Lombardy Poplar - Portsmouth

Cottonshirt

I found these leaves on the ground on my way to work. They are, I think, of the Lombardy Poplar, Populus nigra 'Italica' (it is in any event an extremely fastigiate Poplar). What interests me about them is the growth on the petiole. It looks as though something has tied them in a knot. A friend at work speculated that it was mistletoe but I favour the work of an insect as an explanation. Any ideas what might be causing this?


N.B. It's late summer here now, and some deciduous trees have just started turning from green to gold, but this Poplar seems to have shed quite a lot of leaves already. This may or may not be a clue.

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Brent Ferris

The first may be a viral disease - the name escapes me at moment; the 2nd is prob an insect. Cut them open, if there is tunnelling - an insect; if not likely disease.
The cold nights are seldom a factor except for leaf turning.

bsearcey

I call that kind of thing a gall. Abnormal growth caused by some type of infection.

Brent Ferris

I agree. The 2nd pic is a gall, insect was or is inside; the first probably a viral infection.

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Cottonshirt

In response to the suggestion that the first picture is a viral infection I spent a great deal of time reading about tree viruses in particular and plant viruses generally. I have been unable to find any mention of a virus that attacks the petioles of Lombardy poplar in this way. Unless someone is able to come up with a specific suggestion I am not disposed to agree that it is a virus.

I have, however, found an interesting aphid, Pemphigus bursarius, the Lettuce Root aphid. The adults that emerge from the gall are winged females that migrate en masse to lettuce plants, Lactuca sativa, L., where they feed on the host plant devastating commercial crops. Their offspring colonise the root systems of the lettuce plant, reproducing parthenogenetically (without male fertilisation of the eggs) for several generations until a winged form emerges in the autumn and migrates back to the Poplar tree where the cycle begins anew.

I am, in the absence of any better suggestions, taking this to be the source of these galls.

Many thanks,

TreeEurope

It is a leaf stem gall (Pemphigus spirothecae PASS.): Not dangerous for the tree. Lombardy Poplar

cu