Weeds in Non-Crop Environments

Rangeland Weeds

• Rangeland weeds, environmental weeds, and aquatic weeds.
• Content is protected and should not be shared, uploaded, or distributed.

Rangelands

• Over half of Australia is used for grazing livestock on plant communities, generally denoted as rangelands or grasslands.

Definition of Rangeland

• Grassland: A vegetation community dominated by grasses, grass-like plants, and/or forbs.
• Rangeland: The internationally recognized term for land supporting vegetation suitable for grazing, where livestock are grazed extensively on native vegetation, and where rainfall is considered too low or erratic for agricultural cropping or improved pastures.

Location of Rangelands in Australia

• Tropical 'rangelands'.
• Arid & semi-arid 'rangelands'.
• Temperate 'pastures'.
• Subtropical 'rangelands'.

Animal Production

• Beef Cattle.
• Beef Cattle, Sheep, Goats.
• Beef & Dairy Cattle, Sheep, Goats.
• Beef, Dairy Cattle.

Rangeland Environments

• Spinifex country ($Trioda spp$).
• Mulga woodland.
• Mitchell grasslands.
• Eucalypt woodland.
• A range of different exotic weeds are present in rangeland environments.

Exotic Weeds Present In Rangeland Environments

• Mother of millions.
• Chinee apple.
• Giant rat’s tail grass.
• Coral cactus.

Invasive Native Plants

• $Tribulus cistoides$ (Caltrop).
• $Eremophila sturtii$ (Turpentine bush).
• $Carissa ovata$ (Currant bush). Currant bush ($Carissa ovata$) is a native plant that is invasive.

Impacts of Weeds in Rangelands

• Reduce pasture growth and land condition.
• Threaten the biodiversity of ecosystems.
• Barrier to movement & visibility.
• Affect operation of machinery.
• Physical injury (spines).
• Harbour feral animals (pigs).
• Affect human health (parthenium).
• Hosts to diseases & insects.
• Can be poisonous to livestock.

Conflict or Contentious Plants

• "Those that have attributes that make them useful or desirable and attributes that make them problematic."
• (Clarkson et al. 2010)

Neem Tree ($Azadirachta indica$)

• Was grown for production of a natural insecticide, azadirachtin, found in the seeds and leaves.
• Also widely planted as an ornamental and shade tree.
• In some areas, neem has escaped cultivation and formed naturalized populations.
• Infestations reduce biodiversity and change ecosystem function. They also reduce pasture growth.

Commercialisation of Declared and Non-Declared Rangeland Weeds

1. From time-to-time companies/organizations try to commercialize weeds for a range of purposes.
2. Many of the weeds in Australia are used for many purposes in other countries, and in those they may not be considered a weed.
3. Examples:
   • Biofuels – $Jatropha curcas$ and $Jatropha gossypiifolia$
   • Power generation – $Vachellia nilotica$ (Prickly acacia)
   • Biochar – $Vachellia nilotica$ (Prickly acacia)
   • Insecticides – Neem tree ($Azadirachta indica$)
4. Commercialization is possible in Australia as long as it is consistent with relevant legislation and contributing to management of the weed.

Managing Rangeland Weeds

• Be aware of weed species.
• Prevent introductions.
• Understand life cycle and how spread.
• Detect infestations early and act strategically to control infestations.
• Monitor key entry sites (yards, roads, buildings, water points, riparian areas).
• Integrate a variety of management techniques.

Phases of Weed Increase

• Introduction to the area.
• A latent or lag phase (slow increase).
• Period of rapid growth & expansion.
• Final phase slow expansion of now significant problem.
• Fast for annuals, slower for perennials e.g. trees.

Understand Life Cycle

• Key issues in life cycle:
  • Life span of species
  • Level of seed production & dormancy
  • Frequency of seeding and seedling emergence
  • How spread (dispersal)
  • Whether they vegetatively reproduce
  • How quickly new plants reach reproductive maturity
  • Recovery after physical damage

Prickly acacia spread

• Water dispersal
• Prickly acacia spread down a gully
• Bellyache bush along the Palmer River in North Queensland

Spreading Weeds

• Animal dispersal - Prickly acacia

Passage of Weed Seeds Through Cattle

• Graph showing cumulative % over days for prickly acacia and giant rats-tail grass. Data from Wayne Vogler, QDAF.

