Milk Line - What does it all mean?

  • Sep 16
    Laura Johnston
    Milk Line - What does it all mean? By Laura Johnston on September 16, 2014
    Categories: Grain Corn, Silage Corn

    Harvest maturity (occurring around 25% grain moisture) usually refers to the point at which harvest and mechanical loss are at a minimum. Before this happens, corn develops a black layer which is located at the base of the kernel opposite to the embryo. Typically this occurs approximately 55-65 days after silking.

    Another way to estimate the time left until maturity is by using the milk line. After kernels have dented, a milk line appears across the kernels. This line moves down the kernel towards the cob. When the hard starch line approaches the cob, the black layer will form. It usually takes 20 days for the milk line to progress from the kernel tip (early dent) down to the base. For example, a kernel at ½ milk line will take about 10 days to reach black layer. From the end of the dough stage, it takes about 30-35 days to black layer.

    When the hard starch reaches the kernel base, it cuts off all water and dry matter transfer and forms the “black layer”. This means you have arrived at physiological maturity and frost is no longer a concern. Grain moisture at physiological maturity can range from 25-35%. Black layer formation begins at the tip of the ear and finishes at the base. Kernels are continuing to accumulate dry matter up until black layer.

    Corn that matures earlier (often related to flowering) will dry down faster due to warmer weather. Late maturing corn will dry at a slower rate due to cooler temperatures. Husk leaf coverage and tightness, husk leaf senescence, husk leaf number and thickness as well as ear angle are other factors that play into how fast each hybrid will dry down. Typically, corn that reaches black layer in September will see 1 point of moisture drop per day compared to around 0.5% in October and very minimal in November. Due to this year’s later planting date and cooler summer, expect corn not to dry down as well and be harvesting at higher moistures.

    While you are waiting for your corn to be ready for harvest, take some time to walk your fields and note any issues that could affect harvest such as stalk strength. Put a harvest plan in place to deal with any challenges.

    Laura Johnston, CCA-ON, Maizex Seeds Yield Specialist, West Elgin County
    Twitter: @lmjohnston8