It happens fast. A sycamore leafs out fine in March, April turns cool and wet, and within two weeks half the new leaves are brown along the veins and falling. Homeowners call it dying. It almost never is. It is anthracnose, the regular spring blight of sycamores in North Texas, and the tree has been through it before.
Anthracnose is not one fungus. It is a group of related fungi that attack leaves, shoots, and twigs during cool, wet weather. The sycamore version, Apiognomonia veneta, is the showiest. Oaks, ash, maple, and walnut each have their own, usually milder. What they share is the trigger: rain and temperatures in the 50s and 60s while new leaves are expanding.
What it looks like, tree by tree
On sycamore, the signature is browning that follows the veins. Young leaves develop brown to black areas along the midrib and side veins, the tissue between veins stays green a while, then whole leaves wither. Infected shoot tips die back a few inches. Some years the first flush is nearly wiped out and the yard fills with fallen leaves in April. Planes and London planes get the same disease. It is the main reason our sycamore care guide tells people to expect a messy spring.
On oaks the damage is quieter. Look low and inside the canopy after a wet spring: brown blotches along the veins and midrib, some curled leaves, light leaf drop. Post oaks and white oaks show it more than red oaks. Ash anthracnose drops green leaflets in late spring and alarms people more than it harms the tree.
Why wet springs decide everything
The fungus overwinters in infected twigs and fallen leaves. Spring rain splashes spores onto new growth, and cool temperatures slow the leaf while speeding the fungus. A warm, dry April in Collin County can mean almost no disease. A rainy one, with nights in the 50s, can defoliate a sycamore in weeks. Same tree, same fungus, different weather.
That weather link is the best diagnostic clue you have. Leaf browning that starts during or right after a cool wet stretch in spring, heaviest on the lower and inner canopy where leaves stay wet longest, points to anthracnose. Our diagnosis guide starts every spring call with the weather for exactly this reason.
Not the diseases people fear
Anthracnose gets confused with worse things. It is not oak wilt: oak wilt on red oaks browns leaf margins in late spring and summer and kills in weeks, while anthracnose follows the veins and the tree releafs. It is not bacterial leaf scorch either. Scorch is a late-summer margin problem that returns worse yearly. Anthracnose is a spring vein problem the tree usually outgrows by June.
Repeated defoliation is the honest caveat. One bad spring costs a healthy tree some stored energy. Three or four in a row, stacked on August drought, can weaken a tree enough that borers and canker fungi move in. The blight opens the door. It is rarely the thing that walks through it.
The cleanup that actually helps
Rake and remove fallen leaves under sycamores and oaks in spring and again in fall. The fungus winters in that litter, and hauling it off cuts next spring's spore supply. Bag it or send it out with yard waste. Do not compost it in a home pile; home piles do not get hot enough to kill it.
Fix the wet-foliage problem where you can. Lawn sprinklers that soak the lower canopy every morning keep leaves wet for hours and feed this disease. Aim irrigation at the ground, water early enough that foliage dries, or accept shorter run times near the tree. Pruning for airflow helps too: light thinning so the canopy dries faster after rain, done on the normal trimming cycle, not a panic cut in May.
Water the roots in a dry spring spell even if leaves look bad, and keep the mulch ring flat and wide. A tree pushing a second flush of leaves in May is spending energy; steady soil moisture is the support it can actually use. Skip fertilizer pushes meant to green it up. New soft growth in a wet spring is fresh target tissue.
What about spraying
Fungicides for anthracnose are protectants, not cures. They shield new leaves if they are on the leaf before wet weather arrives, and they do nothing for leaves already infected. Timing that across a mature sycamore canopy, repeatedly through spring, is professional equipment work with a modest payoff for a disease the tree survives anyway. For most yard trees the money is better spent on cleanup and water.
The exceptions are small, high-value, newly planted trees, where a crew can actually cover the canopy and a young tree has less reserve to spend on releafing. If a young sycamore defoliates completely two springs running and is barely pushing the second flush, that conversation is worth having, and it may be time to ask if a sycamore belongs in a low, wet spot at all.
When to worry, and when to watch
Watch, and clean up, when a tree defoliates in spring and pushes a full second set of leaves by early summer. That is the normal script, even when April looks terrible.
Worry when there is no second flush, when twig dieback reaches into limbs an inch or more thick year after year, or when the canopy thins at the top and stays thin. At that point anthracnose is usually not the whole story, and a stressed sycamore near a house becomes a removal question only after the other suspects, root problems, scorch, and plain drought, have been checked. Most springs, though, the right move is a rake, a sprinkler adjustment, and patience.
Common Questions
Will anthracnose kill my sycamore?
Almost never by itself. A healthy, established sycamore releafs after a bad spring and grows on. The risk is repetition plus stress: several hard springs in a row on a young, newly planted, or drought-stressed tree can thin it badly. Established yard trees in Collin County ride it out most years.
Should I spray my tree for anthracnose?
For a yard tree, usually no. Fungicide only works as a protectant sprayed before wet weather on new growth, and covering a forty-foot sycamore canopy completely is not realistic homeowner work. Cleanup, airflow, and dry foliage do more for less money. High-value small trees are the exception worth discussing.
How do I tell anthracnose from bacterial leaf scorch?
Timing and pattern. Anthracnose hits in cool, wet spring weather, browns tissue along the leaf veins, kills some shoot tips, and drops leaves in April and May. Bacterial leaf scorch shows up in late summer, browns the leaf margins with a yellow band, and returns worse on the same branches year after year. Spring and veins: anthracnose. Late summer and margins: scorch.
My oak dropped spotted leaves in May. Is that anthracnose?
It can be. Oaks get their own anthracnose, usually milder than the sycamore version: brown blotches along the midrib and veins on lower, shaded leaves after wet springs. Most oaks leaf back out fine. Heavy leaf drop two springs running, or dieback moving into bigger limbs, is worth a closer look for other problems.