Net form net blotch

Pyrenophora teres f. teres

Net form net blotch (NFNB) is a common disease affecting barley and barley grass in Australia. Two kinds of net blotch occur, net form and spot form. Early sowing increases the risk of infection by NFNB. Yield losses of 10 - 30 per cent as well as reductions in grain quality, particularly increased screenings, can occur if not managed properly.

Refer to the link below for more detailed information on spot form net blotch in barley.

Description

Lesions begin as thin brown streaks which elongate up and across the leaf, and darker lines form within the lesions, producing a net like appearance. Lesions are often surrounded by a yellow leaf margin. In severe infections leaves die prematurely causing reductions in seed weight and yields.

NFNB can be stubble or seed-borne although generally, infected stubbles are the main cause of primary infection and more occasionally, barley grass residues. Spores can survive on infected stubble for up to three years. Early season rains release spores from infected stubbles, which are spread by wind onto barley seedlings. For infection to be successful, moisture and temperatures between 10 °C and 25 °C are required. Following primary infection, lesions produce spores which can be released producing inoculum for secondary infections. This process can occur several times throughout the growing season. Seed infections can occur when humid conditions follow flowering, although seed infections are rare and not considered to be of importance compared to infected stubbles.

Control

NFNB can be controlled effectively by employing a range of tactics. Avoid growing successive barley crops, particularly in areas prone to NFNB, hence a three-year gap between barley crops is suggested. In high risk areas avoid sowing susceptible varieties, instead select varieties with resistance. Removal of infected stubbles by burning, where wind erosion risks are low, and control of ‘green bridge’ volunteers can also help reduce disease levels.

Early sown crops can be prone to infection, therefore delaying sowing may help reduce infections, however the benefits of this need to be considered against the downfalls associated with delayed sowing. Crops sown into soils deficient in potassium are more prone to infection, therefore applications of potassium could help reduce infections.

If seed is suspected to be infected with NFNB, seed dressings and/or in-furrow treatments can be used to provide some level of control. A foliar spray with fungicide is usually necessary to control NFNB in medium to high rainfall areas; Prosaro^® and Aviator^® Xpro^® both provide preventative and curative control of NFNB in barley. Consult CropLife Fungicide Resistance Management Strategies as a guide to the responsible use of fungicides and always follow the product label for specific use instructions.

Related Pest

Spot form net blotch

Pyrenophora teres f. maculata

Spot form net blotch (SFNB) is a common foliar disease affecting barley and barley grass in Australia. Widespread cultivation of susceptible barley varieties, stubble retention and favourable climatic conditions have recently seen this disease become more prevalent. Yield losses of more than 40 per cent have been recorded in addition to reductions in grain quality.

References

Herbiguide (Viewed Nov 2019), ‘Net blotch – Net form of barley’, http://www.herbiguide.com.au/Descriptions/hg_Net_Blotch_Net_Form_of_Barley.htm

Jayasena, K, Thomas, G, Beard, C and Hills A (2018), ‘Managing net-type net blotch of barley in Western Australia’, Department of Primary Industrie and Regional Development (DPIRD), https://www.agric.wa.gov.au/barley/managing-net-type-net-blotch-barley-western-australia

McClean, M (2016), ‘Net blotches of barley’, Agriculture Victoria, http://agriculture.vic.gov.au/agriculture/pests-diseases-and-weeds/plant-diseases/grains-pulses-and-cereals/net-blotches-of-barley