Managing wheat leaf diseases and Fusarium head blight (head scab)

Martin Chilvers<chilvers@msu.edu>, and Martin Nagelkirk, Michigan State University; Albert Tenuta, OMAFRA; Damon Smith, University of Wisconsin-Madison; Kiersten Wise, Purdue University; Pierce Paul, The Ohio State University - May 27, 2016

The when, what and where of wheat leaf and Fusarium head blight (head scab) disease management.

Wheat leaf diseases such as powdery mildew, Septoria leaf spot and stripe rust are prevalent in some fields this season. Many farmers are asking if a fungicide application should be made prior to the typical application for Fusarium head blight (head scab) management at flowering (anthesis, Feekes growth stage 10.5.1, Zadoks 60). There are a few key points to consider when making fungicide decisions in wheat, since multiple fungicide applications are rarely profitable in wheat. The following decision tree outlines when and what actions should be taken by growth stage.

When and what actions to take against wheat leaf diseases
Growth stages	Actions
Full flag Feekes 9 Zadoks 39	If significant foliar disease is present on the leaf below the flag leaf (F-1) or flag leaf, especially stripe rust, consider foliar fungicide to protect the flag leaf. The table below list several recommended products. If no or very little disease is present two leaves below the flag (F-2), continue to monitor, but hold fungicide applications until the head scab timing, which will also protect the flag leaf.
Boot Feekes 10 Zadoks 45	If significant foliar disease is present in the mid- and upper plant canopy, especially stripe rust, consider foliar fungicide to protect the flag leaf. Do not apply fungicides containing strobilurins at or after the boot stage as this can increase DON accumulation.
Beginning flowering Feekes 10.5.1 Zadoks 60	If scab risk factors are present or leaf diseases pose a threat to the flag leaf, make a fungicide application from the beginning of flowering until six days after the beginning of flowering. Preference should be given to applying fungicides four days after the beginning of flowering as this results in the best Fusarium head blight management and DON suppression. Applying four to six days post-flowering also widens the window of protection if an application was made at Feekes 9 (Zadoks 39) to protect the flag leaf.

The first rule is to scout, scout, scout! Knowing the wheat growth stage, what disease is present, variety susceptibility to diseases and where diseases are in the plant canopy is essential to making the most profitable disease management decisions. The stripe rust pressure has been unprecedented in the Great Lakes region this season. The extended cool spring along with significant overwintering of stripe rust in the southern U.S. has resulted in a “perfect storm” for disease development. Rusts tend to move quickly, with a 10-day window from infection to reproduction. At full flag leaf emergence (Feekes 9; Zadoks 39), if disease is only present two leaves below the flag leaf (F-2), then continue to monitor. If disease is present on the leaf below the flag leaf (F-1), applying a fungicide will provide the most protection.

Once leaf damage has occurred, rescue treatments may only halt or slow disease, but won’t rescue dead leaves. Be aware that if a fungicide is applied to fully emerged flag leaves, well in advance of head emergence, then an additional fungicide application will be required to control Fusarium head blight at the beginning of flowering. However, be mindful of the current growth stage. Once wheat plants move into the boot stage (Feekes 10; Zadoks 45), the application of products containing a strobilurin fungicide may actually increase the amount of mycotoxin (DON/vomitoxin) in the grain.

If no significant disease pressure is present or active on fully emerged flag leaves or one leaf below (F-1), then waiting for an application for head scab management makes sense. A fungicide application during flowering will work two-fold. First, it will provide some reduction in head scab and mycotoxin suppression. Second, it will also provide protection of the flag leaf. Susceptible to moderately susceptible varieties will be at greatest risk of head scab and DON accumulation. Other risk factors should be considered such as history of disease, previous crop and current weather conditions.

The Fusarium Risk Assessment Tool is available to give a daily risk assessment for specific locales. The model is correct about 75 percent of the time, but Michigan State University Extension encourages growers to consider their own experience and that of local consultants. Remember that the beginning of flowering is defined as 50 percent or more of the heads in a field with flowers present. The window for fungicide application for head scab was recently found to be optimal from the beginning of flowering (anthesis) until six days after the beginning of flowering (anthesis), with best management achieved with an application four days after the beginning of flowering.

