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.
#1. The symptoms of a deficiency in the major nutrients required for crop cultivation (NPK) all share one thing in common; what is it?
The correct answer is:
Symptoms are seen in the lower leaves first:
Nitrogen, Phosphate and Potassium deficiencies have different symptoms, but share the common factor that it is the lower leaves where symptoms are first seen.
The incorrect answers were:
The leaves turn yellow; the lower leaves turning yellow is the major indication that the plant is short of nitrogen, but that is not true of the other phosphate or potassium shortage.
The very tip of the plant is the first to show symptoms; few nutrition deficiencies are initially seen in the tip of the plant. Symptoms due to calcium and boron are seen here.
Symptoms are seen in the young leaves first; a deficiency of almost all of the minor nutrient’s symptoms are seen in the young leaves first.
#2. Most caterpillars have 4 pairs of false legs on their body, this caterpillar has only 2 pairs (arrowed), what will this caterpillar turn into?
The correct answer is:
Moth
Many caterpillars have four pairs, but some have fewer, as seen here. It is not difficult to identify these caterpillars as “loopers”, based on the way they arch their body as they move.
The incorrect answers were:
Sawfly; sawfly larvae are often mistaken for caterpillars but, rather than having the typical 4 pairs of false legs or fewer, they have more than four pairs.
Beetle; beetle larvae (grubs) don’t have false legs like this, but they do have thoracic legs.
Fly; fly larvae (maggots) have no false legs, and no thoracic legs either.
#3. Leafspots; all quite small and all the same size. What does this indicate is the cause?
The correct answer is:
Insects:
These symptoms are not proof that insects are responsible, but strongly suggest they are the cause. Many sucking pests leave no marks at all, but others such as leafhoppers and planthoppers cause this symptom.
The incorrect answers were:
Bacteria; bacterial leaf spots are often associated with the leaf edge or damage and are water-soaked and of variable sizes.
Fungi; fungal leaf spots are usually larger than this and are not quite so uniform in their appearance.
#4. When assessing symptoms on a diseased plant, which stage of disease development is it best to study?
The correct answer is:
Recently infected material, where the symptoms are still developing:
This is where the pathogen will be most active and the symptoms not modified by other microbes moving in on the dead tissue.
The incorrect answers were:
Dead material, where the symptoms have been fully expressed; it is difficult to work out why a leaf or plant has died as they often look the same (black and shrivelled).
Asymptomatic tissue: after infection but before symptoms appear; if there are no symptoms (even if there is infection) it is not possible to do a field diagnosis.
Material that is almost dead but not quite; the amount of saprobes that will be colonising the tissue will make for confusing symptoms.
#5. What has caused these marks on this potato leaf?
The correct answer is:
Micro-browsing insects.
The contents of the surface cells of the leaf have been sucked out. Pests that commonly do this are thrips and mites, but, in this case, it was leaf hoppers that did the damage.
The incorrect answers were:
Powdery mildew; this common fungal pathogen rarely attacks potatoes. It is not the cause here.
Phytophthora; late blight is very common on potato crops, but the symptoms are not like this. Rapidly expanding black zones, with a pale perimeter are the typical symptoms.
Virus; speckle such as this can be mistaken for a viral mosaic but, look carefully at the photo, this is not a mosaic, there are no panels of yellow and green.
#6. Upper and lower surface of peach leaves. What is the cause of the red colouration?
The correct answer is:
Powdery mildew:
It is unusual for powdery mildew to cause anything other than a white dusty growth over the upper surface of a leaf, but here there is considerable host reaction and the sporulation is on the lower surface.
The incorrect answers were:
Viral infection; viral ringspots are unusual but can look like this; if you missed the white powdery growth on the leaf at the top of the photo viral infection was a good answer.
Unidentified fungal infection; There are fungi that induce considerable reddening of the host (blackberry rust is a good example), but it is unusual AND you could have spotted the sporulation on the underside of the leaf.
Bacterial infection; infection by a bacterial pathogen does not generally cause anything other than tissue death.
#7. These are fungal fruiting bodies growing on the host leaf. Clearly, a fungal pathogen is responsible, but what does it mean if there are no fungal fruiting bodies within the infected area?
The correct answer is:
The cause could be a fungal pathogen:
The presence of small black dots embedded within the host (and cannot be wiped off) is a clear indication that the cause is a coelomycete (ascomycete), however there are many fungi – hyphomycetes (also ascomycete) – that do not produce such structures.
The incorrect answers were:
The cause is not a fungal pathogen; you could not conclude this based on absence of fruiting bodies.
The cause is either bacterial or viral; you could not conclude this based on absence of fruiting bodies.
An abiotic problem of some sort; you could not conclude this based on absence of fruiting bodies.
#8. These are the symptoms of bacterial speck on tomato. This disease breaks many of the rules associated with the diagnosis of a bacterial disease.
The correct answer is:
Small lesions of limited size, not associated with damage:
Typically, bacterial infections are associated with leaf damage or the edge of the leaf. In wet weather, they spread aggressively across the leaf. These symptoms are not seen here, but are typical of this pathogen.
The incorrect answers were:
No fruiting bodies associated with the spots; there are never structures of any sort associated with bacterial infection.
The plant is not wilting; bacterial stem infections frequently give rise to wilt, but leaf infection does not.
Mosaic is not present; a mosaic is typical of viral diseases and not associated with bacterial infection.
#9. Brown and green aphids. What is the relationship between them?
The correct answer is:
Brown are parasitized; green are healthy:
The brown aphids are empty shells, the parasitoid has eaten the interior and has emerged. The green aphids are currently healthy.
The incorrect answers were:
Brown are males; green are females; brown male aphids do exist, but almost all aphids are female.
Two different species of aphid; no, they are all the same species.
The brown insects are not aphids and are predators of the aphids; no, they are all (or were all) aphids.
#10. Friend or foe? Some large insects are predators of pests, what are your thoughts on this one?
The correct answer is:
Foe; this is a pest of crops:
This is the “Giant tip wilter”, a pest of passion fruit. Enzymes are injected into the stems which causes them to wilt rapidly.
The incorrect answers were:
Friend; this is clearly a predator of pests.
Neither; this large insect is not a problem, nor is it a beneficial.
Vector; it is not a pest directly but spreads viruses which damage yield.
