Clusia (Autograph Tree) Problems: Root Rot, Cold Damage, Blackened Leaves, Scale and Spider Mites

Start from the symptom

Clusia rarely gets a serious disease. When it struggles, the cause is water, temperature or light, or a pest. Note where on the leaf the damage is, what color, and what season, and the cause narrows quickly. Because the leaves are thick, symptoms develop slowly and can be well advanced when you notice them, so a monthly look at the leaf undersides and the base of the plant is the best prevention there is.

Root rot from overwatering

The most common Clusia problem. Because the leaves store water, watering before the soil has dried adds up until the roots suffocate and rot. Triggers are a pot too large for the plant, a dense mix, water left in the saucer and heavy watering in winter. Lower leaves yellow and drop, the plant wobbles when touched at the base, and eventually the stem softens and darkens.

1. Stop watering and add air As soon as you notice, stop watering, take the pot out of its cachepot and off its saucer, and set it in bright shade with air moving. Give no water for one to two weeks while it dries.
2. In late spring or summer, cut roots and repot Unpot, trim black and mushy roots with clean pruners, and repot in fresh fast-draining mix in a pot one size smaller. Hold water after repotting until the mix dries.
3. In winter, keep it dry and wait for spring Roots will not recover from a winter repot. Stop watering, keep it above 50 F (10 C) in bright light and repot once new growth moves in spring.
4. Take cuttings as insurance If the base is damaged but the upper stems are still firm, take cuttings and root them in water. You keep the plant even if the parent fails.

Cold damage and blackened leaves

Clusia starts to suffer below 50 F (10 C) and drops blackened leaves at 41 F (5 C). A winter windowsill at night, an unheated entryway, cold tap water or a night with the heat off are the usual causes. Leaves on the window side blacken from the edges and hang limp the next morning. It is not a disease and no spray helps. Damaged leaves do not recover, but if the stems stay firm the plant will push new growth in spring.

1. Away from the glass at night After dark move it at least 3 ft (1 m) from the window or to the room side of the curtain. For a large pot that cannot move, stand cardboard between pot and glass to block the cold.
2. Remove blackened leaves Leaves with only a dark edge can stay. Cut leaves more than half black, or gone soft, at the base. If the stem itself is black and soft, cut back to firm tissue.
3. Room-temperature water at midday, less often Cold water chills the roots. Let it reach room temperature and water around midday on a mild day, and in winter wait two to three days after the soil dries.
4. If the lowest leaves blacken, suspect rot too Cold damage starts on the window side and outer leaves; root rot starts at the bottom. If the soil is wet and the lowest leaves are blackening, cold and overwatering are combining, so stop watering as well.

Scale insects

Small white or brown shell-like bumps stuck to the undersides, stems and leaf bases that do not move are scale. They build up in still indoor air on plants that are never misted. Fed-on leaves lose color, honeydew makes the foliage sticky and black sooty mold can follow. Adults are protected by their shells and shrug off most sprays, so removing them by hand is the foundation.

1. Scrub them off with an old toothbrush Use an old toothbrush or a cotton swab to lift each one off without tearing the leaf. They hide at leaf bases and stem nodes, so go over the whole plant.
2. Cut out heavily infested stems Remove stems that are crusted with scale and bag them for the trash. Wipe the sap from the cut with gloved hands.
3. Spray when crawlers are active In late spring and early summer the unshelled young are on the move and a houseplant insecticide or horticultural oil works. Coat the undersides and recheck in two weeks.
4. Mist and ventilate to prevent Mist the undersides once or twice a week and thin crowded stems in spring so air moves. Inspect the undersides of any new plant, or any plant coming in from outdoors, before it joins the others.

Spider mites

Fine pale stippling scattered across the upper leaf surface that spreads until the whole leaf fades. Tiny red or yellow mites, about the size of a period, move about on the undersides, and in a heavy infestation fine webbing appears. They love dry air, so a window in the path of a heating vent or air conditioner, and plants that are never misted, suffer most. They are weak against water, and a hard rinse in the shower is the best first treatment.

1. Rinse the undersides in the shower Carry the plant to the shower and hose the undersides hard. Repeat about three times a few days apart to catch mites that hatch after the first rinse.
2. Miticide if it persists Apply a houseplant miticide or insecticidal soap to the undersides. Mites build resistance fast, so alternate two different products rather than repeating one.
3. Mist as routine prevention Mist the undersides once or twice a week, keep the plant out of direct vent airflow, and wipe both leaf surfaces with a damp cloth once a month.

Leaf scorch and other disorders

Hot summer sun through glass bleaches the upper surface of window-facing leaves or leaves brown, scabby spots. Clean undersides and damage only on the sun side distinguish it from pests. Other things that look like trouble: new leaves shrinking without any leaf drop (root bound), roots burned by winter feeding (fertilizer burn), and the white marks left wherever the leaf was scratched, which are the plant's famous autograph trait and not a disease.

Cut stems bleed a sticky yellow sap that is hard to wash off and irritates sensitive skin. Wear gloves for pruning and repotting, and keep the plant where small children and pets will not chew it, since the sap is toxic if swallowed.