Trying to identify and eradicate what is/are killing my seedlings. I had the same problem last year and it quickly spread to my houseplants. Everything was thrown out and started fresh this year, but having the same problem. Please help. Thanks



Thank you for reaching out to the Toronto Master Gardeners for help with your ailing seedlings.  I cannot say definitively, but it looks from your photo that spider mites have attacked your Geraniums (also known as Pelargoniums). Unfortunately the new green growth of these and other bedding plants is very attractive to spider mites. The early signs of these mites are speckling and yellowing of the leaves, and general decline in the health of the plant. You can confirm this by closely examining the underside of leaves for the appearance of webbing or indeed the tiny mites themselves. 

If the leaves have a sticky residue, the culprit is more likely aphids. The treatment for spider mites and aphids is somewhat similar, and if caught early can often be controlled with a forceful blast of water. This must be repeated every three to five days to catch the reoccurring hatching of eggs.  Insecticidal soap is recommended for heavier infestations: again it must be repeated often to be effective.

Unfortunately the yellow mottling of leaves may be the result of a virus. There are a variety of viruses that specifically attack Pelargoniums, and sadly, there is no cure for this infection. If you do suspect a virus, the plant as well as the soil should be destroyed, as you have done before.

You may wish to take a leaf (sealed in a plastic bag) to a garden centre to verify the diagnosis. I am adding a number of websites that may help in identifying your pest and learning about controls.

Identify spider mites

Control of Spider mites

Aphids on Indoor plants

Geranium -Pelargonium virus.

Proper use of insecticidal soap

I do wish you the best of luck dealing with your infestation. Don’t get disheartened, it happens to the best of us. If all else fails, start again with a clean slate, including clean containers, new soil and seedlings free of contamination.