Published on Tuesday, June 21, 2022
The R5 growth stage signals the beginning of the end of the grain fill stage. Many believe that once the grain is fully dented, the crop is safe from yield loss, but that is hardly the case. Much is left to be gained or lost during the “dent stages” of grain fill.
The dent stage of grain fill usually begins 30 to 35 days after pollination, but the corn plant is still hard at work accumulating dry matter in the grain. This growth stage requires about 30 to 32 days to complete. Once an ear reaches full dent, it still has only accumulated approximately 45 to 55% of its total dry matter. It is very important to help maintain leaf and plant health to finish the kernel properly. Most of the yield that is to be gained at this point is gained via kernel size and weight, and they are both large factors in the final yield.
Grain loss from early plant death can come in many forms; late-season drought, stalk rots that shut the plant down early, and foliar diseases that reduce the photosynthetic factory can negatively impact the final yield. Stalk rots and foliar health can be managed to some degree via hybrid selection and the use of fungicides. Southern Rust and Tar Spot are two of the most common diseases in corn that are more frequent today, but Northern Corn Leaf Blight and Gray Leaf Spot are still present in many fields.
Although they are certainly not exclusively late-season diseases, both Tar Spot and Southern Rust can invade a field later in the year (as can other diseases) and still negatively impact yield. A PFR Proven™ practice is to apply a fungicide at R1 in corn; however, Beck’s is conducting new research to understand the profitability of a sequential application of fungicide as late as R4. Given that more than 50% of yield can still be lost at this stage, and the dent stage lasts for 30 days =/-, a fungicide that provides an additional 20+ days of protection may be of value, and early data suggests that it can be the case.
One uncontrollable factor that can have a major impact on yield at R5 is a frost or freeze event. A frost event that stays in the 32°F range for a few hours will likely lead to loss of leaf health but may not shut down the plant entirely. In this case, the yield impact is much less than an extended hard freeze of 28°F for four or more hours which will likely completely kill the plant. Depending on the stage, losses from a hard freeze can result in a yield loss of 50% down to less than 10% once the milk line is 3/4 of the way down the kernel (sometimes referred to as 1/4 milk).
Author: Shane Carver
Categories: Agronomy, Agronomy Talk