Sclerotinia knows its limitations. Do you?
Many OSR crops are now in full flower and some of the earliest flowering crops have already started to drop petals. Many people will be thinking about whether to spray.
BASF petal testing results from the beginning of this week show sclerotinia inoculum is present on petals at southern sites and sclerotial germination is over 30% complete in the South West, with Herefordshire germination the next most advanced.
After the presence of sclerotinia has been confirmed, the next important factor to consider is the weather. A period of more than 23 hours where relative humidity is more than 80% and temperature is 7°C or more will allow sclerotinia spores to infect a crop. A preventative spray should, therefore, be applied during this 23 hour period. Updated three times each week, the AHDB sclerotinia forecast shows where our monitoring sites have experienced these periods, and whether they’re forecast to in the next 48 hours.
This map shows infection conditions so far this season: to date the West, and especially the South West, of the UK has experience conditions conductive to infection the most frequently (red + large = more frequent).
This shows which factor(s) limited the length of the infection period in different regions. In the last couple of weeks, the reason for the infection criteria not being met in the north of the UK has mostly been due temperature not being high enough, whereas in the south of the UK the relative humidity has not been high enough.
This year, risk of sclerotinia infection could be increased in crops where stems have split (which have been fuelled by large variations in temperature, which cause rapid growth bursts) which leaves an easy entry point for sclerotinia infection. For example, this crop of OSR in Staffordshire last Friday:
Don’t be a Mr Bean. Don’t wait for sclerotinia to come along. Use the AHDB forecast to get there first.