Effect of Barley-Legume Intercrop and Major Nutrients on Disease Frequency in an Organic Farming System

Summary

The effect of barley-legume intercrop in an organic farming system on disease incidence was investigated. The legumes were lupin (‘Prima’), faba bean (‘Columbo’) and pea (‘Bohatyr’ and ‘Agadir’). The barley variety was ’Otira’. Diseases were detected on pea and barley. On pea, only Ascochyta blight was observed. When either pea variety was intercropped with barley, the level of Ascochyta was reduced. Net blotch (Pyrenophora teres), brown rust (Puccinia recondita) and powdery mildew (Blumeria graminis f. sp. hordei) (in order of incidence) were monitored on barley between flag leaf emergence and heading. The levels of all three diseases were reduced in every intercrop treatment compared to the barley monocrop. However, this reduction was only statistically significant in the Otira plus Bohartyr treatment for net blotch.
Barley cv. Otira grown as monocrop with 50 kg N added as urea was also monitored under the same field conditions. The presence of added nitrogen increased levels of rust and mildew. Subsequently glasshouse experiments on the effect of the availability of N, P or K disease resistance mechanisms were set up. Barley was grown under different nutrient conditions (minus N, P or K). Plants were infected with powdery mildew at the third leaf stage. Plants depleted of nitrogen showed increased resistance to the fungus (effective at penetration). Absence of phosphorous appeared to increase penetration of powdery mildew but the resulting colonies were smaller than control. Depletion of K appeared to increase fungal penetration.