Making use of natureâs predators
As featured in Arable Farming Magazine
Making use of natures predators
by Arable Farming September 2020
While IPM offers no easy answers to pest control, growers are increasingly looking at what techniques they can implement to make better use of it on their farms. Marianne Curtis reports.
As chemical actives disappear from the growers armoury and sustainability of farming systems comes under the spotlight, IPM is receiving increasing attention.
Speaking at a Leaf âIPM in arable virtual field day, Dr Alastair Leake, director of policy and public affairs at the Game and Wildlife Conservation Trust, explained how The Allerton Project had been working on farm ecology for more than 50 years.
We have built up a huge amount of experience on how to deal with pest problems without resorting to chemicals.
Looking back to 1959, US researchers found they had better control of spotted alfalfa aphid when they halved the dose of chemical. Investigating further, they discovered the role of biological control.
The great entomologist Helmut van Emden, author of Beyond Silent Spring, found that in an unsprayed crop there is one predator species to every three pest species, which in normal agricultural circumstances is a problem for the farmer because the pests are getting the upper hand and it is probably costing them money.
However, when spraying with a non-selective pesticide the pests recover more quickly than the predator, which shifts the advantage to the pest and you get into a situation known as the pesticide treadmill where you are continually having to spray to keep on top of the pest because the predators are no longer able to do that. However, if you can use a selective pesticide either through its mode of action or modifying the dose, you can shift the balance in favour of the predator.
Cultivations also have a role to play in pest control, said Dr Leake.
Work we did years ago showed that for zero-till, infection rates for BYDV were very low compared with ploughing. At first we thought it was due to the trash on the surface making it more difficult for the aphids to recognise the green shoots, but later we were challenged with the idea it was to do with spiders and that stubble and trash created a lot more structure for the spider to spin its web than ploughing, where the surface is very smooth.
There is a great advantage to trying to use natural enemies. If you spray you may end up using pyrethroids which are very damaging to spiders and put you
back on the pesticides treadmill.
Work has also been done by The Allerton Project to look at how spiders may have a role in cabbage stem flea beetle control in oilseed rape, said Dr Leake.
In a ploughed system there were fewer spiders; in min-till, 10 times as many and many more in a light-till system, where the pests didnt seem to be a problem. We repeated the work the following year but the spiders didnt turn up for work. This is the problem with biological control, it is valuable but we need to be able to add more certainty to it.
Beetle banks can be helpful in giving natural enemies a head start, said Dr Leake.
We excavated beetle banks in winter to find out whether beetles used them for over-wintering and found up to 1,300 beetles/sq.m in these banks.
In spring the beetles head out into the field looking for something to eat and you have a ready-made IPM agent working for you.
They go into the field looking for aphids as they fly in and because the beetles are already there, they are able to suppress the breeding cycle of aphids and
keep them under control right through the season. If they were not there on arrival of the aphids, the latter would start to breed and go over the threshold for economic damage.
We have had beetle banks since 1993 and have used no summer aphicides on cereal crops in that time. In at least seven of the last 25 years other farms in the area have sprayed.
In the field Emma and James Loder-Symonds, Kent
Emma and James Loder-Symonds, of Nonington Farms, own 161 hectares and contract farm for a number of other businesses.
Recently becoming a Leaf demonstration farm, they apply Leafs sustainable farming principles of integrated farm management to their own land and also to that of their clients.
Mr Loder-Symonds says: We are looking to maximise the return to clients and ensure conservation measures thrive as well. Leaf reflects our core values. We are also looking to reduce costs through benchmarking and add a premium to products we grow on-farm.
Barley yellow dwarf virus-tolerant winter barley variety KWS Amistar has been selected on-farm to reduce the need for insecticides, says Mr Loder-Symonds.
With cabbage stem flea beetle becoming an increasing problem in oilseed rape in Kent, Mr Loder-Symonds has been looking at how companion cropping can encourage the flea beetle to eat the companion crop rather than the OSR.
We tried a clover with OSR mix last autumn which had a beneficial effect but we need to look at many things there is no silver bullet. We need to look at soil management, fertility levels, vigorous varieties and extending the rotation, to name but a few.
Mr Loder-Symonds has also changed cultivation system in a bid to beat the beetle.
Traditionally, we have subsoiled, cultivated and drilled, but there was a cost element and we were losing moisture.
We have changed to a one-pass system using a Karat drill with a heavy set of discs and a Stocks seeder on the back. It is drilled, sealed and rolled twice. This helps prevent the flea beetle from working the top layer of soil, especially on chalk.
Beetle banks on-farm connect different habitats, such as hedges and woodland and help with IPM, says Mrs Loder-Symonds.
They are a good habitat for lacewings and ladybirds which are natural predators of aphids.
Introducing flower-rich margins and field strips has helped with pest control in trials carried out as part of the Achieving Sustainable Farming Systems (ASSIST) project. The project aims to identify best management practices to maximise natural pest control in a manner that fits in with current systems.
Dr Ben Woodcock, of the UK Centre for Ecology and Hydrology (CEH), which is running the trials, said: There is better pest control next to flower-rich field margins. Natural pest control reduced the survival of aphid colonies and maximising spill-over into the crop will likely increase natural pest control.
In one part of the trials, which last for five years and cost £11 million, three treatments were trialled. The trials took place on 19 sites established in two waves in 2017/18 and 2018/19, all conventionally farmed with a wide range of management practices.
The treatments were: crosscompliance; flower-rich field margins and cover crops; and; flower-rich field margins, cover crops, organic matter and in-field flower-rich strips. The latter was said to result in the most parasitised aphids, and the first treatment, cross-compliance, the least, according to Dr Woodcock.
He also said not all predator insect species respond in the same way following sub-lethal insecticide exposure.
Some are more resilient than others. Diversity provides an insurance policy that some predators will continue to deliver pest control, whatever the conditions.