Heavy showers which affected large parts of southern England towards the end of May are expected to increase disease pressure in cereal crops ahead of T3 fungicide applications.
Despite the fact Fera have only recorded low levels of the fusarium pathogen to date, some advisers believe the recent wet weather, combined with delayed T2s in some instances, could leave wheat crops vulnerable to infection.
According to Fera’s Phil Jennings, fusarium infection only requires high humidity for 24 to 48 hours. He says: “It is the weather at flowering that ultimately determines the severity of fusarium infection. In 2016 a number of areas were hit by humid, showery conditions as crops started to flower and 80 per cent of Fera samples had fusarium symptoms that year.”
Bayer’s Tim Nicolson is concerned a delayed T2 may cause some growers to hold off on T3 sprays. “Early to mid-anthesis is the best time to protect against fusarium, but the window is short. Sprays applied after this period will probably result in control being compromised. I can understand why working to a calendar date from GS39 might appear appealing, but growers are then reliant on dry weather to help hold fusarium and foliar disease pressure.
“The storms on the run up and during the bank holiday weekend will have heightened inoculum for crops soon to flower and increased the risk that a toxin threat could still develop.
“With microdochium, the most common fusarium species, already recorded at some sites when monitoring commenced in late April, we could see more than one fusarium species threaten this season,” he says.
In the South West of England, wet weather has caused septoria to spread to the upper leaves of some wheat crops. To help reduce the risk of further spread, growers are also encouraged to consider foliar protection when planning T3 applications.
Bayer technical manager, Gareth Bubb says: “The recent wet weather will have infected upper leaves and the disease will soon express itself. Flag leaves are unlikely to show symptoms yet as most have not been out for long enough, but we are seeing septoria on leaf 2 where fungicide timings have been missed or stretched. I think there will definitely be a need to consider septoria when thinking about T3 sprays.”
If the weather remains warm and dry over the coming days, Hutchinsons agronomist, Sally Morris says brown rust could also be a problem. “If conditions do turn dry it may be worth including tebuconazole in with the T3 to target rust, alongside prothioconazole for fusarium,” she says.