Fusarium infection on leaves has been identified in wheat crops in the west of the country for the first time that plant pathologists can remember.
Confirmed by ADAS Rosemaund after analysing leaves from five different sites in Herefordshire, the fusarium leaf lesions are similar to those caused by septoria and have been found on the top two leaves in the past month.
The very wet season was responsible, believed ADAS research scientist Julie Smith, who pointed out that fusarium development was favoured by prolonged periods of wet weather.
“Disease assessments have been tricky this year,” she said. “We all know that septoria pressure has been high, but not all reported symptoms can be attributed to septoria leaf blotch.”
She has confirmed the presence of fusarium in the leaf. “Septoria is there along with low levels of didymella. But the surprise is fusarium, as it is difficult to find anyone who can remember seeing this before.”
Fusarium usually occurs in a complex, she said. “Most is microdochium species, largely M nivale, but there is some F culmorum present in the lesions, too.”
That corresponded with the survey findings collated by Phil Jennings at Fera. “From the ear samples we've seen so far, almost 90% are infected with M nivale,” he said.
Very little is known about infection of leaves by fusarium species, they acknowledged. “Fortunately, the current levels of sporulation on leaves are unlikely to pose a threat to the ears, as flowering has finished. But leaf lesions are an indicator of a problem in the ear.”
For growers, it's a triple blow, warned Ms Smith. “There's the mycotoxin risk, which we know is higher this year, and there's ear blight infection, which affects yield. In addition, there are foliar lesions, which are reducing green leaf area during the grain fill period, which will inevitably lead to a further yield reduction.”
The symptoms do vary according to species, she said. “The lesions seen tend to start as water-soaked blotches, with either a straw-coloured centre or a bleached, greyish middle with a darker margin.
“They are oval in shape and often occur where the leaf is bending or at leaf edges. And where the lesions have enlarged rapidly, they are beginning to split from the centre.”
Some of the larger lesions had coalesced and caused leaves to become distorted and frayed, she added.
According to Dr Jennings, this is the first time that fusarium leaf infections have been so severe. “In the case of microdochium, which is most of what's being seen this year, the disease starts at the stem base, with the ascospores then blowing up. Where it's landed on the leaves in wet conditions, there has been infection. In previous years, any leaf infections have been lower down.”
Fortunately, microdochium doesn't produce mycotoxins or have a huge impact on yield. “But it is likely the grain will be contaminated.”
To assess how widespread fusarium leaf infection is this season, Ms Smith is asking growers with unexplained leaf lesions to send them to her at ADAS Rosemaund, including the location (nearest town and county, plus variety).