PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
CONTROL
METHODS
(contd)
Select the right
disinfestation
system for your
situation
DISEASE-TESTED PLANTING MATERIAL.
Seed. Many fungal diseases are carried on, in, or in association with, seed.
Using disease-tested seed is an effective way of controlling these diseases, eg loose smut
of cereals, various seedborne diseases of annuals and vegetables.
Vegetative propagation material eg bulbs, corms, cuttings, rootstocks, may
carry fungal diseases from the parent plant and are often treated with heat or chemicals
to free them from disease. Special techniques are used to obtain disease-freedom, eg
– Tip cuttings from chrysanthemums infected with Verticillium wilt, often escape
carrying the disease.
– Continuous culture-indexing includes regular checks of plant material for fungal
infection, eg Verticillium (and other diseases) over a 2-year period. Accurate records
mean that contaminated plant lines can be destroyed.
Certification Schemes provide the grower with seed or vegetative propagation
material, which is “guaranteed free” from the diseases for which it has been tested and
found to be free from. The planting material conforms to certain standards and certain
tolerances for a disease. Zero tolerances may apply to a disease (or pest) that if detected
on a property, would result in severe quarantine restrictions.
PHYSICAL & MECHANICAL METHODS.
Temperature
– Hot water treatment (HWT) of rootstocks, rootlings and cuttings. Surface
treatments, eg 55 o C for 5 minutes, eliminate root rotting fungi, bacteria,
phylloxera and nematodes from grapevine propagation material.
– Aerated steam is used to rid seeds of fungal and other diseases. Soil
pasteurization (60 o C for 30 minutes) will kill Thielaviopsis (Chalara) in soil.
– Composting, properly carried out (60 o C for 30 minutes or longer will kill most soil
disease organisms, while leaving some beneficial ones.
– Sterilizing recycled water by heat.
10 seconds at 95 o C - Kill 100% disease organisms
30 seconds at 95 o C - Kills nearly everything
Lower temperatures may be used for longer periods.
– Solarization prior to planting traps energy from the sun under clear plastic
sheeting laid on soil beds for at least 4-6 weeks when there is adequate sun. Soil
may be heated to a depth of 30-25cm and summer soil temperatures can rise to 60 o C
which may assist control of some soil fungal diseases; acts a bit like pasteurization
with steam. Water beds before solarization to improve control. Home gardeners can
put media in plastic bags and leave in sun for 2-3 weeks. Solarization is not possible
in mixed or perennial plantings, difficult in large areas and depth of treatment is
limited (pages 373, 438).
– Flame burners can be used to burn crop stubble after harvest, eg wheat. But this
causes loss of nutrients and increased wind erosion (page 438).
– Cooling and freezing is used extensively to control bacterial and fungal diseases
of fruit, vegetables, cheese, milk and other food products.
– Pasteurization of soil/media can be used to treat potting and propagation media in
nurseries to kill most plant disease organisms that cause damping off, leaving some
beneficial microflora (aerated steam at 60 o C for 30 minutes). Prevent infested soil
from re-contaminating pots, potting mixes, cuttings, germinating seeds and seedlings
on benches. Because soilless mixes are used today, pasteurization has mostly been
abandoned or used for treating pots and trays. Principal substitutes are bark and
sawdust which when composted provides conditions for a huge growth of
microorganisms several of which suppress plant disease organisms.
– ‘Smart films’ either block or allow through different wavelengths of light which
biologically affect the plants, pests and diseases growing beneath them. They have
been used overseas to eliminate bacteria, fungi and viruses. Flora-Fresh is a
protective packaging film which absorbs ethylene to minimize moisture loss and
damage in transportation and optimizes shelf-life and natural colour of each bunch.
Irradiation destroys microorganisms, eg bacteria and fungi, and insects, eg weevil,
fruit flies, and therefore can reduce the incidence of food-borne diseases and extend the
refrigerated shelf life of foodstuffs. Some non-edible items are irradiated in Australia.
Microwaves can be used to disinfest small quantities of media or soil.
Pulsed UV light kills bacteria and fungi on the skin of many kinds of fruit improving
fruit quality and extends shelf life. Also effective in hydroponic units against Pythium,
Fusarium and Thielaviopsis.
Heat treatment and UV light are currently the most popular methods of disinfecting
recirculating nutrient solutions in the Netherlands. UV light is well-known in nursery
circles for its ability to eradicate water-borne micro-organisms, eg Phytophthora,
Pythium, Fusarium (Rolfe et al 2002).
Filters are used to remove disease organisms from water.
– Membranous filters remove the disease organisms which are causing the
problem. Correct filters must be used.
– Slow sand filtration (SSF) is used to disinfest recycled water or irrigation water
from on-site dams to eliminate disease organisms, eg Phytophthora and Pythium.
SSF is only partially effective at filtering Fusarium, viruses and nematodes.
– Biofilters are used to treat run-off, rain and industrial waste water overseas. They
consist of a medium of heavy scoria and a rotation system. Bacteria are added and
multiply on the scoria grains and eliminate all fine organic matter including Fusarium,
Phytophthora, Pythium and tomato mosaic virus. Non-harmful flora is retained.
330 Fungal diseases - Integrated disease management