Tillage: Beneficial organisms can only do so much for pest control
Published 11/11/2015 | 02:30
The unseasonably warm weather over the last month has allowed for a lot of winter cereals to be sown in excellent conditions and for those crops to emerge well.
Strong vibrant rows bursting from the soil are the order of the day and are a joy to look at in most cases.
However, in some respects, it's easy to get carried away with such excellent conditions.
Warm autumn weather can cause problems too. The priority action is aphid control. High temperatures have allowed for a huge influx of aphids to proliferate, and where seed treatment was not chosen, control is a priority on emerged crops. However, I have noticed very high levels of beneficial organisms such as ladybirds and spiders, no doubt as a result of the high temperatures and abundant food supply.
Ladybirds have been absent for most of the season and a late season flush is notable, but their presence at such high levels does provoke a conundrum.
Even putting aside the environmental implications, in the right circumstances beneficial organisms are a far more effective control mechanism for aphids than any insecticide.
For one thing they don't turn their nose up at knock-down resistant (KDR) aphids when they are selecting their next meal. KDR aphids are resistant to synthetic pyrethroids, the mode of action for all insecticides (except for one, the most non-selective of them all) that have label recommendations for autumn application on cereals.
The question that has to be asked is should aphid control be left to nature?
If nature provides a suite of control mechanisms, why should non-selective pesticides be applied? The reason is that control of aphids is not the target here, control of the virus that the aphids carry is. It doesn't take too many aphids to spread a lot of virus.
In terms of the impact of non-selective insecticide use on the wider environment, while no one likes the idea of offloading little critters that don't need to be offloaded, the reality is that a winter cereal area of even 150,000ha represents only 3pc of the utilisable agricultural area of the country, not to mention non-utilisable agricultural area, where these insects are most likely to hang out. Hedgerows and grassy banks within cropped areas are also safe havens for insects and non-target organisms. The alternative risk of an occurrence of Barley Yellow Dwarf Virus (BYDV) on a crop, where yields can be halved and nothing can be done about it when it becomes apparent, is too big a risk.
On balance, action is warranted on aphids as crops emerge and unless they have been seed dressed, non-selective insecticides are the only available option.
The next risk from good autumn establishment is strong weed establishment. Grassweeds are the expensive target here and while developing problems such as sterile brome, canary grass and even blackgrass get all the press, they are only additions to the old foes of annual meadow grass and wild oats. Strong grassweed problems will need robust control programmes and the sooner these programmes are commenced, the more likely they will be successful. Another threat is disease, especially septoria. The 2014/2015 season was notable for the low levels. This was unexpected, but septoria hasn't gone away by any means.
This was a low disease year because of the prevailing conditions, not from any magic potions or inspired fungicide mixes used.
Next year could well be completely different. At this point, nothing can be done. Sowing date, seeding rate, variety used are all set, early season fungicides have no impact on disease development. The only thing that can be done is to plan ahead.
Strong canopies coming into the spring may need careful management to minimise development and nitrogen application can be used to manipulate these.
The reality is that while good strong establishment results in high to very high yield potential, this potential will have to be protected and robust fungicide programmes are the only option.
Good autumn establishment can provide a raft of problems, but they are problems most growers will gladly take over the alternative of looking at bags of seed in the shed and grabbing every half opportunity to muck-in crops over the next eight weeks.
Dr Richard Hackett is an agronomist based in north County Dublin and is a member of the ITCA and ACA