Targeting winter and spring barley disease management

Abstract

Field experiments tested the mechanisms by which fungicide treatment affects the growth of barley, so that sprays might be better targeted. Experiments were conducted on winter and spring barley at two 'core' research sites: ADAS Rosemaund (Herefordshire) and SAC Aberdeen. Two designs of experiments were undertaken on winter barley. In the first design, different seed rates and N regimes (amount and timing) were imposed to cause variation in the source-sink balance of the crop similar to that which normally occurs between crops due to differences in plant establishment and N availability (here 'source' is defined as the dry matter available for grain filling and 'sink' is the capacity of grains to store the dry matter). The effect of source:sink balance on response to fungicide treatment was then tested. In the other design, fungicide timing was varied to determine the effects of disease control during specific crop developmental phases on canopy growth, light interception, and yield formation. In the spring barley experiments, seed rate, N regime and fungicide timing treatments were combined. Forty seven trials were conducted by industry partners to test the effects of fungicide timing on yield and validate the findings from the core sites across a wide range of varieties and sites.

The effects of fungicide treatment on canopy growth, deposition of stem-storage reserves, and yield components was similar in spring and winter barley and for two and six-row varieties, indicating that the key growth stages for disease management in barley are common - albeit that those growth stages occur at different calendar dates according to sowing date. Protection should start during tillering to maximise grain numbers by protecting production and survival of tillers and spikelets. Early tillering, stem-extension (T1) and, to a lesser extent, booting/ear emerged (T2) applications increased grain numbers per m2. T1 and T2 treatments increased average grain weight - an effect which appeared to be the result of an increase in grain storage capacity (sink) rather than increased supply of dry matter for grain filling (source). At industry sites where there was little or no visible disease, the average yield response to fungicide was similar to those sites where there was disease. Effects on grain numbers were not simply the result of protection of green area, but may have involved direct effects of fungicides on grain site formation or prevention of deleterious effects from symptomless infections. The findings from this project have been incorporated in the HGCA Barley Disease Management Guide.