Farm Ireland
Independent.ie

Wednesday 14 November 2018

Aphicides aren't what they used to be and are wiping out the good guys

Aphids per se are not the problem
Aphids per se are not the problem

Richard Hackett

It seems that many growers have put their faith in winter crops this year. There is hardly a stubble field left in places, such is the amount of progress made.

It's great to get crops sown in such excellent conditions, and many fields have even had their herbicide applied pre-emergence.

The only thing left to consider is the threat of Barley yellow dwarf virus or BYDV.

As seed dressing is being taken away as an option, the issue of BYDV control is getting more complex. Aphicides aren't controlling aphids the way they used to.

What they are very effective at, however is killing the good guys; the parasitic wasps, the spiders, the ladybirds.

The prolonged good weather we have enjoyed over the last few months have given a great boost to natural predators who are out in abundance.

The low sun on balmy autumn evenings is showing up thick mats of cobwebs covering every field.

So by applying an aphicide, we may or may not be controlling the aphids, but we are definitely wiping out the natural predators that could be doing the work for us for free anyway.

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It also has to be borne in mind that aphids per se are not a problem.

Indeed it would be great to have our thick crops knocked back a bit by a bit of aphid feeding, to keep them in check over the warm autumn we are enjoying.

The problem is the virus disease the aphids carry from plant to plant as they feed.

As we don't know what aphids are carrying what disease, our strategy is to annihilate everything in the field and that has been the practice for decades.

Aphicides were cheap and they worked. In the long term, however, we have to look at this approach again. We cannot identify whether or not there are aphids in the field that natural predators cannot control, we cannot tell whether aphids that are in a field are carrying BYDV or not.

We have not developed agronomic tools that we may be able to use to overcome BYDV in a crop, whether through different variety susceptibilities, encouragement of tillering, encouraging compensatory growth in surrounding plants etc.

These questions will have to be answered if we are to achieve long-term control of this disease in an era of ever more expensive and ever less available range of aphicides.

Ammonia emissions

It appears that the reduction of ammonia emissions is going to be very problematic, regardless of dairy cow numbers.

The main culprit is slurry storage and slurry spreading. The current thinking is that expensive and elaborate machinery will be required to carry spread slurry and even these have their limitations.

What doesn't appear to be part of the conversation is alternative ways of housing animals that produce the manure in the first place.

Slatted housing came in as an alternative to loose housing in the 1960s and 1970s when the main advantage was labour reduction.

As a system of manure storage however, slats have considerable faults. These include:

  • The environmental risk from ammonia and nitrate losses;
  • It is extremely expensive to construct slurry storage;
  • It requires elaborate civil engineering techniques involving copious amounts of high grade steel and concrete (both of which have their own emissions problems to contend with);
  • It has significant health and safety implications in terms of slurry gases and drownings.

A lot of the first wave of slats are now coming to the end of their natural life, which raises the terrifying risk of structural failure and cattle falling into tanks.

Despite all this, straw bedded housing is not even being considered as an option.

Granted the price of straw is now an issue, but up until midway through the 2017 harvest, straw was a disposal problem for many growers.

Indeed, the disposal of straw was a reason why many growers gave up on tillage in the first place, which is causing this supply deficit.

Apparently farmyard manure has no emissions issues as the Nitrogen is bound up in the straw fibres and does not volatilise easily.

Straw spreading machinery has improved as has house design to reduce the workload in straw bedding, and the capital outlay for loose housing is a fraction of slatted accommodation.

Given the problem of slurry storage and the necessity to pursue all avenues in the pursuit of emission reduction, perhaps it's time to adjust policy to encourage more loose housing, especially in areas where straw is traditionally widely available?

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

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