Wheat Leaf Rust

Wheat leaf rust has been detected and confirmed this week in a few locations (3) in southwestern Ontario with a field in Port Lambton being the most noticeable (thanks to Chad Anderson for alerting us on this location). Other locations included the U of Guelph Ridgetown campus and West Elgin (thanks to Rich Anderson, BASF) although disease levels were very, very light (a few leaves). A common feature for all these locations is the variety grown was Vienna. Vienna, FT Wonder and Carlisle tend to be more susceptible to leaf rust and therefore, continue scouting these and all varieties for that matter not only for leaf rust but powdery mildew and other diseases. Also continue to monitor the site-specific DONcast (FHB) model for your current FHB/DON situation at: www.weatherinnovations.com.

Figure 1. Wheat Leaf Rust and Powdery Mildew on Wheat

Leaf rust can flourish quickly especially if the weather actually becomes summer-like (can't predict the weather). Maintaining the upper leaves (especially the top two) disease-free during the grain fill period is critical to good yields. Yield losses of 20bu/ac due to leaf rust have been seen the past 2 years on very susceptible varieties.

The question around applying a preventative strobilurin fungicide (Headline and Quadris are in this group) to get rust and other diseases has come up. There are many issues surrounding such a practice. One of particular concern is in some trials an increase in DON (vomitoxin) levels were observed when a strobilurin was applied at flowering or after the head emerged. Don't take the risk, if a fungicide is needed this late in the game, a well timed Folicur application at fusarium timing will not only assist in the management of FHB but will provide excellent leaf rust and powdery mildew control as well. Growers that have already applied Folicur for leaf disease control will need to utilize Proline at fusarium timing since the Folicur registration is for one application per year.

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