White Blister Rust or Staghead of Brassicas
Description:A fungal disease causing soft looking, white patches mainly on the underside of leaves that become raised, powdery and blister like. It starts on the topside of leaves as small raised, yellow green spots. Leaves may become distorted.
On Broccoli it usually starts on the underside of the leaves as white spiral pustules with associated dead spots showing on the upper surface of leaves. The pustules burst releasing masses of spores that may infect heads producing white raised and distorted areas.
Species Affected:Mainly Brassicas.
Bittercress, Chinese Cabbage, Hedge Mustard, Horseradish, Radish, Shepherds Purse, Swede, Turnip and Wild Radish are very susceptible.
Brassica campestris varieties of Rapeseed are susceptible.
Occurs on Broccoli, Cabbage, Cauliflower, Brassica napus varieties of Canola.
Uncommon on other species.
Biology:Favoured by cool, wet conditions.
Infection requires wet leaves.
Survives on crop residues, the soil and on Brassica weeds.
Spread by insects, wind and rain or irrigation.
It is not related to the normal "Rust" diseases.
Life Cycle:Origin and History:
Very damaging to Chinese Cabbage.
Damaging on Brassica campestris varieties of Rapeseed.
Rarely an economic problem on Cabbage, Cauliflower or Brassica napus varieties of Canola.
Occasionally a significant problem of Broccoli at certain times of the year.
Management and Control:Remove crop residues by deep burial or burning soon after harvest.
Control Brassica weeds.
Plant seed harvested from disease free areas.
Increase the time between successive B. campestris crops or grow Brassica napus varieties if the disease is proving difficult to contain in Oilseed Rape areas.
Rotate to tolerant crops for 3-4 years.
Fungicides are generally not effective but can be useful as part of an integrated disease control program.
Plant tolerant varieties of Broccoli such as “Tyson”.
Related and Similar Species:References:
Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.