I am curious if you have noticed any stickiness? Shiny spots?, Maybe they look like black splashes as sooty mold starts to grow in the honey dew. I think your tree has scale insects.. The evidence that its an insect is that I can see several life stages in the photo. Scale can be controlled with an application of ultra fine horticultural oil.

Curry Leaf Tree Pests

One of the other clues this is not a leaf spot disease, the spots would not all be the same size, the closer spots would be growing together as they expanded and there would be evidence of a border or margin around the spots showing some necrosis of leaf tissue .

Live with the disease
Leaf spots are largely an aesthetic problem as few leaf spots seriously damage the host. Also control is seldom achieved after the infection has started.

Remove infected leaves and dead twigs
Raking up and disposing of infected leaves as they drop and pruning out dead twigs can help control the disease by removing spores that can reinfect the new leaves. This will not cure the problem but it can help minimize infections.

Keep foliage dry
Avoid overhead watering. Use soaker hoses or water early in the day so the foliage can dry before night. Watering can also spread the disease by splashing. Prune plants and space plants to allow for good air circulation that promotes rapid drying of foliage.

Keep plants healthy
Since most plants can tolerate some defoliation, keep them in good health so they can rebound quickly. Avoid over fertilization as it promotes a flush of young leaves that are more susceptible to attack by insects and disease.

Use fungicides wisely
In rare cases of severe infection where the size and value of plants make it practical, applications of fungicides may be helpful. Generally fungicidal control is warranted if:
Repeated defoliations occur in one year or subsequent years
The plant is under stress
The plant is in decline
The plant is a needled evergreen
The disease is black spot of roses.
Sprays will not cure the infection but protect leaves from becoming infected. To be effective fungicidal sprays must be begun at bud break before symptoms are noted and be continued at intervals specified by the label (usually 10 to 14 days) through the period of spring rains. Spraying after infection is present will provide little benefit. Recommendations will vary with the disease and fungicide used. It is always good practice to have the disease identified before purchasing a control product. See table 1 for a general listing of active ingredients listed for control of various leaf spotting fungi.

Sostituire la pianta.

Per le piante che sono cronicamente afflitte da macchie fogliari, i giardinieri trovano più conveniente sostituire una pianta con una specie diversa o una varietà più resistente o tollerante alla malattia. Un vivaio può aiutarvi nella scelta.

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