New ADAS research: CSFB’s dual damage affects stem thickness and increases lodging risk
18 Mar 2021
By Sophia Sutherland, Junior Campaign Manager
At the BASF webinar titled ‘Helping spring decisions in OSR ’, ADAS’ Fran Pickering and Dr Pete Berry, joined farmers Steve Crayston and Tim Hayward to talk about the latest research into cabbage stem flea beetles, lodging and spring decision making.
It was a fascinating session, with plenty of practical advice and I’m pleased to be able to share a short summary of the discussion.
I was delighted that ADAS entomologist, Fran Pickering, chose our very own virtual farm’s webinar to share ADAS’ latest trial results, giving insight into how CSFB damage weakens stems, restricts growth and makes crops increasingly prone to lodging.
ADAS Head of Crop Physiology, Dr Pete Berry, picked up on the issue with further research by the organisation into the extent and cost of lodging.
Finally, the two growers discussed their crops, the season so far and their OSR’s longer-term prospects.
Fran’s research sought to quantify and explore the mechanisms behind, what we have long suspected; CSFB damage effects stem strength.
ADAS field trials took 50 plants at the end of flowering in May from two sites in East Anglia. The team assessed stem diameter, breaking strength and the internal damage caused by the CSFB. By assessing the percentage area of stem damaged, the plants were sorted into five categories ranging from ‘minimal’ (plants with less than 5% damage), to ‘severe’ (plants with 76-100% of stem area damaged).
Fran’s team found thicker stems were stronger and higher damage was associated with the thinner stems. It made her question why, and prompted her to look again at the type of damage the CSFB larvae were causing; predominantly mining and browning at the base of the stem. She argued that this type of damage restricts the take up of nutrients and water, which in turn, restricts growth leading to thinner stems.
Plants taken from the second site revealed that for any given stem diameter, more larval damage makes stems weaker. The larval feeding not only restricts stem thickness but hollows stems reducing their strength.
Fran’s take-home message was that even low levels of CSFB damage significantly reduces stem strength. On average stems with less than 25% damage were 29% weaker.
Effects of lodging on yield
Back in 2012, ADAS’ aerial survey of over 2,000ha showed that 35% of the OSR had lodged. 99% of fields had some lodging and 20% of fields had over 70% of the crop lodged. The organisation repeated the survey two years later and found similar levels of lodging.
Pete noted how it is easy to underestimate the extent of lodging and acknowledged that while lodged crops are obvious from the air, they are not so easy to see from the ground.
In another experiment, ADAS researchers mimicked natural lodging in crops to assess the impact at harvest.
Where crops lodged at 900 between flowering and early seed fill, nearly 50% of yield was lost. Where the crop was lodged, at 450, about 20% of yield was lost and even modest leaning at about 22o reduced yield by 7-16%. Severe lodging also reduced oil content by up to 8%.
The reason behind this extreme loss, Pete explained, is that any leaning or lodging squashes the leaves and pods together, which impacts light capture and efficiency of use.
In total, he estimated lodging cost the OSR sector £47 - £120m each year.
There are a number of actions growers can take to minimise lodging and Pete used an example from the audience to offer guidance.
The grower had an OSR crop with a GAI of 3 back in December. Over winter the crop had gone backwards and now stood with a GAI of 1.5. The question was, is this crop still at risk of lodging and what can they do?
In short, Pete said ‘yes’. A GAI of 3 back in December means the crop had quite a large canopy and the amount of N the canopy contained back in December should be used as a guide for fertiliser applications. For PGR decisions, it is best to use the most recent GAI - in this case, 1.5.
ADAS research shows canopy size just before start of stem extension is a good guide for how well a crop will respond to a PGR. Any crops with a GAI of 0.8 - or is covering 40-45% of the ground - at this time year will respond positively to a PGR.
Adaptations on-farm to CSFB increase lodging risk
Steve Crayston from Essex, has 70ha of Jango and 55ha of Acacia in the ground this year. The field used as a case study was direct drilled on 11th August. The variety Jango, was drilled at 5kg/ha into long stubbles.
Ordinally he’d expect crop to go backwards over winter but this year, between 1st December and 5th Feb, more than half the field had grown on. Now the vast majority of the field has a GAI over 0.75.
Pete didn’t think the canopy size was large enough to justify delaying or reducing nitrogen and suggested the wet weather in recent months could have cause significant leaching from soils.
Tim Hayward from Berkshire, has changed how he grows OSR to combat the effects of CSFB.
In previous years, Tim was drilling OSR after spring barley. But by the time he'd harvested the previous crop, baled the straw, completed any cultivation work and applied chicken muck, it was often the first week of September before he had the OSR in the ground. In 2019 and 2020, dry spells in September together with the CSFB damage, meant he had some crop failures.
Now, Tim's direct drilling into long wheat stubbles and paying much more attention to the forecast. He will only drill when the ground has moisture and rain is predicted.
This year he’s assessed the benefits of using chicken muck in an on-farm trial. With a GAI of 1.3, the chicken muck has led to double the biomass of the comparison, DAP (GAI of 0.6).
Tim’s changes correspond with the work ADAS have done. Long stubbles in trials reduced CSFB damage by up to 30% and chicken muck is being shown to be a good option. Avoiding drilling in dry conditions is really important as ADAS have found crops that have moisture at drilling can grow away from damage and tend to be stronger, bigger plants going into winter.
Being on thin chalk soils with restricted potential yields, Tim hasn’t, historically, had a problem with lodging. But moving to conventional seed sown at higher seed rates, combined with some larvae damage, his crops are higher risk. It is an issue that he feels he needs to be more mindful of.