Wheat Disease Update and Fungicide Application Decision Making

Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu

Overall, wheat across Delaware and the Eastern part of Maryland looks very good. I continue to see and hear about excellent stands, little disease, and good yield potential. Many growers have been asking about the need for a fungicide application to the flag leaf this year. My advice has been this: go out and look at your wheat. Really look at it, don’t just drive by at 60 mph with Lynyrd Skynyrd blaring on your radio. Here is what to look for:

  1. Presence of active foliar disease in the mid to upper canopy. The name of the game now is protecting the flag leaf and then the glumes, which contribute the lion’s share of carbohydrates for grain fill. Diseases such as powdery mildew tend to stay low in the canopy due to humidity and temperature constraints. Diseases such as leaf blotch complex move slowly and often make it to the flag leaf after flower. Rusts, for the most part come in late, after flower, if at all. Be aware though, that there were reports of stripe rust in parts of Eastern Maryland a few days ago, although overall disease risk is low. Most of the fields we have been in across Delaware for survey purposes and applied research trials have been largely free of disease.
  2. Yield potential– Are you looking at a field with excellent yield potential? Paying for an application is much easier when you are pushing 100 bu/A vs 60 bu/A.
  3. Costs of inputs up to this point, and disease pressure compared to your projected yield. Fungicide applications are not cheap. If you do not have disease pressure and can save the trip, it will help your bottom line.

If you don’t look at your field or pay someone to do it, you could potentially apply fungicides to low disease potential, low yielding fields. With wheat prices hovering around $4.40 /bu, margins will be tight. This is why it is important to consider the amount of disease loss you are protecting by making a fungicide application. How much will you have to make back? I posted an online breakeven calculator on my blog at: http://extension.udel.edu/fieldcropdisease/2016/04/20/should-i-apply-a-fungicide-to-my-wheat/

The calculator provides you with average costs of products and application costs for the various application timings in the mid-Atlantic. The application cost of the greenup/jointing application only considers product ($US / A) as you will typically be going across the field at this time anyway to apply your second shot of nitrogen. Below is a snapshot of the calculator with average costs included.

Wheat Fungicide Breakeven Calculator

Price per Bushel App. Cost
Application 3.00 4.00 4.50 5.00 6.00 (enter your cost)
Greenup (G) 1.0 0.8 0.7 0.6 0.6 Greenup (G) 3
Flag Leaf (L) 7.7 5.8 5.1 4.6 4.6 Flag Leaf (L) 23
Flower (F) 7.7 5.8 5.1 4.6 4.6 Flower (F) 23
G+L 8.7 6.5 5.8 5.2 5.2 G+L 26
G+F 8.7 6.5 5.8 5.2 5.2 G+F 26
L+F 15.3 11.5 10.2 9.2 9.2 L+F 46
G+L+F 16.3 12.3 10.9 9.8 9.8 G+L+F 49


You can see that at $4.00-4.50/bu, most applications will need to protect roughly 6 bu/A to break even. Over 10 bu/A are required for programs using a flag leaf application plus a flowering application or a three-spray program! That’s a pretty good slug of disease. Most fields out there are not at risk for a 10 bu/A loss.

You have your own deals and discounts, so go to the blog, open up the calculator, and see what you’d need to break even, enter in your application costs in the table on the right (greenup, flag leaf, or flowering). The calculator will do the rest.  Do you have enough disease in the upper canopy and yield potential to justify the application?

That’s one piece of the puzzle. The next is the likelihood of a return. Thankfully, our lab is doing some excellent work answering this question (led by M.S candidate and Kent County Ag. Agent Phillip Sylvester). Phillip’s work will lay the ground work to begin to develop a small grains calculator that will provide growers with estimated probabilities of an application paying off over a range of yield potentials given the application cost and commodity price.

Bottom line- don’t make an application without looking at your fields.

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