Determining a general cause of leaf damage

Hello! :) Lately I’ve been trying to identify some unknowns and I have difficulty classifying observations of leaf damage. Could someone give me the sparknotes version of how to tell insect, fungal or virus damage apart from one another so I could at least help to make kingdom-level IDs wherever possible? And how can I differentiate them from regular wear-and-tear that happens over time?


Copypasta that i use when making IDs:


figuring out what damaged a leaf can be really challenging. i’m not sure that there exists general guidance that you can use in all situations that will allow you to reliably narrow things down to kingdom.

if you know what the plant is and what its general situation is (plant health, local conditions, etc.), that will help. if you know whether the damage is localized (vs other leaves on the plant and vs nearby plants, that will help). if you can find possible disease vectors (like plant bugs), that will help.

i think if you can find obvious signs of animals, like characteristic mines or leaf rolling or chew marks or frass near the damage, then that can be attributed to animals.

otherwise, unless you already know what you’re looking at, it might not always be obvious whether you’re dealing with environmental issues, general plant health or life cycle things, disease, animal damage, other physical damage or wear, etc.


I listened to a podcast recently where a paleobotanist explained that insect damage can be attributed atleast to family or even subfamily in some cases, based on categorization of the damage into different types like shallow mining, deep mining, piercing and sucking, and stripping along the veins to name but a few. The way plants react to such damage and ‘cauterize’ it can be an accurate indicator of the kind of insects that were around as far back as the mid-Miocene

It was really interesting, let me know if you want me to share it :v:

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I can’t help with figuring out the cause of plant diseases, but I have this really long comment I use. :laughing: I do try to act on what I know, but it is pretty limited. I put most in “Life”.

To help direct IDs on iNaturalist, observations typically need to be put into at least a taxonomic kingdom, this can be challenging with plant diseases/infestations/symptoms because these signs can come from diverse organisms and environmental conditions. If you are trying to determine which category to place your potential disease/pest, this website may help:
While not required, when looking for an identification for plant diseases/parasites, it is helpful to include the host plant information. This can be done in a note, comment, or by adding the Observation Field: “Host Plant ID”.
If you do not know the host plant, you can request the plant ID first. Once you have that, you can then duplicate the observation and request ID for the disease. You can add the URLs for related observations as notes, comments, or by adding the Observation Field: “Related Observation”.
There are projects in iNatuaralist that focus on plant diseases. Projects will frequently require information as a condition of adding an observation (such as host plant ID). If you join the project, it will be available in the projects list on the observation on the iNaturalist website.
Plant disease projects for North America include:
Galls of North America:;
Leaf Miners of North America:;
Non-Metazoan Plant Diseases of North America:;
Animal-Caused Plant Diseases of North America:

Obviously, the project portion has a North American bias. I know there are some non-North American projects, but there are likely gaps in coverage.

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Plese give a link to the podcast about insect damage.

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It takes years to know such stuff as fungus, virus, bacteria, insects on plants. I grow just a few plants. Insects are very numerous. There are sap-sucking pests, such as whiteflies. There are grasshoppers and caterpillars feeding on the leaves creating holes. Each species can have different habits. The hole patterns created on leaves can be clues of the species, but it is safer the find the insect making such holes first before filing it in as an observation. Snails make holes on leaves too, as well as birds. There are some birds taking pieces of leaves off my plants. These birds are very smart. I’m not sure why they do that. To line the nest or they need some greens.
Fungus are also numerous. There are some who have interest in mushrooms. Over here, almost all the tropical mushrooms are poisonous. so we don’t have the culture to look into fungus. It is like quite futile trying to find its name. At least fungus fruiting body can be seen sometimes.
The virus that affects plants are mosaic virus. There are Tobacco mosaic virus, cucumber mosaic , cymbidium mosaic virus, chilli leaf curl virus…While experienced plant growers can identify the virus, but it is difficult, as the symptoms can look like fungal/bacteria diseases. There are secondary infections and more pathogenic organisms are present on the leaves sometimes. Advanced equipment are necessary for making the virus visible.
In summary, can find the insect that makes the hole.


I think this will be helpful, thank you!

Here we go:

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