Eyespot of Wheat
Description:Honey coloured elliptical lesions occur on the lower stems within 4 cm of ground level causing stem breakage or bending. The lower leaf sheath normally needs to be peeled back to see the lesion. Young lesions may have a darker border but as they age they tend to go darker in the centre giving an eye-like appearance. Older lesions surround the entire stem and my be up to 4 cm long. A sooty mould is under the leaf sheath near where the stem is weakened. Stems fall in random directions which helps distinguish it from lodging due to wind.
Affected crops have flattened patches from heading to harvest.
It is often associated with high N levels, dense crops and wet years.
Species Affected:Wheat is more susceptible than Barley.
Annual Ryegrass, Barley Grass, Brome Grass and Phalaris are alternate hosts.
There are no resistant Wheat cultivars.
Biology:Spread by air borne spores over long distances or raindrop splash from infected stubble.
Infected stubble may affect crops for up to 3 years.
Infection is most likely in wet conditions with temperatures around 100C.
Weeds like Soursob maintain humid conditions around the base of the plant and assist infection.
Life Cycle:In cool, moist autumn conditions infectious spores are produced on infected cereal or grass stubbles. The spores are spread by wind to seedlings in neighbouring crops or by raindrop splash and direct contact onto seedlings growing in stubble. The spores invade the coleoptiles and leaf sheaths and the fungus grows through to the stem. Lesions can usually be seen by mid tillering to early stem elongation. The fungal growth shows as a sooty mould under the sheath and weakens the stem causing lodging. Spores survive over the summer in cereal and grass straw.
Origin and History:Distribution:
Cool, moist, high rainfall areas especially in dense crops with high soil nitrogen conditions.
Seen in most seasons on the south west slopes of NSW and sporadically in high rainfall areas in other southern states.
It is more common in continuous cereal rotations or grassy areas and usually occurs on paddocks with a history of the disease.
Significance:In severe infestations the whole crop may lodge before harvest.
Management and Control:Avoid continuous cereal rotations.
Allow a 2 year break if lodging due to disease has occurred.
Bury or burn crop and grass stubbles.
Increase time between successive cereal crops especially in high rainfall areas.
Reduce crop density and soil nitrogen levels.
Control grasses in previous crops or pastures.
Control Soursob and other weeds in crop to reduce humidity.
Plant shorter stemmed varieties.
Apply fungicides at the first node stage. Once lodging has commenced fungicides are of little use. Close careful monitoring is required to detect the disease early enough for successful treatment.
Related and Similar Species:References:
Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.