Final fungicide on spring barley

With four distinct cohorts of spring barley crops present on farms, Teagasc Crops Specialist, Shay Phelan delves deeper into timings and product choices for the final fungicide application.

Depending on when they were sown, how much rainfall they got in May and the effect of the record temperatures in late May, spring barley crops are a mixed bag this year.

Given the wet spring, only very dry sites around Carlow, Enniscorthy or Athy saw any early drilled crops; the vast majority were drilled in April.

Those few early drilled crops are now at awns emerged and many already have received their final fungicide. For most, however, this is due in the coming week or fortnight.

Disease levels to date have been very low, with very few reports of common diseases such as rynchosporium, net blotch or indeed mildew.

Regardless, most crops have already received a fungicide sometime over the last few weeks, However, we are hearing that some may not yet have received any at all so far. So, at the moment, there are probably four different types of spring barley crops when it comes to disease control.

1. March-drilled crops – these are already at awns peeping and have received their fungicide where spraying opportunities allowed. If not, these are now due.
2. April-drilled crops – where spray timings are up to date and the first fungicide was applied two to three weeks ago.
3. April-drilled crops – where fungicides were only applied in the last week to 10 days
4. April drilled crops – with poor potential and no fungicide applied yet.

These are the types of situations that we are being asked questions about recommendations on the final fungicide applications. They are all different crops with different levels of control strategies being implemented.

Crops 1 and 2

The decision in crops 1 and 2 above are quite simple: the awns are already peeping or will be in the coming days, so the final fungicide should be applied at the first available opportunity.

Crop 3

Crop 3 is difficult in that the natural inclination if fungicides have recently been applied is to wait for 2- 3 weeks before the final fungicide is applied regardless of the growth stage.

This is where yield can be lost very quickly. Teagasc trials show that there is a potential loss of up to 0.4 t/ha by delaying that final fungicide. It is not unusual for crops to race from late tillering to flag leaf emerged in a few short weeks, especially if they are under drought stress etc. so it is easy to be caught out by the speed of development of these types of crops.

Crop 4

Crop 4 is another tricky one in that those crops with poor plant stands usually don’t yield, so making the decision to not spend money can sometimes be tricky. Fungicide programmes can show yield responses of up to 2.75t/ha, but only in crops with high yield potential and trying to predict that yield potential is tricky.

Often deciding to reduce the spend on fungicide feels like giving up on the crop and there is always the thought that the crop may surprise you. History of the crop on the farm is usually a good indicator of what it will yield given a set of circumstances.

Correct timing

Regardless of the crop, the correct timing of the final fungicide is as the awns emerge (see picture 1). At this stage, we are trying to delay the onset of ramularia in the crop. Net blotch or ryncho should be controlled at this stage, so the need to stretch the interval from the previous fungicide, if any, doesn’t apply.

Ramularia will start to infect the lower leaves and work its way up through the crop; the longer you delay the application of the final fungicide, potentially, the quicker it will spread. Remember you cannot cure it once it starts to infect the crop – all you can do is delay it.

Figure 1: Timing of the final fungicide in spring barley