Animals Carrying Weeds

• Animals carrying weed seeds can be transported long distances to new areas

Longevity of Soil Seed Banks

• Helps determine the potential duration of control programs, but can be influenced by a range of factors:
  • Dormancy mechanisms
  • Rainfall conditions
  • Temperature
  • Soil type
  • Level of cover
  • Burial depth
  • Light

Variability in Weed Seeds

• Mesquite
• Stevia
• Parthenium
• Calotrope
• Pink lantana
• Orange lantana
• Neem
• Leucaena
• Yellow oleander
• Gamba grass
• Prickly acacia
• Chinee apple

Change in Viability of Prickly Acacia Seeds Over Time

• Figure 1. Change in viability of prickly acacia seeds over time averaged across different burial depths, soil types, and levels of pasture cover.

Neem Tree Seed Longevity

• Trial was undertaken incorporating different soil types, levels of pasture cover and burial depths.

Management/Control Options

• Pasture management (competition)
• Fire
• Physical control (e.g. manual removal, Machinery)
• Herbicide control
• Biological control
  • Traditional biocontrol (e.g. insects, pathogens)
  • Browsing animals (e.g. goats, camels, cattle, sheep)

A Competitive Pasture Can

• Reduce the number of weed seedlings that emerge
• Increase seedling mortality
• Make plants take longer to reach reproductive maturity
• Reduce seed production

Pasture Management

• Stocking rates should be set to maintain a competitive pasture
• Undesirable species are often not overly competitive, but opportunists
• They will occupy bare ground and degraded areas
• Once established can be difficult to remove

Bellyache Bush Competition Trial

Fire

• Cost effective technique on a large scale
• Not all weeds are susceptible and some thrive after burning
• Can effect some life-stages but not others
• Need to rest pastures after burning to allow them to recover

Fire Effects on Life-Stages of Some Rangeland Weeds

Weed Control Methods - Physical Control

• Hand removal
• Brushcutters
• Slashing
• Mulchers

Weed Control Methods – Physical Control

• Chain pulling
• Front mounted bladeplough (Ellrott plough)
• Grubbing out plants
• Front end loader

Physical Control

• Range of options can be used, depending on:
  • Type of weed (e.g. grass, herb/forb, shrub, or tree)
  • Size and density of infestation
  • Available resources
• Some weeds will reshoot after being cut off at ground level (e.g. slashing)
• For woody weeds, severing the root system below ground gives the highest mortality
• For techniques that disturb the soil expect large scale seedling regrowth

Herbicide Control

• Range of herbicides:
  • Non-selective (e.g. glyphosate)
  • Selective – (e.g. can control grasses amongst broadleaf plants or can control broadleaf weeds in pastures)
• Biggest challenge is to control grass weeds in pastures
• Range of techniques
• Can be expensive to treat large infestations

Herbicide Application

• Stem injection
• Basal bark
• Foliar
• Cut stump
• Aerial applications

Use of Residual Herbicides

• Preferred option for many landholders in permissible areas
• If effective kills not only the original plants but also seedling regrowth
• Main chemicals contain tebuthiuron or hexazinone
• Can be ground applied or aerially (only tebuthiuron)

Biological Control

• Using pathogens, insects, and animals
• Cattle can heavily defoliate calotrope plants at certain times, but not always.

Selecting Control Options - Bellyache Bush Example

• Depends on:
  • Size of infestation
  • Density
  • Habitat
  • Available resources
  • Regulations

Integrated Management Example: Management of Rubber Vine ($Cryptostegia grandiflora$)

• Mechanical grubbing, aerial spraying, prescribed burning, and biological control
  • Mechanical treatment
  • Herbicides
  • Prescribed burning
  • Biological control

Managing Weed Complexes in Rangelands

• One of the greatest challenges

Rangeland

• Near Charters Towers, North Queensland
• Rubber vine
• Chinee apple
• Parthenium

MANAGEMENT OF ENVIRONMENTAL WEEDS

Environmental Weeds

• Environmental weeds are weeds that invade natural ecosystems
• This can include native species spreading beyond their natural range (e.g. coastal tea tree)
• They affect many types of habitat, therefore their management is on a case-by-case basis

Coastal Tea Tree

• Coastal tea tree ($Leptospermum laevigatum$) is a native plant that is a serious environmental weed outside its natural range.

