Diseases of Stems and Roots

Stems and roots are just as vulnerable to diseases as leaves and flowers. Indeed, because they are often wholly or partly hidden by compost, it is possible for diseases to become established before their presence is even noticed.

To prevent diseases:

  • Don’t keep the compost saturated with water, especially during winter when plants are unable to absorb moisture rapidly.
  • Don’t use unsterilized compost — it may harbour disease spores.
  • Don’t leave plants which are infected by diseases among healthy ones — isolate and treat them separately.
  • Don’t buy infected plants — check all plants thoroughly before putting them among healthy ones. It is a good idea to isolate all new plants until you are satisfied that they are clean and healthy.
  • Don’t crowd plants together — circulation of air around them helps to prevent many diseases.
  • Don’t leave old flowers and leaves which have fallen off plants, lying on the compost. Remove them immediately and destroy, especially if signs of diseases are present in any form.
  • Don’t buy plants from nurseries or garden centres which are dirty or create a feeling of not caring for the plants.
  • Don’t mist spray plants in winter, especially if the temperature is low. Some plants — such as the
  • Screw Pine (Pandanus) — have stems which trap water at their junctions with leaves. This subsequently causes rotting and the presence of diseases. Always mist spray plants in the morning, so that moisture has evaporated by night, when the temperature tends to fall.

Diseases of StemsDiseases of Stems and Roots

Black leg is a disease of cuttings, especially those of pelargoniums. While developing roots, the bases of infected cuttings turn black and become slightly shrunken. Young plants which have been planted in the garden may also collapse if put into contaminated soil.

Prevention and cure

  • Don’t put cuttings into cold, wet compost.
  • Don’t keep the compost excessively moist— it is better to keep pelargonium cuttings barely moist.
  • Avoid compacting the compost, as this prevents excess water escaping from the compost.
  • Don’t cover cuttings with glass or polythene, as this raises the humidity and encourages the presence of the disease in the plant.
  • Keep the conservatory or greenhouse clean.
  • Only use sterilized compost at all times.
  • Destroy infected cuttings, although if those of valuable plants show signs of disease the black part can be cut off with a sharp knife and the cuttings reinserted in clean compost.
  • Use only clean water when watering the cuttings. If water is being taken from a water-butt or tank, add potassium permanganate crystals until the water turns pink.

Damping Off

Damping off is a disease of seedlings, when a fungus attack causes them to collapse at compost level and die. The young stems shrink and turn black, and the seedlings fall over.

Prevention and cure

  • Sow seeds thinly to allow a better circulation of air around.
  • Don’t keep the compost too wet, and ensure that excess water can drain away.
  • Don’t keep the seedlings in a stuffy, enclosed environment.
  • High temperatures encourage the disease.
  • Destroy infected seedlings and compost.
  • If attacks are noticed early, remove infected seedlings and water the compost with Cheshunt Compound or Captan.

Crown and stem rot causes the stems just above compost level to decay and collapse. Young plants, and especially those with a crown of soft leaves, are most susceptible. Once infected the plants ore soon killed off.

Control and prevention

  • Destroy all infected plants and throw away the compost.
  • Compost that is continually water-saturated encourages the disease.
  • Maintain a circulation of air around the plant, but avoid a cool, draughty position.
  • During early stages of the disease, plants can be saved by cutting away infected plants and spraying with Bordeaux Mixture or Captan.

Diseases of Roots

Root rot, also known as tuber rot, is a serious disease of cacti, succulents, saintpaulias, palms and begonias. It initially causes wilting, as well as discolouration and yellowing of the leaves, and later causes collapse of the plant.

Prevention and cure

  • Badly grown and uncared-for plants are most likely to be attacked.
  • Waterlogged and compacted compost encourages the disease, although very dry compost can also cause wilting.
  • Destroy badly infected plants, together with the compost. Usually, once the symptoms are noticed the plant is past being saved.

If symptoms are noticed early and the plant is valuable, remove the plant from the compost, cut away diseased roots and remove as much compost as possible. Then, pot up into fresh compost, cut away some of the top growth so that the plant’s demand for water is reduced, place it in a slightly shaded position and water the compost with Benlate.

Brown core is troublesome on primulas, and especially on the common Primrose. Roots tend to rot back from their tips, so that eventually only a few stubby roots are left. The centres of the roots become brown. Infected plants wilt and can be easily pulled from the soil. It is mainly a disease of plants growing outdoors, but can also be a problem to plants in containers on patios if infected compost has been used.

Prevention and cure

  • Remove and destroy infected plants.
  • In beds outdoors, do not grow plants on the some site for several years. In containers, either remove and discard all compost—at the same time thoroughly scrubbing and disinfecting the container — or do not grow primulas there for several years to be safe.

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