the calls I've been receiving this week from desperate growers, I felt it prudent to highlight the risks of continuing to plant corn beyond the last safe date.
The primary factor for determining last safe dates for corn planting is the estimated length of the remaining available growing season as measured by heat unit accumulation. Even though Peter Thomison (Ohio State Univ.) and I have data that suggest that corn hybrids 'adjust' their heat unit requirements downward to reach maturity when planting is delayed, there still comes the point in the planting season when there are simply too few predicted heat units to mature a corn crop before a killing fall frost occurs, even for a very early relative hybrid maturity.
That point arrived around June 8 or so for the northern third and eastcentral parts of Indiana and around June 15 or so for the westcentral and central parts of the state. While one can gamble and continue to plant after these dates, one needs to definitely be aware of the risks involved in doing so.
IF any portion of the next few months is cooler than normal, development of the crop will be delayed and it will act as if it were planted even later than it was. We've not been batting too well in this department so far in 1996.
A corn crop cannot really get ahead of the game with warmer than normal weather during June, July, or August because 'warmer than normal' during these months usually translates into heat-induced moisture stress. Loss of potential heat units in June, July or August is the real killer for crop development because you can't catch up later. Warmer than normal weather in September and October really doesn't benefit the crop as much because the number of hours of sunshine (the driving force behind photosynthesis) are dwindling fast during the fall.
IF the crop is killed by fall frost before it is mature, yield losses can be severe. Yield loss from death of just the leaves by fall frost is 35, 27, or 6 percent if the immature grain is at soft dough, full dent, or half-milkline stages when the damage occurs. Yield loss from complete plant death by fall frost is 55, 41, or 12 percent if the immature grain is at soft dough, full dent, or half-milkline stages when the damage occurs. Given that the yield potential of such late planted corn is 50 to 75 percent of optimum to begin with, the total yield loss in such situations will be staggering.
Grain moisture when plant death occurs at soft dough, full dent, or half-milkline stages is 65, 55, and 40 percent. Considering that the average fall frost in these areas of the state occur during the first two weeks of October, further grain drying would be extremely slow simply because of the cooler conditions in October and November. Furthermore, the storage quality (and in some cases, the harvestability) of frosted immature grain is greatly reduced.
While many growers have a definite need for feed grain for livestock enterprises, I strongly believe that if soybean planting is possible (i.e., corn herbicides have not been applied yet), corn growers would be better off switching to soybean and using the revenue from the sale of that crop for the purchase of feed grains this fall.
Return to the the Chat 'n Chew Cafe.
The Corn Growers Guidebook , a WWW resource for corn management systems in Indiana and the eastern CornBelt.
Purdue University Agronomy Extension WWW Home Page.
Purdue Agronomy On-Line! , Purdue's Agronomy Department WWW Home Page.