THE NATURALLY occurring fungus Nigrospora oryzae, which causes crown rot in weedy Sporobolus grasses (WSGs), is showing strong signs of occurrence after recent rains on the Mid North Coast.
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The disease is known to kill the pest plant species Giant Parramatta Grass (GPG) and reduce infestations to non-economic levels over a couple of years.
Up to 78 per cent reduction in tussock size (over 15 months) and 64 per cent reduction in tussock presence (over 12 months) has been observed in the field, due to the effects of crown rot.
The symptoms of crown rot become obvious in spring 7-10 days after the first effective rainfall event after winter. By late December through to mid-January the disease is usually easiest to spot.
Crown rot produces pale orange leaves on diseased tillers (leaf stems). The diseased tillers are easy to remove from the crown of the tussock and have a brown to black coloured base instead of the normal white colour. In heavily diseased tillers there is a distinctive black ring above the dead base.
The amount of disease and rate of spread is dependent on rainfall, soil type, topography, and ability for the fungus to proliferate using different modes of spread such as soil water movement, vehicles and animals.
Crown rot disease may need to be introduced to a WSG infestation and managed for maximum effect, or it may already be present in small amounts and only require better management to increase its spread and effectiveness.
Initial research has observed a greater rate of disease spread in GPG infestations that are well grazed. Moderate to heavy grazing produces a flush of new growth. Disease symptoms occur in new shoots while they are still short and green and do not occur in tall, hayed-off plants.
Any management practice that produces a flush of new growth is more likely to help the spread and effectiveness of the disease.
Crown rot is also now known to occur in Parramatta Grass (PG) and Giant Rats Tail grass (GRT). Both these pest plant species have been found with Crown Root Rot disease in the field and surveys have found diseased GRT as far north as central Queensland.
It is still too early to know what economic benefit Crown Rot will have in reducing the occurrence of these species.
Please contact Nambucca Shire Council’s site leader Green Space, Keegan Noble, on 0417 484-906 for a property inspection to determine if the disease is present in your pastures and for information on managing the Crown Rot disease effectively visit this link and browse in publications http://weeds.dpi.nsw.gov.au/Weeds/Details/58
