Gadenin日本語Get the appCrown rot: the one that actually kills the plant
Crown rot starts where the leaf stalks meet the short thick stem at soil level. The cause is water sitting there: overhead watering, a crown buried by settling mix, dead petals or leaves lodged in the center, or a pot standing in a full saucer. Cool wet weather and still air make it far more likely. Once the center of the crown has gone soft and brown the plant cannot be saved, so the whole game is noticing it before that.
The early signs are easy to miss because they look like drought. Outer leaves go limp and stay limp after watering. A leaf stalk browns and softens right at its base rather than yellowing gradually from the tip. Flower stems collapse partway up while the bloom is still fresh. If you see any of those, look straight into the center of the plant. A dark, water-soaked ring around the crown, or a smell when you disturb it, confirms it.
Acting early can still work. Clear every scrap of mix, dead leaf and spent petal away from the crown so it stands clearly above the surface. Pull off all affected leaves and stems with a sideways tug, taking them out at the base rather than cutting and leaving stubs. Stop watering until the top two inches (5 cm) are dry, then resume watering only at the rim. If the mix is dense and holding water, repot into something coarser, setting the crown proud. Prevention is the whole answer here: crown above the soil, water at the edge, saucer emptied, center kept clear.
If a plant collapses, pull it out and look at the roots and crown before writing it off as a mystery. Soft brown crown with reasonable roots means rot from the top; blackened mushy roots with a firm crown means the mix stayed sodden. Those are different mistakes and they need different fixes.
Powdery mildew on the leaves
Powdery mildew shows as dusty white patches on the upper surface of older leaves, spreading into a felt that covers whole leaves and moves onto flower stems and buds. Gerberas are prone to it because a dense rosette of overlapping hairy leaves holds humid still air near the soil, which is exactly the condition the fungus wants. Unlike most fungal problems it does not need the leaves to be wet; warm days, cool nights and poor air movement are enough.
Deal with it by changing the conditions first. Take off the worst affected outer leaves entirely, pulling them out at the base, which both removes spores and opens the center of the plant to air. Space pots so leaves do not touch. Move plants out of a sheltered corner into somewhere with a breeze. Water in the morning and at soil level so nothing is damp overnight.
If it keeps spreading after that, treat with a sulfur or potassium bicarbonate spray, or a proprietary fungicide labeled for ornamentals, following the interval on the label. Spray the undersides as well as the tops, and do not spray in strong sun or above 85F (29C), which burns the leaves. Treatment without also fixing the air movement buys a few weeks and no more.
White patches that rub off between your fingers and leave green leaf underneath are mildew. White stippling that does not rub off, on a leaf that also looks dull and dry, is mite damage, and the treatment is different.
| Symptom | Cause | First action |
|---|---|---|
| White dusty film on upper leaf surfaces | Powdery mildew | Remove affected leaves; improve air movement; spray if it spreads |
| Fine pale stippling, dull leaves, webbing at leaf joints | Spider mites | Rinse undersides; raise humidity; treat every five days for three rounds |
| Center of plant dark and soft, leaves limp after watering | Crown rot | Expose the crown, remove affected tissue, stop overhead watering |
| Sticky leaves, distorted new growth, clusters on flower stems | Aphids | Wash off with water, then insecticidal soap on stems and bud bases |
| Flowers streaked and flecked, petals deformed | Thrips | Remove affected blooms; treat repeatedly; check for tiny slivers in the petals |
| Fuzzy gray mold on spent petals, spreading into stems | Gray mold after wet weather | Strip every faded bloom; keep the crown clear and dry |
| Small white flies rising when disturbed | Whitefly | Yellow sticky traps plus soap sprays to undersides, weekly |
Spider mites, especially indoors
Spider mites are the standard indoor gerbera pest and appear in warm dry air, particularly near a heat source through winter. The first sign is loss of color rather than any visible insect: the leaves go dull, then develop fine pale speckling as thousands of feeding punctures accumulate, then bronze and dry from the edges. Fine webbing between the leaf stalks and across the crown means the population is already large.
Check the undersides of the older leaves with a hand lens at the first hint of dullness. The mites are barely visible dots that move. Because a generation completes in about a week in warm conditions, a population that looks trivial doubles repeatedly while you decide what to do.
Treat by rinsing the undersides of every leaf thoroughly with water, holding the pot on its side so the water does not pour into the crown. Follow with insecticidal soap or a horticultural oil applied to the leaf undersides, and repeat every five days for at least three applications to catch mites hatching from eggs the spray does not kill. A single treatment always fails. Raising the humidity around the plant and moving it away from radiators or heating vents makes recurrence much less likely.
- Isolate the plant Move it away from other houseplants the day you find mites. They spread on contact between touching leaves and on your hands.
- Rinse the leaf undersides Tip the pot on its side and rinse with a firm spray of tepid water so nothing runs into the crown. This alone removes most of the population.
- Treat on a five day cycle Insecticidal soap or horticultural oil to leaf undersides, three or four times at five day intervals. Skipping the repeats guarantees the mites come back.
- Change the conditions Away from heat sources, more humidity, more air movement. Mites keep returning to a plant kept warm and dry in still air.
Aphids, whitefly and thrips
Aphids cluster on flower stems and around developing buds, where they distort the bloom and leave sticky honeydew that sooty mold then colonises. They are easy to deal with if caught early: wash them off with a jet of water aimed at the stems rather than into the crown, then follow with insecticidal soap on the stems and bud bases. Repeat weekly for three weeks because eggs and stragglers survive the first pass.
Whitefly are a greenhouse and indoor problem, rising in a cloud when the plant is disturbed and feeding on leaf undersides. Yellow sticky traps hung at leaf height show you the population trend and catch adults; soap sprays to the undersides deal with the nymphs. Both need repeating weekly to break the life cycle.
Thrips damage the flowers rather than the leaves. Petals come out streaked, flecked with pale marks or deformed on one side, and if you split a suspect bloom you can sometimes see the slender insects moving inside. Remove affected flowers entirely by pulling the stems out at the base and dispose of them away from the plant. Thrips are difficult to eliminate on an ornamental, and removing damaged blooms promptly matters as much as spraying.
What to write down
Note the date you first see each problem and where the plant was standing. Mildew and crown rot are both position problems as much as plant problems, and a pot that got mildew in a sheltered corner in one season will get it again in the same corner. Recording which positions stayed clean is worth more than any spray schedule.
For pests, record the date of each treatment as well as the date you first noticed the trouble. The commonest reason a spider mite treatment fails is that only one or two applications actually happened, and without a written date nobody remembers which. Three treatments at five day intervals looks obvious on paper and is easy to lose track of otherwise.
Note plants you gave up on and why. A gerbera lost to crown rot in a heavy mix tells you to change the mix rather than the plant.