As winter barley crops reach heading and flowering starts, growers should be checking their crops for the appearance of Ramularia leaf spot (RLS) on the upper leaves. The disease is caused by the fungus Ramularia collo-cygni. The fungus colonises the barley plant during the growing season and research has indicated that although the fungus produces airborne spores late in the growing season, the initial infection arises from seed borne infection. Unfortunately, there are no effective seed treatments to control the fungus, so disease control relies on the use of an effective fungicide.
The first symptoms of the disease are a brown pepper spot on the upper leaves. These spots enlarge and give characteristic RLS symptoms. They are differentiated from other barley diseases by the 5R’s.
The spots are reddish brown, they are restricted by the leaf veins, they have a ring of chlorosis or yellowing around the spots, the spots are rectangular and are right through the leaf, in other words the spots are the same on the underside of the leaf. As the spots coalesce and cause early leaf senescence it is sometimes possible to see rows of white sporulating structures coming out of the leaf stomata on the underside of the leaf.
Ramularia disease control is based on late season fungicide use. With the loss of the multisite Chlorothalonil we lost our most effective control option. The pathogen developed resistance to both the strobilurin and SDHI fungicides groups fairly quickly after their introduction, so control now is based on the use of azoles. The most effective azole fungicide is mefentrifluconazole (the azole from BASF found in Revystar and Myresa). There is a cut off for mefentrifluconazole of GS45 (boots swollen), if barley crops are being sent for malting. There is some activity from prothioconazole (the Bayer product found in Proline and mixture products). There is also activity from the other multisite available for barley, folpet (from Adama). Many of the trial results show that folpet is effective in controlling RLS when added to both T1 and T2 sprays in barley programmes.
Sign up to the FAS newsletter
Receive updates on news, events and publications from Scotland’s Farm Advisory Service