By Darren Hefty
Do wheat plants really “save the best for last?” When it comes to leaves, they sure do. The last leaf to emerge is called the Flag Leaf, and it is said to constitute about 75% of the effective leaf area that will feed the head and fill the grain. For this reason, protecting the flag leaf is critical to achieving your yield goals.
As any plant begins the transition to move into reproductive stages, it is at a weak point for disease tolerance. The flag leaf stage will be followed by boot (fully developed head swelling up just below the flag leaf) and ultimately heading. Also, the flag leaf lies much more flat than other leaves (and is obviously on top of the canopy), potentially allowing more rust spores and other diseases to land on it. Common sense tells you the vulnerability and importance of this timing for protection of crop and yield.
At flag leaf, all options for disease control are on the table. Strobilurins (Headline, Quadris, Evito, and premixes that contain one of them) are still safe to use before head emergence. After the head is out, you run the risk of increasing the vomitoxin levels in the grain if you use a strobilurin. Triazoles (Tilt/Bumper, Prosaro, Folicur, and Caramba) are all safe to use, but you may choose to keep them in your shed in case you need them later. In order for you to spray for head scab protection, you must wait until the head is out and has reached about 15% flowering. Here’s the dilemma. Folicur has come way down in price compared to just a few years ago and is a popular choice for rust protection. However, you can only spray a maximum of 4 ounces of Folicur per acre per crop season in wheat, so you probably want to save it until heading in case you need it. Note: Prosaro is a premix of Folicur and Proline, so using Folicur at flag leaf would eliminate the possibility of using Prosaro at heading and leave Caramba as your only decent option. For this reason, we prefer to see one of the following combination fungicides used at flag leaf timing:
- TwinLine (Contains Headline and Caramba) – The use rate at flag leaf is 7 to 9 ounces per acre.
- Stratego (Contains Flint/Gem and Tilt/Bumper) – The use rate at flag leaf is 10 ounces per acre.
- Quilt Xcel (Contains Quadris and Tilt/Bumper) – The use rate at flag leaf is 10.5 to 14 ounces per acre.
All of these products do a nice job protecting your crop from things like stripe rust, powdery mildew, tan spot, leaf blights, various blotches, and more. In order to adequately protect the flag leaf, keep in mind that the flag leaf should be 50% emerged to fully emerged when you make the fungicide application. Also, all of the combination products I just mentioned contain a strobilurin fungicide, so these products must be sprayed by Feekes 10.5.
We have the potential for good prices and a decent wheat crop in many areas. Unfortunately, for good disease protection, you need to spray before the disease infects your crop for best results. As flag leaf approaches on your farm, consider protecting your crop this year. If weather conditions turn favorable for disease, spraying at flag leaf can really boost your yields and provide an excellent return on investment.