Corn Yellowing Update

Jun 12, 2015
By Dave Franzen
NDSU Extension Soil Specialist
Corn Yellowing Update
Most fields with corn have begun to green up with much warmer temperatures. There are some areas, particularly in medium to sandy soils on ridges/slopes that have begun to show signs of N or S deficiency. Again, S deficiency will show on newer leaves, while the lower leaves are greener. N deficiency shows up on bottom leaves, with new leaves greener. Contrasting plant samples will help confirm deficiency, but take one from a ‘good’ area and one from a ‘not-so-good’ area where N/S deficiency is suspected.
Most corn is still very small, less than V4, so over-the-top ammonium sulfate granules will still work. Also, streamed between the rows ammonium sulfate solution or ammonium thiosulfate will also work for S.
If the problem is N, the best for side-dress would be to wait until this wet period is over, perhaps about V6; however, if the corn is very yellow from extreme losses, now is better than later.
My preferences for side-dressing corn have not changed. I prefer coulter-applied UAN between every other row in high clay Valley Soils. Ammonia will work fine west of the Valley on soils that are not too wet. Coulter-applied UAN is more nimble in variable soils with wet and dry in the same field. Go deeper in drier soils and shallower when the soils are wet. Second on my list of preferences would be streamed UAN between the rows. I prefer this over y-tubes in our region because y-tubes are made for areas with heavy dew every morning. In this region, heavy dews happen once in a great while, and considering the cost of y-tubes, streamed every row UAN should perform as well. Last on my list is urease-treated urea over the top of corn. Either an NBPT product, similar to Agrotain from Koch, or the Limus product from BASF will be effective. Any other chemistry is either untried, or tested poorly in urease inhibitor studies.
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