Crab apple.

Thanks, do you know what issues the tree might have?

Sorry - I can't help you with that. I'm in a different country and crabs are pretty trouble free in our climate. And I don't know what conditions or diseases you have where you are.

It looks likely that you have at least two maladies going on. The dark blotches on the yellow leaf (picture 4) look like apple scab. Right across from that one a couple of other leaves have yellow lesions with darker centers, which looks like cedar-apple rust. You might google and compare.

Will any fungicide work at this stage?

Not at this stage of the season.....the damage has already been done. FWIW, neither one of these issues is particularly serious although if scab infestations are severe enough they can lead to partial defoliation and that can weaken the tree if it happens consistently year after year.

Pretty late this season for chemical control. Chlorothalonil (one of several effective fungicides) can be used on both, but for rust it is applied when the orange gelatinous galls are present on cedars (which was much earlier) and for scab it is applied with 3 or 4 sprays at 7-10 day intervals beginning at blossom, also much earlier. As mentioned other products are effective but require annual treatment. As Embothrium states, replacement is a better option than soaking the environment with products when avoidable.

Is it best thing to do now is leave as is and do preventive treatment next early spring?

Will it better with some spray to prevent the disease affect other plants?

Thanks a lot for the help!

I also got some reply from my local Plant Clinic and confirmed with some prior poster's answers. Just to share here.

"Thank you for using the Morton Arboretum Plant Clinic.

This is a crabapple tree. There are many cultivars so we can not tell you which one. It has a disease called apple scab. This leaf fungal disease occurs when new leaves are emerging and we have wet, cool temperatures (that past two years have been like that). The new leaves are vulnerable to infection.

There are preventative sprays that can be applied 3x, 10 days apart, but it is too late this year. If you cannot spray contact an arborist.

Do a good clean up of fallen leaves this year and discard in the trash. Fertilize the tree with a balanced tree fertilizer and water well in dry periods.

Spray next year"

Thanks for the update. I would see how things go next year and if it becomes a perennial thing consider treatment vs replacement.

One minor difference of opinion between Morton Arboretum and myself: Fungal leaf infections, like this apple scab, can be managed without this tedious and otherwise environmentally unsound insistence on removing and placing in the trash all fallen leaves. Very simply, using a mulching mower in the fall, so long as leaf pieces are cut up small, they will easily decompose and the fungus right along with it. The same is true of oak leaves which had so-called anthracnose-chop them up rather than removing from site. Finally, I laughed and laughed at one local expert who recommended all maple leaves be collected and placed in the trash..........for tar spot! Such madness......where does it come from? The insanity of thinking that "all maple leaves" could ever even remotely be collected in a region like this is hilarious.....if not for the sad fact that somebody somewhere will try to apply this "advice".