Scouting For Striped Rust And Other Leaf Diseases In Wheat

By Martin Nagelkirk, Michigan State University Extension

Managing leaf diseases is critical for Michigan wheat growers wanting to improving yields. This season, striped rust might warrant particular attention.

Managing the various fungal pathogens of wheat through the use of varietal selection, proper identification and fungicide use is the single most important reason growers have improved their wheat yields in recent years.

The most costly diseases are those that progress unchecked during the grain-fill period. However, sometime leaf diseases that occur prior to heading can reduce wheat performance as well. The most common diseases in early May are powdery mildew and Septoria leaf spot. As the flag (final leaf) emerges in in the latter half of May, other leaf spot diseases including leaf blotch may gain a foothold. If a variety has little resistance, any of these diseases may progress from the lower leaves up onto the flag leaf under favorable conditions. Where this occurs, a fungicide application should be considered.

Stripe rust on wheat.

Of particular concern each season are the pathogens that cause one of the rust diseases. The spores of the causal organisms blow into Michigan in late May and June from southern states. While Michigan often sees some leaf rust, the rust that is earning a lot of attention this season across the U.S. wheat growing states is called stripe rust. Wheat pathologists across the U.S. have reported its unusual prevalence as it edges its way to the Great Lakes region. The first infections in Michigan are expected to be found within the next couple weeks.

Because this fungal leaf disease can be particularly detrimental to wheat yields, Michigan State University Extension encourages growers to scout their fields. While there are no varieties that are completely resistant to the disease, growers should be especially watchful of the moderately susceptible varieties, which include Red Ruby, DF111R, Shirley, AC Mountain, Ambassador, Aubrey, 9242W and Linebacker. Recommended fungicides, including Caramba and Prosaro, applied soon after head emergence are usually adequate for keeping the disease in check if its development is delayed until early June. See the table at the end of this article for a list of fungicides and their efficacy.

Growers who suspect they might have the disease are asked to send a plant sample to MSU Diagnostic Services. Wheat sampling instructions and a submittal form are available.
Fungicide efficacy for control of wheat diseases

The 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. Effectiveness ratings were determined by field testing the materials over multiple years and locations by the members of the committee. Efficacy is based on proper application timing to achieve optimum effectiveness of the fungicide as determined by labeled instructions and overall level of disease in the field at the time of application. Differences in efficacy among fungicide products were determined by direct comparisons among products in field tests and are based on a single application of the labeled rate as listed in the table. Table includes most widely marketed products, and is not intended to be a list of all labeled products.

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.

2 Product 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. Products including tebuconazole include: Embrace, Monsoon, Muscle 3.6 F, Onset, Orius 3.6 F, Tebucon 3.6 F, Tebustar 3.6 F, Tebuzol 3.6 F, Tegrol, and Toledo. Products containing propiconazole include: Bumper 41.8 EC, Fitness, Propiconazole E-AG, and PropiMax 3.6 EC.  Products containing propiconazole + azoxystrobin include: Aframe Plus, Avaris 2XS.

5Products with mixed modes of action generally combine triazole and strobilurin active ingredients. Priaxor is an exception to this general statement and combines carboxamide and strobilurin active ingredients.

Source: msu.edu