• There are several factors that need to be taken into consideration when changing your planting plans.
• The absolute yield potential of a corn hybrid will be determined by the growing environment at critical growth stages of development.
• The question we need to be asking ourselves is: can the hybrid I am going to plant reach black layer prior to frost?
• This article provides information on how to determine the potential for our hybrid to reach black layer before the killing frost date in a given area.

The slow planting progress seen to date along with the forecasted rains predicted for the last days of May- early June, have brought up the question of: when does it become too late to plant corn? This article is a follow-up to a previous article “HOW EARLY IS TOO EARLY TO SWITCH TO AN EARLIER HYBRID?”

There are several factors that should be taken into consideration when changing your planting plans. These include:

• Average first frost date for your area and long-term average GDU accumulation.
• Adjusted hybrid maturity considering that for every day past May 1^st and through June 15^th, a corn hybrid decreases its GDU requirements to black layer by 6.8 GDU per day.
• Corn Drying capabilities of the operation due to corn black layer happening at a later date and the potential limited window for field dry-down.
• Prospective short-term and long-term weather forecast.

Often times factors use in agriculture such as corn reaching 50% yield potential by a given date in June are intimidating and can be taken out of context After all we don’t know this year’s absolute yield potential and won’t know for certain until after harvest.Absolute yield potential will be determined by the growing environment at critical growth stages of the corn crop. Specifically, how favorable the environment is during the growth stages when rows around the ear are determined (≈V8-V10), potential kernel is decided (≈V12-VT) and pollination and grain fill is occurring (R1-R5).Particularly, cloudy weather at R1 can result in kernel abortion and day and night time temperatures and soil moisture can affect kernel weight. Earlier this year, Bob Nielsen at Purdue University made this same point in a different manner in an article titled “The Planting Date Conundrum for Corn“.If we use the figures of 0.3% yield decline from May 1^st -15^th, 1% yield loss per day from there to May 31^st, and 1.5% yield loss per day from June 1st on, by June 5^th absolute yield potential has decreased by 37%.The question we need to be asking ourselves is: can the hybrid I am going to plant reach black layer prior to frost?The table below (Table 1) contains information from the easily generated Useful-2-Usable website (https://mrcc.illinois.edu/U2U/gdd/) at various counties in IL, representative of different corn maturity zones. Using these numbers and the numbers from Table 2 below, we can estimate if the corn you plan to plant will reach black layer prior to frost using the steps below: 

• On table 1, choose a county that resides in the same corn maturity zone where you will be planting corn and choose an individual year or the average of the last eight years (far right column) of GDU accumulation from June 5^th to first frost date. 
  
• Using Table 2, choose the planting date when you believe you will be able to plant and skim through the row across all hybrid maturities. Are my numbers in Table 2 lower than the number chosen in Table 1? If so, we should have enough GDU’s accumulated prior to frost and depending on the difference between these two numbers we should have some GDU’s left for field dry-down. Keep in mind that typically kernel moisture at black layer is around 30% and to drop 1% grain moisture corn requires 30 GDU’s

WEATHER OUTLOOK

The National Weather Service 3.5-month outlook for the corn-belt states is predicting a 30-40% probability of above normal temperatures (Figure 1). Additionally, this same outlook predicts a 33% chance of normal precipitation and a 33% probability of above normal precipitation (Figure 2).

Figure 1:Temperature Outlook (below)

The decision of what to plant during late planting seasons is never an easy one. Fortunately, we have scientific, historical data and evidence to help us make these tough decisions and hopefully make this “unseasonable” 2019 a successful one.For more information on planting concerns and hybrid maturities in your area, contact your local FS crop specialist.