These spots weaken plants by interrupting photosynthesis.
There are many causes for leaf spot diseases, but most often, the cause is fungal.
Because many common fungal diseases are similar, they can usually be managed the same.
The Spruce / K. Dave
What Are Brown Spots on Leaves?
Brown spots on leaves are typically triggered by a variety of fungal diseases calledleaf spot diseases.
While these problems are usually termed “leaf spot diseases,” many conditions lead to brown leaf spots.
Venturia disease on leavesThe Spruce / K. Dave
This is common inlilacs.
These spots will eventually merge causing the entire leaf to turn dark black-brown.
What Causes Leaf Spot Diseases?
Anthracnose on leavesThe Spruce / K. Dave
Knowing the causes makes it much easier to develop a treatment plan.
Septoria
Septorialeaf spots are round, with black margins.
It will look like there is mold growing on the leaf.
The leaves will eventually shrivel and blacken, then fall to the ground where the spores will overwinter.
Venturia
With Venturia, brown and black spots form in early spring causing irregular leaves.
Infected shoots turn black and weaken.
The stems twist and turn and become contorted.
Only young shoots and leaves are susceptible.
As the spring and summer continue the tissue matures and becomes resistant.
Death of new growth reduces height and can deform small trees by causing bends in the stems.
Untreated infections of Venturia can weaken trees and make them susceptible to attacks by other organisms.
Rust fungispots appear on the leaves shortly after leaves bloom.
Late in the summer, brownish clusters of threads appear beneath the spots or on fruits and twigs.
The spores associated with the threads infect the leaves of deciduous trees and shrubs.
You will also find it in twigs and needles ofjunipersduring wet, warm weather.
Symptoms of anthracnose include small beige, brown, or black spots.
Dead areas on leaves can be more irregular on trees such asashandmaplewhilesycamoreandoakanthracnose spots will show along the leaf veins.
If the infection is mild, yes, remove any leaves that have brown spots.
You also should isolate the plant as quickly as possible to prevent the fungus from spreading.
No, not usually.
