The growing season is well underway, with many cereal crops in or nearing the stem elongation stage (growth stage 30). Many farmers may be wondering when they should apply fungicide to their crop. There isn’t a simple answer to when fungicide should be applied, however, depending on the year the decision to apply it earlier, later or at all may make a big difference.

As of the first week of June, most regions in Manitoba have received less than 70% of normal precipitation. The good news is that spring cereal crops are not yet suffering. It is important to note when considering fungicide application timing that dry situations do not favour leaf disease development. Sound economics necessitate timely weed control, since weed competition for scarce soil moisture is the principle competitive threat to crops withstanding ongoing dry conditions.

Reasons to consider an early fungicide application for wheat:

• You have planted wheat on wheat stubble, or immediately adjacent to last year’s wheat crop.
• You have selected a variety that is less resistant to the leaf spot complex than the current standards – Cardale, Faller and Carberry are listed as MS (moderately susceptible) while AC Domain is fully susceptible.

Reasons to consider later fungicide application for wheat:

• Even when symptoms of tan spot are present on the earliest emerging leaves, those leaves contribute very little to grain production and filling.
• By the time flag leaves emerge (and they are the principle contributors to yield), an earlier fungicide application will have disappeared from the plant and provides no protection against leaf rust, or the other leaf diseases, that predominate later in the season.
• Delaying herbicide, to maximize disease control with a fungicide/herbicide pass, is a poor compromise because early weed pressure is a bigger yield robber.
• Multiple applications of fungicides with the same mode of action in the same season (e.g. seed treatment, flag leaf timing and head blight timing) increases the odds of disease-causing pathogens developing fungicide resistance.

Article written by David Kaminski, Crop Industry Specialist (Plant Pathology) with Manitoba Agriculture.

As posted on Manitoba Wheat and Barley Growers Association Website