Flag smut in wheat
DPIRD Plant pathologists Jason Bradley and Kylie Chambers recently found flag smut in wheat near Wyalkatchem (GS41) and Elabbin (GS65).
Dani Whyte (Braeleigh Consulting) has seen flag smut in wheat near Merredin.
Flag smut is a fungal disease that occurs across the WA grainbelt but appears to be more common through the medium to lower rainfall regions of the central, eastern and northern grain production zones. Barley, oats and broad leaf crops are not affected by wheat flag smut.
This disease generally occurs only sporadically, usually following successive plantings of susceptible varieties without use of fungicide seed dressings. To check flag smut resistance ratings of wheat varieties refer to DPIRD’s 2022 Sowing Guide for WA – Wheat. A number of popular varieties grown in WA are Susceptible or worse and are more likely to exhibit higher incidence of disease. At the Elabbin location, unusually high levels of disease arising from soil borne inoculum were evident in experimental plots. Disease ranged from ~10% incidence of infected plants in a moderately susceptible-susceptible variety to >25% in a susceptible-very susceptible variety.
Flag smut infection occurs as the wheat plant germinates and emerges from soil. The fungus grows systemically within the plant and affected plants are often stunted and infected leaves may be curled and distorted with long grey-black streaks of flag smut spores (which rub off easily). Initially, the spore masses are invisible under the leaf surface, but between stem elongation and heading, they break through the surface as distinct, long, raised streaks of sooty black spores on leaves and leaf sheaths. Infected plants can tiller excessively, but symptoms do not always occur on all tillers. Flag smut differs from other cereal smut diseases by exhibiting symptoms in the leaves/leaf sheaths rather than the heads. Occasionally stems can also be infected.
Flag smut is quite common at trace levels in wheat crops, however at higher incidence it can reduce yield as affected tillers do not usually produce grain.
During harvest, flag smut spores are distributed onto the surface of seed or onto the soil. Spores of the fungus can survive in soil for several years and can be moved to adjacent paddocks by wind, plant debris or equipment. Machinery that has handled contaminated grain should be thoroughly cleaned to avoid contamination of other paddocks/grain.
Seed sown into contaminated soil is at risk of developing the disease as is infected seed sown into clean soil.
Managing this disease next season
Spores of this fungus are carried on seed and in soil, so it is important to consider management strategies now to avoid having significant recurrence of the disease in next season’s wheat crops.
This disease is well-managed by registered fungicide seed dressings, use of more resistant varieties (refer to DPIRD’s 2022 Sowing Guide for WA – Wheat) and rotation with nonhost crops (although spores can last for a period of years in soil).
In paddocks contaminated with flag smut and adjacent paddocks, use clean seed treated with a fungicide seed dressing at a registered (high) rate to reduce disease risk. Registered seed dressings are highly effective. Ensure even, full coverage of grain to maximise protection of all grains sown. Information on which seed dressings are registered for specific diseases is available from DPIRD’s Seed dressing and in-furrow fungicides for cereals page.
Further information is available at DPIRD's Diagnosing flag smut of wheat and Cereal smuts and bunts management pages.
For more information contact Plant pathologists Kithsiri Jayasena, Albany on +61 (0)8 9892 8477, Ciara Beard, Geraldton on +61 (0)8 9956 8504, Geoff Thomas, South Perth on +61 (0)8 9368 3262 or Andrea Hills, Esperance on +61 (0)8 9083 1144.
Article author: Ciara Beard (DPIRD Geraldton).
Article input: Geoff Thomas (DPIRD South Perth) and Kithsiri Jayasena (DPIRD Albany).