Copy R2103 5.1 Plant Disorders Flashcards
What is meant by the term “plant disorder”?
Physiological/abiotic disorders
Disorders not caused by pests or disease but by a problem in the environment in which the plant is being grown.
How are plants affected by frost?
Frost causes cells to freeze, contents expand, cell ruptures and is killed. Plants blacken and die.
Happens to non-hardy plants.
- Scorched and damaged leaves
- Distorted buds
- Damage to young shoots and tips
- Reduced production of flowers and fruit
- Frost heave: root system not established and lifted from soil
State one method of avoiding frost damage.
- Provide protection such as straw, fleece,cloches etc or bring tender plants under cover.
- Avoid planting in a frost pocket, take care planting against east-facing walls. Planting against a west- or south-facing wall will give some protection.
- Plant selection is important, choose hardier plants (use RHS plant hardiness ratings)
- Do not plant out half-hardy plants until all risk of frost is passed.
- Spray fruits buds with water after a frost as this can help p prevent damage.
- Planting of shelterbelts can reduce damage from wind frosts.
Describe how plants are adversely affected by shade.
Etiolation with long weak stems, small sparse leaves
- Etiolation = pale, spindly growth, lacking in chlorophyll (yellow)
- Long and spindly because they develop long internodes.
- Leaves fail to expand.
- In Britain light in the winter can be limiting, particularly for plants grown under glass.
How to avoid problems associated with shade.
- Plants outdoors should be selected for the correct location,.
- Supplementary light may be used in protected environments.
- Indoor plants often suffer form lack of light and here plant selection is important, as well as picking the best interior location for plants.
Describe how plant growth is adversely affected by drought.
- Dieback occurs
- Wilt and turn brown, fruit may fail to set, some run to seed and if permanent wilting point is reached then the plant will die
- Often causes premature leaf drop
- Droughts can occur in the summer
- Frost can also occur in the winter/spring period where transpiration rates are high due to cold winds and when soil is frozen
Describe how to avoid problems from drought.
- Plant selection essential in areas prone to drought, plants have many adaptations to cope with water stress
- Soil structure/water-holding capacity can be improved by addition of organic matter, which will prevent moisture loss
- Shade and wind protection can be provided
- Regular watering using irrigation systems or by hand
- Mulching
Describe how plant growth is adversely affected by water-logging.
- Roots: require oxygen to respire and need to release carbon dioxide; anaerobic conditions can lead to root death, dieback and eventual death
- Leaves: yellowing, wilting (often similar to drought symptom, defoliation, oedema (plant cells rupture – particularly the underside of leaves – due to too much water pressure)
- Crown: dieback
- Growth: stunted
State one method of lessening the affect of water-logging on plants.
- Improve the structure/drainage of the (outdoor) soil (sand, grit)
- Provide the correct air-filled porosity for container composts
Describe how plant growth is adversely affected by high temperature damage.
- Scorched areas of leaves, typically on the sunny side of plants (south)
- Reduced growth
- Blistering, longitudinal cracking and death of tissues – all entry point for potential plant diseases
- Under glass seedlings and softwood cuttings can die
- Damage can also be done to newly planted urban trees due to heat reflection from nearby buildings
How to avoid damage from high/low temperatures?
High temp:
- Plant selection essential in areas prone to high temperatures, e.g. Mediterranean plants will go dormant over the summer months to cope with high temps.
- Shade can be provided to help reduce temperatures
- Avoid watering in bright sunlight (droplets focus light)
Low temp:
- Plant selection is essential
- Do not use fertilisers late in the season, as they stimulate sappy growth that is prone to chilling injury
- Plants can be protected from cold weather by wrapping horticultural fleece
- Plant in a sheltered spot
- Keep containers in dry, sheltered areas, grouped together for mutual protection. Prevent roots freezing in containers by wrapping with bubble polythene or straw
- A cold and windy site will often require windbreaks such as hedging
Describe how plant growth is adversely affected by soil pH.
In soils with high pH (chalky or alkaline soils) iron tends to be locked up in insoluble compounds; roots unable to absorb a balance of nutrients
Iron needed to produce chlorophyll; leaves turn yellow or brown in margins and between veins; poor-quality/quality fruit
Describe how plant growth is adversely affected by fasciation.
- Fasciated stems are produced due to abnormal activity in the growing tip of the plant.
- Often an abnormal number of flowers are produced on affected stems. Normal branches may arise from fasciated stems.
- Apical meristem becomes flattened and elongated and has appearance of many shoots together.
- Can be caused by aphids or mechanical means. Not necessarily fatal.
- Plants affected include Delphinium, Euphorbia, Forsythia, foxglove, lily, Primula and Veronicastrum.
- Fasciation is unpredictable and is usually limited to a single stem. It seldom recurs the following year, although some plants, such as Forsythia and Veronicastrum virginicum ‘Fascination’ do suffer repeat occurrences, perhaps indicating a genetic tendency.
State a method of avoiding or dealing with fasciation.
- Cut out the damaged part of plant.
- Fasciation seldom recurs on herbaceous plants the following year.
Describe how plant growth is adversely affected by rose balling.
Outer petals of rose bud die and become stiff so inner petals cannot emerge. Buds go brown and drop off or can become covered in grey mould.
Cool, wet weather saturates the outer petals and then the sunshine dries and fuses them into a tight, papery shell, preventing the bud from opening.
Thin-petalled, double flowers such as rose, peony and camellia cultivars are most susceptible to this condition.
