Control

Plant diseases and their treatments can be categorised into broad types, and similar responses are recommended within these types.

 

Note

The advice provided in this site is intended as a guide only.
 
In undertaking any suggested method for destroying diseased or infected trees or plants that involves applying any chemical treatments, it is important to read the manufacturer’s instructions for use and associated safety data.
 
Take all necessary safety precautions if burning infected plant material and never burn material where there may be any risk to life or property. You should always consult SEPA prior to burning material to ensure you have any required permissions or licences.
 
You should seek further advice from the relevant authorities listed in this site if you are in any doubt as to how to treat or destroy infected plants or trees.

About This Page

If you can identify the cause of a plant disease, it is always best to check specific resources for tailored advice to control it. This is particularly true for notifiable pests. It is often the case however that notifiable diseases can be ruled out, yet the precise cause is not known or falls into a broad category such as 'fungal root rot' or 'leaf rust'. For this situation we have compiled generalised advice for the control of different kinds of plants diseases. This advice will usually apply to most diseases within the category and may be taken as general guidance, but note that exceptions will abound!

Getting Started

If you are uncertain of the type of problem affecting a plant, follow these steps:

  1. Determine the general cause and the extent of the disease symptoms. Look for insect damage such as leaf galls or insect exit holes in the bark, or for signs of fungi or other organisms such as brackets on boles of living trees or leaf spots. Note that some damage can be caused by abiotic factors (such as frost). A field guide such as the CABI Field guide for the identification of damage on woody sentinel plants can help to pinpoint causes of disease.
  2. Use Recommended Sources to try to identify the causal organism and to determine if it is a common and or/native species, and whether it is disease-causing or just a saprophyte (living of the dead plant that something else has killed).
  3. Search the Threats page by Host for diseases on the Pest Risk Register to determine whether you need notify authorities. If you think it might be a notifiable organism notify authorities and follow their instructions – do not try to eradicate it unless so instructed.
  4. If you can identify a causal organism, consult the listed resources for specific guidance on control. For generalised advice, check these Prevention – Biosecurity  and Control pages to learn ways to help keep the disease from spreading, and what kinds of control responses are available for non-notifiable diseases.

Disease Types

  • Most diseases associated with roots and stems are ultimately problems of water or sugar conductance. Pests and pathogens that degrade roots or block xylem prevent water uptake. Those that infect collars and cause trunk cankers degrade the phloem, interfering with sugar transport. These diseases can appear as either a slow decline, cause rapid death of the entire plant or one or more sections, cause rotting of roots, or crown thinning and wilting from new growth downward. Most diseases associated with wood-boring insects are wilts; fungi that grow in the galleries carved by the insects’ larvae interfere with water conductance. Visible signs and symptoms of wilts and vascular diseases can include oozing cankers on the stem or collar, insect exit holes or galleries, fungal fruiting bodies, or knots or galls on roots.

    • Check specific threats for statutory listings, and promptly report any suspected cases or any unusual outbreaks.

    Avoidance

    • Follow biosecurity guidance to keep pests and pathogens out.
    • When purchasing plants, buy from trusted, local suppliers, repot to fresh compost on arrival, disposing the old potting media into landfill, and keep plants secluding for several weeks. This gives any latent diseases that may have been suppressed by chemicals, or are becomung established, time to emerge.
    • Be especially careful with projects restoring sensitive lands or threatened species. Where there are severe or specific disease threats it may be wise to keep new plantings physically separated from established populations. See for example the Forestry Commission Scotland guidance for planting juniper and the California Oak Mortality Task Force guidelines for restoration and fieldwork.
    • Select sites appropriate for the species, especially with regard to drainage. Disease is most likely to occur where water collects, and many of the pests and pathogens behind these diseases are transmitted through water and mud. New plantings in the runoff zone from existing disease centres are highly likely to become infected. On the other hand, drought can compound root and stem problems, and a plant already stressed by disease can be killed off by drought, or vice versa.
    • Maintaining airflow and separation among plants will likewise help to reduce the conditions that favour disease, especially root and bole rots. Paradoxically, increased airflow can increase the likelihood of individual plants contracting diseases with propagules that spread in wind or blown rain.

    Management

    • The appropriate response when disease occurs will be determined by the identity and severity of the disease.
    • Oozing cankers can have many causes, and a canker or the presence of wood rot fungi in the absence of other signs of decline, or only slow decline may not require a management response.
    • However, keep in mind that an infected plant will be a source of inoculum to plants around it. In cases of severe disease, the plant should be removed and destroyed by burning or in landfill. In most cases, the roots should be excavated and removed. The soil around the roots will most likely contain infectious propagules, so excavation equipment must be carefully cleaned and the soil prevented from moving. For some pests and pathogens the risk associated with disturbing the soil may be greater than the benefit of excavation; check specific guidance for these.

    Treatment

    • There are few chemical treatment options that are appropriate for root and stem diseases in the natural environment. Avoidance and management of disease, including removing infected materials, are the best course of action.
    • In some cases, phosphite compounds (also known as phosphonate) can be useful to provide systemic protection against both oomycete (eg Phytophthora species) and fungal pathogens. These can be used to protect individual plants, but treatments must be repeated, and protection wears off after the treatment is discontinued. Phosphite compounds and other fungicides can also suppress symptoms of infection allowing pathogens to be transmitted undetected, and so should not be used on plants in propagation contexts.
    • Check specific threats for more detailed advice.

    Wood-boring insects

    • Several wood-boring insects are of great concern for arrival and spread in the UK. It is important that any suspected cases are reported promptly, so that their identity can be confirmed and control measures can be enacted quickly. Be sure that authorities have a chance to identify the insects; do practice biosecurity measures to contain them but do not use insecticides or other treatment measures on notifiable pests unless instructed by national plant health authorities.  
    • Wood-boring insects are generally attracted to stressed trees. Managing stands of trees to reduce stress will reduce susceptibility. New stands should be planted far from infestations, while it is necessary to inspect thinned or otherwise felled trees for infestations, and if found peel bark to expose brood chambers.
    • Biocontrol agents may be available, depending on the pest species.