Morris Says It Best

Corn harvest has not gone as quickly as we hoped.  It looks like the end of March, rather than the 1st of November, judging by the state of the local creeks and rivers.
Elevators have been reporting a lot of 51-53 lb test weight corn coming in.  Despite earlier fears of wet corn, moistures are in the low 20's in many fields.  The range of yields has been huge, as low as 100 and as high as 200.  
A tremendous amount of chatter has circulated about certain hybrids and their lack of performance.  I posted back in September about the amount of Norther Corn Leaf Blight present and showed some hybrid differences.  A lot of what growers are experiencing, whether good or bad is directly related to the amount of NCLB pressure in their fields.

Morris Sagriff, Pioneer Agronomist has put together a detailed account documenting the unique conditions that caused NCLB to flourish and overwhelm a number of different hybrids.  The remainder of this post is based on points from Morris' summary.

When disease pathologists speak they often refer to the disease triangle.  A big problem occurs when all three parts of the triangle line up.

1. Pathogen
Northern Corn Leaf Blight is present every year and easy to diagnose due to the unique lesions observed on the corn leaf.  Normally NCLB infects the plant late in the growing season and has little effect on yield.  It actually helps drydown most years by killing off leaf tissue.  Low corn moistures this year are directly related to NCLB pressure.

If the disease is present early in the growing season the lesions destroy effective leaf tissue reducing the size of the factory in the corn plant.  The effects of the smaller factory are witnessed as reduced yields and test weight. 

A severe infection will look like this picture and is sometimes mistaken for frost injury.  The corn plant fights back by mobilizing reserves in the stalks to make up for leaf loss.  Stalk quality suffers as a result.  Corn infected with NCLB tends to be a pain to harvest.  Standability can be reduced, but plants infected with NCLB are also brittle and the cob does not separate easily from the stalk.  The whole plant comes into the feeder house. 
NCLB over winters on corn trash.  Corn on corn fields are more prone to heavier pressure.  Last week we were witness to a 30 bushel yield difference on the same farm where part of the farm was 2nd year corn vs the rest of the farm planted to first year corn.

2. Environment
In 2013 the weather pattern produced a perfect storm condition that greatly favoured NCLB development.

The chart shown above is meant to depict the timeline of corn development vs disease timing.  Corn tasseled during the last week in July and first week in August.  This is slightly later than a normal tassel date of mid July, which in itself is not unusual.  Cooler than average June and July temperatures were the reason for the 2 week difference.  We have witnessed this in years past and still not had a serious NCLB problem.
What was significantly different in 2013 was the timing of infection.  A heavy infection occurred in early August versus a more typical mid-September date in a normal year.

NCLB lesions were observed as early as August 9.  The disease had more time to attack the plant during the critical stage of grain fill.  NCLB takes away effective leaf area, reducing the factory available for sugar production.  Cool, cloudy conditions continued into August.  Just think back to that frustrating wheat harvest for a reminder of what the weather was like at the time.  NCLB is a fungal disease and fungal diseases love cool damp weather.  Early infection combined with ideal conditions for development and spread creates a significant problem if you are a corn plant surrounded by NCLB spores.
Morris speculates that the disease pressure was heavier in a triangle from Goderich to Woodstock and back to Grand Bend due to the storm patterns off southern Lake Huron in July.  The storms created a much heavier than normal NCLB spore load.

These wind storms left a trail of goose necked corn in the same area.  I would add that because of the storms corn plants were weaker and more susceptible to infection. 
It needs to be noted that other factors including soil health, soil tilth, drainage, fertility and planting date can have adverse effects on plant health.

3. Host
Diseases evolve and change over time.  A fungal disease such as NCLB is made up of populations of different races.  The dominant races will change and shift from one year to the next making life challenging for breeders trying to stay one step ahead of the disease.  A resistant gene that breeders used, known as Ht1 is no longer effective against NCLB.  Breeders are forced into taking a muti-gene resistance approach to give protection against NCLB.
Despite the advances in technology allowing breeders to bring products to the market faster it still takes years to evaluate a new hybrid's potential.  Usually severe weaknesses are identified during this time, but exceptions still happen. 

In summary it is reasonable to conclude the disease was more prevalent in Huron, Perth, north Oxford and north Middlesex counties this year due to the three components of the disease triangle, namely pathogen, environment and host all lining up in perfect order.

The management techniques growers can  employ to reduce NCLB infection include

1.Reduce corn residues with crop rotation.
2.Leave no more than 30% residue on the soil surface.
3.Plant timely into good soil conditions.
4.Use a foliar fungicide at tassel time to control fungal diseases like NCLB.
5.Select hybrids with an above average score against NCLB. 

Keep in mind the exact conditions that favoured NCLB this year are not likely to repeat next year.  That is why I put hybrid scores at the bottom of this list.  There will be a different disease that assaults the corn crop next year.  The first 4 techniques listed are important tools in the fight against all diseases.