NSW WRM system - Feasibility of Coordinated Control

Feasibility of Control

The feasibility of control section is also broken down into three main criteria;

Control costs, Persistence and Current distribution.

In the feasibility of coordinated control section, higher scores indicate a lower feasibility of coordinated control.

Control costs considers the weed management costs of detection, on-ground control, enforcement/education needs and landholder participation.

Persistence refers to the expected duration of control works.

Current distribution considers how widespread the weed is.

Scores for each of these criteria (each ranging between 0 and 10), are multiplied to give a feasibility score out of 1000.

In each species case, assess the feasibility of coordinated control for the land use you considered the weed risk for. This will mean that the resulting feasibility score can be directly compared to the weed risk score from the same land use to set control priorities.

All questions should be answered assuming control is specifically targeted to the weed being considered.

Control costs

Before answering questions in the Feasibility of Control section, list any additional targeted weed management methods that would be used to reduce the weed problem in the assumptions section.

The feasibility of coordinated control questions are divided into three main criteria: Control costs; Persistence; and Current distribution.

Remember, higher scores indicate a lower feasibility of coordinated control.

This section indicates the control cost per hectare in the first year of targeted control, for an infestation of the weed that has reached its maximum density in the land use at risk. The four main cost factors associated with coordinated control programs are in searching for the weed, accessing and treating infestations and landholder/volunteer participation in the management of the weed.

Control costs Question 1

How detectable is the weed?

Importance of the question

Detection of a weed will impact on the feasibility of management for that weed. Weeds that are more easily found are often more easily managed.

Explanation and assumptions

This question accounts for the cost of finding and treating infestations of the weed. Parts (a), (b) and (c) relate to finding new infestations while part (d) relates to finding weeds prior to reproduction.

Answer each part question.

Although detection is usually undertaken by weed professionals, for example weed officers or agronomists, responses to this question may need to consider detection by landholders or members of the community if these stakeholders are routinely involved in reporting and detecting new weeds.

Distinguishing features indicate how conspicuous the weed is amongst other vegetation. Distinguishing features may include the growth habit (for example upright, spreading or prostrate) and architecture of the plant; the colour and shape of the flowers, fruits and leaves; unique features such as unusual seed pods, bark, perfume of flowers and the smell of the leaves when crushed. The timing of the plants growth, seeding or maturity, (for example, leaf fall) may also be distinguishing features. Examples include the shape and foliage of a Pine tree (Pinus species) amongst most native vegetation, the smell of Blue heliotrope (Heliotropium amplexicaule) flowers, Lantana (Lantana camara) or Mintweed (Salvia reflexa), the unusual seed heads of the Devil claw species (Ibicella lutea and Proboscidea louisianica) or the Burr species (Xanthium species), or the leaf fall of deciduous trees such as Box elder (Acer negundo).

Shoot growth visible indicates the length of time that the plant shoots are actively growing and likely to be visible throughout the year. Annuals, for example the Burr species (Xanthium species), and some perennials, for example Bridal creeper (Asparagus asparagoides) have shoots present for a limited period of the year and can therefore only be detected during this limited time period.

Seedlings of perennial species may be difficult to see amongst existing vegetation. Consider this in part (d) only.

Height at maturity is important as it has a bearing on being able to locate new infestations of a weed. Taller plants can be spotted from greater distances.

Pre-reproductive height refers to locating the weed for management prior to it setting seed or new vegetative structures such as bulbs. Control must occur prior to reproduction for local eradication. The pre-reproductive height will often be less than the height of the plant at maturity and the weed will also probably be growing in amongst other vegetation. For this reason, the height of the weed is described relative to the height of the canopy of the other vegetation. For example, in a Dryland cropping land use the height of the canopy will be the crop height. Weed examples may include Wild oats (Avena fatua) growing amongst a wheat crop, Paterson's curse (Echium plantagineum) growing amongst pasture, or Lantana (Lantana camara) growing underneath a Eucalyptus woodland canopy.

Seedlings of perennial species may be difficult to see amongst existing vegetation (they are of similar height or below the canopy). To account for this, consider the total time a perennial species is pre-reproductive and then the relative proportions of time the species spends above, at the same height as, or below the canopy. Average the result when answering the question.

