Leek rust is a disease caused by the fungus Puccinia porri (syn. P. allii). It is important on leeks and garlic but also affects onions, chives and other Allium spp. The rust pathogen is comprised of

Genes are small sections of DNA that code for particular traits. During sexual reproduction, genes of both parents are mixed to create a genetically different offspring. Plants grown from seed may not be 'true to type' and look like their parents, but genetic variation can be beneficial, creating new, interesting characteristics and sometimes improving resilience to environmental conditions or disease. On the other hand, plants grown from cuttings are genetically identical to their parents.

You may see the following symptoms:

• On leaves: Bright orange pustules on both sides of infected leaves. These are initially enclosed by the surface tissues of the leaf, but break open to release dusty, orange, airborne spores
• Severe attacks may cause leaves to shrivel prematurely and will reduce vigour

Non-chemical control

• Infection is worse on nitrogen-rich soils with low potassium, so take care with fertiliser applications
• Do not crowd plants, as this raises
  The concentration of water vapour in the atmosphere. This affects the rate at which plants transpire (lose water from their leaf pores), which in turn affects how much water their roots absorb from the soil. If air humidity is low, plants transpire quickly and become at risk of wilting if water is lost from the leaves faster than it can be absorbed by the roots. Different plants require different levels of humidity to thrive. Many tropical houseplants need high humidity and are best grown in a steamy bathroom, misted regularly or placed on a saucer of damp pebbles. In a greenhouse, humidity can be raised in hot weather by damping down (wetting) the floor or overhead misting.

  humidity and increases the likelihood of infection
• Dispose of all plant debris at the end of cropping
• Suppliers sometimes claim a degree of resistance for certain varieties, check the latest catalogues for those currently available

Chemical control

There are no fungicides approved for use by amateur gardeners to control leek rust.

The rust fungi are described as biotrophs; that is, they grow within the living tissues of the plant and extract

To grow well, plants need a wide range of nutrients in various amounts, depending on the individual plant and its stage of growth. The three key plant nutrients usually derived from soil are nitrogen, phosphorus and potassium, while carbon, oxygen and hydrogen are absorbed from the air. Other vital soil nutrients include magnesium, calcium and sulphur. Most garden soils contain enough nutrients to promote healthy plant growth.

Rusts are not able to survive in an active state on dead plant material, so those affecting

Annuals are plants that complete their life cycle in one growing season. They are generally easy to grow from seed or can be bought as young plants from garden centres. Annuals are ideal for growing in summer containers and filling gaps in borders. Some examples of annuals include sunflowers, cosmos, sweet peas and zinnia.

Perennials are plants that live for multiple years. They come in all shapes and sizes and fill our gardens with colourful flowers and ornamental foliage. Many are hardy and can survive outdoors all year round, while less hardy types need protection over winter. The term herbaceous perennial is used to describe long-lived plants without a permanent woody structure (they die back to ground level each autumn), distinguishing them from trees, shrubs and sub-shrubs.

perennial

Dormancy refers to a period of inactivity in plants, during which they slow down or stop their growth, conserving energy and resources. This is a natural process that helps them survive harsh conditions, such as winter or drought. Dormancy in seeds is a mechanism that prevents them germinating until environmental conditions are favourable for growth.

dormant

The leek rust pathogen seems to fulfil its entire life cycle on leeks, without the need for an alternate host. On some other Allium species the fungus begins to produce dark resting spores within the orange pustules as the foliage dies down. These resting spores have been observed occasionally on leeks, but the role that they play in the disease on this crop is currently unknown. It is likely that there are simply sufficient leeks in the ground at all times of the year to ensure continuity of infection, without the need for resting spores.

Puccinia porri (syn. P. allii) has been confirmed as being seed-borne, but this is not currently thought to be of any great significance in the spread of the disease.

It is thought that a number of strains of P. porri (syn. P. allii) exist, varying in their ability to infect different Allium species.