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Planning for wheat

Once a wheat plant starts to move from vegetative growth to reproductive growth in early spring it can be thought of as an upright cylinder.

All leaves are approximately the same size and live for approximately the same length of time. This means that in theory they could deliver the same yield for the plant. And they would if it wasn’t that the lower leaves, those below final leaf two (counting down from the flag leaf), receive far less light than the upper leaves due to canopy shading.

The result is that the top two leaves of a wheat plant deliver around 70% of the yield, while the ear contributes a further 20%. Therefore these leaves and the ear must be kept disease free for as long as possible, to fully express a crop’s yield potential.

How well do you know your farm?
Below is an editable PDF designed so that you can record simple but powerful data which will allow you to make informed decisions in future years.

What data do we suggest you record?
We suggest keeping it simple, focusing on plating date, crop growth stage and fungicide application dates. The aim is to strengthen your position in future years about the date GS39 will occur as this is a critical fungicide application timing for wheat. Once you know when this will occur, the other fungicide timings tend to fall into place. As your data set grows with time, it will be an invaluable record for you from your farm.

Would you be prepared to share?
Recording data on your farm in really important, but being able to benchmark how your crops perform alongside your neighbours and others in your region is invaluable. Use the downloadable PDF below to keep your own records or share your data by clicking ‘submit’ on the PDF and Bayer will collate the data and distribute findings from across the region.

Bayer Fungicide Disease Planner

Fungicide timing for wheat

There are three critical timings for fungicide application to a wheat crop and these should be adhered to almost without exception. These are GS32, GS39 and GS65. This programme has stood the test of time being the approach taken to control disease in wheat since the 1970s.

Wheat Stage GS32

GS32 APPLICATION

The first critical fungicide application should be made at GS32. At this growth stage final leaf 3 has emerged and importantly part of final leaf 2 is visible.

While leaf 3 can contribute 10% of the final yield the real importance of protecting this leaf from disease is that it prevents disease epidemics from getting established.

An effective fungicide application at GS32 will give 25-28 days protection to leaf 3 and to part of leaf 2, allowing the crop unhindered growth as it lays down the foundations for yield.

Wheat Stage GS39

GS39 APPLICATION

GS39 is the most critical, the “must-do”, fungicide application for wheat.

At GS39 both the flag leaf and leaf 2 have fully emerged and are vulnerable to disease attack.

With these leaves contributing 70% of yield that can’t be allowed to happen.

Applying a robust fungicide application at GS39 will give 25‑28 days protection to the flag leaf.

It will also help to reduce disease development on leaf 2 even though this leaf has been present for a while.

Wheat Stage GS65

GS65 APPLICATION

A fungicide applied at full ear emergence serves three main purposes.

It protects the ear from disease infection thereby protecting 20% of the final yield, it protects against diseases reducing grain quality and it tops up the fungicide protection of the flag leaf.

Then there are some other, less critical timings which deserve mention. They are described here because at times they are necessary and also they are discussed in a European disease control articles.

Wheat Stage GS30

GS30 APPLICATION

This application should be considered when crops emerge from winter with a heavy burden of Septoria leaf blotch or stripe rust that needs to be controlled urgently.

This application is in addition to a GS32 application.

Wheat Stage GS33

GS33 APPLICATION

Last year Bayer was faced with a situation in its wheat fungicide trial on the lower North Island where the crop grew slower than normal due to cold, cloudy weather. Here the interval between the GS32 and GS39 stretched to 35 days and fungicide control began to break down.

Consultations with Bayer experts in the UK showed that in some seasons they experience similar problems.

The solution is to apply an additional fungicide at GS33. To adopt a GS32, GS33 and GS39 programme.

Clearly this isn’t ideal and it can be made worse when a GS30 spray has also been applied. The most effective way of minimsing this happening is to ensure that the GS32 spray isn’t applied too early. Wait until GS32 and don’t be tempted to spray early at GS31.

Wheat Stage GS75

GS75 APPLICATION

In NZ a mixture of two fungicides, Folicur® plus a strobilurin fungicide are sometimes applied at this late growth stage, especially on irrigated crops, to prolong green leaf area.

This approach protects against most of the late season diseases while providing a sound resistance management approach. Ensure the withholding period of both fungicides is adhered to.

Wheat growth charts

Wheat Spray Programme Diseases Growth Chart

Illustrated above is a high performing but cost effective fungicide programme to protect an autumn or winter planted wheat crop. This programme will provide disease protection throughout the season.