Next to pollination, the largest influence on corn yield is the grain fill timeframe. Grain fill starts when tassels come out and continues until the black layer is formed. This is usually a 50 to 60 day process, depending on GDU accumulation. This period can be overlooked because corn is 10 to 14 feet tall and the ability to make instant changes is limited especially in areas without a center pivot.
In 2019, AgriGold agronomist Todd Steinacher did a study where he went into a field and gathered several corn ears that were at ¾ milk line and let them dry. Then he came back to that same field after the corn had naturally finished and gathered more ears. After weighing each of the ears he found that there was a 25 percent reduction in yield on the ears he harvested early. Universities have done similar studies and concluded similar results.

Pre-Tassel Strategy

A lot can be done that will help with grain fill pre-tassel.

“Anything that you can do to get seeds blasting out of the ground growing fast and building a big and robust root system will be a great start,” says Josh Johnston, AgriGold agronomist. “The bigger and better the root system is when we head into those dry dog days of summer, the more access it will have to deeper water and nutrients.”

Different approaches to improving root systems early, and therefore grain fill, are safe, low salt in-furrow fertility and insecticides, early season PGR’s and 2X2 fertilizer. A good herbicide program to keep fields free of weeds will help as well. Every weed is using sunlight, water and nutrients that could be going to the corn plants.

According to Johnston, growers should also adjust planting populations for their yield environment. Overpopulating fields will create plant to plant competition that is counterproductive. Matching your fertilizer to the field’s yield environment is also important.

“Under fertilizing will cause plants to cannibalize leading to lodging risk and premature death, both of which are serious yield robbers,” says Johnston. “These are all things we should be thinking about pre tassel to help with grain fill.”

Post-Tassel Strategy

While corn plants are in the midst of grain fill, the strategy is somewhat similar. Johnston says to keep the bugs out and make sure all fertility needed is there, but that other problems may start to arise. Pre-tassel the corn plant is more likely to keep disease away.

“Once the tassel comes out, the plant begins to focus on reproduction with less emphasis on disease prevention,” Johnston says. “In many cases a foliar fungicide needs to be added to help keep disease off the plant.”
According to the Purdue Extension Field Guide, a 25 percent reduction in leaf surface could lead to up to a 7 percent reduction in overall yield. Other benefits to adding a foliar fungicide are the reduction of ethylene and lowering respiration. Ethylene is a plant hormone that is responsible for ripening. Fungicide also lowers respiration, which is the burning of sugars to keep the plant cooler. When plants’ respiration rates are lower, this leads to more available sugar to make grain.

“If the combination of these two can add just 5 extra days of grain fill that’s a 10 percent addition in the length of grain fill,” says Johnston. “Anything that you can do to help your plants have a good day is going to benefit the grain fill process. Extended grain fill will always equal more bushels.”