Parson, Kansas —
With the wide range in planting dates this year, corn growth and development is variable across west central Missouri; early planted corn is near or already in the R5 (dent) growth stage. At this stage in corn’s development, preserving yield potential should be the primary objective. Although yield potential was determined by the VT (tasseling) growth stage, whether that yield potential is realized or not depends on the conditions experienced by the corn through the R6 (physiological maturity) growth stage.
At the dough (R4) stage, corn kernels will have accumulated approximately 50 percent of their dry weight. Starch continues to accumulate in the kernels until the plant reaches maturity. When stress occurs in the dent (R5) stage, it will affect kernel weight, because stress reduces the accumulation of starch in the kernel.
Late-season stress can greatly impact the realized yield potential of a corn crop. For those involved in corn production, we should consider how we might help preserve yield potential during these late growth stages.
Although most fungicide applications are made at the VT (tasseling) or R1 (silking) growth stages, there is speculation that a later application may prove more beneficial; specifically, in maintaining or improving kernel weight. Since a foliar fungicide provides only 14-21 days of effective protection, an early application does not protect the latter growth stages (the R5 growth stage occurs 35-42 days after silking).
Iowa State University researchers have shown that when disease severity on the ear leaf at the dent (R5) growth stage is greater than five percent, an average yield loss of 9.5 bushels per acre resulted. ISU recently compiled a three-year corn fungicide study and reported that on average, the overall yield response to a fungicide application was 4.0 bushels per acre. They noted that yield response to a fungicide application was greatest when disease severity at the dent (R5) stage was high.
To gauge the effectiveness of management decisions made this year, corn growers are encouraged to examine their fields and compare the uniformity of kernel set from the base of the ear to the tip. Examine the depth of the kernels as well; if under stress, the corn plant will respond by adjusting its kernel depth. For example, in fields with nitrogen deficiencies, the ear row number and length may appear normal but the depth of the kernels shallower than normal.
If you would like to sign-up for email updates regarding local crop conditions, pest alerts, and other agronomic topics, please contact Julie at abendrothj@ missouri.edu or 816-776-6961.
Corn Development from R1 to R6: www.agronext. iastate.edu/corn/produc tion/management/growth /yield.html
Summary: Foliar Fungicide on Corn in Iowa (2007 – 2009) www.extension.ias tate.edu/CropNews/2010/ 0706muellerandrobertson. htm
Crops
Preserving yield potential and increasing kernel weight
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