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We have several Viburnum farreri in our garden. Last year one out of seven died, but we thought it was because of the heat/dryness.

This year another one has just died, but I don't think it has been very dry.

It has this weird white goo on the leaves, but I don't know if that is related.

1 plant 2 plant 3 plant 4 plant

A neighboring bush has lice on the underside of the leaves as well as ants "milking" the lice:

ants and lice

Here is the currently "healthy" neighboring plant (5 meters away), same plant as above

undead

Location: Southern Sweden

What is killing these plants?

2 Answers 2

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Your neighbour's plant has an insect infestation - it might be aphids, specifically black fly, but it's hard to tell from the photo. Treatment is with a suitable insecticidal spray, preferably a systemic one, not a contact one, and all parts should be sprayed, including beneath all leaves as well as the tops.

As for your plants, the 'white stuff' is significant - I am not 100% sure what is. I would suggest scraping off some of it from the bark/stems to see what, if anything, is inside the deposits - it might be scale insect or a fungal problem. Did you notice any toadstool/mushroom growths near it at any time, or are there any soft or soggy areas in the woody stems?

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After reading user Bamboo's answer (white stuff => fungal) I dare to suggest Downy Mildew (Plasmopara viburni)

This disease first appears as light green spots on the upper leaf surfaces. The dots grow to create angular patches between the leaf veins. Downy greyish-white fungal growth forms on the undersides of the leaves.

Downy mildew illness differs from powdery mildew in that the fungal growth is seen on the bottom rather than the upper leaf surface.

From this source (emphasis mine)

If your spring has been cold and wet also consider Viburnum-Bacterial Blight

Symptoms Spots are at first water soaked, then turn brown and irregular in shape. Oregon observations are that spots may be angular. Margins frequently develop a bacterial exudate. Numerous spots during early shoot growth can deform leaves. Stem lesions are elongate and generally not as obvious. Severe infections can result in a shoot dieback.

Perhaps you have access to a microscope and can examine the white stuff further.

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  • Downy mildew is a possiblity, but I ruled it out because these deposits are on stems/bark as well, putting me in mind of woolly aphid, which occurs on apple trees.
    – Bamboo
    Commented Jul 19, 2022 at 11:11
  • Thank you for your answer. After closer inspection I now believe the white stuff is en.wikipedia.org/wiki/Icerya_purchasi Commented Jul 19, 2022 at 20:47

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