Joined up thinking on fungicides

Correct fungicide selection and application is a key part of an IPM (Integrated Pest Management) strategy, writes Ciaran Collins

The employment of an anti-resistance strategy is vital to prolong our existing fungicides
The employment of an anti-resistance strategy is vital to prolong our existing fungicides

Ciaran Collins

A typical spring barley grower in Ireland will spend €90/ha on fungicides. This increases to €135/ha for a winter barley grower and further increases to €190/ha for winter wheat.

Can two farmers spend the same amount of money on a fungicide programme and get different results? The answer is YES. From the Teagasc e-PM the top one third of winter wheat growers produced 0.6t/ha more yield yet spent €15/ha less on fungicides.

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All professional users (farmers) are required to apply the general principles of Integrated Pest Management (IPM) under the Sustainable Use Directive (SUD). Many of these measures are already practiced on farm and all that is required of many farmers is to record them.

Prevention and suppression is the biggest and most important part of the IPM triangle where crop rotation and varietal disease resistance scores are important factors. But in April, May and June the focus turns towards fungicides and how we use them.

How fungicides are used is a key part of any IPM strategy.

This involves the decision making process as to whether a fungicide is required or not, fungicide selection, rate and most importantly the timing that it is used on the crop.

The employment of an anti-resistance strategy is vital to prolong our existing fungicides and all of this is underpinned by evaluation and recording of results.

Timing is everything

In an era when the efficacy of our current suite of active ingredients is struggling to control septoria in wheat, an incorrect timing can be very costly.

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The optimum time to apply a fungicide to control septoria on winter wheat is on a fully emerged leaf 3 and leaf 1 (flag leaf).

A late application results in disease gaining a hold on the unprotected leaf surface, and if applied too early the base of the leaf won't have emerged fully, so you'll be leaving this part of it unsprayed.

Components of yield

To understand why timings differ between wheat and barley it is important to look at the components of yield for each crop and how these differences influence the optimum timing of fungicide application.

In wheat, grain number/m and grain size have equal influence on yield.

Ear number has the biggest influence on grain number but the crop can compensate for low ear numbers by increasing grain number per ear and increasing grain size.

The focus on disease control in wheat is protecting the green leaf area at the top of the plant as the top three leaves account for over 70pc of yield in wheat.

Barley yield is closely related to grain number/m. The main factor influencing grain number is the number of ears/m.

Barley cannot compensate for lower ear numbers like wheat so the focus of disease control in barley is earlier to ensure tiller survival to maximise ear number.

Timings: Winter Wheat

It is well established from research that leaf 1 (the flag lead or the upper most leaf when the crop is headed out) will make the largest contribution to yield followed by leaf 2 and then leaf 3.

The critical fungicide timings are a fully emerged leaf 3 where the upper proportion of leaf 2 is covered and a fully emerged leaf 1 where the lower proportion of leaf 2 is treated.

It is also well established that deviations from these timings can be costly especially in high disease pressure situations.

The only way to identify the correct leaf is to dissect the plant by unrolling the inner leaves to ensure that the fungicide is applied at the correct timing.

Pick the most advanced shoot (the main stem) from a plant and strip the leaves off by rolling the leaves away from the stem.

Once you've figured out the direction of roll for the first leaf, then the next leaf rolls out in the opposite direction. Continue to roll away the leaves carefully until you see the developing head.

When dissecting plants in early April you may need a magnifying glass to see leaf 1 which is hooked around the ear.

In 2019 it looks like the leaf 3 is not out any earlier than normal despite the mild winter.

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