Corn harvest is underway, but it looks like it may happen in fits and starts, going back to varied planting dates. Stalk quality will be an issue in some fields, where corn was stressed by too much moisture early and then not enough late in the growing season. When we get into an extended harvest season, especially if frequent rainfall returns, lodging and harvest loss increase.
The October 8th issue of the OSU Extension CORN newsletter contained an article by OSU Extension specialists Peter Thomison and Pierce Paul on corn stalk quality concerns and an article by OSU Extension educators Jason Hartschuh, James Morris, Will Hamman and agronomic field specialist Elizabeth Hawkins on combine adjustments and loss assessment for this year’s corn harvest. I am excerpting some selected content from those articles for this column. If you have interest, I suggest reading the entire articles at https://agcrops.osu.edu/newsletter/corn-newsletter/2019-34 or contact the Wayne County Extension office at 330-264-8722 and I can provide a hard copy of the articles.
“When corn is subjected to stress (due to weather, esp. drought, foliar diseases or insects) during grain fill, photosynthetic activity is reduced. As a result, the carbohydrate levels available for the developing ear are insufficient. The corn plant responds to this situation by removing carbohydrates from the leaves, stalk, and roots to the developing ear. While this "cannibalization" process ensures a supply of carbohydrates for the developing ear, the removal of carbohydrates results in premature death of pith cells in the stalk and root tissues, which predisposes plants to root and stalk infection by fungi.
The presence of stalk rots in corn may not always result in stalk lodging, especially if the affected crop is harvested promptly. It is not uncommon to walk corn fields where nearly every plant is upright yet nearly every plant is also showing stalk rot symptoms! Many hybrids have excellent rind strength, which contributes to plant standability even when the internal plant tissue has rotted or started to rot. However, strong rinds will not prevent lodging if harvest is delayed and the crop is subjected to weathering, e.g. strong winds and heavy rains.
Nothing can be done about stalk rots at this stage; however, growers can minimize yield and quality losses associated with lodging by harvesting fields with stalk rot problems as early as possible. Scout fields early for visual symptoms of stalk rot and use the "squeeze test" to assess the potential for lodging. Since stalk rots affect stalk integrity, one or more of the inner nodes can easily be compressed when the stalk is squeezed between the thumb and the forefinger. The "push" test is another way to predict lodging. Push the stalks at the ear level, 6 to 8 inches from the vertical. If the stalk breaks between the ear and the lowest node, stalk rot is usually present. To minimize stalk rot damage, harvest promptly after physiological maturity. Harvest delays will increase the risk of stalk lodging and grain yield losses and slowdown the harvest operation. Since the level of stalk rot varies from field to field and hybrids vary in their stalk strength and susceptibility to stalk rot, each field should be scouted separately.
Checking harvest loss and combine settings
When assessing combine settings there are four areas of loss to consider. The first is preharvest loss. Desirable is less than one ear weighing ¾ of a pound, for a 29-foot length across 6 rows or across 8 rows for 21.8 feet in length. This standard is for 30-inch row spacing and measures 1/100th of an acre. Direct combine loss sources include header loss, then threshing and sieve loss. When counting individual kernels, a loss of one bushel per acre is realized when you find two kernels per square foot.
In order to determine which part of the combine to adjust you need to calculate loss from each area. To check header loss, stop the combine and back up the length of your combine. For 30-inch rows, count the number of kernels in front of the combine from center of row to center of row for 4 feet of length. This equals 10 square feet. Divide the number of kernels found by 20 to get bushels per acre loss. Each row of your header should be checked, since only one may be out of adjustment, record each row separately. Also check for additional ears that may have been lost by the header and not pre harvest. Record header loss to subtract from separator and cylinder loss. Preform the same kernel count behind the machine as you did in front. Subtract each row individually from header loss to calculate separation loss. Watch for any cobs that still have corn on them. This is threshing loss. A study conducted in Iowa found the best set combines have a total loss, pre and post-harvest loss, of 1.5 bushel per acre.”
Recommendations for specific combine adjustments, particularly important if corn is harvested at 22% or greater moisture, is provided in the article available on-line at https://agcrops.osu.edu/newsletter/corn-newsletter/2019-34/managing-corn-harvest-fall-variable-corn-conditions.
Rory Lewandowski is an OSU Extension Agriculture & Natural Resources Educator and may be reached at 330-264-8722.
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