THE leaf spot disease, ramularia, now has a new guide to allow grower to 'spot' the specific spots much more surely.

Described within two new AHDB publications, the guidance has been issued following reduced efficacy of key fungicides used to control this foliar pathogen of barley, which has a particular fondness for Scottish crops.

The hope is that improved identification and quantification of ramularia symptoms will help farmers and their advisers better assess the effectiveness of control and devise appropriate management strategies.

The pathogen which causes ramularia grows from infected seed and moves systematically through both winter and spring barley crops. Symptoms, which often develop rapidly, appear on dying leaves throughout the season but occur most frequently on upper leaves after ear emergence.

Frequently mis-diagnosed, these new guides illustrate how mature ramularia lesions can be distinguished from other foliar symptoms by applying the '5Rs’:

• Ringed with yellow margin of chlorosis

• Rectangular shape

• Restricted by the leaf veins

• Reddish-brown colouration

• Right through the leaf

The ‘Ramularia leaf spot in barley’ factsheet also includes information on its life cycle and gives control options, while an accompanying guide allows symptoms to be identified and severity scored.

Paul Gosling, who manages disease research at AHDB, said: “All barley varieties on the AHDB Recommended Lists are relatively susceptible to ramularia. This means protectant fungicides, applied at the booting stage, GS45 to GS49, are often required.

“Fungicide performance trials, however, show resistance to foliar fungicides is increasing, so chemistry needs to be used with care. Strobilurins haven’t been effective against ramularia for quite a while and there have been changes in sensitivity to SDHIs and azoles recently too.

“As chlorothalonil has no recorded issues with resistance development, it should be included in programmes to ensure effective control and to slow the spread of insensitivities to other fungicides.”

Farmers should also note that once symptoms develop on the upper leaves, treatment with fungicides is ineffective and that seed saved from heavily infected crops should be avoided.