Mint rust is a disease caused by the fungus Puccinia menthae. Mint rust infects several mint species as well as some related plants including marjoram and savory. Mint rust symptoms can be expected from spring until autumn.

You may see the following symptoms:

• Pale and distorted shoots in spring
• Dusty orange pustules on the stems and leaves. These may be followed by dusty yellow or black pustules
• Large areas of leaf tissue die and plants may lose leaves

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods,

Gardeners often use the word variety when referring to a specific plant, but the correct botanical term is 'cultivar'. Whichever word you use, it means a distinctive plant or plants, given a specific cultivar name and usually bred to enhance certain characteristics, such as flower or fruit size, colour, flavour or fragrance, plant size, hardiness, disease resistance, etc. Additionally, it is worth knowing that, botanically, variety has another meaning - it refers to a naturally-occurring distinct plant that only has slight differences in its looks. For example, Malva alcea var. fastigiata differs from typical plants by having an upright habit.

Regular cleaning and tidying not only keeps a garden looking neat, but can reduce pests and diseases too. Beneficial jobs include collecting fallen leaves, promptly removing diseased growth and debris, cleaning tools, and weeding. Still, too much tidying can discourage wildlife, so it’s a fine balance.

garden hygiene

Non-chemical control

Remove affected plants promptly before the black resting spores are formed and contaminate the soil. In the case of garden mint it is also necessary to remove infected rhizomes. In an infected bed, try to locate any uninfected stems and carefully dig these out and move to another location in an attempt to start a new, healthy colony.

Heat treatment is a method used by commercial nurseries, but could be adapted for the home gardener. Wash

Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. See plants such as Anemone nemorosa, bamboo, canna, border iris.

Fungicides

The RHS recommends that you don't use fungicides. Fungicides (including organic types) may reduce biodiversity, impact soil health and have wider adverse environmental effects. If you do intend to use a fungicide, please read the information given in the links and download below to ensure that use, storage and disposal of the product is done in a responsible and legally compliant manner.
  
The products listed in the ‘Fungicides for gardeners’ document below are legally available for use by home gardeners in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally. Homemade products are not recommended as they are unregulated and usually untested.

No fungicides with activity against mint rust are available for use on mint or other herbs that will be used for culinary purposes.

Download

Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners).

Link

Chemicals: storing and disposing safely

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.

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

Puccinia menthae completes its entire life cycle on one plant host and produces resting spores to pass through winter.

In garden mint, the general consensus was that the fungus grows into the rhizomes, where it spends the winter, causing a systemic infection throughout the tissues of the plant.  However there is currently some debate as to whether this really is the case. It is known that resting spores present in the soil or contaminating the outside of the

Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. See plants such as Anemone nemorosa, bamboo, canna, border iris.

The fungus has several spore stages, the first being the orange pustules that appear in spring or early summer, followed later by yellow spores and finally by black resting spores.