PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Conditions favouring
CONDITIONS
FOR
DEVELOPMENT
SPECIFIC
REQUIREMENTS
CLIMATE
CHANGE
WARNING
SERVICES
GENERAL CONDITIONS
Most insects prefer warm and humid weather.
Some insect pests are favoured by lush growth, eg nitrogenous fertilizers.
Weather the previous season can be as important as that in the current
season, eg plague thrips cause most plant injury after unusually moist
autumns and winters, which favour survival of pupae in the soil.
The significance of a disease outbreak also depends on the stage of crop
development, eg seedling, or just before harvest; or its place in a cropping
sequence, eg continuous cropping favours certain pests (and diseases).
TEMPERATURE
Nearly all insects become inactive at temperatures below 4-15 o C (no insect
damage occurs below 4 o C). Many insects can hibernate at temperatures
much lower than this.
No insects can survive for long at 60-65 o C. Generally 3 hours at
51-56 o C will kill most insects.
The body temperature of insects is closely related to the temperature
of the surrounding environment. The growth of an insect increases as
temperature increases until the optimum temperature for a particular type
of insect is exceeded, at this point the growth rate rapidly declines.
MOISTURE
Moisture may or may not be essential for some stages of insect
development. For example moths and butterflies cannot emerge from
pupae unless moisture is present.
Rain, can kill off large numbers of some insects, eg thrips.
MANY INSECT PESTS HAVE SPECIFIC REQUIREMENTS, eg
Cineraria leafminer - Cool and moist (a late winter and spring pest)
Gladiolus thrips - Hot and dry
Greenhouse whitefly - Warm and moist (glasshouse/outdoor pest)
Redlegged earth mite - Cool and moist (winter pest)
Twospotted mite - Hot and dry/hot and humid (glasshouse/outdoor pest)
Woolly aphid - Cool and moist (mostly a spring and autumn pest)
CHANGES WHICH MIGHT TAKE PLACE IN SOME REGIONS
Some pests may spread to new areas, eg fruit fly to Tasmania.
Some pests may be more or less serious in certain regions.
New pests may emerge.
MAY NEED TO BE REGULARLY UPDATED
Warning services for insect pests, eg are based on temperature, rain,
humidity, length of leaf wetness etc.
Fact Sheets and other information about pests require constant updating.
ENVIRONMENT
Does it favour the crop or the aphids?
SUSCEPTIBLE
CROP PLANT
Aphids
INSECT PEST
PRESENT
Fig. 34. Pest triangle.
38 Insects and allied pests - Plant damage