1. Rule out the site first
Reaching for a spray before checking conditions wastes money and frequently makes things worse.
Is the soil waterlogged? Dig a small hole beside the root ball. Soggy soil hours after watering means roots are suffocating. This produces yellowing, wilting and decline that looks like disease.
Is there enough light? A sun-loving species under canopy thins and stretches. No treatment substitutes for light.
Was it planted too deep? A buried root flare stays wet and rots slowly. Look at where the stem meets the soil — you should see it flare.
Is it chlorosis rather than disease? Yellow new leaves with green veins is iron lockout in alkaline soil, not an infection. See yellow leaves.
Work through those four before considering anything else. They account for the large majority of what we are shown.
2. Scale insects
What you see: small immobile bumps on stems and the undersides of leaves — brown, white or grey depending on species. They do not look like insects, which is why they are often missed. Sticky residue on leaves below, and sometimes black sooty mould growing on that residue.
Why it matters: scale feeds on sap. Light infestations are cosmetic; heavy ones weaken a plant progressively.
Response: horticultural oil smothers them, which is why it works where contact insecticides often do not — the shell protects them. Thorough coverage including leaf undersides matters more than product choice. Repeat treatments are usually needed. Prune out heavily infested material.
3. Whitefly
What you see: tiny white insects that lift in a cloud when you disturb the foliage. Sticky honeydew on leaves and surfaces beneath, often with sooty mould.
Why it matters locally: whitefly has caused significant defoliation across South Florida, particularly on ficus. It is one of the strongest practical arguments against planting ficus hedging.
Response: encourage natural predators by avoiding broad-spectrum insecticides, which kill the beneficial insects that would otherwise control it. Horticultural oil and insecticidal soap help. Heavily affected ficus hedging is a recurring cost — worth factoring in before planting it.
4. Mealybug and mites
Mealybug: white cottony masses in leaf joints and stem crevices. Sticky residue similar to scale. Horticultural oil or insecticidal soap, applied thoroughly and repeated.
Spider mites: fine stippling or speckling on leaves, sometimes with very fine webbing on the undersides. They thrive in hot dry conditions, so they are more common through the dry season and on plants under water stress. Increasing humidity and correcting water stress often resolves it without treatment.
5. Fungal problems
Miami humidity makes fungal issues routine rather than exceptional.
Leaf spot: dark or discoloured patches, often with a defined margin. Usually cosmetic. Improve airflow, avoid overhead evening watering, remove badly affected leaves.
Sooty mould: black coating on leaf surfaces. Not a disease of the plant — it grows on honeydew excreted by scale, whitefly or mealybug. Treat the insect and the mould clears.
Root rot: the serious one. Wilting that does not recover overnight, yellowing, soggy soil, sometimes a sour smell. Frequently fatal once advanced. Prevention through drainage is the only reliable answer — see soil preparation.
6. A note on restraint
Broad-spectrum insecticides kill the predators that keep pest populations in check, which frequently produces a worse problem a few weeks later.
Systemic products are worse still in one specific respect: the plant carries the compound in its tissues, including nectar and pollen. On a flowering plant that actively harms pollinators.
Start with the least aggressive option that addresses the problem — correct the conditions, remove affected material, use horticultural oil or soap. Escalate only if that genuinely fails.
Send a close photograph of the affected leaves and stems. Most Miami plant problems are identifiable from a good picture. Send it over.