1. How detectable is the weed? Total (a+b+c+d) Score
(a) Distinguishing features (b) Period of year shoot growth visible  
non-descript 2 < 4 months 2 6, 7 or 8 3
sometimes distinct 1 4-8 months 1 3,4 or 5 2
always distinct 1 >8 months 1 1 or 2 1
do not know 1 do not know 1 0 0
(c) Height at maturity (d) Pre-reproductive height in relation to other vegetation  
< 0.5 m 2 below canopy 2
0.5-2 m 1 similar heigh 1
> 2 m 0 above canopy 0
do not know 1 do not know 1
Source and comments

Control costs Question 2

What is the general accessibility of known infestations at the optimum time of treatment?

Importance of the question

The general accessibility of weed infestations impacts on the cost of doing surveys to find the weed and the cost of control of the weed. Easily found and treated weeds are more easily managed.

Explanation and assumptions

Sites can be difficult to traverse due to a number of factors including slope, rockiness, dense vegetation and/or the presence of surface water. These difficulties will slow down both searching and management activities.

There may be seasonal differences in accessibility, for example due to water logging, so the answers should be in terms of optimal search and control times for the weed.

Conventional methods of access include four-wheel drive (4WD) vehicles, while sites that are more difficult to access may require quad bikes. In 'difficult to access' sites, specialist machinery may be needed such as a helicopter or a boat. In addition, 'difficult to access' sites may only be accessible by walking in or even abseiling. Similarly, riparian areas may be particularly difficult to access with any equipment and may have low accessibility.

2. What is general accessibility of known infestations at the optimum time of treatment? Score
low Most infestation sites are difficult to access via conventional methods and always require specialist equipment, for example, helicopter or boat. 2
medium Most infestation sites are readily accessible at most times of the year, or may require some additional equipment, for example, quad bikes. 1
high All infestation sites readily accessible via conventional methods. 0
not present Not known to be present. 0
do not know   1
Source and comments

Control costs Question 3

How expensive is management of the weed in the first year of targeted control?

Importance of the question

The cost of weed management will impact on how feasible a weed is to manage.

Explanation and assumptions

The question examines the costs of weed management in the first year of targeted control, for an infestation that has reached maximum weed density. Techniques used will be those that both maximise efficacy and minimise off target damage. It is assumed that the costs of management in the first year will be the most expensive in any program. Answer each part question.

Herbicides are usually the main means by which weeds are controlled. Physical and mechanical control methods may include cutting/slashing, cultivation, or extraction. The costs of mechanical control such as ploughing should be recorded as equipment costs. Do not consider capital costs for purchasing application equipment in this question.

When answering this question assume that you are already at the location of the weed infestation (that is you do not need time to arrive) and there is good water access nearby (that is there is no lengthy travel time to fill up for chemical applications throughout the process). Labour costs should include any volunteer labour used such as bushland regenerators, and the time needed for landholders and/or contractors to manage the weed, not just Local Control Authority labour costs.

Chemical and labour costs are calculated per hectare.

If the weed is not known to be present, indicate this in parts (a), (b) and (c) of the question. Even if this is the case, supplying information on the costs of control (if known) would be appreciated. Please record this information along with the source in the 'Source and comments' response for this question. This information will be kept on file in case these weeds are found at a later date. Although not mandatory, supplying information on the control methods to be used in 'Source and comments' response would also be appreciated.

3. How expensive is management of the weed in the first year of targeted control? Total (a+b+c) Score
(a) Chemical cost - How much chemical will you use per hectare? (b) Labour costs - How many person hours will it take you to control/ha?   
Very high (>$500/ha) 4 Very high (>$500/ha) 4 8.5-11 5
High ($250-500/ha) 3 High ($250-500/ha) 3 6.5-8 4
Medium ($100-249/ha) 2 Medium ($100-249/ha) 2 4.5-6 3
Low (<$100/ha) 1 Low (<$100/ha) 1 2.5-4 2
None, or not present 0 None, or not present 0 1-2 1
do not know 2 do not know 2 0 0
(c) Equipment costs - What equipment are you going to use? Source and comments (Even if the weed is not present, please consider adding management costs if known)
High e.g. earthmoving equipment like bulldozers. 3
Medium e.g. helicopter or boat. 2
Low e.g. slasher/tractors, quad bike/4-WD/quick-spray. 1
None - physical control of the weed occurs, or not present. 0
do not know 1.5

Control costs Question 4

What is the likely level of participation from landholders/volunteers within the land use at risk?

