The when, what and where of wheat leaf and Fusarium head blight (head scab) disease management
Martin Chilvers 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
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 fungicide wheat decision tree outlines when and what actions should be taken by growth stage.
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. in 2016, the stripe rust pressure was unprecedented in the Great Lakes region. The extended cool spring along with significant overwintering of stripe rust in the southern US resulted in a “perfect storm” for disease development in 2016. 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) or a very susceptible variety is grown, 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.
Stripe rust was confirmed by Agris Co-op in Stoney Point (Essex) on May 3, 2017. The timing of stripe rust in Ontario this year (May 3) is very similar to last year (May 5- Elgin County by Dr. Dave Hooker). In both years, lesions were found mid canopy and not on the lower leaves. This would suggest aerial distribution and not overwintering. The sequence of detection progressed from the southern US up the Ohio valley into Ontario would also support air dispersal. If overwintering is occurring in Ontario, stripe rust detection dates would be expected to be very similar across the region and not sequential.
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 (www.wheatscab.psu.edu/) is available to give a daily risk assessment for specific locales. The model is correct about 75 percent of the time, but growers are also encouraged to consider their own experience and that of local consultants. In Ontario, the DONcast model (www.weathercentral.ca) can assist in predicting DON risk. Remember that the beginning of flowering is defined as 50% 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 6 days after the beginning of flowering (anthesis), with best management achieved with an application 4 days after the beginning of flowering.
Fungicide Efficacy for Control of Wheat Diseases (Revised 3-30-16). 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 for use by the grain production industry in the U.S and Ontario. Efficacy ratings for each fungicide listed in the table 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 and all products may not be registered in every State or Canada. Always read and follow the label. Click on link to view the table.