The ever-present threat of sclerotinia

Date:05-08-2023

Sclerotinina isn’t a disease that UK growers will see circulating every year, but when it takes hold the effect on oilseed rape yields can be devastating.

Losses can be as high as 60%, but better forecasting, well-timed spray programmes and, most recently, genetic advances in varieties all help prevent such circumstances becoming common. 

At the time of writing 2023 is shaping up to be a year where disease will be seen. The AHDB’s sclerotinia forecasting tool shows a high risk in Devon and Cornwall, with warnings for much of the west coast of England.

″The risk of infection can be in the soil from previous crops, and the pathogen can last up to eight years,″ explains Andy Stainthorpe from Corteva Agriscience’s seed brand, Pioneer.

″Like most diseases, sclerotinia likes wet and warm conditions, and when the crop is in early to mid-flower, the petals can fall from the plant and stick to the stem which creates the perfect storm for infection.

″Examples of infected crops can be extremely localised, usually indicated by a dying plant with an infected stem, leading to early senescence which obviously affects yield.″

Andy says spray programmes to protect crops are common, but that thanks to advanced genetic breeding, in-built tolerance now exists to put growers on the front foot.

PT303 Protector Sclerotinia topped the AHDB’s UK Recommended List for 2021-22 with a gross output of 107%, and showed its consistency in this year’s List returning 104%. 

It offers a suite of genetic protection against sclerotinia as well as resistance to Turnip Yellows Virus (TuYV), light leaf spot, and phoma.

Corteva’s trials show that when sclerotinia infection levels are 25% or above the severity of the disease in PT303 is reduced by up to 75%.

Andy said: ″In one of our trials in Essex, we have observed the visible lack of the disease when compared to a different hybrid sown adjacent in the same field.  Sclerotinia infection seemed to have taken hold despite the whole trial field having received one fungicide at flowering time. 

″This comparison confirms our view that the Protector Sclerotinia trait incorporated into PT303 is a crucial one for growers looking for consistent protection against this damaging and unpredictable disease.

″Where possible, a really strong genetic yield potential should be combined with the strongest agronomic package and PT303 also offers proven TuYV resistance in addition to its unique Sclerotinia tolerance.

″PT303’s early vigour and good early stem development characteristics will also appeal to growers who want their crops to grow away from pests during the autumn.″

With crops now in flower, Andy expects farmers to soon start thinking about variety choice for autumn drilling.

The planted area of oilseed rape has jumped dramatically over the past two years as strategies to counter flea beetle damage have developed and, more significantly, oilseed rape prices have risen sharply.

The UK’s 2022-2023 oilseed rape area has been estimated to be around 413,000 hectares, up from 360,00 hectares the previous year.

UK oilseeds markets have looked bullish, driven by increased global demand for soya beans and cuts to South American production.

″Prices have come back a lot compared to the middle of last year but are still strong and the benefits of oilseed rape in rotation are well known,″ Andy said. ″It remains the most profitable break crop.″

PT303 scores 7 for phoma, enhanced by the RLM7 gene, and 6 for light-leaf spot.

Corteva’s seed pipeline has now produced a second variety with in-built tolerance to sclerotinia. PT312 is awaiting UK registration and is due to become Corteva’s second hybrid to offer UK farmers this cutting edge benefit.

Similarly to PT303, PT312 is provides resistance to TuYV, and has a very high oil content and is stiff strawed.

″Having this genetic potential in our armoury is a huge step that Pioneer has taken. PT303 is the first ever winter oilseed rape variety with a claim for tolerance to the stem disease,″ Andy said.

″This varieties are ideal for those looking to add a further layer of built-in protection against disease, particularly sclerotinia which can be devastating to yield in wet and humid conditions.″

What causes sclerotinia?

Sclerotinia requires at least 24 hours of continuous high humidity and night-time temperatures above seven degrees for infection to occur.

Wet weather during flowering creates the biggest risk to the crop because this encourages fallen petals to stick to the crop’s leaves.

These petals act as a nutrient source for the pathogen, which then grows down the leaf stem to the main plant stem where it presents as large white lesions some two weeks after the plant has become infected.

From infected petals, spores can germinate and infect the crop.