Corn is Tasseling! Points to Ponder to Determine Fungicide Applications

The continuing wet weather has many growers asking questions about foliar applications of a fungicide on tasseling corn. In my area, we have corn that is now tasseled and even corn that has just been planted! It's wise to review the labels of fungicides to ensure adherence to the label. Most labels dictate that applications be made between the VT and R1 stages.

VT - Tassel

• Last tassel branch is visible but prior to silking.
• Complete leaf loss will cause nearly 100% yield loss.

R1 - Silking

• N and P uptake are rapid.
• About 50% of total N is taken up after R1.
• K uptake is nearly complete.
• Water needed for pollination. Pollination occurs.

The labels I reviewed also (Miravis Neo) require that adjuvants or other additives not be used after corn has reached the V8 stage. However, some offer this option on fully tasseled corn. Recent Agronomy Journal Publications have shown the formation of beer can ears as a result of adjuvants applied near VT. With recent Tar Spot reports, our State Crop Pathologists have offered guidance to manage that particular disease along with the other diseases common as corn progresses. Essentially, if you manage tar spot similar to gray leaf spot, you will use similar tactics. The wet weather has caused extremely uneven emergence of tassels. The emergence of silk and tassel applications between VT and R1(blister) is the key time to apply the fungicides. It is wise to default to until the youngest of the plants are at or beyond this stage to avoid damage.  Below are some considerations to better decide whether to treat or not.  

Finally, on some products, there is a 30-day harvest restriction for forage and grain, so bear in mind that early forage harvest might need to be delayed should an application be made. This is not a straightforward recommendation on corn, and growers should look at each field and best determine its needs. We have a bumper crop in the making right now, and this application on many fields would really make the most difference in preserving potential yield!!

Fungicide Selection

There are numerous options to select from to manage foliar diseases. In 2014, Dr. Collins and I conducted a test of 5 different fungicides on corn and applied the product at the V6 and Tassel stage, as well as two applications, one at V5 and followed by a R2 stage of various fungicides. For this demonstration, in 6 out of the 10 treatments, there was a significant response exceeding 11 bu/acre overall to the application of a fungicide. In all cases, there was a response, but not all due to the treatment. The decision is not as much about which product to use but rather whether the hybrid will respond to an application. The hybrid in our trial last year was susceptible to leaf diseases.  Dr. Collins and Dr. Esker have conducted many trials in the last two years. These are included in the Fungicide tables within the Agronomy Guide to assist you in sorting out the best product for your fields.

Questions to Determine the Need for a Fungicide

Ask some simple questions to determine the benefit that might come through a foliar application of a fungicide to VT-R1 Corn. We cannot make a decision for you but if you ask some simple questions of yourself to address your fields and also to address your seed representative and seed guides to determine the benefit of an application. 

Disease History?

Low-lying fields with a history of disease are more likely to respond to a fungicide.

• No
• Yes

High-Yield History?

High-yield fields are more likely to show an economic response.

• Poor
• Average
• High yielding

Hybrid Resistance?

The lower the genetic resistance to tar spot, gray leaf spot, northern corn leaf blight, and anthracnose, the more potential for an economic response.

• Highly resistant
• Average
• Poor resistance

Crop Rotation?

Corn following corn tends to harbor more disease inoculum.

• Following other crops
• Following corn

IPM?

Corn diseases are just starting to appear, especially in no-till corn on corn fields. The greater the presence of disease on the leaf, the higher the risk of further development.

• Less than 5% visible disease
• 5–10% visible disease
• 10% or greater disease

Fertility?

Low K levels and compacted soils could exacerbate disease effects on lodging and yield. If the field has poor fertility, the likelihood of increased disease invasion is higher. 

• High fertility
• Average
• Poor fertility

If you go through these simple questions and more than one meets the criteria, it lends the field to infection, then spraying might be a profitable venture. You might find the 2025 crop season to be more challenging than most years.