Managing powdery scab

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By Gemma Carroll 

Information sourced from Dr Calum Wilson’s article in Potatoes Australia, with his permission. 

A four year research programme at the Tasmanian Institute of Agriculture, has resulted in a greater understanding of the Spongospora root disease known commonly as Powdery Scab. 

Powdery scab is prevalent in New Zealand soil and is known to reduce potato crop yields. 

The study across the ditch has revealed the following outcomes: 

  1. A detection system has been developed which could monitor infection in roots. 
  2. A deeper understanding of infested soil and dormant/active spores was gained. It was found that compounds released from potato roots, stimulate dormant disease spores. The then active spores can only survive a matter of hours in the soil, therefore treatment could involve stimulation of dormant spores using stimulatory compounds  and then leaving the active spores to die naturally in the soil. In effect, teasing the disease out of hibernation and then allowing a natural death. This has not yet been field tested. 
  3. There are limitations in the use fungicides for disease control. Dormant spores are not affected by fungicides, yet active spores are. It was concluded that fungicides are unlikely to be fully effective in disease control, however with the new found understanding of spores, fungicide development may improve efficacy in the future. 
  4. A closer look at alternate host crops and their control following potato crops also appears to be critical. 
  5. Varietal assessment was undertaken in glasshouses and in the field, using the new root monitoring tools, indicating it to be a fast, robust and cost effective measure in variety screening. 
  6. Foliar growth regulation treatments were found to have compensatory possibilities in regards to loss of root function, due to Spongospora infection. Root mass, crop yield and incidence of powdery scab were all shown to improve significantly with these treatments. 

There are a number of corresponding recommendations due to these outcomes and though Powdery Scab remains a very challenging disease, the outcomes of the Australian study offer opportunities to target the disease’s weakness and potentially minimize its effect.