Research and agronomy news from AHDB Cereals & Oilseeds View this email in your browser. Agronomy Focus
22 October 2026
Cereals & Oilseeds research and agronomy news
Pests, diseases and weeds | Varieties | Soils, nutrients and the environment | General
Pests, weeds and diseases
Is BYDV getting more common? During autumn, we publish data on the proportion of aphids that carry Barley yellow dwarf virus (BYDV). Typically, Rothamsted Research tests over 1,000 aphid samples for the virus each year. The samples are collected during the main autumn aphid flight period from a small number of insect suction traps. Bird cherry-oat aphid samples dominate the trap catches, as they fly in far higher numbers during the autumn, compared to grain aphid. We’ve done this for several years and know that most aphids do not carry BYDV. Based on 2020 to 2024 average data, less than a quarter (22.3%) tested positive for the virus. This is why we set the default as 20% in the new BYDV tool. The default value is replaced with actual regional values during the autumn. However, based on recent data, there may be a concerning trend emerging. The average proportion of aphids carrying BYDV was relatively high in autumn 2025 (34%) and in 2026 (36%), so far. We still need to process several more aphid batches this autumn, before conditions turn too cool for aphid flights. If virus pressures consistently start to track higher than the historic average, we may need to review the BYDV tool’s default value.
See the latest virus monitoring data
Use the BYDV tool today
CSFB flies late (again)
We’ve used yellow water traps to monitor cabbage stem flea beetle (CSFB) migration at seven oilseed rape sites in England since the start of August.
As in previous years, August was quiet. In fact, the traps hardly caught any beetles until the middle of September. Activity peaked towards the end of September and the start of October.
Based on several years of observations, numbers often peak between the start and the middle of September. It means that migration was later than average in autumn 2026, which caused issues for some newly emerged crops. Migration was also relatively late in autumn 2025.
As per BYDV, the monitoring data helps us understand trends, including any significant shifts in patterns.
See the latest migration data for 2026
This data is being collected as part of CSFB Research+
Herbicide resistance risks of precision application
The potential herbicide resistance risks of precision application methods are examined in a new joint technical note from the UK Weed Resistance Action Group (WRAG) and the Herbicide Resistance Action Committee (HRAC) Europe.
As per conventional approaches, it is critical to stop weeds surviving herbicide applications.
However, precision application has unique risks. For example, it focuses on foliar-acting herbicides, where there are fewer options for control. This is potentially an issue because repeated use of the same or limited herbicides or mode of action groups is generally associated with higher resistance risks.
Applying too-low doses also drives resistance risks. For example, variable rate application or patch spraying may mean some weeds do not receive the full effective dose.
The technical note examines the resistance risk of various application methods and how to use such approaches within integrated weed management.
Access the technical note from the WRAG web page
Autumn phoma forecast
At the start of October, we released the autumn 2026 phoma leaf spot forecast.
Key messages
The online forecast models when 10% of oilseed rape plants may develop symptoms at hundreds of GB sites It is important to treat small plants and varieties with relatively low Recommended Lists (RL) stem canker disease resistance ratings first when 10% of plants develop phoma leaf spots Disease onset was forecast to be a little later in autumn 2026, compared to recent seasons, with the treatment peak starting around the middle of October See our article
Source: press release issued by AHDB Cereals & Oilseeds View.