PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
CONTROL
METHODS
Sanitation may
assist in controlling
certain virus diseases,
eg if plum pox virus
arrived in Australia
protocols would probably
include destruction of
infected trees and
constant monitoring
for disease
Virus-resistant
plants reduce
the use of
insecticides
to control
vectors
.
LEGISLATION
Relevant legislation includes Plant Quarantine Acts, Seed Acts, etc.
CULTURAL METHODS.
Overplanting and later thinning can be useful for home gardeners to assist in
controlling tomato spotted wilt in tomatoes (see roguing below).
Proper fertilizing and watering can often offset the adverse effects of infection,
eg daphne plants infected with virus diseases.
Planting at times when vectors are absent or low.
SANITATION.
Insect-transmitted viruses. Do not plant young crops near virus-infected crops or
crop residues. Destroy surrounding weeds hosts and infected dying crop plants
as soon as practical after harvest as vectors may migrate to healthy crops. Clean out
all autumn crops grown in greenhouses where spring crops will be grown.
Rogueing. As there is no cure for virus-infected plants, rogue infected crops, especially
herbaceous crops, eg ornamental flowers, bulbs and vegetables. Because symptoms
caused by virus diseases are often more obvious in the cooler months, rogueing
should be carried out during spring and autumn. For viruses that 'overwinter' in host
debris in the soil, remove diseased plants.
Handling plants. Some virus diseases are spread during handling, eg tobacco
mosaic and cucumber mosaic. Handle plants as little as possible. Wash hands when
moving between sections of a collection of plants.
Sterilize pruning implements by heating to red heat or dipping in 10% trisodium
phosphate solutions for 10 minutes after every plant or plant group (check that this
is appropriate for your situation). Thoroughly clean tools first.
Personnel hygiene. Wash hands, clean clothes, foot baths with disinfectant can be
placed at the entrance to greenhouses. Do not smoke when handling Solonaceous
plants (page 282).
BIOLOGICAL CONTROL.
To date it is not possible to control virus diseases biologically.
Vectors, eg thrips, have potential for biological control (page 139).
Trap plants, eg rows of tall plants around fields of beans. Incoming aphids which
carry virus diseases that attack beans, will first stop and feed on tall ryegrass. Most
aphid-borne viruses are non-persistent in the aphid so many of the aphids will lose
the bean-infecting virus by the time they move to feed on the beans (Agrios, 2005)
RESISTANT, TOLERANT VARIETIES.
Resistant varieties provide a long-term approach for control of virus diseases, eg
Traditional plant breeding programs whereby hybrids are produced which have
resistance to a specified virus disease.
Genetic engineering (GE) allows the transfer of genes for resistance into
susceptible crop varieties, eg grapevine fanleaf virus. Genes can also be silenced.
Vaccination with attenuated strains of the problem virus can protect some plants
from virulent strains and extends their commercial life. This may be inherited, eg
barley yellow dwarf virus.
Cross protection describes the protection of a plant by infecting it with a mild
strain of a virus, which prevents later infection by more severe strains of the same
virus, eg citrus tristeza virus, papaya ringspot virus.
Systemic acquired resistance (SAR). Plants may be treated with chemicals which
activate the plant’s natural resistance mechanisms, eg tobacco mosaic virus.
PLANT QUARANTINE.
Australian Quarantine & Inspection Service (AQIS). Recent arrivals include Iris
yellow spot virus (IYSV) which infects onions and leeks and Capsicum chlorosis
virus (CaCV) which infects capsicum, peanut and Hoya. For the many virus
diseases and their vectors which occur overseas, contingency plans are in place
should they enter Australia.
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 virus diseases (or strains of),
occur only in certain regions. NSW legislation aims to prevent the introduction of
Tomato Yellow Leaf Curl Virus (TYLCV) and its vector, silverleaf whitefly, into
NSW because diseases caused by similar strains of TYLCV in other states, cause
severe economic losses in tomato crops overseas.
Local quarantine. Virus diseases may be introduced into gardens and nurseries by
the purchase of infected plants, eg roses.
DISEASE-TESTED PLANTING MATERIAL.
As virus-infected plants usually remain infected for a lifetime, plants propagated
vegetatively from such material are infected.
Certification schemes provide propagation material, conforming to cultivar
characteristics and guaranteed free from the diseases for which it has been tested
and found to be free from. Periodic testing of parent plants producing such
propagation plants is necessary to ensure their continuous freedom from viruses.
284 Virus and virus-like diseases