Set by Dr Eric Boa
This is another set of ABC questions: look at the symptoms and decide whether they suggest an Abiotic or Biotic cause. If you can’t make your mind up then you are Confused. Don’t worry – some of these I’m not sure about either. If this is the first ABC test you’ve done then you might like to start with the May 2023 plant doctor quiz. All examples are from crops in Colombia – but they could be from anywhere, with one or two exceptions. The ABC method can be used for any unhealthy crop, regardless of your prior knowledge. It’s a first step towards finding an exact cause.
#1. What causes these symptoms on runner/french beans.
#2. Lulo, a popular solanaceous fruit, also made into juices.
#3. Detached shoots of oregano; contrast the different growth forms. Both forms appear in the same plants.
The correct answer is Confused.
Without further information – did the farmer spray glyphosate, for example; or the results of lab tests – it’s difficult to be certain what’s going on here. But it’s strange enough to warrant further investigation. These revealed a close association between phytoplasma and the altered growth form.
#4. Why have some potato leaves gone yellow?
#5. More strange growth, this time on tomato plants in a polytunnel.
The correct answer is Abiotic.
Once you become familiar with phytoplasma symptoms there’s an early tendency to see them everywhere.
Common sense suggests that this is an unlikely explanation for small, stunted leaves.
This is in fact glyphosate (weedkiller) damage.
#6. Can you suggest why all the peach leaves are curling?
#7. Abutilon and powdery leaves. What’s happening?
The correct answer is Healthy.
It’s not a rust, simply pollen scattered over an adjacent leaf.
Sometimes the most obvious answer is the correct one.
Don’t over-complicate diagnoses. Flower production is big, big business in Colombia and growers are always on the look out for imperfections. This isn’t one.
#8. What are these strange growths on Mountain papaya caused by?
The correct answer is Biotic.
Vasconcellea pubescens looks like normal papaya except it can grow up to 3000 masl in Colombia.
There are at least two possible reasons for these bud massess or malformations: fungus (mango malformation looks similar and is caused by Fusarium spp.); or phytoplasma. Or it could be induced by insect feeding. Either way, it definitely looks biotic.
#9. Why are the leaves going yellow at the edge of these geraniums?
#10. More strange growth and profuse branches produced from the trunk of a native willow
The correct answer is Confused.
Although many will be familiar with willows, I doubt you will have seen anything like this before (unless you’ve been to Colombia).
This is Salix humboldtiana, a native species. It is in fact a phytoplasma, disrupting growth (and killing trees on a spectacular scale).
Results
We hope you enjoyed the quiz and learned something!
See how your score matches up…
1-3: You need to do a few more of these quizzes to become a field diagnostics expert.
3-5: You have made a start in your field diagnostics but there is some way to go…
5-7: You are getting more right than wrong so keep on learning!
7-9: Impressive you are getting pretty experienced in your field diagnostics!
10: Well done! But make sure you do the quiz again next month.
We hope you enjoyed the quiz and learned something!
See how your score matches up…
1-3: You need to do a few more of these quizzes to become a field diagnostics expert.
3-5: You have made a start in your field diagnostics but there is some way to go…
5-7: You are getting more right than wrong so keep on learning!
7-9: Impressive you are getting pretty experienced in your field diagnostics!
10: Well done! But make sure you do the quiz again next month.
