BASF/ADAS Sclerotinia Monitoring

Key Point Germination of sclerotia is now at 4% in the warmer SW, and 2% in the Hereford area. Conditions look suitable next week for germination to increase in the SW and begin soon in the South East and East. Flowering stages of the South West crops are now in early flower which is the start of the phase when crops are most at risk for infection.

Overview Germination of sclerotia at the Devon site near Exeter has increased to 4%. Germination has started this week at the Hereford site (2%), but has not yet been seen at the other sites. Average soil temperatures have reached 8oC and many soils will be moist with the recent rain, so conditions appear to be suitable for germination of sclerotia in most of the south, midland and eastern areas, as long as the soils remain moist. The weather outlook for the next week remains showery and mild, which will continue to promote germination. Oilseed rape crops at the sclerotinia monitoring sites now range from early‐flower in Devon to green bud in Yorkshire. Light leaf spot continues to be being reported in crops in all regions.   

Weather conditions and OSR growth stages

There was higher than average rainfall in the past week (120% of normal), with most in the South West and North West. Oilseed rape crops at the sclerotinia monitoring sites now range from early flower at the southern sites, to green bud at the Yorkshire site, but there is variability in the flowering stages reached within localities. Many crops are now close to or at full height, and the most forward crops were already at mid‐flower in the past week. Average soil temperatures are now at the threshold (8‐10oC) for sclerotial germination in the south, midlands and east sites.  

National picture by Region

South East

There is still no germination at this site. Average soil temperatures have reached the threshold of 8‐ 10oC, and germination is likely soon, as long as the surface soil continues to stay moist. With mild temperatures and moist soils, there may be germination elsewhere in the region from natural sclerotia, and therefore infection is possible at early flower, i.e., as soon as there are open flowers for spores to land on.

East Anglia & East Midlands

Sclerotial germination has not started yet, but recent rain showers have moistened many soils. Germination is likely to start soon as the soil temperatures increase. Last week, crops were at yellow bud, but progress has slowed a little this week, with the surrounding crops still on average at yellow bud. Light leaf spot is being reported in many fields.

South West

Germination has increased from 1% last week to 4% this week, encouraged by increasing soil temperature and the recent rain. Last week, crops were at GS 3.7‐4.0 or BBCH 59‐61 (first petals visible to 10% flowers open on main stem), and this week are now in early flower (GS 4.2, BBCH 62). The first petal samples have been taken, and plated on agar to test for the proportion of petals with sclerotinia inoculum present. Suitable conditions for infection of petals by spores have not yet been recorded (night time temperatures need to be above 7oC for several continuous hours). The presence of apothecia from germinated sclerotia means that airborne spores are now present, and therefore there is a risk of infection and fungicide applications at early flower are recommended.

W Midlands & Wales

Germination has now progressed from zero to 2% in the past week; soil temperatures are now at 8oC which should encourage further germination provided the soils remain moist. Crops are continuing to progress rapidly. Most are at GS 4.0 (BBCH 60), with first flowers now open. Again, apothecia appearance means that airborne spores are now present.

N England

No germination has been observed yet; soil temperatures are still under the threshold. The crops at the site near Malton last week were at GS3.6 / BBCH55‐56 with flower buds above the youngest leaves, and this week are at GS 3.9 / BBCH 59‐60, at yellow bud.