What is Growing on These Tree Leaves? (Image)

Question

I found a seemingly diseased tree when I was out playing tennis yesterday... What is growing on this tree leaf? Is this a disease? If so, is it contagious? I have zero knowledge in botany, but I'm curious about what is happening to these trees. :) enter image description here

I'm just wondering if you still play tennis in that location to confirm if you see any Juniperous virginiana (eastern red cedar) nearby. — theforestecologist, Feb 27 '16 at 14:02

theforestecologist · Accepted Answer · 2023-05-08T14:13:01.393

24

This is actually not a gall as other answers have suggested. This is likely a fungus called Cedar-apple rust (Gymnosporangium juniperi-virginianae).

The fungus only thrives in the presence of both Juniperus virginiana (Eastern red cedar) and apple (Malus spp.) trees.

The leaf in the picture belongs to some species of the apple genus and the growths are aecia of G. juniperi-virginianae. You can read about this interesting fungi through Rutger's Plant & Pest Advisory here.

You can see a picture of the fungi here, and I've included Sabrina Tirpak's (Rutgers PDL) photo of its aecia below:

http://plant-pest-advisory.rutgers.edu/3859/

Below is a visual of the telia of the rust fungus on J. virginiana:

^{(Photo source: Ada Hayden Herbarium)}

edited May 08 '23 at 14:13

answered Jan 21 '16 at 06:22

theforestecologist

29,867
10
122
204

7

What a fascinating organism! – augurar Jan 21 '16 at 07:15
2

Right?! I've never seen the tentacled glob that grows on the Juniper – theforestecologist Jan 21 '16 at 14:12
1

That's so cool :) – Aleksandr Hovhannisyan Jan 22 '16 at 01:13

score 2 · Answer 2 · edited Jun 16 '20 at 11:19

2

Briefly, these look like insect galls; which are reactions of plant tissue caused by parasitic insects (often wasps) laying eggs inside the leaf. I'm sure someone can answer in more detail, though!

Cf. How do plant galls form?

edited Jun 16 '20 at 11:19

Community

1

answered Aug 26 '13 at 00:54

Oreotrephes

5,799
1
29
54

Would the tree die because of this? Most of its leaves are growing "insect galls"... – StephenChen Aug 26 '13 at 06:21
I imagine that it depends on the galling species and tree species, but most leaf galls don't hurt trees – Oreotrephes Aug 27 '13 at 02:49

What is Growing on These Tree Leaves? (Image)

2 Answers2

Linked