Net blotch [Pyrenophora teres]
The fungus survives on infected crop residue and volunteer barley, or in contaminated seed. Primary infection by ascospores occurs in winter barley after barley. The secondary infection in the crops is by conidiospores spread by the wind. Spore formation only takes place on necrotic tissue. Temperatures between 5 and 35 °C (optimum: approx. 20 °C) as well as a humidity of above 95% are conducive. The spores are spread via the wind at low humidity. In turn, high humidity is required for an infection. Leaves are infected starting from the base moving up the plant as the disease develops. In summer humid-warm weather, a dramatic infection increase should be anticipated. The leaf tissue yellows because of the pathogen toxins, and chloroses are formed. There are two forms of pathogens: the net-type and the spot-type. There are barley varieties which are resistant against the net-type, however, there are only minor differences in the tolerance of varieties with regards to the spot-type.
Winter and spring barley.
Pattern of damage
The infection of the seedling originates from the mycelium in infected seed. The cotyledon already shows first symptoms in the form of brighter striated spots. Leaves, leaf sheaths, ears, and grain may be affected. A definite diagnosis is only possible under 30-fold magnification, since there are many variabilities and possibilities for confusion. The individually standing, dark, walking-stick-type looking stromata on the leaf necroses are typical. The two forms of pathogens may occur simultaneously or individually. The net-type forms necroses with a characteristic net-type pattern (Picture 1 to 3). These are surrounded by yellow lighter sections. This type can easily be confused with leaf stripe, but it does not have the brownish longitudinal and crosswise stripes of Drechslera teres. The spot-type forms striated, rectangular to punctiform or oval, light- to dark-brown necroses with surrounding chloroses. In the advanced progression of infection, the affected surfaces converge and the leaves die off. The spot-type can be confused with defensive reactions of mildew, an infection of partially resistant varieties with the Rhynchosporium scald pathogen, brown spot disease, nutrient deficiency and physiological changes associated with variety and weather conditions.
Good tilling of harvest residue. Promoting straw rot. Removal of volunteer barley and barley growth in oilseed rape crops. Do not cultivate barley after barley. Do not seed winter barley too early. Avoid direct vicinity to spring and winter barley. Use of healthy, stained seed.
Targeted control from ES 32. The appropriate time is when the spores start forming in the crop on the lower affected leaf levels.