2nd April 2024
KEEP DOSE RATES HIGH FOR BEST SCLEROTINIA CONTROL
Controlling Sclerotinia disease in oilseed rape crops will be more important than ever this season, as the UK’s rapeseed area is considerably down, which makes optimising yields of those crops in the ground critical.
Sclerotinia stem rot is a significant disease of oilseed rape in the UK; Sclerotinia prevents movement of water and nutrition through the plant’s vascular system and in some circumstances can reduce yields by 50% or result in complete loss through plant death.
Sclerotinia sclerotiorum infects crops in the spring when the fungal ascospores are produced, with the highest risk being during warm humid weather when the crop is in flower, as the spores use petals and pollen as a food source in order to develop.
Effective control of the disease relies largely on protectant fungicides that should be applied during mid-flowering before there is any significant petal fall. Ascospores released during sclerotinia germination need a nutrient source, which petals provide, otherwise growers risk yield losses.
Ruth Stanley, Life Scientific’s country manager for UK & Ireland, explains how the next few weeks will be vital for growers to control the disease as the majority of crops are coming into flowering.
“Flowering is relatively on track in rapeseed crops this season and will begin in mid-April. Some forward crops are already starting to flower,” she says.
“By spraying during mid-flowering, the peak number of flowers receive the fungicide active, which limits disease spread,” she adds.
“Another challenge with Sclerotinia decisions is that the fungicides only have a protectant role and have to be applied ahead of infection taking place.
“In some years, a prolonged flowering period can also mean that a second spray is required to maintain protection – adding to the crop’s growing costs at a time when all expenditure is being scrutinised and has to be justified.”
She adds: “Sclerotinia is the reason given for almost 30% of total fungicide use in the crop.”
“Against this background, the weather has become less predictable.”
However, Mrs Stanley points out understanding the persistence of fungicides after application is key. “As Sclerotinia control relies on protectant treatments, it is important to recognise the persistence of control and how this is linked to dose rate, in order to cover the periods, the crop is at most risk from the disease.”
To better understand the persistence and potential impact on activity of fungicides, Life Scientific commissioned trials with ADAS Boxworth. The trial looked at the effect of dose rates of the fungicides Boscler and Aurelia against Sclerotinia over time.
Manufactured by Life Scientific, Boscler is a reverse engineered form of Boscalid (50%) and Aurelia is a reverse engineered form of prothioconazole ((250g/l).
Trials Methodology
- Oilseed rape was sprayed in the field on 13th April at GS59 with rates of:
- Boscalid 500 WG ranging from full (0.5kg/ha) to a 30% dose.
- Prothioconazole 250 EC ranging from full (0.7L/Ha) to a 40% dose.
- Ten leaves per plot were then sampled 1, 7, 14 and 21 days after application.
- The sampled leaves were placed in sealed humid containers with each one inoculated with a petal that had been dipped in a suspension of Sclerotinia ascospores
- The leaves were then assessed 8 days after inoculation and any Sclerotinia lesions were measured. From this, the percentage disease inhibition for the 21 day period after spraying could be calculated for the different dose rates.
Percentage inhibition (lesion area of treated plots relative to untreated plots) 1, 7, 14 and 21 days following fungicide application.
As expected, all the treatments containing Boscler and Aurelia significantly reduced lesion size and development and showed good persistence with an average decline of 15% efficacy for the 21-day period after the crop was sprayed, says Mrs Stanley.
“However, the most effective and persistent treatments in this trial giving good control for up to 21 days, were those where Boscalid 500WG had been applied at the full rate (0.5kg/ha) – and this is a significant factor. Using less than full rate in the mixtures, gave lower levels of efficacy and increased decline in activity over the 21-day trial period.”
She notes field conditions were dry when the trial crop was sprayed and stayed dry for the 21-day period after application. But in warm, wet conditions, ideal for the development of Sclerotinia, it is likely that the sprays would be less persistent.”
“The season can have quite an effect on the disease, so it means the stakes are getting higher, however these results demonstrate that by maintaining high dose rates, it is possible to provide protective activity against Sclerotinia after spraying, for as long as 21-days.”
PANEL
For sclerotinia infection to occur there must be a minimum of 23 consecutive hours of temperatures greater than 7C and a relative humidity of over 80%.
Growers are advised to use the AHDB disease-monitoring service, which maps weather and humidity patterns of specific UK sites to produce a risk-based scenario of when regions are likely to become under attack from the disease.
“It’s absolutely essential growers continue to monitor their crops and keep an eye on weather conditions in order to calculate the impact and timing of Sclerotinia, to limit its spread and avoid yield losses,” says Mrs Stanley.
The forecasts can be found at the ahdb.org.uk/sclerotinia.
Boscler and Aurelia are commercially available through distribution partners, ProCam and Hutchinsons. For more information on these products, please visit see the Life Scientific website https://lifescientific.com/products/
