Ramularia Leaf Spot in barley

Abstract

Ramularia leaf spot, caused by Ramularia collo-cygni, is one of the major fungal diseases of barley in the UK. It reduces both yield and quality of harvested grain. Control of the disease relies on the appropriate use of fungicides but visual symptoms only appear late in the growing season, after the last stage at which fungicides can be applied legally. Therefore, farmers have to decide whether to protect their crop in the absence of visible disease symptoms. A robust risk forecast would help inform their decision and allow them to use an appropriate treatment or alternatively decide not to treat the crop.

This project had three aims; i) to refine the Scottish model by comparing leaf wetness after stem extension with disease levels in the crop over years and sites, rather than a calendar based forecast, ii) to extend the forecast used in Scotland to the rest of the UK by using information from the meteorological network funded by AHDB and disease scores from RL and other trials, and iii) to gather information on disease levels across the UK and quantify levels of fungal DNA in grain and plant samples using a real time PCR. In addition data on RLS levels in winter and spring barley RL varieties was generated to assist in the calculation of resistance scores.

Through the course of the project it became apparent that the existing Scottish model was not refined enough to be utilised further and more factors which could influence disease levels had to be considered. A wide range of influences on disease levels including weather conditions during crop growth, crop factors e.g. sowing date and variety, and also the presence of other diseases, were examined. The only factors which appeared to have any influence on disease levels were rainfall, temperature and leaf wetness in the crop over the course of the growing season. More research is needed to establish the influences of these factors on disease development at different sites and over a number of years in order to construct a risk forecast.

Current guidelines to growers on the risk of ramularia leaf spot disease in their crop are based on geographical location i.e. higher risk in the north and west of the UK. Our findings show that within these regions disease levels can be varied but that the highest levels are generally seen in the high risk areas. The variation of disease levels within a region is still considerable and it may be that risk could be associated with more distinct climate regions in future.

The link between environmental conditions and movement of the fungus within the crop was difficult to establish from the plants grown in the field and more detailed work in controlled conditions may be required to establish the relationships between the environment and fungal colonisation of barley.

Ramularia leaf spot is a problem which is on the increase in the UK and control is increasingly problematic. This project has given some potential avenues of research which could be explored in order to help farmers protect their crops. However more work is still required in order to produce a robust forecast scheme.