Determining when this 2023 corn crop will mature will be a challenge. This spring m
ost areas received little moisture after planting and soil variability and lack of rain has resulted in high variations in germination and subsequent corn height and growth stage within the rows of corn. When drenching rains returned the corn crop responded and the variation is more prominent. This is most evident in the non uniform tassel emergence that we are experiencing in early July. For this article we will use the tassel/silk emergence timing to predict when black layer/ physiological maturity(PM) will take place. PM is the time the kernal is filled and all flow or fill of the kernal is complete kernal moisture is about 32% moisture well past silage harvest parameters. The plant is beginning to dry down rapidly at PM most of the green tissue is now brown and the ears are drying down rapidly for dry grain harvest and or high moisture corn.
There are two methods to arrive at a PM timetable. One is simplified days to PM from tassel emergence. If a field is observed to tassel/silk @ July 4 then in 55-65 days(accounting for hybrid and heat accumulation differentials) most hybrids will be mature. For this season that would place PM at between August 31 to Sept 12 or thereabouts. Silage harvest is typically between 42 and 47 days from Tassel/silk. This would be day estimate to half milk line which might be dry for a bunker and wet for a oxygen tight structure. Th
is would place silage harvest from between August 15 to August 20, 2023. The practical implication is that if a field is typically harvested around labor day for silage and that is applied this year just going by a calendar date the result might be a dryer or wetter harvest for the structure it is intended to be placed into for ensiling. There is no substitute for checking the crop ear for relative maturity as it develops to better time the harvest to maximize forage quality and ensure proper ensiling for the silage whichever structure it is to be placed for winter feed out.
The second method is to use growing degree days(GDD). GDD are calculated daily and represents the average heat units the crop receives from sunlight and therefore offers a more accurate measure of when to harvest a crop. Simply put it takes the average heat by taking the high temperature and the lower temperature and average the temperature for the day. This then is subtracted from the minimum growth of the crop(base). The base for corn would be 50 degrees. So on a normal day high of 80 low of 60 would equate to an average (80 +60)/2 = 70 degrees. Then by taking the average minus 50(base temp) the crop would receive (70-50) or 20 growing degree days for that day. One would then do this everyday until the GDD to silage or PM achieved, and this will vary by hybrid. This explains why there could two week differences in calculated and realized maturities that we see from year to year. Many times I will follow a selected field in my area that I know the date and the hybrid, I then check to see when it produces a silk and tassel. From there I use the Bushels App to then adjust my PM estimates of black layer based on the hybrids predicted GDD requirements. As that date nears I begin taking whole plants and using a chipper process the whole plant and run a Koster test to determine moisture. Its pretty accurate. I can then check each 7 days and determine the dry down rate and better predict optimal harvest timing for silage. 
If we understand this relationship with GDD and crop growth we can then look to technology to better time harvests. Computer and Phone applications such as Bushels, Climate view, and man
y others will allow growers to map a field or fields and then check daily for comparisons of this years GDD compared to either 10 or 15 year averages and better adjust estimated harvest timing. Penn State employs these technologies to predict harvests as well as pest activity.
By beginning to keep tabs on the 2023 corn crop better silage harvest timing may result and ensure high yield and quality this coming year. With cloudy overcast days and an estimate of cooler than normal conditions it is highly recommended to keep scouting fields until ideal timing is noted by field observation.
