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Clubroot Prevention In Oilseed Rape

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Author: Jimmy Staples 

Cover crops are a fundamental element of any sustainable arable farm and provide many benefits to both our soils and wider farming enterprises. These benefits include but are not limited to improving soil health, preventing soil erosion, combating weeds, increasing soil water infiltration and availability, mopping up nutrients, helping to break pest cycles and increasing biodiversity.

There has also been a large increase in the acreage of cover crops sown this year, which has mainly been driven by the new Nitrates rules, particularly the stubble cultivation rule. Most farmers opted to plant a cover crop while carrying out stubble cultivations. Farmers understand their importance in a sustainable farming system and should be acknowledged for embracing cover crops of their own volition.

There are many different species used in the cover crop mixes that are popular across the country but a number of these, particularly the grazing mixes, have a high inclusion of brassicas. The fodder rape and leafy turnip mix are the main ones. The continuous use of cover crop mixes with a high inclusion rate of brassica species in the same field can increase the risk of clubroot occurring.

While I haven’t personally come across a case of clubroot in oilseed rape, anecdotal evidence would suggest that it is more of an issue where fodder rape and leafy turnip cover crops are being grazed continuously with sheep or cattle over a number of years in the same field. I and many of my colleagues work with farmers who have been using cover crop mixtures for 10, 15 and even 20 years now, with oilseed rape in their rotation, and have never had a case of clubroot on their farms. With that said, prevention is always better than cure and being aware of any possible risks and making informed decisions about rotation and cover crop mixes is good agronomic practice.

What is Clubroot?

Clubroot is a soil borne fungus that can affect all cultivated and wild members of the brassica family. Clubroot can live in the soil for up to 15 years and infected plants develop characteristic galls on the roots which reduce the plant’s ability to take up water and nutrients, leading to stunted growth and reduced yields.

In the UK, yield losses of 0.3 tonne to the hectare per 10% of oilseed rape plants affected have been reported. Total crop failure is also possible in extreme cases.

 

 

 

Clubroot Prevention

As with any IPM strategy, early identification is crucial. There are several simple and straightforward measures that can be taken to prevent clubroot from becoming an issue on farm:

  • Maintain drainage: Clubroot will move through the soil water. Poorly drained, compacted soils are at a higher risk for clubroot infection. Keep field drains flowing and if drainage work is needed, make it a priority where oilseed rape is intended to be sown.
  • Limit the movement of infected soil: Clubroot can spread from field to field on affected soil. If clubroot is identified in a field, then a plan should be formulated to minimise soil moving from that field to a clean field via machinery, footwear, straw or crops.
  • Keep the pH right: Crops grown in lower pH soils have a greater risk of developing severe symptoms. Another reason to ensure your soil pH is optimum.
  • Control weeds and volunteers: Weeds such as charlock, shepherd’s purse and volunteer rape will all host clubroot. Ensuring control of these weeds throughout the rotation will help to reduce the risk of clubroot developing.

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tractor mowing grass silage

Maximising Grass and Silage Growth

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Over the past number of weeks, we have experienced very little grass growth due to a 75mm soil moisture deficit. Growth rates in this area dropped to around 30kg DM/ha which led to a lot of animals receiving a buffer feed. Luckily, we have got a welcome dash of rain over the past few days which in the presence of available nutrients has brought growth levels back up to 90kg DM/ha. As we are all starting from low farm covers, we need to maximise growth to deal with the recent shortfall of grass production. First cut silage has also been affected by drought conditions with 25-30% reduction in yields being reported locally. The quality of this first cut silage should be very good and most crops were saved in great conditions.

Grazing ground

Nitrogen N

Paddocks that have received nitrogen in the past few weeks should take this up now. Fields that have not been spread for over 3 to 4 weeks should get nitrogen immediately. The increased growth after the rain should enable 2 units a day to be taken up.

Phosphorous P

P is a key driver of growth, root development, and grass tillering. Available P will help stressed plants recover and promote water and nutrient uptake. In addition, it will promote grass tiller development to help swards recover after the dry spell. Therefore, apply low to medium rates of P in your next fertiliser application. Low index soils will require larger amounts of P depending on when they last received it. Earlier spring applications of P in low index ground will need to be topped up at this stage as P is locked up in these soils.

Potassium K

K has a major role to play in the uptake and regulation of water within the plant. Now more than ever sufficient levels of soil available and applied K will be essential for the plants to withstand drought and aid rapid recovery. K at sufficient levels will keep good quality leaf in the grass and stop it from droughting out, pushing up a seed head and going to stem. Stem has one third less feed value to the cow as green leaf.

Sulphur S

Sulphur increases the efficiency of N uptake which is very important at this time of the year. Sulphur aids in plant protein production and therefore grass that has sulphur will remain higher in protein and retain feeding quality later into the season. Sulphur should be a part of all fertiliser applications. In most cases an application of a compound containing N P K S will be the best solution to get farm covers back up where they need to be. Take the full advantage of the growth while we have it to build up much needed reserves.

Silage ground

The present damp dull weather makes it ideal for slurry applications. Most slurry spread during the dry spell will have lost all its nitrogen content. It is important to know your offtake when it comes to spreading your second cut silage, with each tonne of dry matter removing 25 kg (20 units) of N, 4 kg (3 units) of P, 25 kg (20 units) of K and 4 kg (3 units) of S. In low index P we must add 10 kg (8 units) per index lower than 3 and in low index K 30 kg (24 units) per index lower than 3. In general, we are low in sulphur so as a rule of thumb it is best apply 15 to 20 units per acre for your second cut. A 3 tonne DM/ha crop on an index 3, 3 will take 75N 12P 75K and 12 to 15 S out of your soil.

 

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