Wheat growers are being urged to get out into their crops to assess them for signs of fusarium ear blight in the run-up to harvest as the disease could lead to toxins being found in the grain.

Ear blight diseases can cut yields by up to 3t/ha in very bad years. Wet weather over the next few weeks will help spread the disease, which can result in milling wheat crops being rejected for human consumption.

Not all of this group of fungal fusarium diseases, which cause ear blight, will produce mycotoxins, so growers need to assess crops and segregate any grain from infected fields.

Phil Jennings, fusarium disease expert at the Food and Environmental Research Agency (Fera) says although it is too late for fungicide spraying, growers should look out for the disease species which can cause toxins.

“In the next few weeks, growers should look out for ears that bleach out, which is a sign of toxin-producing diseases,” he tells Farmers Weekly.

See also: A guide to the key fusarium ear diseases in wheat

Toxin producers 

Close-up of fusarium © Fera

There are two species of microdochium which produce ear blight symptoms – nivale and majus – and neither produce mycotoxins, while two important fusarium species – graminearum and culmorum – do produce toxins.

Dr Jennings points out that the microdochium species infect individual spikelets, whereas the toxin-producing fusarium species infect single spikelets, then spread to all the spikelets above the point of infection.

If there are multiple microdochium attacks, it can look as if the ear is bleached, so Dr Jennings suggests looking at the rachis (centre spine of the ear) as this stays green with microdochium attacks, while the two fusarium species turn the rachis white.

Rain around the time of wheat flowering, usually in mid-June, can cause an initial infection, but rain in the following month of July can lead to toxins moving into the grain.

“Rain in July is critical, as it will move the infection from the chaff into the grain,” he says.

A wet winter followed by a cold spring was not conducive to fusarium disease inoculum surviving this season, but wet weather around flowering is ideal for the disease to develop.

Potential risk 

Close-up of microdochium © Fera

Simon Edwards, plant pathologists at Harper Adams University in Shropshire, says local crops were wet for so long at flowering that there could be a potential issue with the disease this season.

“It’s worth checking fields now, because as soon as crops start to fade as they ripen, the symptoms are more difficult to identify,” he says.

There is quite a bit of fusarium disease around in his area of Shropshire and this can reduce grain specific weights as well as overall yield.

“If the disease is seen in a particular field, it would make sense to keep the grain separate especially if it is a milling wheat crop,” says Prof Edwards.

Jonathan Blake, fungicide expert at crop consultant Adas, reiterates that conditions up to harvest will be critical to see the disease develop from the current low levels of mycotoxins.

He says there is little point in any further fungicides unless wheat growers need to top up on late rust control. Specific fusarium sprays are usually applied at early to mid-flowering (GS61-65) and all crops should now be past that stage.

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