10 Questions and Answers About Early Season Fungicide Application

10 Questions and Answers About Early Season Fungicide Applicaton

Randy Myers, Ph.D.Sometimes you just want to sit down and ask someone direct questions and receive some no-nonsense answers. We’re here to help.

Randy Myers, Ph.D., might be a fungicides product development manager for Bayer, but don’t let the “product” part of his title deter you from his expertise. Randy has a knack for taking very complex, agronomic situations out of the lab and into the field.

We asked him to explain a topic that Bayer gets asked about a lot: early season fungicide application in corn.

We even wrap up with the question you want to ask but aren’t sure if anyone will give you a straight answer.

Before we get to the specifics of early season application, let’s talk about fungicides. With commodity prices half of what they were a few years ago, why would I change to a planned fungicide application?

Growers need to consider that cutting an input cost does not automatically improve profitability. In fact, we’ve done a series of field trials that show an early season fungicide application can improve yield by almost 7 bu/A. If that application was tankmixed with a planned postemergence herbicide when commodity prices run roughly $4/bu, that fungicide application will net you about $19 more per acre. On 500 acres of corn, that is an additional $9,500 in profitability.

When you reference early season fungicides in corn, you’re talking about V4 to V7. Why would I apply a fungicide that long before disease symptoms show up, if they show up?

You won’t have many disease symptoms present early in the season because the plants are growing rapidly and you just do not have a high level of inoculum yet. A fungicide application at this time works to protect the middle part of the canopy by preventing or delaying infections affecting the leaves in the vicinity of the ear.

Furthermore, this is a critical growth period for the corn plant, ultimately influencing how the plant will yield. The plant interprets signals from the environment which can impact the number of rows on the ear. Additionally, the nodal root system is becoming dominant and the tassel, while still microscopic, is beginning to form. A fungicide application during this time can lend support for these developments by reducing abiotic stress and preventing interference from disease.

Isn’t it a waste of money, to apply a fungicide before symptoms are seen?

It really is flipping conventional thinking around, but once you look at how and why this application timing works, it really changes your perspective.

Essentially, the goal is to get ahead of disease, which is why we’re making the application before infections occur.

Beyond the impact on foliar diseases, one of the biggest benefits from early season fungicide application is improved stalk quality.

If there’s no disease present, how can I protect stalk quality?

Microscopic pathogens can actually live in the stalk all season long, whether or not their growth becomes extensive enough to present obvious visible symptoms. To protect stalk quality, you need to keep those pathogens out of the stalk, or at least limit their growth. You can do that by applying a fungicide early. Even though you initially can’t see symptoms, the plant can eventually be under disease-related stress from an infection that occurred weeks earlier.

Controlling these pathogens leads to healthier stalks later in the season, which translates into greener, healthier stalks during the grain fill period. Even if there’s some type of stress on the plant during grain fill, stalk quality is one of the biggest advantages of early season applications. Many growers have been commenting that they are spraying for just the benefits of stalk strength and easier harvestability.

Why is stalk quality so important?

There are two reasons. First, strong stalks mean the plants stand up nice and straight. There is less lodging; when that happens, it translates directly into yield loss. Plus, if plants are standing straight you can go through the field faster. Your combine burns fuel by the hour. Getting more acres through that combine in that hour contributes directly to your bottom line by reducing fuel costs. That’s a very important consideration.

Second, is the general health of the stalk. I want nutrients and water coming out of the roots through the stalk up into the leaves throughout the entire grain fill period. If the vascular tissue is compromised and cuts off that flow, those leaves will die prematurely. Dying leaves means no more photosynthetic potential. If that happens before black layer, grain fill is cut off, which then directly affects test weight. You can see how an unhealthy stalk creates a snowball effect. Healthy stalks prevent leaf tissue from dying prematurely, and actually affect an increase in yield.

Say I decide to make an early season fungicide application. Some companies claim their fungicides have longer residual than anything Bayer offers, so why choose a Bayer product?

