It seems too early in the growing season yet to be seeing corn diseases like Northern Corn Leaf Blight (NCLB), but I happened to spot a few corn plants with NCLB lesions on them in an isolated area in a corn field in southeast Iowa.
This disease was widespread in Iowa in 2014 and again last year in 2015, and it was severe on susceptible hybrids. Since the fungus (Exserohilum turcicum) survives the winter in corn residue, we likely have above normal inoculum present this year.
Why are we seeing NCLB so early?
That goes back to the disease triangle, which describes the three necessary factors for disease development: 1) pathogen presence, 2) a susceptible host, and 3) the favorable environmental conditions (aka weather).
With NCLB, favorable environmental conditions for fungus and disease development are cool weather (65 to 80°F) with frequent precipitation. Warm and dry conditions will slow or halt disease development until favorable conditions return.
With the warm and dry weather we experienced last week, I am thinking that this corn was infected prior to the warmer and dryer weather, and that the weather actually halted the NCLB from spreading more. Although we have chances of rain this week, temperatures look like they will remain on the warm side, providing less than ideal conditions for NCLB.
Agronomists and farmers are encouraged to scout fields, especially at-risk fields (susceptible hybrids, corn-on-corn fields), for NCLB. Keep an eye out for NCLB by looking for the cigar-shaped lesions that are pale gray to tan in color.
If the disease is present on 50% or more of the plants in the field, the hybrid is scored susceptible, and cool, wet weather is in the forecast, a foliar fungicide application may be required.
Additional resources on northern corn leaf blight: