POWDERY mildew is present in many canola crops and some lupin crops surveyed by the Department of Primary Industries and Regional Development (DPIRD) in the Geraldton port zone, from Northampton to Walkaway.
The infection is on the stems and lower branches and in canola crops almost all plants in a paddock are affected, with different mildew species affecting each of these crops.
A low incidence of pod infection was also observed in a couple of canola paddocks.
DPIRD plant pathologist Ciara Beard said powdery mildew can infect leaves, stems and pods of canola and lupin.
"Symptoms may first appear on older leaves in the form of dirty white floury patches and all leaves become infected as the plants age," Dr Beard said.
"Severe infection of leaves causes premature defoliation and patches can also appear on stems and pods and resemble talcum powder.
"These patches enlarge and coalesce to cover the entire stem."
Severely infected plants may grow poorly and produce fewer pods.
Infected pods remain smaller and produce fewer seeds and the seeds generally are shrivelled and are of poor quality.
Presence of the disease may not be noticed until swathing or harvest, when white clouds of dust are released.
In lupins, powdery mildew may be confused with botrytis grey mould which is also being reported this season.
MORE STORIES:
Botrytis grey mould appears more fluffy and grey/black in colour.
"The disease development is generally favoured by dry conditions with moderate to high humidity (50-95 per cent) and moderate temperatures (15-25pc)," Dr Beard said.
"The disease is also favoured by dense canopy and in canola by high nitrogen fertilisation."
Powdery mildew is not considered a serious problem in Australia since the disease is fairly uncommon and most infections occur too late in the season to cause significant yield loss.
However, in northern New South Wales the disease occurs regularly in canola and is thought to reduce yield in some seasons, particularly if the infection progresses to pods.
"The loss of photosynthetic area appears to be the main cause of yield loss but there is limited data available," Dr Beard said.
"The pathogen may survive between seasons on volunteer host plants or brassica/lupin weeds as well as old canola/lupin stubble."
Currently no fungicides are registered for the control of powdery mildew in canola or lupin in Australia.
