Butt Rot, Smut and Drippy Nut – Analysing Risks to Plant Health

Why do we need to identify plant pest risks?

Throughout university, and at nearly every plenary lecture concerning plant health I have ever attended, whenever people would talk about the importance of plant health they would always mention one thing: the Irish potato famine

Now in no way am I trying to downplay the magnitude of the impacts of the Irish potato famine. The population of Ireland today is still below that of what it was pre-famine. But I feel it is easy to forget that famines and mass migration are still being caused by pests and diseases of plants today.

The fall army worm,  Spodoptera frugiperda, is a pest of crops native to the Americas which has spread rapidly in Africa since its introduction in 2016 and is causing major food insecurity. In 2018, the pest jumped continents again with the first outbreak reported in Asia. 

In Europe, we are lucky enough that plant pests won’t lead to famine – we have enough money to buy food elsewhere when crops fail. But pests and diseases can still cause landscape-scale changes. In the North of England and Scotland, a disease caused by Phytophthora austrocedri is killing juniper and potentially changing ecosystems permanently. Ash dieback, caused by the fungus Hymenoscyphus fraxineusis killing ash trees in woodlands and hedgerows across the UK – as Dutch elm disease did several decades before.

And these landscape-scale changes aren’t just occurring in Europe. Since the detection of the emerald ash borer in North America in 2002, American ash trees have gone from being some of the commonest tree species in North America to being listed by the IUCN as critically endangered. And it isn’t just trees that can be hammered by pests and disease. Rose rosette virus is killing roses in gardens across the USA, and could do the same in Europe if it should arrive.

Horizon Scanning?

Horizon scanning is the process by which pest risk analysts try to identify potential pest threats before they arrive. It is a lot like being an Intelligence Analyst for GCHQ, except of course pest risk analysis is way cooler…

Pest risk analysts monitor a range of sources in order to keep up with developments in plant health worldwide. The three key things we are interested in are:

  • New species – reports of pests new to science, or a species acting as a pest for the first time.
  • New locations – reports of pests spreading to new locations. This can be an indication a pest has the capability to spread in trade. Also, a pest may spread to a region with a different climate, showing it can adapt to new environments.
  • New hosts – pests can, especially when they spread to new regions, be reported attacking a new host plant for the first time. Northern European countries might not be very interested in pests of grapevine, but if that pest is then reported attacking apples it might present a risk.

This sort of information isn’t just in the scientific literature. You may find information about it in the media, within trade journals or, increasingly, social media channels. I have a horizon scanning feed on Twitter, a bunch of users and organizations that tweet about plant health and help keep me in the know. Another excellent one-stop shop for your plant health news is the EPPO reporting service, which is released once a month.

Pest Risk Analysis

Pest risk analysis is officially defined by the IPPC as “The process of evaluating biological or other scientific and economic evidence to determine whether an organism is a pest, whether it should be regulated, and the strength of any phytosanitary measures to be taken against it”.

Basically, we identify pests that could pose a risk via horizon scanning and then we ask ourselves the questions:

  • Can the pest arrive?
  • Can it establish and spread?
  • Will it be damaging?

And if the answer to all of those questions is yes, then we look at how we can exclude the pest – or reduce impacts should it arrive. These could include phytosanitary measures – these are requirements placed on traded commodities the pest is associated with (e.g. host plants, timber, fruit and vegetables). Under international trade laws, if a country wants to place phytosanitary measures on a trade – these need to be technically justified. PRA is the internationally recognised method to technically justify phytosanitary measures.

So…er…butt rot?

Now to answer the question you’ve probably been asking yourself from the start: can smut lead to butt rot and drippy nut? Well, you can relax, the answer is no.

Believe it or not, butt rot, smut, and drippy nut are all genuine plant diseases. Butt rot is a disease of trees caused by various fungi – these fungi infect the stumps of felled trees (called butts in some regions), colonize the wood and then infest living trees via root to root contacts. Smuts are the name used for fungi that highjack plants reproductive system and are best known for turning cereal grains into massive spore structures. Drippy nut is a disease called by the bacterial pathogen  Erwinia quercina that causes the acorns of oaks to, well, drip bacterial ooze!