Corn Stunt: Facts, Not Fear

Friday, February 21, 2025

Understanding The Risks & Realities Of This Disease As It Edges Toward Ontario

By Paul Hermans

I had an interesting call last fall from the United States. No, it was not Donald Trump calling to tell me that he got back in. It was from Mike Hunter, field crops IPM specialist working at Cornell University in New York State. I got to know Mike over the years of travelling together to various agronomy conferences in Ontario. When Mike calls, it must be something important that he wants to share – and in this case it was.

Mike phoned to say he had found corn stunt just 10 km south of the Ontario border. I was taken aback, as, quite frankly, I have never heard of this corn problem until just recently. Mike said he was lucky they had a Brazilian researcher on their team who had seen the disease before, and when scouting fields, brought this to the attention of the group at Cornell.

So, you may be asking yourself, ‘What is this new corn disease?’

The primary causal organism for corn stunt disease is Spiroplasma kunkelii, a bacterial pathogen commonly referred to as corn stunt spiroplasma (CSS).

Corn stunt is one of the most economically important diseases affecting corn in the Americas and the Caribbean. The disease is transmitted from unhealthy plants to healthy ones by corn leafhoppers. Just to be clear, these leafhoppers are different than other ones like alfalfa leafhopper.

How exactly do these leafhoppers find their way north to New York State?

Their main movement is through prevailing winds over long distances. If we think about the 2024 weather season, we had numerous tropical storms moving up from the Southern U.S., which would explain the reason behind the leafhopper movement north.

Fortunately, during most parts of the year, the spread of the corn leafhopper north is limited by cold temperatures and the lack of secondary hosts, which provide year-round food sources.

Corn stunt disease is characterized by severely stunted plants that often produce multiple small ears with loose or missing kernels. Yield loss associated with corn stunt disease can be severe – over 70 per cent – during major outbreaks that have impacted yields in Brazil and Argentina in recent years.

Corn stunt disease is less known in the U.S. because outbreaks have been rare and confined to the southernmost parts of the country. Added to this, they tend to blow into smaller areas in North America and show up later in the growing season, and thus, affect the corn crop less than southern areas like Mexico and Brazil.

Foliar symptoms usually show up as small chlorotic stripes that develop at the base of the plant. Over time these chlorotic stripes expand and develop a reddish/purple colour. Infected plants can have shortened internodes, hence the name for the disease corn stunt.

There are currently no management tools available to combat corn stunt. Foliar insecticides can be applied to control corn leafhoppers, but again, severe outbreaks are highly unlikely in Eastern Canada.

In South American corn-growing areas, differences in hybrids exist in terms of resistance to corn leafhopper feeding. Ratings for this are available in those countries. However, since corn stunt currently is an exceedingly small issue, hybrids are not rated in the U.S. and Canada for this disease.

This may change in five to 10 or more years down the road if the corn leafhopper pest adapts and changes its life cycle to survive in our climate.

There is no need to run for the hills to date and quit growing corn because of corn stunt. I am suggesting we will not see dire consequences of this disease in the future, but it is something we need to know about – what it is and what to watch out for as we scout fields, if we do find abnormal plants that fit the description of this disease.

Other diseases like tar spot are more common and will require our attention in terms of hybrid selection and fungicide management in the future – more so than corn stunt.

The call with Mike also conveyed two themes to me.

1. Keep yourself surrounded by excellent agronomy advisors. Mother Nature has a unique way to adapt to what is thrown at her. As a producer, you have a lot going on, on your farm. Having trusted advisors, Certified Crop Advisors, and/or government/industry experts available to help is a key part of keeping your farm operation sustainable.
2. Be thankful we have a great agricultural industry that can evolve and adapt to changing trends and issues, producing solutions so we can all keep farming and providing food and fuel for the world. This is where continual re-invested research dollars come into play, to keep moving the agronomic and yield needle forward.

So, the next time someone asks you about corn stunt, you can breathe and say “it’s not a big player in the area to date,” and you have some facts to back that up.

Here is to the upcoming 2025 growing and crop-scouting season. BF