Winter OSR: Managing Forward Crops, Protecting Potential

Crop Development and Disease Outlook

Crops that established early and continued growing through the mild autumn are exhibiting high biomass, strong rooting and large, healthy canopies. But this increased leaf area, combined with prolonged periods of warmth and moisture, has also heightened disease pressure.

“Phoma risk is elevated this year, particularly for varieties still leaning heavily on single-gene resistance,” Sarah explains. “We’re seeing early lesions in some forward crops, and with plants still growing vigorously, they remain physiologically susceptible.”

As temperatures begin to fall, maintaining regular monitoring is essential. The speed of phoma development will slow, but the risk has not passed — particularly in fields with susceptible varieties or a history of disease.

Key nutrients under pressure

• Manganese remains the most commonly limiting micronutrient in OSR, especially on lighter soils or fields with high organic matter. Deficiency risk increases as biomass expands and soils remain moist and aerated.
• Magnesium is central to chlorophyll formation and efficient light capture. Forward crops with high leaf area index (LAI) have correspondingly high magnesium demand.
• Boron – OSR is one of the most boron sensitive crops. The highest demand is during flowering and pod set, but bBoron is also essential in the early stages for root growth and sugar/nutrient transport within the plant. Boron in soil is less available in:
  • Sandy soils
  • High pH (alkaline) soils
  • Drought conditions, because boron moves with soil moisture
  Boron deficiency can lead to hollow stems and stem cracking, which leaves crops vulnerable to sclerotinia infection.
• Molybdenum is essential in nitrate metabolism and required in highest quantities during vegetative growth stages when nitrate based fertiliser has been applied. Deficiency is more common in acidic soils, with deficiency showing up as pale green leaves and stunted growth associated with nitrogen deficiency.
• Sulphur availability continues to decline in many systems due to reduced atmospheric inputs, and early-season uptake significantly influences amino acid and protein formation.

Zinc and early root–shoot function

Although the peak requirement for zinc occurs earlier in the growth cycle, some high-pH soils or companion-crop systems continue to exhibit restricted availability later into autumn. Where crops lack root depth or have been under stress from CSFB grazing, additional zinc from foliar nutrition like Manzi, may still offer value in supporting ongoing cell division and improving winter hardiness.

Broadleaf Weed Control: Maximising Performance with Water Conditioning

Many growers are now applying broadleaf weed (BLW) herbicides — or final grassweed post-ems where label timing still permits — to tidy up canopies before winter. However, the performance of these products is influenced by water chemistry and growers are advised to utilise a true water conditioner in hard water areas.

Hard water remains prevalent across much of the UK, and high levels of calcium, magnesium and other metal ions in the water can lock-up active ingredients in the spray tank before they ever reach the leaf. With forward OSR crops carrying large canopies, achieving clean control of mayweed, cranesbill and other hard to control BLW species requires the herbicide to be working at full strength.

This is where true water conditioners such as X-Change play a critical role.
“Conditioning the spray water ensures the active ingredient remains fully available,” Rob explains. “It prevents lock-up with cations, improves compatibility in complex tank mixes, and helps the herbicide perform consistently — especially in areas where hard water is the norm.”

For OSR growers tackling BLW populations that have escaped earlier passes, getting the water right is one of the simplest ways to protect herbicide efficacy and avoid unnecessary repeat treatments.

Propyzamide: Stewardship, Soil Temperature and Adjuvants

As soils cool, attention turns to propyzamide, and growers are urged to ensure the correct conditions for optimal application, advises Rob.

“Soil temperatures should be at 10oC and falling at 30cm soil depth, with adequate moisture to support movement to the root zone. However, care should be taken to avoid heavy rainfall after application, he stresses.”

It is recommended operators download and study the propyzamide Water Protection Advice Sheet (WPAS) from the Voluntary Initiative website here.

Rob points out that this season, the inclusion of a spreading adjuvant like Silwet-L77 could be extremely beneficial to help spray droplets reach the soil – that’s the target not the foliage. “The trouble this year is that many OSR crops are very forward in their development, with large leaves that will intercept spray droplets. An effective spreading adjuvant will help these droplets run off the leaf and hit the soil. With propyzamide we need to get the active to the root zone of weeds in the top 5cm of the soil.

“The additional benefit of including an adjuvant like Silwet-L77 is that it will also enhance lateral distribution of propyzamide to areas shaded by the crop canopy where difficult grass-weeds like black-grass and ryegrass could be lurking,” he adds.

Companion Crops: Interactions and Management

Companion species have continued to gain traction, with buckwheat being the most widely used this season. In many fields, companions are now dying back naturally or being suppressed by cooling temperatures.

Their presence can influence nutrient cycling, microclimate, and early weed suppression — but they may also alter nitrogen dynamics and Zn/Mn availability in the rooting zone. Foliar nutrition helps moderate these shifts and stabilise the growth trajectory of the OSR plant as companions senesce.

Looking Ahead to Winter and Early Spring

With crops now entering the phase where growth will slow before dormancy, the aim is to ensure they cross into winter with:

• Fully functional, disease-free leaves
• Adequate reserves of Mn, Mg, B, Mo, Zn and S
• Strong root systems capable of supporting early spring nitrogen uptake
• Weed pressure minimised through accurate late-autumn BLW and grass-weed control

Rob summarises: “This has been an excellent establishment year for OSR — one of the best we’ve seen in a long time. The challenge now is simply to protect that potential. Managing nutrition intelligently and ensuring late-season herbicides work to their full capability will help forward crops carry their advantage through to spring.”