#1. All you can see here is a leafspot. Although you know nothing of the host plant, you should be able to determine the cause. Which of these is the cause?
The correct answer is:
Fungus:
These are leaf spots caused by Septoria on a floating water weed. Septoria is a Coelomycete fungus which means it makes these little black fruiting bodies within the leafspot. Zymoseptoria is a common pathogen on wheat and these pycnidia can usually be seen within leafspots at the base of wheat plants.
The incorrect answers were:
Insect feeding: rarely causes necrosis most sucking insects leave no mark on the leaves.
Water mould: they sporulate as, either: 1) microscopic hard oospores that cannot be seen, as they are too tiny and are deep within the tissue, or 2) as fluffy growth, usually on the underside of leaves.
Rust fungus: this specialist fungal group does not create leaf spots and the host tissue will only become necrotic (dead) once the host can no longer support the demands of the pathogen.
#2. The symptoms in this photo are due to a fungal disease; “citrus scab”. The leaf distortion seen here is an unusual symptom of fungal infection and is more often associated with which group of pathogens or problem?
The correct answer is:
Viral infection:
Mosaic (not seen here) and leaf distortion are both classic symptoms of infection by a virus. This is an example of leaf distortion NOT due to viral infection.
The incorrect answers were:
Bacteria: distortion of leaves is not associated with bacterial infection.
Nutrient deficiencies: there are few examples of nutrient deficiencies causing distortion in leaves but this is extremely unusual.
Water moulds: very occasionally, downy mildews can systemically infect the host, which then produces small, thick (distorted) leaves, but this is rare.
#3. This is a pod bug. The young of this insect resemble which of the following?
The correct answer is:
Similar to the adult, but shorter and without wings:
Pod bugs belong to the Hemiptera, which do not undergo complete metamorphosis during development. The young of Hemiptera often look broadly similar to the adults, but are smaller and often lack wings.
The incorrect answers were:
Caterpillar: All caterpillars turn into butterflies or moths.
Grub: All grubs turn into beetles.
Maggot: All maggots turn into flies.
#4. What is the best description of this symptom?
The correct answer is:
Ringspots:
The spot on the leaf has a green centre, thus the spot is a ring. This symptom is almost always due to viral infection and, more often than not, vectored by a nematode.
The incorrect answers were:
Frass: frass is a term for excrement (usually applied to that of insects but not exclusively).
Mosaic: a mosaic as a symptom literally looks like a mosaic, with hard, angular edges to the blocks of colour. Mosaics are almost always yellow and green.
Spots: the definition of a spot on a leaf is a tricky one and there are lots of definitions. This clearly is a spot BUT ringspot is a far better answer.
#5. These are ergot; fungal material that grows in the ear of cereals in place of the seed material. Why are ergot such a nuisance for farmers?
The correct answer is:
They are toxic and, if present in even modest quantities, will render the grain poisonous:
Ergot are very toxic and must not be eaten. The limits on ergot contamination for animal feed is one per litre of grain, whereas for human consumption, the tolerance is nil.
The incorrect answers were:
They are a missed opportunity for grain production; each ergot produced is a loss in yield: this is true, but the numbers of ergot never substantially reduce the yield.
They have a bitter taste and will make the grain unpalatable: you don’t really want to eat one to find out.
They will discolour the flour when milled and reduce its value: it is not visible in milled flour. Historically, there are examples of unscrupulous millers selling contaminated flour and, when baked into bread, the whole village dying from the ergot poisoning.
#6. These galls on grapevine are due to Grape phylloxera; an aphid-like insect that has both root and leaf feeding phases in the lifecycle. It is an extremely unusual symptom for this group of insects. Leaf galls such as these are much more often associated with group?
The correct answer is:
Mites:
Galls on leaves such as those seen here are commonly produced by eriophyid mites.
Incorrect answers were:
Whitefly: small white flies producing plenty of white wax are the symptoms of whitefly, not galls.
Leaf miners: there is no leaf-mining group of insects as such; several different species of insect have adopted this habitat. Long, silvery, winding trails through the leaf are the symptoms and typically not galls.
Mealy bugs: “white slow-moving waxy insects hiding in crevices,” is how they are often described, and they are not associated with gall production.
#7. This symptom seen on these cherry leaves is “interveinal chlorosis” i.e. the zones between the leaf veins have turned yellow. It is often a characteristic sign of a deficiency in which nutrient?
The correct answer is:
Iron:
Interveinal chlorosis in the upper leaves is a common symptom of iron deficiency.
The incorrect answers were:
Nitrogen: a yellowing (including the leaf veins) of the lower leaves can be the result of nitrogen deficiency.
Phosphate: stunted plants, which are dark green with a slight red tinge, are symptoms associated with phosphate deficiency.
Boron: the tip of the plant suffers necrosis and tiny leaves are produced when there is a boron deficiency.
#8. These are smut balls on the leaf of an ornamental plant. Smuts are very specific in which areas of the plant they attack; they are mostly associated with which region of a plant?
The correct answer is:
Floral parts:
As for Ergot (Question 5), smuts usually infect the flowers of a plant and grow down into the ovaries.
The incorrect answers were:
Roots: Stems: Leaves: Smuts often have complex lifecycles, and there are exceptions to the rule that all smuts infect the floral parts of the plant (see photo above), but there are not many.
#9. “Alternate host” is a phrase often heard in plant pathology. What does “alternate host” mean?
The correct answer is:
An additional species of plant which is required for the pathogen to complete its full lifecycle:
Some rust fungi have complicated life cycles. Whilst farmers are generally familiar with the asexual spore production on crop plants, they are less familiar with the sexual phase of the same fungus which often takes place on an unrelated plant. It is this “other plant” that is termed the alternate host.
The incorrect answers were:
Any wild plant that is susceptible to a pathogen: this is not considered an alternate host; it is just part of the host range of the fungus.
A crop plant that is slightly susceptible to a pathogen, but not as badly as another crop: this is not considered an alternate host; it is just part of the host range of the fungus.
A plant that the pathogen will survive on when the crop is not in production: it is often the case that the alternate host allows the fungus to over-winter when the crop is not in production, but that is not what makes it an alternate host.
#10. This is a knapsack sprayer with a hooded shroud over the nozzle. The hood is used to reduce drift as the spray fan is enclosed within the hood. When should such a shroud be used?
The correct answer is:
Spraying around seedlings when applying herbicide:
The shroud prevents drift which theoretically makes it possible to spray round seedlings, however it is extremely easy to kill the seedlings by doing this (as I know to my cost). As it takes several days for the seedlings and the weeds to die, you don’t know you have killed the crop until several days later.
The incorrect answers were:
Spraying insecticides: it may be appropriate to use a shroud but it would be unusual to do so.
Spraying especially toxic chemicals: the shroud is not considered part of personal protective equipment. You should protect yourself from all agrochemicals when spraying using appropriate PPE.
Spraying fungicides: it may be appropriate to use a shroud but it would be unusual to do so.
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.
