Plant problems

Plant problems, A to Z

The pests and diseases most likely to reach a houseplant, a vegetable bed or a rose, each with the signs, the lookalikes, the plants it favours, a treatment plan and how to keep it away. Sourced from university extension services and the RHS.

These guides follow one shape so you can compare problems side by side: what it is in a sentence, the signs in the order you notice them, the problem it gets mistaken for and the single detail that tells them apart, then treatment from the gentlest step upward. Chemical controls are named only by type. The product label and your local extension service decide the rest.

Pests

Insects and mites that feed on sap or leaf tissue. Most announce themselves with honeydew, webbing, holes or distorted new growth before you see the animal.

Fungal diseases

Spots, powders, molds and rots. Fungi spread on wet leaves and in still air, so airflow and watering habits matter as much as any spray.

Water molds

Fungus-like organisms that need free water to spread. Downy mildew and the root-rotting Phytophthora and Pythium belong here.

Downy mildew Downy mildew is caused by oomycetes, water molds rather than true fungi.

Stress and viruses

Not every curl or yellow leaf is an infection. Some are the plant reacting to heat, drought or pruning, and some are viruses carried in by insects.

Tomato leaf curl Tomato leaves curl for two very different reasons, and which leaves curl tells you which one.

The app's own library covers thirty threats, including bacterial blight, canker, clubroot, damping off, leaf scorch, mosaic virus, nematodes, scale insects, slugs, sooty mold and verticillium wilt. Guides for those follow as they pass review.