PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
BIOLOGY, CLASSIFICATION & IDENTIFICATION
Flowering plants, ferns, etc
NO. SPECIES
IN AUSTRALIA
WHAT ARE
WEEDS?
(pest plants)
WHY ARE SOME
PLANTS LIKELY
TO BECOME
WEEDS?
Noogoora
burr
Some consider that
rats, cockroaches,
nettles and thistles
will flourish at the
expense of more
specialized wild
organisms
CO2
+
H2O
+
chlorophyll
= plant tissue.
Australia has more than 3000 species of ‘weeds’ but probably only a few hundred have
major impacts on food production and ecosystems. Main websites include:
Weeds in Australia www.weeds.gov.au/
Weeds Australia www.weeds.org.au/
The Australian National Weeds Strategy of 1999 defines a weed as
‘a plant that has or has the potential to have, a detrimental effect
on economic, social or conservation values’
A common definition is:
‘a plant growing where it is not desirable or wanted’
Most plants, including those usually considered beneficial, may be weeds at times.
The 3 most important factors influencing plant weediness are their ability to
colonize areas, impact on crop yields, bush areas and their potential for wide distribution.
EFFICIENT AND SUCCESSFUL REPRODUCTION AND SPREAD
Weeds produce large numbers of seeds, fruits and vegetative propagules, eg stem
fragments, leaf propagules, tubers, corms and cormlets, bulbs, suckers, stolons,
rhizomes and root layers. Weeds also spread efficiently, eg
Wind can spread light seeds of many weeds, eg dandelion, serrated tussock.
Running water. Other weed seeds, eg docks are adapted to float on water or are
moved by the force of running water, willow parts are washed down stream.
People and animals. Some seeds have adaptations which enable them to
attach themselves to clothes and wool, eg Noogoora burr.
– Soil. Seeds, stolons, bulbs, may be carried in soil in containers, soil or gravel
deliveries and on contaminated machinery.
– Vehicles and machinery can spread soil, weed seeds and plants.
– Birds and other animals pass seed in their dropping, manure deliveries.
SURVIVE UNDER UNFAVORABLE CONDITIONS
Weeds are persistent, mechanisms of survival include:
Invasiveness. Weeds are able to rapidly invade, establish and dominate
disturbed or new sites and consequently extend their distribution and their impact.
Seed dormancy/seed banks. Some seeds can survive long periods in
conditions unfavorable for germination, eg chickweed and lamb's tongue can
germinate after surviving for 10 years in the soil. Hence the saying:
‘1 year's seed, 7 years' weeds’
Seeds have a wide germination range, short life cycle, quick maturity, quick
production of seed, and rapid early growth after seed germination.
Strongly competitive with rapid root growth; flourish in disturbed environments.
Able to self-pollinate or pollination not required.
Can enter dormancy, eg bulbs, corms; possession of deep roots or tap roots.
Wide ecological adaptation, eg waterways to deserts. They can tolerate drought,
frost, salt, low nutrient levels.
Weeds are generally fast growing, hardy and highly adaptable.
Often unpalatable to stock.
TYPE OF PHOTOSYNTHESIS
Photosynthesis is the combination of carbon dioxide (CO 2 ) with water (H 2 O) in the
presence of chlorophyll to produce plant tissue (Parsons and Cuthbertson 2001).
Plants use one of 3 different chemical pathways to achieve this reaction.
– C 3 or Calvin cycle plants. Most crops cultivated by humans belong to this group,
eg wheat, apples, sunflower, soybean, most vegetables were originally developed
in temperate regions of the world. Weeds in this group include fat hen, wild oats.
– C 4 or dicarboxylic acid plants. Crops in this group include sorghum, sugarcane
and maize. Weeds in this group include couch grass, Johnson grass, summer grass.
– CAM (crassulacean acid cycle) plants, eg prickly pear.
While only a small proportion of all plants are either C4 or CAM, many plants in
these 2 groups are weeds. The competitive advantages of C4 or CAM plants
include reduced transpiration rates, increased high light-intensity and temperature
tolerance and more efficient photosynthesis which make them more suited to semiarid
subtropical and tropical areas, and more efficient as weeds than most C3 plants
(Parsons and Cuthbertson 2001).
410 Weeds - Biology, classification and identification