Leaf rust [Puccinia hordei]
Leaf rust - image 1
This disease can only survive on living plant tissue, surviving as asexual mycelium after the harvest of late maturing and volunteer grain, before affecting the winter barley crop and in spring the spring barley. The pathogen is spread in the crop by wind dispursed asexual uredospores. It is highly temperature-tolerant, and is still able to grow at 5 °C and can cause re-infections in mild winters. Temperatures of 15-20 °C and a humidity of 100% are optimal conditions for the production and germination of spores. The infection takes place when the leaves are wet (e.g. dew-covered), whereby the spore forms a germ tube. At average daytime temperatures above 15 °C, a rapid spread of the pathogen must be anticipated. Hot summer days of above 30 °C reduce disease development.
Winter and spring barley.
Pattern of damage
Visible fruiting bodies are on the upper side of the leaf, leaf sheath, and sometimes on the underside of the leaf. They break through the epidermis and form light-brown pustules of maximum 0.5 mm (Picture 1). Green zones can be found on the yellowed leaf around the pustules ("Green islands" since the parasite is dependent on living tissue).
Multiple stubble tillage. Do not seed winter barley too early. Do not plant summer and winter barley adjacent to each other. Cultivate early-maturing, more tolerant varieties.