PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
INTEGRATED DISEASE MANAGEMENT (IDM)
MAIN STEPS
CONTROL METHODS
Legislation
Cultural methods
Sanitation
Biological
Resistant varieties
Plant quarantine
Disease-tested material
Physical/mechanical
Pesticides
Organic, BMP, etc
CONTROL
METHODS
1. Plan well in advance to use an IDM program that fits your situation. Keep records
of the crop, eg source of planting material, planting/sowing dates, temperature,
irrigation, fertilizers and pesticides.
2. Crop/region. IDM programs are available for some bacterial diseases on a range of
crops in particular regions.
3. Identification of disease must be confirmed, consult a diagnostic service if
necessary (page xiv). Have an understanding of the life cycle and of conditions
favouring the disease. Obtain a Fact Sheet on the bacterial disease.
4. Monitoring. Know when, where, what and how to monitor. Early detection,
together with appropriate control measures, can halt spread of disease. Monitoring
can also indicate the effectiveness of earlier control measures.
5. Threshold. How much damage can you accept? Have any thresholds been
established? There is a nil threshold for some diseases under an eradication
program, eg citrus canker.
6. Action/Control may include rogueing, strategic spraying, etc. and should be
carried out at the right time. Institute preventative controls, eg sanitation, diseasetested
planting material. There may be legal requirements. There are contingency
plans etc for some diseases on some commercial crops, eg citrus canker.
7. Evaluation. Review your program to see how well it worked. Recommend
improvements if necessary, eg use of disease-tested seed.
Once established bacterial diseases are usually difficult to manage.
LEGISATION
Relevant legislation includes Plant Quarantine Acts, Seed Acts, Certification and
Accreditation Schemes, etc.
CULTURAL METHODS.
Rotate crops if the disease has a limited host range, eg bacterial blight of bean.
Space plants to allow good air circulation to reduce disease levels.
Do not wet foliage unnecessarily. Avoid overhead irrigation and working in
wet crops if practical. Water with as little splashing as possible.
Adjust cultural practices, eg fertilizing and watering, to avoid lush growth.
Ensure seedbeds are well drained.
Avoid windy sites or protect plants from wind to reduce plant injury and
minimize bacterial aerosol formation.
Monitor and adjust environment around crops to reduce disease pressure.
Lower humidity in greenhouses and optimize soil pH and moisture levels
consistent with plant needs, not those of the disease organism.
Sanitation is especially
important if plants cannot
be treated effectively with
chemicals, eg bacterial
blight of pelargonium
(Xanthomonas campestris
pv. pelargonii)
SANITATION.
Sanitation practices reduce the inoculum in the field and in greenhouses.
Rogue infected crops, dispose of diseased plants and those immediately adjacent
before disease spreads throughout the crop. It may be necessary to discard all plants
belonging to one cultivar especially if it appears that only that cultivar is
susceptible. Dispose of infected crop residues.
Prune out and destroy infected plant parts as soon as observed, if practical, to
assist control on woody plants, eg bacterial gall of oleander.
Sterilize pruning tools before each cut and/or between plants to prevent the
transfer of bacteria on secateurs, eg bacterial canker of stone fruit.
Disinfect benches, used containers.
Clean trash from machinery before disinfecting it after working in diseased
crops and before working in disease-free crops.
Sanitize soil or media, water and soil.
Do not handle diseased material before handling healthy seed or moving
through the crop. Avoid movement of machinery and workers from infected to
disease-free crops especially when crops are wet.
BIOLOGICAL CONTROL.
Soil bacteria.
– Crown gall is controlled in commercial plantings by the ‘bio-pesticide’,
Agrobacterium sp. (Nogall ). The bacteria grow on the outside of susceptible
nursery stock, cuttings or seed and are antagonistic to crown gall bacteria.
– Beneficial bacteria are incorporated into soil and seed treatments (page 298).
Bacteriophages are viruses that attack bacteria. They are being researched as a
means of controlling bacterial diseases such as bacterial leaf and stem rot of
pelargonium (Xanthomonas campestris pv. pelargonii).
302 Bacterial diseases