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Thursday, 16 October 2008 00:34

Endophytes - what are they and what can you do about them?

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With late summer and autumn approaching, you will be hearing a lot more about endophytes and ryegrass staggers in grazing livestock – and it can all seem very complicated to the lifestyle farmer.  This article explains what endophytes are, why they are important and what you can do about them.

  • Fungal endophytes are fungi that live within plants, and they are common in New Zealand ryegrass.
  • Ryegrass is the basis of most of NZ’s farmed pastures.  However it is susceptible to attack from grass grub and Argentine stem weevil. 
  • The interaction between the endophyte fungus, the host ryegrass and environmental conditions results in varying levels of toxin production. 
  • The toxins are alkaloids, and the three most important are:
    • Peramine that gives the plant resistance to Argentinean stem weevil
    • Lolitrem B that causes ryegrass staggers
    • Ergovaline that causes heat stress in stock - and also possibly increased retention of water in faeces (resulting in dagginess)
  • In addition, some strains of endophyte don’t taste good, so animals selectively avoid pasture containing them
  • Peramine is found mainly in young ryegrass leaves, and lolitrem B and ergovaline are found in the base of the plant, old leaves and seed heads. 
  • The endophyte fungi grow in late summer and autumn and this is when the animal health problems they cause are most evident, especially when conditions are humid and warm. 
  • In the south of the South Island, the endophyte does not usually grow well enough in ryegrass to cause animal health problems or affect pasture growth.
  • There are various strains of ryegrass and various strains of endophyte, and the various combinations of ryegrass and endophyte produce more or less of the various toxins.  This is why some types of ryegrass produce more ryegrass staggers than others.
  • Ordinary high endophyte ryegrass seed tends to be drought-resistant and resistant to Argentinean stem weevil, but (except in the south half of the South Island) it has the disadvantage of causing health problems such as ryegrass staggers and heat stress. 
  • Low endophyte lines of seed don’t affect stock health in the same way but tend to be more drought susceptible and more susceptible to Argentinian stem weevil.
  • New types of endophyte have been developed that produce peramine (giving resistance to stem weevil) but not lolitrem B (the cause of ryegrass staggers).  Examples of this include Endosafe ARI ryegrass cultivars. 
 Resowing paddocks to avoid the endophyte problem

 If you are resowing paddocks with ryegrass, you have various options:

  • Choose ryegrass seed with a high level of endophyte infection that will produce pasture that is resistant to drought and Argentinean stem weevil, but (in all parts of NZ except the south half of the South Island) run her risk of ryegrass staggers and the other animal health problems associates with endophytes. 
  • Choose ryegrass seed that will produce pasture that will not cause ryegrass staggers or the other animal health problems outlined above, and that will not be susceptible to Argentinean stem weevil.
  • Ask your seed merchant for an appropriate type of seed. 

 Of course, to avoid endophyte problems altogether, you can sow grass species other than ryegrass, eg, cocksfoot and tall fescue.  Although some of these are costly and more difficult to establish than ryegrass, they have the added advantage of being resistant to many ryegrass pasture pests.

Note:  Facial eczema is another disease of grazing livestock in summer-autumn caused by fungal toxins.  But facial eczema has nothing to do with endophytes.  It is caused by a fungus that grows in the dead litter at the base of pasture, not by a fungal endophyte (ie not by a fungus that grows within the grass plants).

Dr Marjorie Orr, lifestyle farmer and veterinarian (retired)

Dr Marjorie Orr - veterinarian and lifestyle farmer. Dr Orr is a recognised authority on animal welfare in New Zealand and has served on several government committees, especially those concerned with writing codes of welfare for sheep and dogs. Her service to animal health and welfare has also been recognised by awards from the NZ Veterinary Association and MAF. She is also a strong SPCA supporter.

Website: www.lifestyleblock.co.nz/images/imgDrMarjorieOrr.jpg