PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
CONTROL
METHODS
(contd)
RESISTANT, TOLERANT VARIETIES.
Use disease-resistant or tolerant cultivars suited to local conditions if available. Some
walnut varieties show some resistance to bacterial blight (X. campestris pv. juglandis).
PLANT QUARANTINE.
Australian Quarantine & Inspection Service (AQIS). Some exotic
bacterial diseases which have entered Australia have been eradicated, eg ryegrass
bacterial wilt (Xanthomonas translucent pv. graminis) from Victoria and citrus
canker (Ralstonia solanacearum) from Qld. There are many bacterial diseases
overseas which are not as yet in Australia, eg
– Bacterial wilt (Ralstonia solanacearum race 1) of Eucalyptus.
– Moko disease (R. solanacearum race 2 biovar 1) of bananas.
– Fire blight (Erwinia amylovora) of apples and pears which occurs in NZ.
– Sumatra disease (Pseudomonas syzygii) of eucalypts, syzygiums
– Target list of diseases which might enter Australia
www.daff.gov.au/aqis/quarantine/naqs/target-lists
Padil - Pests and Diseases Image Library www.padil.gov,au
Interstate and Regional Plant Quarantine. Some bacterial diseases occur
only in certain regions, eg halo blight of beans. Check state websites.
Local quarantine. Bacterial diseases may be introduced into nurseries and
gardens by the purchase of infected plants, eg bacterial diseases of carnation,
bacterial gall of oleander.
DISEASE-TESTED PLANTING MATERIAL.
Seed. Many bacterial diseases are seedborne.
– Bacterial cells which get into the water and food-conducting tubes of plants
spread quickly to fruits and seeds.
– Certified bean seed guaranteed free from halo blight and certain other specified
diseases is available for beans and other crops. Certified seed of some crops does
not necessarily mean it is 100% free from a specified disease, a designated amount
may be tolerated.
– Do not save seed from infected crops unless it is treated with hot water, aerated
steam or fumigated. Seek advice.
Vegetative propagation. Do not propagate from infected plants. For some
crops disease-tested planting material is available which is guaranteed free from
certain bacterial diseases.
Only plant disease-tested planting material in disease-free seedbeds, or in soil
which does not contain infected plant residues.
PHYSICAL & MECHANICAL METHODS.
Seeds may be treated with hot water (HW) or aerated steam to kill internal
bacteria. Prescribed HW treatment can penetrate seeds sufficiently to eradicate
bacterial infections inside some of the seed only. Careful temperature regulation is
required but some seeds, eg fleshy seeds such as beans and peas, cannot be treated
with aerated steam or HW.
Soil pasteurization (60 o C for 30 minutes) kills disease-causing bacteria in soil
(page 330). Practical only for raising seedlings in greenhouses and frames.
Irradiation destroys microorganisms, eg bacteria, fungi, and insects). Some nonedible
items are irradiated in Australia (page 330).
Pulsed UV light kills bacterial and fungi on the skin of many kinds of fruit, also
improves fruit quality and extends shelf life up to 80 days.
Note - many biocontrol
agents are registered
as pesticides
BACTERICIDES.
The use of chemicals to control bacterial diseases has not been very successful.
In Australia only a few fungicides, eg copper and mancozeb, are registered as foliar
sprays. These are non-systemic and only prevent infection; they have no effect on
established infections inside seeds or other plant parts, so that control is often
unsatisfactory. Copper is used when conditions favour infection, development and
spread; mancozeb may be used on young plants which may be damaged by copper.
Formulations of copper are now available which are ‘flowable’ and easier to apply
(pages 341). Note that copper fungicides have a ‘POISON’ signal heading.
There is a low risk that bacteria will develop a resistance to copper (page 341).
Excess copper can harm plant growth, persist in the environment over a long time,
may accumulate in some soils and be toxic to earthworms and some soil microbes.
Disinfectants such as sodium hypochlorite also do not reach inside seed.
Overseas systemic antibiotics such as streptomycin are available, but resistance
may develop and they are not allowed on edible plant produce.
Biological pesticides such as Agrobacterium sp. (Nogall ) are used to control
crown gall (pages 302, 306).
Pre-plant soil treatments with fumigants (or pasteurization) are suitable only for
treating small quantities of infested soil, eg cutting beds. Only plant disease-tested
seeds, cuttings and bare-rooted nursery stock into treated soil.
Bacterial diseases 303