Where Do They Come From?

• Most environmental weeds were deliberately introduced
• Dispersal is by abiotic means, animals, or humans
• They threaten disturbed and undisturbed native vegetation
• New weeds are still being introduced and spreading
• Ornamentals dumped in bushland or sold by nurseries, compounding problem; public education needed

Impact: On Natives

1. Environmental weeds affect biodiversity and ecological processes in native ecosystems
2. Direct impacts include shading, competition, change in fuel load affecting fire regime
3. Indirect impacts occur through changes in other species (e.g. weed presence may affect abundance of pollinators)

Impacts: On Natives (cont.)

5. Severe weed invasion can displace native species through competition and cause extinction of some rare taxa.
6. Threatened taxa, often in remnants and degraded habitats, are at increased risk.
7. Seed bank composition is also modified as weed propagules enter the soil.
8. Reproductive capacity of weeds often greater than native plants.

Impacts: On Natives (Cont.)

9. Weeds cause changes to the composition and structure of vegetation, altering sources of food and shelter for fauna
10. Weeds can favour some native animals but harm others
11. Where native animals feed on weeds, management strategies need to supply alternative plants
12. Management also must control spread of weeds by feral animals

Environmental Weed Management

• Aims of environmental weed management:
  1. Effectively contain spread of existing weeds
  2. Manage the environment to prevent new invasions
  3. Rehabilitate the disturbed ecosystem as far as possible
• Ecological information is needed to develop strategies, including that of native species
• So, weed management approaches used must facilitate native plant regeneration

Management Techniques

• Chemical management must be applied with care but can be very effective e.g. cut-stump, stem injection, weed wipers to apply herbicide directly
• Mechanical (cutting/mowing) can be impractical
• Biological control if effective agents can be found
• Physical (hand pulling) removal by volunteers near populated areas
• Physical (fire) can be an important tool

Fire

• Factors for consideration in using fire to manage environmental weeds:
  1. The response of the weed to burning
  2. The type of ecosystem infested with weeds
  3. The season of fire
• Fire can be used in conjunction with other methods e.g. herbicide on new seedlings after burning

Revegetation Techniques

• Revegetation is the reintroduction of plant species into a degraded habitat
• Exotic or native species can be used, natives are preferred
• Revegetation can help prevent weeds by choosing competitive native plants

National Tropical Weeds Eradication Program on Environmental Weeds

• $Miconia racemosa$
• $Miconia calvescens$
• $Miconia nervosa$
• $Mikania micrantha$

Recent Examples of Eradication Programs that Transitioned into Containment Programs

• Siam Weed ($Chromolaena odorata$) eradication program ended in 2012
• $Clidemia hirta$ (Kosters curse) eradication ended 2015

Conclusions

• Impacts of EW include biodiversity loss, loss in aesthetic values, lower wilderness quality in addition to increasing costs for land management
• IWM of EW requires application of general weed management principles that take into account the particular situation
• Proper management requires detailed ecological knowledge of the weed and the native plant community

AQUATIC WEEDS

Introduction

• Water is an essential resource and is used for a variety of purposes
• Aquatic plants are an important part of healthy aquatic ecosystems
• However, populations of aquatic plants can also have serious adverse impacts on aquatic ecosystems and their use (native and introduced)

Aquatic Ecosystems in Australia

• There are three main types of aquatic ecosystems in Australia:
  • Permanent rivers and creeks (problem with weeds)
  • Permanent lakes and wetlands (problem with weeds)
  • Temporary aquatic systems (less so)

Source of Aquatic Weeds

• Illegally brought in (e.g. smuggled in) - Limnocharis ($Limnocharis flava$)
• Aquarium trade - e.g. Cabomba ($Cabomba caroliniana$)
• Ornamental - Water hyacinth ($Eichhornia crassipes$)
• Horticulture - e.g. Pond apple ($Annona glabra$) – root stock for custard apple plants
• Pasture plants - e.g. Hymenachne ($Hymenachne amplexicaulis$)

