A few thoughts on crop pests
The agronomy meeting at York earlier this year provided an opportunity to revisit several important themes discussed at Monitor Farm meetings, namely crop protection, soils and nutrient management. Each of these is a huge area in itself but several important messages came up again as well as new ways of looking at similar things – which made you think.
The news that we face a future with fewer actives for protecting our crops will not have been a surprise to anyone. But this reduced number could become more expensive and also, there is an increasing threat of resistance developing.
On this basis, ADAS entomologist Steve Ellis proposed the question, ‘Do you need to treat?’
To make such decisions you need to have full confidence in the available information and thresholds will be crucial. Unfortunately, Steve reported, that some thresholds are 20 years out of date. Fortunately more robust systems are under development to help growers decide whether to apply insecticides. Something to look out for.
Steve also made the point that the impact of a pest on a crop is more important than the pest that does it. This seemed like one of those points that should have been obvious but wasn’t until you thought about it. It must depend a lot on the nature of the damage, which part of the plant is affected and so on.
Have you any idea what the average number of buds is that one pollen beetle damages on an oilseed rape plant? ADAS experiments (which involved artificially infesting crops with beetles) indicated nine.
Other interesting and related points from this presentation were that excess flower number in oilseed rape is inversely related to plant number. This is significant because the pollen beetle threshold (to treat or not) varies with plant number. Add on to this the fact that pigeon damage makes the oilseed rape crop more susceptible to pollen beetle, and you have plenty to think about. Developing accurate and practical thresholds is not a straightforward business.
AHDB produces a wide range of guides and bulletins on crop pests which are available for you to download or order on the AHDB Cereals & Oilseeds website: https://cereals.ahdb.org.uk/crop-management/pest-management.aspx These include pest monitoring services (aphids) which you can sign up to and receive weekly updates, as well as information on controlling specific pests of cereals and oilseed rape.
The thresholds in the encyclopaedia are based on best available data.