Importance of the question

Weeds that are more likely to be managed by landholders/volunteers are more feasible to control.

Explanation and assumptions

Aside from the "on-ground" costs of searching and control, a coordinated control program will have overarching costs of extension/education, enforcement, project management and administration. The ease of motivating and coordinating landholders/volunteers in an ongoing program will also vary between land uses, particularly in relation to the financial capacity of landholders/volunteers to support a control program, or the amount of funding available from external sources.

Assume existing levels of financial and technical capacity of landholders/volunteers. Do not consider any future funding that has not been received.

Assume there are no potential conflicts of interest with the weed species that are to be managed, for example, that the weed being considered is not of economic use in another situation. Further information on conflict of interest species can be found in the Positive impacts section.

4. What is the likely level of participation from landholders/volunteers within the land use at risk? Score
low Weed management is rarely undertaken in the land use. Cost of control is beyond the financial and/or technical capacity of landholders/volunteers. 2
medium Management of the weed will require significant change to existing weed management practices, but this will be within the financial and technical capacity of landholders/volunteers. 1
high Management of the weed will require minimal change in existing weed management practices. 0
do not know   1
Source and comments

Persistence

This section indicates how long it takes to try and eradicate the weed or achieve some desirable level of control. It considers the efficacy of targeted management treatments, reproductive age, seed bank longevity and the likelihood of ongoing dispersal.

Persistence Question 1

How effective are targeted management treatments applied to infestations of the weed?

Importance of the question

The efficacy of targeted management will affect the persistence of the weed.

Explanation and assumptions

The question seeks to gauge the success or efficacy of targeted management treatments applied to infestations of the weed on an annual basis.

Herbicide and physical means of management may not kill all individuals of the weed. Efficacy can be reduced by:

  • tolerance of weeds to, or recovery from, treatment, for example fleabane (Conyza species) after they have been sprayed with some herbicides
  • incomplete application of a treatment, for example some weeds may not receive a lethal dose of herbicide, or may miss treatment altogether, for example Salvinia (Salvinia molesta) under overhanging riparian vegetation plants, or when gaps occur in spraying
  • vegetative regeneration from missed weed parts after treatment, for example from roots of silver-leaf nightshade (Solanum elaeagnifolium) or pads of cactus (Opuntia species)
  • "out of season" growth, for example early or late germination flushes of annual species such as caltrop or cathead (Tribulus species) and Chilean needle grass (Nassella neesiana). This means that if one management treatment is used per year, and seedlings germinate or plants regenerate after this, then the efficacy of treatment will be reduced. This will also include germination flushes that occur after treatment, for example with contact herbicides. These flushes may then grow and produce seeds or other vegetative propagules.

Consider the annual success or efficacy of all targeted management treatments applied. For example if herbicide application allows 30% of the total plants to survive, but subsequent cultivation allows only 10% of the total plants present at the start of the year to survive, then annual efficacy is 'medium' because 10% of all plants have survived.

1. How effective are targeted management treatments applied to infestations of the weed? Score
low More than 25% of weeds survive annual targeted treatment/s. 3
medium 5-25% of weeds survive annual targeted treatment/s. 2
high 1-5% of weeds survive annual targeted treatment/s. 1
very high <1% of weeds survive annual targeted treatment/s. 0
do not know   1.5
Source and comments

Persistence Question 2

What is the minimum time period for reproduction of sexual or vegetative propagules?

Importance of the question

The minimum time period for reproduction will impact on the persistence of a weed. Management before reproduction will reduce the persistence of weeds.

