Set by Dr Phil Taylor of CABI.
This months quiz is all about material on the surface of leaves. There is all manner of things that can grow or be deposited on leaves and it is useful to be able to identify them.
#1. What is the material on the lower side of this laurel leaf?
The correct answer is:
Powdery mildew caused by either Podosphaera tridactyla or Podosphaera pannosa. Unusually, the growth is on the underside of the leaf. The developing fruiting bodies (cleistothecia) are clearly visible. The infection can become so severe that portions of the tissue fall out resembling insect damage.
#2. What is the material on the lower side of this leaf?
The correct answer is:
Downy mildew, Peronospora farinose, is sporulating profusely on the underside of these fat hen leaves. Note that there is almost no host reaction to the pathogen.
#3. What is the material on the upper surface of these plants?
The correct answer is:
Roadside dust. These beans were planted close to a very dusty road and became coated in dust. Note that the colour of the leaves is the same as the soil.
#4. There is a velvety coating on the underside of these lychee leaves. What is the cause?
The correct answer is:
Mites. These are the symptoms of the lychee rust mite. The microscopic mite induces the hair-like outgrowths from the underside of the leaf, among which the mites live.
#5. What is this coating the upper leaves of this citrus tree?
The correct answer is:
Sooty mould. The sooty mould fungi are growing in the honey dew deposited by sucking insects on the upper branches.
#6. What is the material on the upper surface of these leaves?
The correct answer is:
This is red algae growing over the surface of the leaf.
#7. What is this material on the upper surface of these citrus leaves?
The correct answer is:
Honey dew. There is no sooty mould growing on the honey dew which is why it remains clear (and sticky). Insects in the upper branches have deposited it on the leaves, where it will remain, until rain washes it off.
#8. What is growing on the surface of this leaf?
The correct answer is:
Lichen. Not normally a problem in crop production, lichen can grow epiphytically on leaves. As they grow slowly, only older leaves will accrue a lichen population.
#9. What are these light areas on this aubergine leaf?
The correct answer is:
Insect feeding damage; this is speckle due to micro-browser feeding, in this case thrips.
#10. What is this unusual material on this okra leaf?
The correct answer is:
Hyper parasite: This is Ampelomyces quisqualis, a hyper parasite of the powdery mildew. It is a form of biological control.
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.
