Lecture 3: Biological Control of Weeds Flashcards
1
Q
3 biological control strategies:
A
- classical control
- conservation control
- inundative control
2
Q
classical control:
A
the introduction of exotic insects or pathogens from one geographical area to another with the object of controlling naturalised, invasive weeds
3
Q
conservation control:
A
this refers to the use of indigenous predators & parasitoids, usually against native weeds
4
Q
inundate control:
A
this uses pathogenic fungal spores in the same way as chemical herbicides i.e. spores are sprayed onto a crop containing weeds with the objective of killing the weeds
5
Q
classical control of weeds acts on two types of weeds:
A
- Aquatic weeds
- Water fern (Slavinia molesta) controlled by the water beetle Crytobagous salviniae)
- Terrestrial weeds
- -Prickly pear cactus (Opuntia species) controlled by the moth Cactoblastis cactorum
- Japanese knotweed (Fallopian japonica) in the UK
6
Q
Characteristics of classical control: The pathogen or pest is;
A
- only introduced once
- must be very host specific
- must have a negative impact on plant individuals and the population dynamics of the target weed
- must be prolific
- must be good colonisers
- must thrive & become widespread in all habitats & climates that the weed occupies
7
Q
problems of aquatic weeds:
A
- clogging of grids and sluiced in hydro-electric plants
- inteference with navigation & fisheries
- depletion of oxygen from the water leading to death of fish
- act as habitats for vectors of human diseases
- increases water loss through evapo-transpiration
8
Q
Water Fern (Salvinia molesta) is native to:
A
South America
9
Q
Water Fern (Salvinia molesta) reproduces how?
A
efficiently by the spreading of buds that easily break off when disturbed
10
Q
Water Fern (Salvinia molesta) affects other plants by
A
forming floating mats that shade and over crowd native plants. These mates also form in rivers & irrigation ditches which constrains agriculture
11
Q
spread of Salvinia molesta in Australia:
A
- 1952 :Introduced into Australia
- 1976 : Widespread in rivers& lakes (as there was a lack in parasites/pathogens & because it posses a v rapid growth rate
- 1978: Largest infestation in Lake Moondara in N. Queensland
- 1979: Use of herbicides stopped
- Search for a biological control agent began
12
Q
Biological control agent used against Salvinia molesta: Where was it discovered?
A
Cyrtobagous salviniae (water weevil) was found by CSIRO Entomology scientists in Brazil - the home of the weed
13
Q
Biological control agent used against Slavonia molesta: how does it work
A
- adult female lays her egg sin a cavity that she creates by chewing into the leaf bud
- larvae that hatch feed on the base of the leaf bud and eventually tunnel into the rhizomes
- Weevil larvae become adults in 17-28 days during the warmer parts of the summer
14
Q
biological control action on Lake Moondara Australia (Agains Salvinia molesta
A
- 15000 Water weevils individuals were released in June 1980
- by June 1981 the weed was under control
- Salvinia has been controlled in tales 13 other tropical countries has a direct result of the research
15
Q
Where have successful biological controls been used against Salvinia molesta in the world:
A
- Australia (Lake Moondara)
- Sri Lanka
- Botwana
- Senegal
- Mauritania
- Benin
- South Africa
- USA
- Papua New Guinea
-Is a problem in many tropical & sub tropical areas in thew world
16
Q
biological control of terrestrial weeds: Prickly pear cactus
A
- Opuntia species,
- controlled by larvae of the moth Cactoblastis cactorum
17
Q
biological control of terrestrial weeds: Japanese knotweed
A
- Fallopia japonica
- in the UK controlled by a plant louse Aphalara itadori
18
Q
Prickly pear cactus (Opuntia species) General facts:
A
- native to S. America
- is a succulent up to 7m in height
- stems are fleshy jointed into pads with spines
- large brightly coloured flowers
19
Q
Problems the Prickly Pear cactus causes:
A
- propogates by seed or pads in contact with the ground
- Nasty spines
- if eaten by livestock spines cause damage to the animals mouth
- forms dense thickets and excludes livestock & other species
20
Q
control of prickly pear cactus:
A
- 1925: prickly pear had spread from being used as a paddock divider on a few farms in South Australia, to covering over 4 million hectares of farming land unusable for livestock
- 1928 - Cactoblastis cactorum moth larvae was introduced (from Argentina) to prickly pear populations in New South Wales and Queensland.
- Within ten years the Cactoblastis larvae had virtually wiped prickly pear out.
- One of the first major successes in biological control
21
Q
____ is reached between the weed and biological control agent
A
EQUILIBRIUM
22
Q
When biological controls go wrong:
A
- during 1950’s C. cactorum was introduced to the Caribbean island of Nevis to control prickly pear
- however, the adult moth crossed 3km of weak to the nearby island of St Kitts
- More recently C. cactorum has spread more widely in the Caribbean, and in 1989 it reached the mainland USA in Florida.
- By 1999, alarm was growing for endemic prickly pear species in the USA and Mexico.
- Opuntia is a key member of major ecosystems and an important agent in the fight against desertification and in soil regeneration
- It has a wide range of uses in food products, medicines, cosmetics, agriculture and in energy production.
- In Mexico 360,000 ha of Opuntia are under cultivation and 3 million hectares of wild Opuntia are also utilized.
- The sector is estimated to be worth some US$80 million per annum, with exports valued at $30 million.
