Many fields this past season showed signs of Northern Corn Leaf Blight (NCLB).  The lesions of NCLB appear as long elliptical (2-15 cm) grayish-green or tan streaks, usually found on the lower leaves first.  As the disease progresses, the lesions will usually merge together forming large blighted regions.  In worst cases, the entire leaf will become blighted.  Early infections with favourable environments can cause yield loss upwards of 50% (Albert Tenuta – Ontario Grain Farmer, January 2014). The NCLB organism overwinters in diseased corn residue.  The following season, spores are spread by rain splash & wind. Heavy dews, high humidity and moderate temperatures allow this disease to spread.

Hybrid Selection – Resistant genes bred into the corn hybrid have been very successful at reducing NCLB, but over the past few years it has been shown that there are several races of NCLB and not all the races are controlled by the resistant genes used in certain corn hybrids. Hybrid selection is key, but don’t forget all the other important traits that you need to have; strong emergence, stalk strength & yield are a few.

Tillage – any type of soil movement that places soil in contact with the diseased residue allows for quicker breakdown of residue and decreases the amount of inoculum that survives to the following year. No-till or continuous corn will have a much higher risk of infection the following year. 

Foliar fungicides – There are many foliar fungicides registered to help control NCLB.   However, most fungicides are only active for 7-21 days after application. Timing is everything.  Early signs of the disease can usually be found just before tasseling.  Your crop rotation, hybrid selection and weather forecast should play a major role in determining if you spray a fungicide.

Kirk Van Will, CCA-ON, Maizex Seeds Yield Specialist, West Middlesex & Lambton Counties
Twitter: @KirkVanWill