• Moisture is key, as dry conditions can slow establishment – always wait for moisture (present or forecast) before sowing
• Avoid the traditional end-of-August/early-September sowing dates, as this is when peak CSFB migration usually occurs (typically, late-August to mid-September)
• Sow early (early- to mid-August) to maximise tolerance to adult feeding (note that these crops may have higher larval loads later in the season)
• Sow late (mid-September onwards) after migration has peaked to minimise adult damage and reduce larval load*

Further information

*Sowing crops from mid-September may negatively impact yield, depending on how late the crop is sown and the earliness of frosts. Plants must reach a sufficient size to reduce overwinter losses to frost. However, the yield impact may be small. This information is based on research conducted in the 1990s and may no longer apply to today’s varieties. Early sown crops are also at higher risk of some diseases (e.g. clubroot) and pests (e.g. turnip sawfly and cabbage root fly) and may require extra care to manage canopies.

• Give crops a strong start with the best possible seedbeds:

1. Moisture is key, as dry conditions can slow establishment – always wait for moisture (present or forecast) before sowing
2. When moisture levels are lower, consider lower-disturbance establishment methods that help retain soil moisture (such methods are also associated with  stronger populations of natural pest enemies)*
3. Ensure good seed-to-soil contact, through cultivation selection and rolling. Roll and, where possible, roll again at 90 degrees to the drill to create a better surface and help conserve moisture (taking care to avoid capping). Rolling may also create a more adversarial environment for egg laying
4. Optimise nutrition to support good growth and reduce plant stress (apply all nutrients in accordance with crop need/soil testing results)**
5. Monitor slug activity and control populations, as required

• If sowing from late-August, consider a variety with good autumn vigour
• A vigorous variety will reach the four-true-leaf stage quicker, making it more tolerant to adult feeding damage***
• When drilling early, consider a slower-developing variety that does not reach stem extension too early
• Using quality seed is critically important, irrespective of source. For example, poor seed from a heap or old seed (without a fresh germination test result) can result in slow/poor establishment and make the crop more vulnerable to damage
• Screen any farm-saved seed for larger seed (1.8–2.2 mm) – thousand seed weight (TSW) can be used as a proxy measure. Large seeds are associated with better germination and provide a stronger start for seedlings. However, over-sized seed can be a disadvantage, particularly where moisture is sub-optimal
• Leave the previous cereal crop’s stubble, which can make it harder for CSFB to locate OSR****

Further information

*CSFB may also be attracted to disturbed soil. There is little robust evidence to show this definitively reduces CSFB damage, but it is supported by encouraging anecdotal evidence and limited trial results.

**The AHDB Nutrient Management Guide (RB209) provides guidance on the application of nutrients to oilseed rape in the autumn – worked into seedbeds (starter fertilisers) or applied as a top dressing. For example, the application of phosphate and potash to seedbeds is particularly important for soils at Index 0 and 1. Autumn nitrogen can encourage autumn growth, but research suggests that crops sown after early September are unlikely to respond. When applying nutrients, always consider local conditions, comply with relevant rules and regulations and consult a FACTS Qualified Adviser, if necessary. 

***Good varietal autumn vigour (in terms of establishment) is associated with lower levels of leaf area loss from adult CSFB grazing.

****Longer cereal stubbles may reduce pressure, although the evidence for this effect is mixed. However, stubbles do support spider populations and their webs, which can trap insects. Be aware mats of straw can prevent moisture reaching the soil, especially during periods of low or sporadic rainfall.

• Grow OSR as far away from the previous OSR crop as possible (your own and your neighbours’)
• CSFB can fly several miles but any distance (space and time) between the previous and current crops will help

Further information

Swedish growers are recommended to leave 800m between crops to reduce risk from CSFB.

• Stick to the recommended seed rate of 50 to 60 seed/m2 to encourage big, vigorous plants in the spring, which are more tolerant to larval feeding

1. The use of lower seed rates also decreases the number of adults emerging from the field the following summer, which helps to reduce local pressure
2. Increasing seed rates has a limited benefit in diluting adult feeding damage
3. Pigeon risk, relative to thick/thin crops, will also be lower

• Choose a variety with good early spring growth and biomass to limit larval damage*
• Crop management that enhances crop resilience (e.g. through nutrition and plant growth regulation) could make the crop more tolerant to larval damage. However, robust evidence is lacking

Further information

AHDB view: Generally, in terms of yield, increasing the seed rate beyond that needed to achieve optimal plant populations – 25–40 plants/m2 – results in little benefit, unless conditions are dry during establishment.