23
Q
biocontrol of Japanese knotweed (Fallopia japonica) in the UK: native to:
A
Eastern Asia
24
Q
biocontrol of Japanese knotweed (Fallopia japonica) in the UK: introduced into gardens in Europe + spread where
A
- 200 years ago
- subsequently spread to North America
25
biocontrol of Japanese knotweed (Fallopia japonica) in the UK: description
strong-growing, clump-forming perennial, with tall, dense annual stems.
-stem growth is renewed each year from the deeply-penetrating rhizomes (creeping underground stems)
26
biocontrol of Japanese knotweed (Fallopia japonica) in the UK: growth over the year
- winter: plant dies back beneath ground but by early summer the bamboo-like stems shoot to over 2.1m (7ft) suppressing all other growth
- grows through concrete & destroys properties forcing building contractors to abandon infested building sites
- in the UK half-million homes are currently uninsurable
27
biocontrol of Japanese knotweed (Fallopia japonica) in the UK: eradication & damage costs
- eradication requires determination as it is very hard to remove by hand or with chemicals
- damage & removal costs £288 million per annum in the UK
28
is japanese knotweed a problem in japan? & WHY
No, it is attacked by 168 insects and 40 fungi
29
how did they source a biocontrol for knotweed?
- 6 years ago Dr Richard Shaw & colleagues at CABI Switzerland brought back 40 potential control agents for testing
- literature search of each species diet narrowed it down to 9
- these 9 were tested on 90 British plant species & close relatives of Japanese knotweed
- 2 mm long plant louse (psyllid) Aphalara itadori was found to be host specific
- 2010 UK government gave permission for a limited field trial at isolated site
- after 3 months knotweed was infested with louse
- Released at 8 sites across Eng & Wales has been approved
- its too early to assess impact
30
inundative biological control strategies involve :
the mass release of natural enemies (usually fungal diseases) to kill the weed in a manner analogous to the use of chemical herbicides
31
inundative biological controls in the case of fungal diseases:
(myco-herbicide) spores are sprayed onto a crop containing weeds with the objective of killing the weeds
32
inundative biological controls: Natural enemies must be::
- highly virulent
| - highly specific (to avoid damage to other weeds or crops, livestock & humans)
33
plant pathogen example:
-Crop: small grain crops
-Weed: Roundeaf mallow (Malva pusilla)
fungus? Myco-Herbicide?
- Myco-herbicide: BioMal
| - Fungus: Colletotricum gloeosporioides
34
Northern Joint Vetch (Aeschynomene virginica) is a
leguminous weed of rice and to a lesser extent sorghum in E. Arkansas USA
35
Northern Joint Vetch (Aeschynomene virginica) competes with crop how?
- erect annual about 2m tall and it competes very successfully with the rice by shading it
- also severely contaminates rice crop with vetch seeds
36
Northern Joint Vetch (Aeschynomene virginica) Old control + disadvantages with it
- for a long time only control was the use of proposal and pheenoxy herbicides
- however:
- -they injure the rice
- - they fail to kill the vetch unless applied at exactly the right time
37
biocontrol for Northern Joint Vetch: naturally:
- Anthracnose (Colletotricum gloeosporioides) an endemic disease of vetch, present in low amounts in the environment
- it is dispersed by rain splash & therefore doesnt spread very far very fast
38
biocontrol for Northern Joint Vetch: commercially
by applying heavy dose of spores in the form of the mycoherbicide Collego
- field trials aerial sprays of fungal spores killed 99% of the vetch plants
- farmers mix the formulated dry spored with a wetting agent & mix with 250L of water
- The suspension is sprayed from the air when the crop is well watered and relative humidity is likely to be high for the next 12 h.- Within a week the vetch plants begin to show lesions and within 5 weeks are dead.
39
how is College marketed?
- as a dry formulation (15% viable spores, 85% inert ingredients)
- each pack contains 757 billion spores (treats 2.5 hectares)
40
development of mycoherbicide
* Field search for specimens of the target weed showing symptoms of infection.
* Isolate and grow the fungus in the laboratory so that it produces spores.
* The effectiveness/specificity of the pathogen is then tested by spraying spores onto detached leaves and seedlings.
* If the fungus passes the preliminary screen a much wider range of species will be tested for specificity.
* It must grow and produce spores in cultures in industrial conditions.
* The developer must apply for a patent, which means that the fungus must not have been exploited before.
* Other pesticides applied to the crop must not harm the fungus.
* A suitable formulation in which to apply the fungus must be designed to ensure that the fungus has the maximum chance of infecting adult plants.
* Very expensive to produce a mycoherbicide
41
advantages of biocontrol :
- Target specificity
- Continuous action
- Long-term cost effectiveness
- Often gradual in effect therefore environmentally friendly
- Self dispersing (even into difficult terrain)
- Can be used as part of an IPM strategy
- Reduces the vigour and competitiveness of a weed
42
disadvantages of biocontrol
- Initially high research cost -Protracted time until impact likely
- Uncertainty over ultimate scale of impact
- Uncertain ‘downstream effects in ecosystems (hard to predict or quantify)
- Only targets a single weed species
- Suitable agents may not exist Irreversible
43
biological control is not appropriate when
- A species is a weed in one area but valued in other situations
– blue weed (Echlum vulgate) is a serious pasture weed in the
USA but is also a desirable plant for honey production.
- Weeds are close relatives of economic crops.
- Lots of weeds are present. As biological control agents are highly specific to one weed species little would be gained from controlling one weed amongst a large variety of weed species.
- Eradication of the weed is desired (e.g. poisonous weeds).
