PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
SYMPTOMS
AND DAMAGE
Some symptoms that
appear to be
abnormalities are
normal plant structures,
eg ‘burr’ knots’ and
lignotubers which
can produce shoots
if the upper parts of
the tree is damaged
Symptoms are often
indistinct and closely
resemble those caused
by fungi, bacteria,
viruses, root pathogens
Symptoms and damage caused by non-parasitic pests and diseases are literally
infinite and include:
DIRECT DAMAGE.
LEAVES
Blights, eg frost, pesticide injury
Chlorosis, eg nutrient deficiencies and excesses, pesticide injury,
senescence, natural variegated varieties
Dead areas within the leaf margin, eg sunscorch
Dead tips and edges, eg too little/too much water, salt toxicity
Distortion, eg hormone herbicide injury
Galls, eg oedema
Leaf spots, eg contact herbicide injury, senescence
Stunting, eg herbicide injury, deficiencies, sports
FLOWERS Blights, eg frost
Mechanical damage, eg wind, rain
FRUIT
STEMS
CROWNS
ROOTS
Distortion, eg boron deficiencies (pome fruit)
Colour changes, eg sunscorch, lack of light
Mechanical injury, eg rain, hail
Russet, eg pesticide injury, frost
Rotting, eg calcium deficiency (blossom end-rot of tomatoes)
Splitting, eg rain, hail, uneven watering
Etiolation, eg lack of light
Dieback, eg senescence
Distortion, eg fasciation
Mechanical injury, eg lawn mowers, cars, stakes, sprinklers
Dead areas, peeling bark, eg sunscorch damage
Galls, eg ‘burr’ knots (Prunus spp.)
Galls, eg lignotubers in eucalypts
Dead areas, peeling bark, eg waterlogging, sunscorch
Forking, eg poor soil structure, excess fertiliser
Distortion, eg pot bound plants
Rotting, eg waterlogging
Splitting, eg overmaturity (carrots, parsnips, etc)
INDIRECT DAMAGE.
Environmental effects on development of pests, diseases and weeds. Nutritional
imbalances, high and low temperatures, high humidity, over or under-watering
and other factors, can predispose plants to diseases or pests.
DIAGNOSTICS
SOME NON-PARASITIC PROBLEMS CAN BE DIFFICULT TO IDENTIFY
Some are easily recognized by distinct symptoms the cause of which is known.
Often, though symptoms are indistinct and closely resemble those of some parasitic
pests and diseases. Some are misleading, eg the cause of wind blown trees may be
wood rot, borer attack or wet soils.
Know what a healthy or normal plant looks like, eg
– Leaves of many deciduous trees and shrubs at the end of the season (autumn) look
tatty before finally falling.
– Evergreens such as camellia loose their older leaves after flowering as new leaves
are emerging in spring.
– Frost damage in field peas can be difficult to recognize; flowers are most vulnerable
to frost, developing seeds shriveled or absent, blackening inside, pods blister.
Be able to recognize symptoms of common non-parasitic problems, eg
iron deficiency symptoms which are common on your crop.
– A magnifying glass or small stereo microscope can assist identification and
eliminate certain parasitic problems. Identification is often complicated because
proof of absence of a parasitic pest or disease may be required.
– Tools which assist with the diagnosis of non-parasitic problems include pH and
conductivity meters, maximum and minimum thermometers, soil and water tests,
light meters. Grow-on tests may confirm certain non-parasitic problems where plants
recover after initial exposure whereas pathogen-related problems persist into new
growth.
– Seek expert help. They can perform specialist media and plant tissue analysis
and other tests, and confirm the absence of a parasitic problem (page xiv).
Know the problems that affect your crop in your area. Obtain a Fact
Sheet for each problem.
Know potential local problems. Some problems may be widespread in
some areas, eg phosphorus sensitivity of Proteaceae plants.
Manage the crop as recommended and record its history, eg irrigation,
fertilizer, herbicide, insecticide, fungicide applications, salinity problems.
Non-parasitic pests and diseases 389