Common Tree Diseases in Florida’s Rainy Season: How to Spot and Treat Them
The tree diseases most likely to show up during Florida’s rainy season are anthracnose (dark blotches and spots on leaves), sooty mold (a black film coating leaves and branches), root rot (trees wilting even though the soil is soaked), and ganoderma butt rot (a hard, shelf-like conk at the base of the trunk). The good news for Sarasota homeowners: the first two are mostly cosmetic and manageable with sanitation and smarter watering. The second two are serious – root rot can kill a tree from below, and ganoderma has no cure at all. The skill worth having in August is telling the ugly-but-harmless problems apart from the dangerous ones, and this guide walks you through exactly that.
Why the Rainy Season Sets Off Tree Disease
Sarasota gets roughly 60 percent of its annual rainfall between June and September, and fungi could not ask for better working conditions: leaves that stay wet for hours after each afternoon storm, humid nights, and soil that never quite dries out. Fungal spores that sat dormant all spring germinate on wet leaf surfaces, splash from the ground onto low branches, and move into any wound – which is one reason pros avoid heavy pruning cuts on disease-prone species in the wettest weeks. Trees stressed by compacted soil, poor drainage, or trunk damage get hit first and hardest.
The Big Four: Symptoms at a Glance
| Disease | What You’ll See | How Serious |
|---|---|---|
| Anthracnose | Brown or black blotches on leaves, early leaf drop | Low – mostly cosmetic on established trees |
| Sooty mold | Black, soot-like film on leaves and branches | Low – the real issue is the insects behind it |
| Root rot | Wilting and thinning canopy despite wet soil, dieback | High – can kill the tree if drainage isn’t fixed |
| Ganoderma butt rot | Hard shelf-like conk at the trunk base, slow decline | Severe – no cure; tree becomes a falling hazard |
Anthracnose
Anthracnose is a group of fungal leaf diseases that flare in wet weather, leaving irregular dark blotches, often along the leaf veins, followed by early leaf drop. It looks alarming, but on an established tree it rarely does lasting harm – the tree simply regrows leaves when conditions dry out. Rake and dispose of fallen leaves so spores don’t recycle back into the canopy.
Sooty Mold
That black film wiping off the leaves isn’t attacking the tree at all – it’s a fungus growing on honeydew, the sticky residue left by aphids, scale, and whiteflies feeding above. Treat the insects and the mold starves. If your car or patio under a tree keeps getting sticky, that’s the same honeydew, and the tree above deserves an inspection.
Root Rot
Root rot fungi like Phytophthora thrive in waterlogged soil, and the symptom pattern is the giveaway: the tree wilts, yellows, or thins at the crown even though the ground is wet. Roots drowning in saturated soil can’t absorb water, so the tree dies of thirst in a swamp. Fixing drainage – regrading, redirecting downspouts, easing irrigation – matters more than any spray once rot takes hold.
Ganoderma Butt Rot
Ganoderma attacks the lower trunk of palms and hardwoods alike, hollowing out the wood’s structure while the canopy declines slowly above. The tell is the conk: a hard, shelf-like bracket at the base, white-edged when fresh and rusty brown as it matures. There is no treatment. Once a conk appears, the conversation shifts to safe removal timing, because an infected trunk can fail without warning in a storm. UF/IFAS Extension has excellent photos and identification guidance at EDIS if you want to compare against your tree.
What You Can Do Right Now
- Rake and bag fallen diseased leaves rather than mulching them back under the tree
- Water at the ground, not overhead, and only when rain has genuinely skipped town
- Fix ponding and drainage problems before they become root rot
- Avoid wounding trunks and roots with mowers and trimmers – wounds are open doors in humid weather
- Have crowded canopies thinned so air moves through and leaves dry faster after storms – that airflow is one of the quiet benefits of professional tree trimming
When an Arborist Visit Is Warranted
Call in a pro when the problem goes beyond spotted leaves: a thinning crown that worsens over weeks, dieback starting at branch tips, mushrooms or conks at the base of the trunk, oozing or sunken bark, or any leaning that’s new. We covered the general diagnostic process in our post on tree leaves turning yellow in Sarasota, and explained what the credential actually means in our guide to hiring an ISA Certified Arborist in Sarasota. If an inspection does find ganoderma or advanced rot, planned tree removal on your schedule beats emergency removal on the storm’s schedule every single time. Not sure what you’re looking at? Snap a photo and call us at (941) 451-9730 – we’re happy to tell you over the phone whether it’s worth a visit.
Frequently Asked Questions
What does anthracnose look like on trees?
Look for irregular brown or black blotches on leaves, often following the veins, sometimes with curling or distortion, followed by leaves dropping earlier than normal. It flares during wet, humid stretches like Florida’s rainy season. On established trees it’s mostly cosmetic – rake up fallen leaves to reduce reinfection and the tree typically recovers on its own.
Is sooty mold harmful to trees?
Not directly. Sooty mold grows on honeydew secreted by sap-feeding insects like aphids, scale, and whiteflies – it doesn’t infect the tree. Heavy coatings can block some sunlight, but the real fix is controlling the insects producing the honeydew. Once they’re handled, rain gradually washes the black film away and it doesn’t return.
Can a tree recover from root rot?
Sometimes, if it’s caught early and the underlying water problem is fixed. Improving drainage, redirecting downspouts, and cutting back irrigation give surviving roots a chance to regrow. A tree with major crown dieback or extensive root decay usually can’t be saved, and because rotted roots anchor poorly, it should be evaluated as a fall risk.
Can ganoderma be treated?
No. There is no fungicide or cultural fix for ganoderma butt rot – once conks appear at the trunk base, internal decay is already established and the tree will continue to decline. The priority becomes safety: an infected tree can fail suddenly in wind. Have it assessed promptly and plan removal before storm season forces the issue.
Rainy season disease in Sarasota mostly sorts into two buckets: cosmetic problems that dry weather and a rake will solve, and structural ones – root rot and ganoderma – that deserve a professional look before the next big storm. Check your trunks, watch your drainage, and when in doubt, call Josiah and Scott at (941) 451-9730 for an honest opinion.
