Fungicide strategy – Cereal Rusts

Fungicide Strategy – Cereal Rusts

Hopefully, you will have done one of the following to fight leaf rust in your cereal crops this season:

• ensured that the ‘green bridge’ has been destroyed prior to seeding either by heavy grazing or herbicide use
• selected resistant varieties
• treated seed
• crop rotation to avoid stubble born inoculum (spores)
• active monitoring of susceptible crops

The recent report from Sydney University on cereal rust status has discussed that stripe rust has been detected as early as the 25^th of May this season.  Often early detection can result in more disease, so this information is concerning.

Please see the below table for a list of resistant (R) through to very susceptible (VS) varieties from Agriculture Victoria:

These ratings are provisional – treat with caution.

R = Resistant

RMR = Resistant to Moderately Resistant

MR = Moderately Resistant

MRMS = Moderately Resistant to Moderately Susceptible

MS = Moderately Susceptible

MSS = Moderately Susceptible to Susceptible

S = Susceptible

SVS = Susceptible to Very Susceptible

VS = Very Susceptible

If you are running crops that are in the moderately susceptible à very susceptible range, it’s important to continue monitoring crops for rust, as fungicide timing is critical for effective control.  Foliar fungicides are translocated from the point of contact towards the leaf tip, needing to cover a larger plant area than herbicides.  Although earlier sprays can reduce inoculum levels, foliar fungicide spraying will protect only the portion of the leaf that is visible at time of spraying.

Medium to medium-coarse droplets provide the best coverage. Fine droplets have poorer penetration of the crop canopy and present a greater risk of spray drift. Coarse droplets are not always retained on a waxy leaf surface as they can bounce off.

Some tips for optimal fungicide efficacy from the GRDC below:

• Ensure thorough boom decontamination.
• Use a minimum of 70 to 80L carrier volume and medium to medium-coarse droplets. In denser canopies, more volume may be required if the product needs to reach the lower parts of the canopy.
• Limit speed to less than 20 kilometres per hour. Higher speeds risk spray coverage being concentrated on only one side of the plant.
• Consider a narrower nozzle spacing (for example, 25 centimetres), with one angled forwards and one backwards, or twin jets. If using this option, limit speed to 16km/h.
• Use the correct surfactant, if advised, as per label recommendation

The StripeRustWM app, released last year, from the Department of Agriculture and Food WA uses a forecasting model to assist wheat growers with fungicide application decisions, on a paddock by paddock basis, and the likely economic returns from those decisions.  Download here for apple and here for other Smart Phone devices.

For detailed advice on fungicide applications, please contact your local Crop Smart agronomist.

For information on fungicide supply this season, please see our recent market update here.

References:

Stripe rust: understanding the disease in wheat (nsw.gov.au)

grdc-fs-cereal-fungicides-n.pdf.pdf

Cereal disease update 2021 – GRDC

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