Confused about symptoms and causes? It's an everyday challenge for horticulturists at the Eden Project

21 Nov 2016

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At the BSPP annual meeting this September I talked with Rachel Warmington, the plant pathologist for The Eden Project, about training for horticulturists (don’t call them gardeners!). I proposed a one day course on the principles of field diagnosis: the recognition and interpretation of symptoms. The aim was to increase confidence in making quick decisions about plants that ‘didn’t look quite right’.

The Eden Project occupies a reclaimed clay pit in Cornwall and is famous for its two dimpled domes (or biomes, as they are called). I especially like the emphasis on crops and useful plants which the million or so visitors each year will come across: bananas, cocoa trees, tobacco and others whose products we consume without always realising what the original plant looks like.

Keeping the many different plants healthy inside the tropical forest biome and the Mediterranean biome, plus surrounding gardens, is a major undertaking. What’s good for plant growth all year round is also good for pests and diseases. Mildews, rusts, mites and aphids are some of the common problems the horticulturists encounter, but there are others that are less easy to diagnose. Fortunately, Rachel and her colleague Katie Treseder, an entomologist, are on hand to investigate and can send samples to other labs for further tests.

It’s a good setup, but laboratory tests don’t always yield the positive results you hope for. And there’s always scope to expand one’s knowledge of symptoms and what they mean, especially for the less well-known causes. People often underestimate the range of different biotic and abiotic causes that can produce similar symptoms. Field diagnosis is never as straightforward as you think.

I’ve been holding courses on field diagnosis for nearly 20 years, for scientists, extension workers, farmers and people with no formal training in agriculture. This was my first time with a group of horticulturists. They all looked a little nervous at first. I suggested that they knew more than they thought they did, and so it proved during the one day course, which used a mixture of photosheets, live samples, short written exercises and presentations.

The first exercise, called ‘looks familiar’, tested recognition of major groups of pests, such as rusts and aphids, mixing true examples with lookalikes. The exercise helps to tell me how much people already know. We looked at leaf spots, wilts and rots before considering stunting, extra growth, galls and other features that are more difficult to interpret. I liked the fact the everyone was a keen observer of plants, even if they didn’t always know why they appeared unhealthy.

I’ve learnt from my teaching and field experiences how easy it is to confuse the ‘obvious’ with something else. Entomologists and pathologists see things differently; that’s why some confuse whiteflies and aphids and others smuts and rusts. As my friend Jeff Bentley says, ‘what you don’t know, can’t help you’. I gave a global tour of symptoms before introducing the ABC test: do symptoms suggest an Abiotic or Biotic cause – or are you Confused? The ABC test is done by crop and I added a new one on ornamentals to help the group feel more at home.

The ‘looks familiar’ test revealed a lack of knowledge of nematodes, which surprised me. A side benefit of the course is that it also identifies training needs. I showed quite a few phytoplasma diseases, most from outside the UK. Although I said there were ‘more out there than you think’, I also emphasised that phytoplasmas are relatively uncommon – and added a rider that witches’ broom and gross distortion could also be caused by fungi, such as Taphrina.

A one day course is not going to tell you all you need to know about field diagnosis. Managing the health of the many different plants grown at the Eden Project will always involve scratching your head – as I did when shown some samples brought to the course. I hope that the enthusiastic group who attended now feel more confident in making a field diagnosis, as indicated in the course feedback.

I enjoyed this opportunity to work with horticulturists and hope to do more in future. Maybe next time we can combine hands-on exercises with modern diagnostics. Or look more closely at decision making in crop protection. Going back to basics, but looking forward with science.