Help with fungus on quince

Asked May 5, 2018, 5:55 PM EDT

I believe I have a Japanese quince bush. 2 years ago we got a bunch of fruit off of it, which was out first summer with the bush. Last year and again this year, it shows signs of a fungal infection (see pictures). We planted some arbor vitae and peach trees nearby (arbor vitae about 100 feet upwind and peaches about 25 feet downwind). Last fall and winter, and again this spring, I sprayed the quince bush with chlorothalonil as what I observed last year looked like cedar-hawthorn rust. I also have to prune it back several feet twice a year. I think it might need thinning in the center? It is very large and dense. Any guidance for this bush would be appreciated. I see evidence of rust again this year and even some leaf curl, which I did not think could jump from my peaches to the quince.

Prince George's County Maryland

1 Response

The organism that causes peach leaf curl is not related to this plant at all. It is affected by a different organism. It is possible that there could be aphids. Check under the leaves for these soft-bodied insects.
Arborvitae shouldn't be a problem either.
We agree that you have a rust disease, Cedar-quince rust. This disease needs two hosts to reproduce. Our native Eastern Red Cedar (Juniperus virginiana) is one of them, and unfortunately, they don't have to be nearby to complete the cycle. Even if you cleared your property of them, you could be infected by ones miles away.
We don't usually recommend spraying fungicides for them. You would have to start as the leaves unfurl, and then repeat every two weeks through June. It's just not worth it. The rust disease does not kill the plants.

Without knowing the named cultivar we can't say for sure, but these shrubs grow like crazy and would like to be ten feet tall and almost as wide.
If you need to use both those pathways on either side, it is a tough situation.
These plants are primarily grown for their flowers, and to get the full effect, you should only prune just after they bloom. Under those circumstances, the whole bush would be covered with those flowers. You might want to see what that looks like next year.
If you can move it to the open area on the other side that would be ideal.
Otherwise, it will always want to eat your mailbox and path, and pruning it will be at the expense of flowers (and fruit, but they usually don't produce that many).