*AGRII view on variety choices:

• Varieties differ significantly in their relative autumn and spring growth, and those differences are relatively consistent between trials and over years
• High autumn biomass is considered useful for challenging autumns. For example, it can reduce pigeon damage and build a big crown that is more resilient to CSFB larval attack over the winter
• There is good evidence that high biomass combined with early spring regrowth reduces the severity of CSFB larval symptoms
• There is limited evidence from our 2023 trial to suggest that spring vigour is the best way to mitigate against yield loss when CSFB larval damage is high 

• Use organic materials (amendments/manures/chicken muck/sewage)
• Apply at sowing and/or during establishment to reduce adult damage and help establishment
• It is not clear if this is a nutritional benefit or due, in part, to the smell making it harder for CSFB to locate OSR

Further information

AHDB view: The addition of organic materials could reduce CSFB damage, but reports are largely anecdotal and supporting trial data is sparse. Effects could be due to improvements in crop growth or the reduction of CSFB infestation (e.g. by masking the crop or deterring the pest). Application timing may be important, with applications that coincide with CSFB migration possibly maximising the disruption effect.

When applying organic materials/nutrients, always consider local conditions, comply with relevant rules and regulations (such as the farming rules for water) and consult a FACTS Qualified Adviser, if necessary.

• Pyrethroid resistance in CSFB is widespread and severe in England, so pyrethroid sprays are unlikely to be effective and may increase resistance spread (in target and non-target species)
• Resistance is less severe in Scotland, Wales and Northern Ireland, although there is evidence of it increasing in the Scottish Borders
• Consider testing pests to confirm whether pyrethroid resistance is present
• As pyrethroids can harm beneficial insects, spraying may be counterproductive and make the situation worse

Further information

An AHDB-funded research project monitors insecticide resistance in key UK pests. In recent tests (2023), 13/14 samples collected at OSR harvest contained fully pyrethroid-resistant adults, ranging from 7% to 95%. One of the samples was from Scotland (contained 27% resistant beetles).

Resistance map of the UK

• Recent ADAS trials show that some companion crops can reduce adult and larval pressures
• Beneficial crops include oats, buckwheat and berseem clover
• Sow companions about a week ahead of OSR, providing moisture is not an issue (particularly for clover species)
• Some companion plants may encourage natural enemies
• OSR intercropped with faba beans (Vicia faba) significantly reduced pest damage in OSR, including feeding by CSFB, according to a 2024 research paper

Further information

AHDB view: Companion crop species may reduce CSFB pressures through several mechanism, such as improving soil structure (e.g. berseem clover), masking the crop from CSFB or offering a shelter for natural enemies. Some, such as mustards, act as sacrificial plants that are eaten in preference. Several trials have detected significantly less pest pressure in crops companion-cropped or intercropped. Choose a companion crop that will not outcompete OSR and/or can be removed easily (e.g. killed by frost or taken out with a herbicide).

• Leaving OSR volunteers to grow as trap crops until late September (or later) reduces adult and larval pressure in nearby fields of OSR
• Border and in-field strips of turnip rape (which is relatively attractive to CSFB) can reduce CSFB pressure in OSR
• Late-summer-established cover crops containing brassica species may also act as trap crops, reducing CSFB pressure in nearby OSR (if trap crops are present during migration)
• Destroy any brassica cover crops or OSR volunteers used as a trap crop by the end of February to reduce the risk of them becoming a source of CSFB

Further information

AHDB view on trap crops: Oilseed rape volunteers in fields coming out OSR can act as a trap crop and divert CSFB away from cash crops in nearby fields. In trials, the approach reduced adult CSFB infestation (by up to 88%) and damage (by up to 76%) in the OSR cash crop. It also resulted in higher plant populations (by up to 56%) and reduced larval populations (by up to 69%). When trap crops are destroyed, CSFB eggs or larvae in them will die, reducing local CSFB pressure the following year. However, benefits were variable and not always observed. It is likely that relatively large areas of adjacent trap crops (at least 2 ha) are more likely to deliver benefits, especially if left in place until after the bulk of CSFB migration has occurred (i.e. late September). It is also believed that volunteers at an early growth stage at the end of August are most attractive to CSFB. Use cultivations to encourage a fresh flush of volunteers or broadcast home-saved seed to produce a cheap, sacrificial trap crop.