Explanation and assumptions

A shorter time period to reproduction will result in more frequent targeted management needed to prevent this, and a greater chance that weeds will be missed prior to reproduction. Propagules are any part of a plant that is potentially able to produce a new plant. This includes parts from sexual reproduction such as seeds, and parts from vegetative reproduction such as bulbs, root fragments, tubers or rhizomes. Some plants can produce both sexual and asexual propagules.

Examples of weeds with rapid reproduction include Spiny burrgrass (Cenchrus incertus and C. longispinus) and aquatic plants such as Salvinia (Salvinia molesta).

2. What is the minimum time period for reproduction of sexual or vegetative propagules? Score
<6 months. Minimum generation time <6 months. 3
6-12 months Minimum generation time 6-12 months. 2
<1-2 years Minimum generation time <1-2 years. 1
>2 years Minimum generation time >2 years. 0
do not know   1.5
Source and comments  

Persistence Question 3

What is the maximum longevity of sexual or vegetative propagules?

Importance of the question

The longevity of sexual or vegetative propagules will impact on the persistence of a weed. More persistent weeds have longer lasting seeds or vegetative propagules.

Explanation and assumptions

The longevity of the seed bank, or of vegetative propagules is one of the primary determinants of how long an infestation must be treated with targeted management to achieve eradication or a desirable control level.

If a weed produces both seeds and vegetative propagules in the geographic area under consideration then answer the question with the longest lived propagules in mind.

3. What is the maximum longevity of sexual or vegetative propagules? Score
>5 years Sexual or vegetative propagules can remain viable for at least 5 years. 2
2-5 years Sexual or vegetative propagules can remain viable for 2-5 years. 1
<2 years Sexual or vegetative propagules remain viable for less than 2 years. 0
do not know   1
Source and comments

Persistence Question 4

How likely are new propagules to continue to arrive at control sites, or to start new infestations?

Importance of the question

More persistent weeds are likely to have propagules that continue to arrive at control sites, or start entirely new infestations.

Explanation and assumptions

This question looks at how likely a weed is to continue to arrive at a control site or start a new infestation in the presence of targeted management. Do not consider weeds already at the site or seeds in the soil as these are already under targeted management.

Long distance dispersal (>100m) should only be considered in this question. New plant propagules (whether sexual or vegetative) are likely to arrive by either natural or human means. Spread by human means may be accidental, for example in contaminated produce, livestock or on vehicles, or be deliberate because the species is also an important agricultural, forestry, horticultural or garden plant (known as a conflict species).

Targeted management is needed to treat new infestations as they arise.

Answer each part question.

Information on conflict species should be recorded in the Positive impacts section.

4. How likely are new propagules to continue to arrive at control sites, or to start new infestations? Total (a+b) Score
(a) Long-distance (>100 m) dispersal by natural means (b) Long-distance (>100 m) dispersal by human means  
frequent 2 frequent 2 4 3
occasional 1 occasional 1 2 or 3 2
rare 1 rare 1 1 1
do not know 1 do not know 1 0 0
Source and comments

Current distribution

This section indicates the total extent, number and geographic distribution of infestations of the weed within the land use.

Mapping of a weeds distribution will be needed in order to answer these questions. A nationally consistent approach to recording the area of weeds has been developed in Australia (McNaught et al. 2006).

If a species has, or has been grown in gardens or on farms in the past then it is quite likely to be present in many places.

Current distribution Question 1

What percentage area of the land use in the geographic area is currently infested by the weed?

Importance of the question

The area infested by a weed will affect the feasibility of managing or eradicating the weed. The greater the area of a weed, the less feasible it will be to contain or eradicate.

Explanation and assumptions

The Current distribution of a weed will affect what the size and types of possible management responses will be. As a general rule, the more widespread a species is, the less feasible it will be to either manage or eradicate it.

Eradication of a species is generally difficult to achieve for infestation areas greater than 100-1000 ha (Groves and Panetta 2002, Panetta and Timmins 2004).

