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Independent.ie

Sunday 11 December 2016

Our Farm: Clouds on the horizon as first winter crops begin to emerge

Richard Hackett

Published 28/10/2016 | 07:30

As crops emerge and thoughts turn to weeds and BYDV control, there are further clouds on the horizon.
As crops emerge and thoughts turn to weeds and BYDV control, there are further clouds on the horizon.

Looking around over the last few weeks, it seems that despite the economic outlook for crops being far from positive, there are a lot of autumn crops sown and the vast majority of these have been sown in excellent conditions.

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This should give a huge boost towards achieving good yields next harvest.

It has been noted that fields that are in a good rotation where organic manures have been applied are coming on particularly well.

Some land is not necessarily showing the benefit directly after a break crop but over the course of a rotation, land seems to be better able to withstand adverse conditions as the extra fertility builds in 'reserve' into the crop.

As crops emerge and thoughts turn to weeds and BYDV control, there are further clouds on the horizon. The first thing to note is that this is the final year for use of IPU or Isoproturon.

We will have to become more adept at utilising expensive grassweed mixes in low to moderate risk situations, which is not something that is welcome.

In this the final year, perhaps it might be prudent to get used to the alternative arrays of alternative chemistry available. Or perhaps from a resistance management perspective and to give other chemistry as good a chance to operate for as long into the future as possible, perhaps a better route is to utilise the remaining IPU to the maximum and get used to other options only when we have to.

Another fly in the ointment, or perhaps more correctly in the leaf, is our increasing difficulty in controlling aphids. At this time of year, an emerging crop has no difficulty in carrying a few passengers so aphids, per-se, cause no difficulty in a crop.

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However, it's the virus that the aphids can carry - Barley yellow dwarf virus, or BYDV, that is the problem at this time of year. Despite its name, BYDV attacks all cereal crops with equal effect and can cause severe stunting of affected plants.

Most work carried out on BYDV was carried out decades ago and generally focused on the removal of aphids, the basic premise being: remove aphids, remove the risk of BYDV spread. In an era of cheap effective chemicals which were very good at killing aphids, and indeed most other little critters caught in the crossfire, this was a rational approach.

However, now that aphids seem to have evolved to tolerate cheap insecticides, strategies may need to change. The main problem with applying aphicides to control tolerant aphids is that any natural predators that are around will be eliminated, so tolerant aphids have now a free reign to spread even more disease.

A lot of work in the late 1990s in the UK focused the development of 'beetle banks', - a technique which left areas in a field uncropped and unsprayed.

This would allow for the development of beetles and other natural predators which feast on aphids, therefore acting as natural aphicides. In this country, we have small field size, regulations controlling buffer zones and hedgerows, not to mention the ever increasing uncropped and uncroppable areas due to neglect and poor management.

So there really isn't any necessity to purposely develop beetle banks as there are plenty already around, yet still BYDV is an issue.

The reason for this is that aphid populations can explode at a huge rate in suitable conditions, but the population of natural predators cannot respond as quickly, and it is during this lag phase most problems with aphids arise.

With regulations governing new pesticides, there is little or no hope of new aphicides coming available at a reasonable enough price. However, I wonder if we are taking our eye of the ball trying to control aphids rather than focusing on the organism that really causes the harm, the BYDV virus itself.

Could crops be managed better to overcome BYDV outbreaks, or are there varieties more tolerant to BYDV? In most outbreaks at a field scale, BYDV has little effect other than cosmetic as stunted plants are compensated by more healthy plants alongside which have more nutrients and sunlight available to them.

It is only in extreme cases, which rarely happen, that overall yields are diminished. Where the tipping point is, where cosmetic effect turns to actual yield effect, no up to date research is available.

Richard Hackett is an agronomist based in north Co Dublin and is a member of the ITCA and ACA

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