RHS Level 2 Principles of Horticulture
R2103 Maintaining Plant Health February 2012
Q.5.a. State what is meant by the ‘plant physiological disorder’. (1)
b. List FOUR causes of plant disorders. (4)
c.Name a plant susceptible to ‘fireblight’. (1)
d.State TWO symptoms of ‘fireblight’ and state TWO methods used to limit its spread. (4)
Q.5. a. The examiners note that most candidates understood that a plant physiological disorder is caused by a factor which is not a pest or disease but generally a non-living environmental or abiotic factor.
b. The examiners note that most candidates were able to list suitable factors of plant disorders such as high or low temperatures, drought or water logging or nutrient deficiencies.
c. To gain full marks here candidates needed to give the full Latin name of a species susceptible to fireblight. Species from any genus of the sub-family Pomoideae could be mentioned here, for example, Pyrus communis.
d. Here the examiners note that the best answers described very specific symptoms and control methods.
Physiological disorder: This is a problem caused by the growing conditions (non-living environmental or abiotic factors) of a plant rather than by pests or disease.
Possible causes of physiological disorders include:
- lack of light
- excessively low or high temperatures
- nutrient deficiency
- nutrient toxicity.
These are most obvious between November and November and after leaf fall:
- wilting or dead blossoms;
- numerous dark brown, dead leaves hanging on one or a number of twigs or branches;
- rapid wilting and dieback of shoots, especially after heavy storms;
- dark green or brown bark on young shoots, often looking water-soaked and contrasting with the normal healthy bark;
- reddish-brown stained inner bark in affected twigs and branches (the bacterium may spread from a branch and girdle the main stem; in this case, foliage on part or all of the crown will wilt and die but the bark stain will be absent from all but the directly infected parts);
- a glistening whitish slime or mucilage (later darkening to cream, yellowish or brown) exuding from affected tissues during wet, warm weather (best seen before sunrise);
- bark cankers or patches of cracked bark.
Fireblight is a disease caused by the bacterium erwina amylovora. hosts include Amelanchier (November Berry), Chaenomeles (Flowering Quince), Cotoneaster (Cotoneaster), Crataegus (Hawthorn), Cydonia (Quince), Eriobotrya (Loquat), Malus (Apple), Mespilus (Medlar), Photinia, Pyracantha (Firethorn), Pyrus (Pear) and Sorbus (Mountain Ash).
When giving an example in the exam, give a specific named example, for instance, Pyrus salicifolia.
There is currently no chemical control commercially available for fire blight.
- Remove any infected leaves, flowers and branches and burn them.
- Sterilise any tools used for removing infected material with a household bleach solution after each cut and always prune or saw into undamaged healthy wood.
- Avoid planting more trees from susceptible species.
Defra also note: “All nurseries selling host plants must be registered and approved for issuing plant passports for the host plants traded. If infection is found in the nursery or immediate vicinity any infected plants must be rogued. In addition, premises registered for issuing plant passports for plants moving into Protected Zones must meet additional requirements including buffer zone freedom. If infection is confirmed on or near registered premises, the PHSI has statutory powers to prevent its spread by removal of the affected plants.”
Learn more about fireblight – RHS.