As it happens, the plant is growing so rapidly this early in the season, the leaves you sprayed are going to fall off the plants as stalks increase in girth. This senescing process will usually begin about 10 or 12 days after you apply the fungicide, so 21 or 28 days of residual from an early fungicide application really doesn’t mean much.

What is important is that you use a rate of product that will provide a biologically active concentration on the leaves’ surface giving residual activity to protect the leaves until senescence. More than that just doesn’t bring much value. With a product like Stratego® YLD fungicide, you can use a size-appropriate rate when the plants are small. You can apply less fungicide but get the full value and full performance.

When comparing products at tassel-timing rates, most have very similar lengths of residual activity.

What do you mean by a “size-appropriate” rate?

It’s a rate that is appropriate for the smaller size of the corn plant in the V4 – V7 timing. You have less tissue to cover at this time than you do at tassel, so you can use the amount of fungicide that’s appropriate to the size of the plant. In fact, even with a lower rate, the concentration of the product on the leaf surface is actually 40 percent higher than you would have on the ear leaf when applying a full rate at tassel. For Stratego YLD, the rate is 2 to 3 oz/A early season and 4 to 5 oz/A at tassel.

Why does the window for early season application stop at V7? Can’t I apply it a little later and still get the same benefit?

As corn plants grow, you start getting more tissue to cover and you have leaves that are going to be on the plant longer. That’s why our window for that lower rate range stops at V7. Once the plants pass V7, the leaves stay on the plant a lot longer and there’s more surface area to protect. A higher rate will provide longer residual activity, which is important at this stage and later. Spraying a fungicide after V7 to protect the field is fine, but the higher rates are needed to get the desired protection.

Some researchers are actually advising against early season fungicide application and using a lower rate, saying the practice will aid in the development of disease resistance. Is this a valid concern?

If the fungicide concentration is high enough on the leaf surface to be biologically active for the length of time the leaf is on the plant, there’s little concern about resistance development. It’s also important to have two modes of action that are each effective on the target pathogens.

To better understand why resistance won’t develop specifically due to the practice of early season fungicide application, we need to look at why resistance develops in the first place.

Fungicide resistance develops when the pathogen population shifts to predominantly strains that are less sensitive to the fungicide active ingredient. Two conditions that contribute to that shift are, 1) The residual activity runs out, so you have less of the efficacious rates on the leaves; or 2) You apply the product in a curative fashion, where the efficacy of the fungicide is impaired. Both of these can be avoided with proper early season sprays.

This window only goes up to V7. After that, we now get value out of the longer residual and it’s important to use the full four or five ounces of Stratego YLD.

Assume I’m on board with early season application of Stratego YLD. At harvest, I do a side-by-side yield comparison between treated and untreated fields and there’s no difference. Does that prove there’s no need for an early season fungicide application?

A lot of variables go into corn production. We have to consider that a fungicide doesn’t fix all the deficiencies a plant or field or crop might have. A fungicide, especially one containing a strobilurin component like Stratego YLD, can help the plant utilize limited resources better but it can’t make up for true shortages. You’re not going to see as much value from the fungicide if there’s something much larger limiting your field.

Strobilurin-containing fungicides tend to help on both ends of the spectrum where disease or resource limitations have an effect. If resources such as nitrogen or moisture are limited, or disease pressure lowers the yield potential for the field, fungicides can address the disease part of the equation while assisting the plants to more efficiently utilize the limited resources.

V4 to V7 On-Farm Yield ResponseAt the other extreme are the “race horse” hybrids, which might have the genetics for higher yields, but often are prone to susceptibility to diseases, or the genetic potential may outstrip the resources present in the field. These fungicides improve the likelihood that the yield reflects the genetics.

With that said, there are some years when everything is near perfect for that particular hybrid and it experiences few stresses. Disease pressure is low, and moisture, nutrients and other factors are abundant. In those situations, the fungicide benefit can be limited. However, we can’t always plan on having a year like that, so it’s better to plan on helping the plants to be as productive as possible.

In fact, replicated field trial data demonstrate that a fungicide application will pay for itself more than 80 percent of the time, or about 8 out of every 10 years.

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