Fungicide efficacy for control of wheat diseases

The multi-state North Central Regional Committee on Management of Small Grain Diseases (NCERA-184) has developed the following information on fungicide efficacy for control of certain foliar diseases of wheat in the U.S. (revised March 30, 2016). Efficacy ratings for each fungicide listed were determined by field testing over multiple years and locations. Efficacy is determined by direct comparisons among products in field tests. The products are used in a manner consistent with label instructions. This table includes most widely marketed products. It is not intended to be a list of all labeled fungicide products.

Efficacy of fungicides for wheat disease control based on appropriate application timing
Fungicide(s)				Powdery mildew	Stagonospora leaf/glume blotch	Septoria leaf blotch	Tan spot	Stripe rust	Leaf rust	Stem rust	Head scab	Harvest restriction
Class	Active ingredient	Product	Rate/A (fl. oz)	Powdery mildew	Stagonospora leaf/glume blotch	Septoria leaf blotch	Tan spot	Stripe rust	Leaf rust	Stem rust	Head scab	Harvest restriction
Strobilurin	Picoxystrobin 22.5%	Aproach SC	6.0-12	G1	VG	VG2	VG	E3	VG	VG	NL	Feekes 10.5
	Fluoxastrobin 40.3%	Evito 480 SC	2.0-4.0	G	—	—	VG	—	VG	—	NL	Feekes 10.5 and 40 days
	Pyraclostrobin 23.6%	Headline SC	6.0-9.0	G	VG2	VG2	E	E3	E	G	NL	Feekes 10.5
Triazole	Metconazole 8.6%	Caramba 0.75 SL	10.0-17.0	VG	VG	—	VG	E	E	E	G	30 days
	Propiconazole 41.8%	Tilt 3.6 EC4	4.0	VG	VG	VG	VG	VG	VG	VG	P	Feekes 10.5
	Prothioconazole 41%	Proline 480 SC	5.0-5.7	—	VG	VG	VG	VG	VG	VG	G	30 days
	Tebuconazole 38.7%	Folicur 3.6 F4	4.0	NL	NL	NL	NL	E	E	E	F	30 days
	Prothioconazole19% Tebuconazole 19%	Prosaro 421 SC	6.5-8.2	G	VG	VG	VG	E	E	E	G	30 days
Mixed modes of action5	Tebuconazole 22.6% Trifloxystrobin 22.6%	Absolute Maxx SC	5.0	G	VG	VG	VG	VG	E	VG	NL	35 days
	Fluoxastrobin 14.8% Flutriafol 19.3%	Fortix	4.0-6.0	—	—	VG	VG	E	VG	—	NL	Feekes 10.5 and 40 days
	Benzovindiflupyr 10.3% Propiconazole 11.7% Azoxystrobin 13.5%	Trivapro A EC + Trivapro B SE	4.0 + 10.5	VG	VG	VG	VG	E	E	VG	NL	—
	Metconazole 7.4% Pyraclostrobin 12%	TwinLine 1.75 EC	7.0-9.0	G	VG	VG	E	E	E	VG	NL	Feekes 10.5
	Fluxapyroxad 14.3% Pyraclostrobin 28.6%	Priaxor	4.0-8.0	G	VG	VG	E	VG	VG	G	NL	Feekes 10.5
	Propiconazole 11.7% Azoxystrobin 13.5%	Quilt Xcel 2.2 SE4	10.5-14.0	VG	VG	VG	VG	E	E	VG	NL	Feekes 10.5
	Prothioconazole 10.8% Trifloxystrobin 32.3%	Stratego YLD	4.0	G	VG	VG	VG	VG	VG	VG	NL	Feekes 10.5 and 35 days
	Cyproconazole 7.17% Picoxystrobin 17.94%	Aproach Prima SC	3.4-6.8	VG	VG	VG	VG	E	VG	—	NR	45 days

¹Efficacy categories: NL=Not Labeled; NR=Not Recommended; P=Poor; F=Fair; G=Good; VG=Very Good; E=Excellent; -- = Insufficient data to make statement about efficacy of this product.

²Product efficacy may be reduced in areas with fungal populations that are resistant to strobilurin fungicides.

³Efficacy may be significantly reduced if solo strobilurin products are applied after stripe rust infection has occurred.

⁴Multiple generic products containing the same active ingredients also may be labeled in some states and Ontario.

⁵Products with mixed modes of action generally combine triazole and strobilurin active ingredients. Priaxor and the Trivapro copack include carboxamide active ingredients.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).