PLANT PROTECTION 4

PLANT PROTECTION 4 – How to Diagnose Plant Problems
NON-
PARASITIC
PESTS &
DISEASES
Living
causes
Mushrooms grow
around the edge
of fairy rings
Non-living
causes
Etiolation
The incidence and
severity of nonparasitic
diseases are
influenced by the
severity and length of
exposure to the
adverse factors
Living causes. (plants and animals) damage plants mechanically, or in some way other
than by obtaining food from the damaged plants. They are not parasitic, eg leafcutting
bees, fairy rings in turf, lichens, slime moulds, sooty mould, liverworts, moss, algae, cats,
dogs, earthworms, vandalism!
Signs
You can see mushrooms, sooty mould, slime moulds.
Fungal fruiting body produced
by mycelium growing on organic
matter in potting media
Sooty mould – daphne leaves.
Growing on honeydew secreted
by soft brown scales
Symptoms
Leafcutting bee damage, the uneven grass growth of fairy rings.
Vandalism, dog and cat urine on lawns.
Leafcutting bees cut portions
of rose leaves for nest making
Fairy rings – stimulated grass growth in
turf due to nutrients produced by fungi
growing on organic matter in soil
10 Background briefing – Causes of plant problems
Slime moulds – turfgrass
Vandalism – eucalypt ringbarked
by home owner seeking views
Non-living causes. eg cultural and site-related problems, are usually more common and
more difficult to diagnose than those caused by parasitic pests and diseases. Many soilrelated
problems are difficult to identify. Symptoms caused by non-living causes are
almost infinite.
Non-living causes may directly affect:
– A susceptible plant. Problems arise mainly from the type of plant being grown, eg
poor location and cultural practices.
Above the soil surface, eg plants may be affected by hail, frost, wind, sun, rain,
light, air pollution, spray drift.
Below the soil surface, eg plants may be affected by soil compaction, poor
drainage, over or under-watering, over or under-fertilizing, poor planting
techniques (trees and shrubs) and physical damage to bark or roots. Salinity and
herbicide residues may also occur.
– The development of a pest, disease or weed. For example, the severity of
fungal leaf spots increases the longer leaves remain wet.
Examples of non-living causes include:
– Environment agents. Temperature and moisture have the greatest influence on the
development of pest and plants. Some of these conditions can be avoided or alleviated,
others not. Temperature, eg unseasonable cold, frost or hot weather, sunscorch, low
soil temperatures, ‘winter kill’. Moisture, eg waterlogging, drought stress, uneven or
inefficient irrigation, poor drainage. Lack of oxygen, eg lawn compaction. Light, eg
insufficient light may cause seedlings to become long and thin (etiolated), flowering
may not occur or be delayed. Soil structure, eg forked roots on carrots, compacted
clay soils. Wind, eg stressed plants, abraded fruit, trees blow over.
– Nutrient deficiencies and excesses often show up as yellowing, stunting or death of
new growth or older leaves, depending on the missing or extra nutrients. Iron
deficiencies are common on azalea and citrus, magnesium deficiency on shrubs during
autumn. Excess fertilizer is commonly found in nurseries and gardens.
– Acid soil. Soil pH extremes affect nutrient deficiencies and excesses, eg deficiencies
of iron in alkaline soils. Acid soils commonly occur in turf areas.
– Salinity is widespread across Australia.
– Pollution of air, soil and water, eg poor chemical choice, application and drift.
– Mechanical injuries, eg machinery damage to roots, stems, vandals, lightning.
– Genetic abnormalities, eg mutations such as fasciation.