• After harvest, CSFB still emerge from the soil in certain circumstances, according to an initial study by NIAB*
• In this situation, shallow cultivations of OSR crop stubble can significantly reduce beetle numbers
• However, such cultivations may have a negative impact on beneficial species and limit the potential for the use of OSR volunteers as trap crops

Further information

 *Further studies are needed to improve information about this strategy.

A. Monitoring

• Monitor CSFB adults in harvested oilseeds for an early indication of the potential population, including whether a large bulk of adults have already emerged
• Check for classic shot-holing symptoms on the leaves of volunteer oilseed rape
• Monitor for adult pest damage as soon as crops begin to emerge

Use yellow water traps to monitor beetles, which can help indicate when peak migration has occurred (to guide late sowing).

Set two yellow water traps on the headland and two in the field along a wheeling during beetle migration (usually around early September). Fill traps with water and a drop of detergent. Empty and reset the traps weekly (counting the number of beetles each time). Record the cumulative number of beetles in each trap until the end of October. Calculate the average number of beetles per trap for the whole monitoring period.

Yellow water traps can also provide an indirect measurement of potential larval populations by counting beetles. Larvae can also be dissected out of or passively extracted from a random sample of 15–25 plants. Dissections are best done by an accredited laboratory. Passive extraction can be done on the farm by suspending the plants on some mesh over large plastic boxes filled with water and detergent. Leave the plants to dry for about two weeks. The larvae will drop into the water, where they can be counted.

Use monitoring data (for adults and larvae), treatment thresholds and information on insecticide-resistance status to determine if treatment is appropriate.

There is also an automated beetle monitoring trap on the market (Bayer MagicTraps).

B. Seed treatments

Very few seed treatment products are approved for OSR seed in the UK. Some other products are approved for application to OSR seed in the EU, which can currently be imported and sown in the UK. UK field trials (for example by NIAB) show some positive effects associated with some products, such as Lumiposa (cyantraniliprole). Always check the date when treated seed needs to be sown by.

AHDB view: Although seed treatments may become part of the solution, the impact of such approaches is currently far from clear.

C. Promote natural enemies

• Well-supported populations of natural enemies can potentially deliver moderate control of CSFB
• Pesticide applications (especially broad-spectrum pyrethroids) and intensive tillage are likely to have a negative impact on natural enemy populations, such as parasitic wasps and ground beetles
• Cut out ineffective pyrethroid sprays to support beneficial insects
• Flower strips provide nectar resources for parasitic wasps and beetle banks provide habitats for ground beetles
• Make use of stubbles and companion plants

AHDB view: Carabid beetles (Trechus quadristriatus) feed on CSFB eggs and young larvae before they enter OSR. The parasitoids Tersilochus microgaster and Microctonus melanopus parasitise the larval and adult stages respectively. Two entomopathogenic fungi (Beauveria bassiana and Metarhizium anisopliae) can infect cabbage stem flea beetles, but their impact on the field populations is unknown.

D. Grazing or topping

Grazing or topping can reduce larval damage. This needs to be done before the new year and must ensure the growing point remains intact (only remove leaves to avoid too severe defoliation).

AHDB view: CSFB larvae are far more likely to be present in leaf petioles than in the stem. Managed defoliation reduced larval numbers significantly in trials (by 23–55%), with late defoliation, before stem extension, most effective. Linked on-farm trials found that sheep grazing and topping/flailing reduced larval numbers on average by 51% and 25%, respectively. Interestingly, defoliation also decreased the severity of phoma stem canker to levels equivalent to a fungicide spray. However, researchers did not detect significant/consistent yield increases in crops with reduced larval populations. Indeed on-farm trials often showed yield reductions. Results suggest that this approach is best suited to early drilled crops, which will have the highest larval numbers but also be best able to recover from the defoliation. Defoliation is likely to be most beneficial between November and December, as this gives the crop more time to recover. Later defoliation is riskier and certainly should not be after stem extension. Crop recovery is strongly affected by spring weather, with cool, dry springs detrimental. Further work is needed to optimise the approach.

Grazed cereals and oilseed rape (grown for grain and seed, respectively) are also treated as fodder crops, which restricts the use of plant protection products. Authorisations must include appropriate qualifiers, such as ‘for animal fodder’, otherwise treatment is not permitted.

E. Silica

Some limited trials, research and anecdotal evidence suggest that the application of silicon-based products may reduce CSFB damage and reduce disease pressure. However, further research is needed in this area.

F. Seed priming

Consider priming seed before sowing to get germination started early.

G. Biostimulants

Some vigour-enhancing treatments may boost early growth and emergence.