There are exceptions to this general rule, for example the eradication of Kochia (Bassia scoparia), which was previously planted as a salinity remediation species in Western Australia. Such exceptions are generally due to quite unusual circumstances. The eradication of Kochia was achieved because seed sales and planting areas were well known and documented, in addition to a number of other factors. Alternatively, it is possible to achieve eradication if a single spread event has resulted in weed establishment, and little if any reproduction has then occurred. This has previously occurred with Parthenium (Parthenium hysterophorus) contaminating planting seed in a once-off planting event.

Localised eradication from parts of the total infested area may be possible in areas larger than 1000 ha, although it is likely that management efforts will need to focus on containment and management of the weed to reduce, not eliminate, the weed and the impacts it causes. Good weed management aims to prevent weed spread within a susceptible area or to other areas that are susceptible to infestation.

All currently infested areas that are in the geographic area should be determined

The land use under consideration has been defined previously.

The geographic area is the total area under consideration, for example a Local Control Area, the group of councils, a Catchment Management Authority, or the state of NSW. Such areas may include where the species is cultivated in gardens or on farms if the weed is a conflict of interest species.

In answering the question, it is important to consider what percentage area of the land use is currently infested by the weed. Answer the question by selecting the most appropriate area above the thickened line in the answer table. It is still important to answer the question if the weed does not infest the land use but is present in the geographic area.

For example, the weed being considered may not occur in a Dryland cropping pasture rotation but may be present in the Grazing modified pasture land use in the geographic area. Remember the geographic area being considered may be a region, catchment, an individual Local Control Area or even a property. If the weed is not present in the land use but is present in the geographic area answer the question by selecting the most appropriate area below the thickened line in the answer table. It is unlikely that a weed would infest more than 40% of the geographic area and not be present in the land use.

Infestation areas should be calculated as actual areas covered by the weed, that is, a border that bounds all known plants. Isolated plants found away from core infestation areas should be treated as separate areas. All known infestations are then summed to give a total infestation area.

Infestation areas are not calculated by summing total areas such as fields that have infestations on part of the area.

Percentage areas can then be calculated considering infested and total areas in the land use.

1. What percentage area of the land use in the geographic area is currently infested by the weed? Score
>80% of land use The weed infests more than 80% of the land use in the geographic area. 10
60-80% of land use The weed infests 60-80% of the land use in the geographic area. 8
40-60% of land use The weed infests 40-60% of the land use in the geographic area. 6
20-40% of land use The weed infests 20-40% of the land use in the geographic area. 4
10-20% of land use The weed infests 10-20% of the land use in the geographic area. 2
5-10% of land use The weed infests 5-10% of the land use in thegeographic area. 1
1-5% of land use The weed infests 1-5% of the land use in the geographic area. 0.5
<1% of land use The weed infests less than 1% of the land use in the geographic area. 0.1
0% of land use but 20-40% of area The weed is not known to be present in the land use but does infest 20-40% of the geographic area being considered. 2
0% of land use but 10-20% of area The weed is not known to be present in the land use but does infest 10-20% of the geographic area being considered. 1
0% of land use but 5-10% of area The weed is not known to be present in the land use but does infest 5-10% of the geographic area being considered. 0.5
0% of land use but 1-5% of area The weed is not known to be present in the land use but does infest 1-5% of the geographic area being considered. 0.1
0% of land use and <1% of area The weed is not known to be present in the land use but does infest less than 1% of the geographic area being considered. Alternatively, the species has not naturalised but is cultivated e.g. Olive (Olea species). 0.05
not present The weed is not known to be present in the geographic area. 0
do not know   5
Source and comments (Please attach relevant maps or other information if not published)

Current distribution Question 2

What is the number of infestations, and weed distribution within the geographic area being considered?

Importance of the question

The number of infestations, and distribution of the weed in the geographic area will impact on how feasible the weed is to control. The greater number of infestations and geographic spread of the weed, the less feasible management aimed towards eradication or containment will be.

Explanation and assumptions

A weed which is widespread will be more difficult to contain than one which is restricted to smaller areas or patches. A widespread weed will expose more landholders to the spread of the weed and hence decrease the feasibility of coordinated control.

All infestations within a geographic area, regardless of land use should be considered.

