Fungicides on Wheat - How Do they Compare?

Albert Tenuta - Field Crop Pathologist/OMAFRA Ridgetown
07 May 2008

First thing when using a fungicide or for that matter any pesticide – READ THE LABEL! Fungicide use directions on the product labels are based on the unique uptake and movement characteristics for each fungicide and different fungicides (even those in the same chemical class) are not necessarily equal when it comes to efficacy, uptake and movement in the plant. Fungicides vary as to how quickly, and to what extent, they are taken up by the plant. This is one reason fungicide manufacturers often recommend the use of adjuvants with certain fungicides. Table 1 summarizes the differences between the various fungicides against some of the most common Ontario wheat leaf diseases.

Timing is critical to good control and while we do not want to wait till disease levels are extremely high, applying a fungicide too far in advance of any significant disease is a concern. Knowing how long the product remains active is important. In general, systemic products (strobilurin, triazole and premixes of strobilurin/triazole fungicides) at labeled rates provide 14 to 21 days of activity whereas protectant products are shorter at 7 to 14 days. Remember, efficacy and residual activity can be influenced by a number of factors such as application timing, fungicide product/rate, disease pressure, application method, environmental conditions, as well as other factors. Also, take into consideration the winter wheat variety susceptibility/tolerance to disease when considering disease risk. Please refer to Ontario Winter Wheat Varietal Characteristics for specifics on varieties (Table 2).

The bottom line is to SCOUT AND PAY ATTENTION TO THE WEATHER FORECASTS! Scouting will help in determining fungicide timing and risk based on disease levels and if weather conditions will be favourable for disease development. But just as importantly, scouting will help determine if fungicides are not needed based on little or no disease pressure and unfavourable weather conditions.

Table 1. Summary of Differences between the various Fungicides

E - Excellent, VG - Very Good, F - Fair, NR - Not Recommended

Table 2 Ontario Winter Wheat Varietal Characteristics

1 For ratings 0-9, a high score is undesirable.
2 Heading may vary from year to year and should only be used to indicatie relative differences.
4 Fusarium ratings are based on Fusarium head blight ratings and deoxynivalenol (DON) levels from inoculated provincial trials.
MR=moderately resistant (best); S=moderately susceptible; S=susceptible; HS=highly susceptible (worst).