September 5, 2017 at 3:32 p.m.
Silk emergence predicts corn maturity date
A cool, wet spring delayed planting, and, in some cases, made replanting necessary. Joe Lauer, University of Wisconsin-Madison corn agronomist, talked about predicting maturity dates during a silage management meeting Aug. 8 at Taylor, Wis.
"Often, the range in planting dates has implications at harvest time, especially for silage," Lauer said. "Grain and dairy producers often negotiate the sale of corn in fields that are borderline for development."
This year, corn planting in Wisconsin generally began around May 5, Lauer said. That was later than the April 14 date a year ago, and later than the five-year average date of April 21.
Corn planting generally wrapped up this year around June 30. Again, that's much later than last year's June 2 and the five-year average of June 9.
Approximately 35 percent of Badger State corn went into the ground in June this year, he continued. Farmers in southern Wisconsin can plant as late as June 10 and still get ripe corn, but those farther north will probably have to make silage out of corn planted June 10 or later.
How can farmers predict whether or not their corn will mature before Jack Frost comes nipping? Don't go by plant height, Lauer cautioned. He said he has observed record yields from corn that was short enough for him to see over.
Instead, pay close attention to when the corn silks. When most of plants' silks have emerged, figure on needing roughly two months for the grain to mature.
"Most hybrids require about 55 to 60 days to develop from the silk stage to physiological maturity," Lauer said. "Hybrid maturity differences in development time occur primarily from emergence to silking, not from silking to maturity."
Farmers should start watching for silks to emerge soon after the tassels are out. In general, said Lauer, silks start emerging two days after tasselling. But that's not true for all hybrids, he added.
"Growers are concerned when corn does not reach the silk stage until early August or later," Lauer said. "Killing frosts can easily occur by late September, so corn silking in early August would not be safe from major yield reductions due to frost until October."
Lauer mentioned that on his drive from Madison to the Jackson County meeting, he saw a number of cornfields that weren't tasseling yet, let alone silking.
It's not just the date of the first killing frost that matters. The agronomist said that corn needs about five to 10 days of good weather so it can dry after a frost and before combining or picking.
Farmers can note other stages of their corn's development, too. The kernel milk stage arrives about 20 days after silking. Twenty days after that, the kernels begin to harden and dent. Twenty days after that, the black layer in the kernels has developed. So, in all, corn progresses from silk emergence to kernel black layer in approximately 60 days.
"At the dent stage, corn has accumulated 75 to 85 percent of its silage yield and 60 to 75 percent of its grain yield," Lauer said. "It needs about 27 to 32 days to avoid significant yield reductions due to frost. Corn intended for silage should be silking by late August, while corn intended for dry grain should reach the dent stage by Sept. 1."
Research has been conducted at the Arlington Agricultural Research Station on how full-season and shorter-season hybrids actually perform. Last year, a 105-day hybrid was planted from March 28 to June 15.
Silks emerged between July 9 and Aug. 6. The dent stage arrived between Aug. 10 and Sept. 9, or 32 to 34 days after silking.
The 50 percent kernel milk stage was reached between Aug. 31 and Sept. 28, or 48 to 53 days after silking.
Looking at silage yields for that 105-day variety, Lauer said they averaged 7.3 to 8.7 tons per acre. In terms of grain, that variety yielded 106 to 236 bushels per acre and its moisture content ran between 19 and 50 percent.
A year earlier, a 98-day variety at Arlington was planted between April 13 and June 17. It silked between July 19 and Aug. 7.
That variety reached the dent stage between Aug. 20 and Sept. 12, or 28 to 36 days after the silks emerged. The 50 percent kernel milk line arrived between Sept. 4 and Oct. 7, 48 to 61 days after silking.
The 98-day variety yielded 177 to 231 bushels per acre. Its moisture content at harvest stood at 15 to 27 percent.
After reviewing the Arlington data going back to 2009, Lauer noted that the idea of using the silking date to predict the grain maturity date is not perfect. He said, "It's not quite fitting the theory as well as I'd like."
For the four years of the trials, the number of days from silking to the dent stage ranged from 28 to 45, depending on the year and the planting date. From silk emergence to the 50 percent kernel milk line took 45 to 62 days.
Summing up, Lauer offered this advice: "To predict whether corn will mature before frost, note the hybrid's maturity, the planting date, and the silking date of the field. For silage corn planted early, add 42 to 47 days onto this, to predict 50 percent kernel milk. For grain, add 55 to 60 days to predict the maturity date."
He added that those numbers are guidelines - not chiseled into granite. Farmers will likely need to make decisions as the season progresses.
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