Features of Aquatic Weeds

• Plants that grow in aquatic ecosystems are often specifically adapted to such environments
• They may have attributes that allow them to:
  • Tolerate low $O_2$ levels in the water or substrate,
  • Respond to rapidly changing water levels,
  • Float on or near the water surface – (example – water hyacinth),
  • Survive in low light intensities,
  • Reproduce rapidly during favourable periods,
  • Survive long periods without water, and
  • Tolerate marked changes in the amount of dissolved salts & organic matter present

Types of Aquatic Plants

1. Submerged plants
2. Emergent plants
3. Floating plants:
   • attached floating plants
   • free floating plants

Examples: Submerged Plants

• Hornwort ($Ceratophyllum demersum$)
• Hydrilla ($Hydrilla verticillata$)
• Dense waterweed ($Egeria densa$)
• Curly pondweed ($Potamogeton crispus$)

Examples of Emergent Plants

• Water plantain ($Alisma plantago-aquatica$)
• Cumbungis/Bullrush ($Typha spp.$)
• Sacred lotus ($Nelumbo nucifera$)
• Spikerushes ($Eleocharis spp.$)

Examples of Free-Floating Plants

• Ferny azolla ($Azolla pinnata$)
• Duckweeds ($Spirodela$ and $Lemna spp.$)
• Water lettuce ($Pistia stratiotes$)
• Salvinia ($Salvinia molesta$)

Examples of Attached Floating Plants

• Monochoria ($Monochoria cyanea$)
• Java pondweed ($Potamogeton javanicus$)
• Water primrose ($Ludwigia peploides$)
• Water snowflake ($Nymphoides indica$)

Impacts of Aquatic Weeds

• Aquatic weeds can:
  1. Interfere with water flow in rivers, irrigation channels, drains
  2. Clog the intakes of pumps and irrigation equipment
  3. Interfere with movement of boats on lakes and rivers
  4. Interfere with commercial and recreational fishing activities
  5. Inhibit recreational use of water bodies

Impacts of Aquatic Weeds

• Aquatic weeds can:
  6. Be a safety hazard to livestock/humans
  7. Enhance water loss through increased evapotranspiration
  8. Replace plants that provide important habitats and food sources for aquatic animals and birds
  9. Reduce the biodiversity of aquatic environments and threaten the survival of rare native plant species
  10. Reduce the aesthetic appeal of natural areas
  11. Harbour pest and disease organisms

Management Methods

Mechanical Control Methods

• In aquatic ecosystems, this usually involves weed removal using mechanical harvesters
• Slightly different methods of removal are required for different types of aquatic weeds

Chemical Control Methods

• Chemical control is most suitable for smaller infestations
• Herbicides-generally not recommended or available for controlling submerged aquatic weeds

Biological Control Methods

• Biological control involves introducing the natural enemies of the weed into the aquatic ecosystem
• Though it can be extremely useful in some circumstances, it is rarely the complete solution for a weed problem

Examples

• Example 1: Salvinia ($Salvinia molesta$)
• Example 2: Water Hyacinth ($Eichhornia crassipes$)
• Example 3: Alligator Weed ($Alternanthera philoxeroides$)

$Salvinia molesta$

• Salvinia is a free-floating fern of tropical and sub-tropical water bodies
• This species is also capable of very high growth rates
• It is sterile and therefore relies totally on vegetative reproduction

Example $Salvinia molesta$

• Biological control has been spectacularly successful in some situations
• Chemical herbicides can be used, but they require a surfactant to break down the hydophobic action of the upper leaf surface

Example $Salvinia molesta$

• Mechanical barriers, such as booms and nets, have been used to contain infestations
• Successful management relies on early detection and implementation of an integrated weed control (IWM) program

Conclusions

• There are a variety of aquatic ecosystems in Australia, with varying levels of susceptibility to aquatic weed problems
• There are also several different types of aquatic weeds, with different characteristics and impacts, each requiring an emphasis on different control methods

Conclusions

• Aquatic weeds are often difficult to manage because they are not easily accessed and there are restrictions on using chemical herbicides near waterways
• Early detection and action are important for successful management, and so is the implementation of an integrated management program