Building yield all the way to black layer

By John Brien, Eastern Agronomy Manager for AgriGold

Raising corn is a complex and challenging endeavor no matter the year or the environment, but one of the most challenging parts of raising corn is ensuring the corn crop is producing yield all the way to black layer. Why is this so important? Because at dent stage, also known as R5, 65% of the dry weight of the kernel still needs to be accumulated. That 65% could easily equate to 20% to 25% of the final yield or 40 to 60 bushels of grain.

The adage that once the corn reaches dent the yield is made and nothing can hurt it is a false statement. In corn production, agronomists talk about the length of grain fill and the longer a corn plant can accumulate dry matter, the higher the yield (not potential, actual yield). The extra time correlates directly to the importance of the R5 stage. If a grower can add 5 to 10 more days to the grain fill process the more yield is harvested. 

Yield is easily defined as number of ears per acre x kernels per ear x weight of kernel. At R5 a grower no longer has any effect on number of ears or kernels per ear, only weight per kernel — approximately 65% of the weight yet to influence. An easy visual for a grower is to examine the actual kernel size at harvest. Under a long grain fill window, the kernel will be deep, wide, and thick due to ample time to accumulate starch, versus small popcorn sized kernels from a corn plant that had a limited amount of time from R5 to black layer.

When corn is at the R5 stage it is extremely challenging to manage, thus planning now will help ensure two of the largest robbers of grain fill length can be managed. The first robber is the lack of late nitrogen. Nitrogen is critical from the beginning all the way until black layer and if it is short, the plant will prematurely shut the plant down due to a lack of resources. Most current corn genetics need 40% to 60% of their nitrogen post tassel, meaning there is a tremendous pressure to keep early-in-the-season applications present long enough for the corn plant. If a grower is pushing for higher yields and applied all their nitrogen preplant or if there has been an excess amount of moisture, a late pre/post tassel application will still add yield in nitrogen-limited environments.

The second yield robber is late season diseases, mainly southern rust and/or tar spot. Both southern rust and tar spot are devastating diseases that move in late in the plant’s life and both are extremely aggressive. Once they are identified in the field, within 10 to 14 days the plants’ photosynthetic processes can be shut down and dry matter accumulation is stopped. There are reports of both diseases in our surrounding states and it will only be a matter of time that we need to deal with them.

The unique challenge of these two diseases is they can typically infect a corn field after the VT fungicide application has stopped protecting the plant. Under normal conditions, the VT fungicide application provides adequate protection to get that plant to black layer, but these two diseases can interrupt that protection. If there is only 10 to 14 days left before a plant black layers and one of these diseases is heavily infecting a field, most growers are not going to want to spend the extra $20 to $30 to spray a fungicide. Remember, an extra 10 days can equate to 7% to10% extra yield and at 225-bushel corn, that is 15 to 22 bushels of corn. At $5.50 that is an $80 to $120 in revenue for a $30 investment. Simply put, if your corn plant is threatened to be shut down prematurely, spend the money to help provide more grain and more revenue for your farm.

I live my agronomy life with the motto: never give up on a corn plant! Ensuring the corn crop is fed and healthy all the way to black layer is critical to maximize yield and profit potential no matter the year or commodity prices.