R.L. (Bob) Nielsen
Agronomy Dept., Purdue University.
Given the near record late planting of the 2019 Indiana corn crop and the continuing agony of delayed development of the crop, much of the coffeeshop talk down at Cecil’s Corner Cafe in recent weeks has centered on the risk of the late crop not maturing before a light frost damages the crop or an outright lethal freeze (28F) kills the crop.
Where does Indiana’s corn crop stand at the moment relative to maturity and risk of frost or freeze injury to immature corn? The current USDA-NASS estimates of the kernel development progress of the 2019 Indiana corn crop (Sept 16 report) indicates that 90% of the crop is at the dough stage of development or beyond (Fig. 1), 59% of the crop is at the dent stage of development or beyond (Fig. 2), and only 16% of the crop is physiologically mature (Fig. 3).
Those numbers can be misleading because they represent the percentage of the crop at a given stage OR BEYOND. For example, when 59% of the crop is at the dent stage OR BEYOND and 16% of the crop is mature, then only 43% of the crop is actually in the dent stage of development.
One needs to do similar “reverse” calculations to estimate the actual percentages of the crop that are at specific kernel stages of development. Doing so results in estimates that suggest approximately 10% of the state’s corn crop remains in the milk stage of development, approximately 31% of the crop is in the dough stage, and approximately 43% of the crop is in the dent stage of kernel development (Table 1).
An earlier article of mine offered some guidelines to help growers estimate the number of days to maturity for corn based on current stages of kernel development (Nielsen, 2019b). Those estimates are summarized in Table 1, along with the calendar dates that match up with the estimated days to maturity as of mid-September. Obviously, the corn fields most at risk for experiencing a frost or freeze event prior to maturity are those at the younger grain fill stages (milk and dough) that may not reach kernel black layer development until the third week of October or later.
Also included in Table 1 are estimates of possible yield losses if immature fields were damaged or killed by frost or freeze events (Carter & Hesterman, 1990). The difference between the estimates of yield losses in the last two columns of the table is based on whether the plant is completely killed or whether there is opportunity for surviving stalk tissue to remobilize stored carbohydrates to the immature grain before kernel black layer occurs.
Given the estimated percentage of the state’s corn crop yet in the dent stage of development or younger (84%), the significance of an early-occurring fall frost or freeze event in the next few weeks should not be underestimated. The good news is that I have not yet seen any forecast that suggests those events will occur in the near future.
Keep your fingers crossed!