Last week I was in a field of winter barley, a decent crop of two-row which was largely finished flowering and the developing grains had expanded to about half full length.
In terms of the traditional diseases, this crop was clean – no signs of mildew, rhyncho, net blotch or even rust to be seen.
There was no visible barley yellow dwarf virus either but there was quite a bit of something else in this crop.
There were atypical disease lesions present on many of the lower leaves and it also looked like the same disease was moving to attack the stems. I have seen similar leaf lesion on crops occasionally in the past, but a bit more often in recent years.
This crop was quite different though. There were many such lesions, particularly on the third and fourth leaves but it seems to be moving further up the canopy with occasional symptoms visible on second last and flag leaves.
The leaf lesions are quite distinctive but I wondered if I was looking at one disease or perhaps two different diseases.
An individual lesion is best described as diamond-shaped, with a dark oval to diamond spot in the centre of a grey/brown lesion. Many lesions had dark lines running along some of the veins within the lesion (see picture one).
Some older leaves appeared to have been killed by the quantity of lesions present (picture two).
These lesions were more peach than grey/brown in colour.
Whether these are two different diseases or not, I do not know, but I think not. But it is possible that a lack of light down in the canopy may be a factor in how these lesions developed. The lesions I have seen before but not to the same extent as they were present in this crop.
A diamond-shaped lesion that is not rhyncho might be either the Septoria nodorum form that attacks barley or possibly foliar lesions of Microdochium nivale, better known as a cause of ear blight or browning at the base of a stem.
My initial consensus was that this looks more like nivale than septoria. The oval spots in the centre were a questionable element but what made me most suspicious was the presence of lesions on the leaf sheaths on the stems.
This alone did not mean a lot but it was also obvious that the lesions seemed to be progressing into the actual stem, as browning was evident behind these lesions.
This made me more suspicious of nivale as the cause because this is a common stem symptom, but not this far up the stem.
However, conversation with researchers would point to Septoria nodorum as being the most likely cause. There have been a few incidences in recent years of high levels of infection and the lesions appear to be quite specific.
Variety seems to be a significant factor in infection but not every field of the same variety gets infected.
Lesions are normally isolated and down in the canopy but they can grow to a big size and coalesce with each other. This also seems to be the case on the stem lesions, as shown in picture three. The symptom showed dead tissue with most of the veins being a dark brown colour.
As well as the leaf sheath being infected, the disease seemed to be penetrating the stem beneath the lesion (picture four).
The overall consequence of this problem is not yet known in terms of its implications for yield or quality. Neither is there robust information on the ability of current fungicides to contain or control this disease.