Inoculum of two mycotoxin-producing fusarium species has been found at Fera (Food and Environment Research Agency) trial sites, just ahead of the T3 spray timing.
According to Phil Jennings of Fera, the two species starting to show on-leaf isolations are Fusarium culmorum and F graminearum, both of which can withstand very low winter temperatures and, with the right weather conditions at flowering, have the potential to cause toxins.
“Obviously the disease isn’t there yet, as ears are only just starting to emerge, so there’s nothing to see. But through isolation techniques, we know that inoculum is around and the spores are moving about,” he says.
Warm, dry weather in recent weeks will have favoured inoculum build-up, he adds. “Now it all depends on the weather at flowering. If we have wet, unsettled conditions, the chances of fusarium ear infection increases. If it’s hot and dry, nothing will occur.”
In contrast, levels of Microdochium nivale, which doesn’t produce mycotoxins, are very low. “The cold winter has had an effect on its survival,” notes Dr Jennings.
“That’s no surprise, as we know that those spores can’t be frozen for research purposes. But spores from both F culmorum and F graminearum can be frozen down to minus 26C without any adverse effect.”
This year echoes the situation found last year, he continues. “Microdochium levels were low then as well, following a cold spell. But after the mild winters of 2007 and 2008, it was the prevalent species.”
F culmorum has been found at all five of the Fera trial sites to date, while F graminearum is present at just two, he notes.
“Looking ahead to the T3 spray, farmers should be aware that inoculum is around,” he advises. “It would be wrong to think that there’s no risk of disease.”
James Taylor-Alford of Bayer CropScience points out that early maturing wheat varieties, such as Cordiale, are just starting to flower, coinciding with the arrival of some much-needed rain.
“Rain is forecast for this week and next, so for these crops there’s every chance of creating the perfect conditions for fusarium infection to take place,” he says.
T3 spray timing is notoriously difficult to get right, he acknowledges. “Early flowering, around GS63, is the ideal timing, but mid-flowering is all right. As a rule of thumb, it’s better to be a bit early than a bit too late, so GS61 is preferable to GS69.”
Although it is possible to reduce fusarium inoculum with the T1 and T2 sprays, T3 remains the key timing, he adds.
“Many growers were tempted to cut dose rates at T2, given the absence of foliar diseases,” he remarks. “That means that their fusarium management may have suffered.”
The fusarium risk this season is high, warns Jonathan Blake of ADAS.
“Crops at early to mid-flowering, together with high humidity and rainfall, all create the right conditions,” he says. “And that’s exactly what we have in the west at the moment. In the east, there’s probably still a week to go until flowering.”
Controlling fusarium can be done with one of three azoles – prothioconazole, metconazole or tebuconazole – none of which should be applied below half rate, he adds.
“Priority should be given to milling wheats, especially those being grown after maize,” he says.