Up-to-date fungicide performance information forcontrolling light leaf spot is now available from HCGA. Results from 2012/13and recent years show that, although tricky to control, fungicide treatmentscan prevent significant losses from the disease.
At high-risk sites, autumn sprays are needed tokeep the disease in check, says Dr Peter Gladders of ADAS. Light leaf spot isnow the most important disease in winter oilseed rape and it is affecting allregions of the UK, including the south of England. Following autumn decisions,all crops need careful monitoring in January and February, if any light leafspot is found, deal with it promptly.
In the trials, there have been some differencesbetween products and prothioconazole is the leading active. Control is likelyto be improved by increasing the number of applications rather than byincreasing dose.
Looking at application rates, some of the trialsites have shown benefits from increasing dose above half rate. However,increases in disease control dont always translate into significantly higheryields, explains Peter Gladders. There are also concerns that we are seeingreduced sensitivity to azole fungicides in certain parts of the UK. HGCA isaware of this challenge and will continue to monitor the situation in trialsand in commercial crops.
The light leaf spot forecast from Rothamsted offersmore positive news as it indicates a lower risk with forward crops being morevulnerable than later sowings. Growers and agronomists need to remember thatthe forecast is based on pod infection, there was quite a lot of stem infectionlast harvest which may increase the risk in certain locations, adds Dr Gladders.Varieties grown in the south tend to have lower resistance ratings to thosegrown in the north and this needs to be factored in as well.
When choosingproducts, requirements for phoma activity and plant growth regulation activityshould also be considered. Many crops are very advanced and growth regulationeffects are, therefore, likely to be important this year.