PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
CAUSES & DIAGNOSTICS
WHAT ARE NON-
PARASITIC
PESTS AND
DISEASES
THOSE CAUSED BY LIVING AGENTS
These living agents (plants and animals) which damage plants mechanically, or
in some way other than by obtaining their food from the plants. They are not
parasitic on plants. Examples include:
Insects , eg leafcutting bees, soldier beetles, fungus gnat larvae.
Fungi, eg fairy rings, lichens, slime moulds.
Lichens, liverworts, moss, algae.
Animals, eg cats, dogs, earthworms, and humans, eg children, adults.
Weeds, also come within this group, but because of their economic
importance and number, are studied as a separate group (page 409).
Fig. 208. Leafy and bushy lichens on a dead limb. Each lichen consists of an alga
and a fungus which are mutually beneficial (symbiosis). The green alga manufactures
the food and the fungus absorbs and stores moisture. They do not obtain their food from
the tree. Lichens commonly grow on cooler southern shady sides of trees in the southern
hemisphere, and on rocks, fences and sheds. They can be used to monitor atmospheric
pollution especially sulphur and hydrogen fluoride. PhotoNSW Dept. of Industry and Investment.
THOSE CAUSED BY NON-LIVING AGENTS
Non-living agents are by far the largest group and are almost infinite in number
and type, and include:
Environment agents, eg heat/cold, drought/waterlogging, etc.
Nutrient deficiencies and toxicities.
Acid soils.
Salinity.
Pollution, eg pesticide injury.
Mechanical injuries.
Genetic abnormalities.
Fig. 209. Wind damage. Very young citrus fruits showing the
effect of abrasion during wind. Windbreaks filter wind, reducing the
velocity of wind in protected areas. They reduce plant stress and
physical damage. PhotoNSW Dept. of Industry and Investment.
388 Non-parasitic pests and diseases