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To keep the benefits, manage resistance

Written by Dr. Jason Weirich on .

Weed resistance isn’t the only threat; let’s take care of fungicides

Fungicides grow more popular. Over the winter you probably had the opportunity to attend producer meetings in your area. And, you probably heard a company representative or an agronomist talk about the use of fungicides to increase yield. Most of the presentations promoted “plant health” or stress reduction as a way that fungicides help increase yield on your farm.

Interest in the use of foliar fungicides has increased since the highly publicized arrival of rust a few years ago. Until recently, use of fungicides had been limited to fields where diseases were known to be present as well as soybean and cornfields used for seed production.

The market introduction of strobilurins, a broad-spectrum fungicide registered for control of a number of foliar diseases across a number of crops, increased the adoption of fungicide use in our trade territory. However, the current trend in our trade territory and through the Midwest is toward an increased use of fungicides for “plant health.” That general description covers improved stress tolerance and growth efficiency to increase yields instead of simply disease management.

From my perspective, it might be useful to discuss what university research tells us about fungicide use on corn and soybeans and what strategies the row-crop industry is adopting.

Disease management
The highest probability of seeing an economic response from an application of a fungicide is in the presence of disease or when conditions are favorable for disease. Fungicide use in this scenario increases yield by eliminating or controlling yield-limiting diseases in your field when conditions are favorable for disease development.

Some of the factors that are favorable for diseases in corn include: susceptible hybrid, continuous corn, no-till, late planting, high plant population, high-yield scenarios, irrigation, disease activity at tasseling, disease favorable weather conditions, or a history of disease in the field.
Some of the factors that are favorable for diseases in soybean include: susceptible variety, early planting, historical disease presence, dense crop canopy, favorable weather conditions, irrigation or a continuous no-till soybean field.

With the factors listed above, you will see there is some overlap between the two systems, but there are also several differences listed for corn and soybean production. While decisions for fungicide use based off the two cropping systems cannot provide 100 percent accuracy, they will provide a baseline justification for use of fungicides.

Just as I have recommended in the past, you must be able to see if it works on your farm. When you are applying fungicides to a field with low risk it is always a good idea to leave a portion of the field untreated as a comparison to evaluate the use of fungicides on your farm.

“Plant health”
We have all heard the discussions about the use of fungicides for plant health. We have seen applications of fungicides on corn or soybeans stay greener longer. Does that always result in higher yield? I don’t believe it does 100 percent of the time. I have seen significant yield increases from applications of fungicides, but on the flip side, I have seen cases where there was no yield responses.

Some of the potential plant health attributes include, but are not limited to, greening effect, corn stalk strength and drought/stress recovery.
Most claims about the greening effect suggest if it is greener longer, its healthier. Yet, this effect can have a negative impact as well. It can slow or even delay harvest, and it may require grain drying after harvest.

Stalk quality appears to improve with the use of strobilurin fungicides. Some university research shows improved stalk strength after strobilurin use, even where disease pressure was low. More research is being conducted to validate industry claims.

Fungicide resistance
I wouldn’t be doing my job if I didn’t talk about fungicide resistance. The use of any fungicide increases the risk for resistance. Anytime a fungus is exposed to a fungicide, even when fungal activity is low, the selection pressure on the fungus is increased toward resistance.
While there is no way to prevent every case of resistance to strobilurins and DMIs, we can hope to delay the development of resistance by minimizing the use of at-risk fungicides.

Factors that increase potential for fungicide resistance might include: repeated/overuse of fungicides of the same mode of action; applying half-rates of fungicides and applying fungicides when disease pressure is already high.

Most of the products on the market include two modes of action. Also, when you read the label of most fungicides, you will see it covers resistance management and the importance of utilizing resistance management strategies. Always read and follow the label.

I believe proper use fungicides are going to help us reach the full potential of our crops. If you have other yield-limiting factors eliminated on your farm and are looking for ways to potentially increase production, fungicides might be an option for you.

Scouting can be another way to avoid loss from diseases in your field. Again, leave a check strip on your farm so you can see the result in your fields. If you are looking for a proper fungicide program or a field scouting program, contact your local MFA retail location.

Dr. Jason Weirich is the MFA's director of agronomy. READ MORE by Dr. Weirich HERE.

 

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