As chemical actives disappear from the grower’s armoury and sustainability of farming systems comes under the spotlight, IPM is receiving increasing attention.
Speaking at a Leaf ‘IPM 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 didn’t seem to be a problem. We repeated the work the following year but the spiders didn’t 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.”