If the scattered or restricted infestation options are chosen, please define the size of existing infestations in the 'Source' part of this question.

Refer to the diagrams as a guide to answering this question.

2. What is the number of infestations, and weed distribution within the geographic area being considered? Score
widespread The weed occurs as large and small infestations across most of the geographic area. 2
scattered The weed occurs as mainly small infestations across much of the geographic area. 1
restricted The weed is localised in a small number of outbreaks within the geographic area. 0
not present The weed is not known to be present within the geographic area. 0
do not know   1
Source and comments

Comparative feasibility of coordinated control score

The score for feasibility of coordinated control is calculated by adjusting the Control costs, Persistence and Current distribution scores to range from 0 to 10, and then multiplying these. Feasibility of coordinated control will have a maximum of 1000 and a minimum of 0. The electronic form does this for you.

Control costs: Divide by 12 and multiply by 10. Round score to nearest decimal place.
Persistence: Divide by 11 and multiply by 10. Round score to nearest decimal place.
Current distribution: Divide by 12 and multiply by 10. Round score to nearest decimal place.
Feasibility of Coordinated Control = Control Costs × Persistence × Current Distribution (Round to the nearest whole number)

The higher the score, the less feasible a weed is to control because of the large control costs, the persistence of the species and its current distribution.

Splitting up these possible scores into bands of 20% gives cut-offs for categories of feasibility as follows:

Frequency bands and weed feasibility of coordinated control categories (matrix)

To calculate manually, adjust the raw scores as follows:
Frequency band Feasibility Score Weed Feasibility
80-100% (top 20% of possible scores) 113+ Negligible
60-80% 56-113 Low
40-60% 31-55 Medium
20-40% 14-30 High
0-20% (bottom 20% of possible scores) <14 Very high

Note that a zero feasibility of coordinated control score is possible and generally occurs if the weed is not yet present in the geographic area.

The feasibility of coordinated control categories can be combined with the weed risk categories to determine appropriate weed management priorities and principles.

If there is a zero feasibility of coordinated control score and Medium, High or Very high weed risk, refer to the 'Alert' section at the right of the weed management priorities matrix. Consider treating weeds of Low or Negligible risk that are not yet present in the geographic area as for Very high feasibility of control weeds with Low or Negligible risk.

Again, do not compare scores between land uses.

Why multiply the Control Costs, Current Distribution and Duration of Control scores?

  • Multiplying gives a greater spread in the scores than adding (i.e. range from 0-1000 compared to 0-30).
  • Multiplying is logical as it recognises the interactions between the criteria. Say the Control costs of a weed can be measured in dollars per hectare per year, the Current distribution is known in hectares, and the duration of control is known in years:
Control Costs × Current Distribution × Duration of Control
$ / hectares / year hectares years

When multiplying, all the hectare units cancel so that feasibility of control is measured in total dollars. In multiplying the Control costs, Current distribution and duration of control criteria scores, we are mimicking the above calculation, without having the actual dollar and hectare figures.

Feasibility of coordinated control uncertainty score

The uncertainty score for feasibility of coordinated control is determined by calculating the percentage of 'do not know' answers that have been recorded in the Control costs, Persistence and Current distribution sections. In the case of part questions, for example Control costs Questions 1 and 3 and Persistence Question 4 record the individual scores for each 'do not know' question in each part to determine the section uncertainty score. Do not combine the scores from each 'do not know' question to calculate a score for that question as was done to calculate the question score. See How to calculate scores in the Background information book for an example. The electronic form (XLS, 241.5 KB) does this for you.

To calculate manually, adjust the section uncertainty score as follows:

Control costs: Divide by 12 and multiply by 100. Round to nearest whole number.
Persistence: Divide by 6 and multiply by 100. Round to nearest whole number.
Current distribution: Divide by 6 and multiply by 100. Round to nearest whole number.

The resulting uncertainty percentage scores from weed risk assessment and from above will be used to determine the overall uncertainty score.

Acknowledgements and References

Author: Dr Stephen Johnson
Industry and Investment New South Wales
ORANGE NSW 2800
September 2009

Other acknowledgements

References cited

Other information sources