Large Cuckoo Wasp – Stilbum cyanurum (Vinegar Hill)
Some of the most spectacular wildlife in the Lockyer Valley isn’t necessarily the big stuff like kanagroos, koalas or kookaburras. The small stuff can be absolutely entrancing.
The Large Cuckoo Wasp above is one example. It was found dead on the floor in our house (hence the bits of detritus caught up in its exoskeleton). Before you start thinking that we are a bit casual with our housekeeping, the critter itself is less than 20mm long, so the “fluff” is actually fairly minute particles. Having said that this species is so small, it is known as the Large Cuckoo Wasp, which suggests that in general Cuckoo Wasps are pretty small insects.
Just how small they are can be seen in the image below.
The individual in the photo at the top of this page is on the right here. The one on the left is a different species (one of the two shown below). This Australian 20 cent coin has a diameter of 28mm.
The females of these wasps parasitise the nests of mud wasps, laying their egg in the mud nest next to that of the host species. If they are discovered in the nest they roll into a ball like an armadillo, to protect themselves from the sting of their much larger host with the armour plates of their outer skeleton. It seems to be a common feature of Cuckoo Wasps that the surface of the exoskeleton is pitted; perhaps to increase its strength, or to foil the probing sting of an angry mud wasp? The defensive posture is often also used if they are threatened in some other way – such as a human trying to capture them.
The “appendage” at the rear is the ovipositor, used for laying eggs. I’m curious about the structure of this ovipositor – you’d think that an insect that just lays its egg in the open nest of another wasp wouldn’t need something as robust as this to do the job. Some other species of parasitic wasp have large teeth on the ovipositor in order to ‘drill’ through wood to reach their host(1). For example, in the sawflies the ovipositor is saw-like and is used to insert the eggs into plant leaves, stems or wood(2). Is this a relic from a previous evolutionary stage?
Large Cuckoo Wasps feed on the nectar of flowers in the woodlands, heaths and urban areas which are their habitat.
For a beautiful image of this species, have a look at this shot from Stanley and Kaisa Breeden.
After we found the second, smaller Cuckoo Wasp (dead on a window ledge in the house), and than another small one, I contacted Ken Walker at Museum Victoria and offered to send him the specimens to be identified. Ken was happy to do this and to send me photos of the specimens.
Not only did Ken take fantastic photos, he also spent a lot of time cleaning up all the dust and debris off the specimens and then “relaxing” them so that they could be properly displayed. Compare the photo on the left immediately below to the one at the top of this post – they are the same specimen.
Here are some of his photos. These are photos of the most “diagnostic” parts of the bodies. The scale bars for the whole body photos are 5mm for the top photo and 2mm for each of the others.
Stilbum cyanurum (Photo Ken Walker)
Praestochrysis lusca (Photo Ken Walker)
Chrysis lincea (Photo Ken Walker)
You can find more about this species at the following links:
Thanks to Ken Walker from Museum Victoria for his willing assistance with identifying these species, and for the many other times when he has provided helpful advice on invertebrate wildlife. Ken is the driving force behind Bowerbird, a huge job which he undertakes in addition to his many other duties, and he manages to produce the monthly issue of the Bowerbird Bugle newsletter.
The conflict between urbanites and wildlife recently developed a new battleground: the small coastal New South Wales town of Batemans Bay, where the exceptional flowering of spotted gums has attracted a huge influx of grey-headed flying-foxes from across Australia’s southeast.
In response to intense and highly publicised community concern, federal Environment Minister Greg Hunt has announced he will seek an immediate National Interest Exemption to facilitate dispersal of these bats – a move that risks undermining legal protections afforded to this and other threatened species.
With the ongoing expansion of the human urban footprint, animals are increasingly confronted with urban environments. Human encroachment into natural habitats generally negatively affects biodiversity. However, urban landscapes can present wildlife with an irresistible lure of reliable food supplies and other resources. While urban wildlife can provide a range of benefits to health and wellbeing, it can also be cause for frustration and conflict.
Urban human-wildlife conflict is a growing area of management concern and scientific research. But the research suggests that the current strategies for addressing NSW’s conflicts between humans and flying-foxes might not have the intended results.
Ruling the urban roost
Australian flying-foxes are becoming more urbanised, and the noise, smell and droppings from their roosts can have huge impacts on local residents.
A fundamental problem underlying current approaches to urban roosts is a lack of understanding of the extraordinary mobility of flying-foxes. They are some of the most mobile animals in Australia, with movements that range from foraging trips of up to 120 km in a single night to long-distance nomadism covering thousands of kilometres in a single year.
While roosts can remain active for decades, they are more like backpacker hostels than stable households, housing a constantly changing clientele that comes to visit local attractions. Roosts are connected into large networks through which flying-foxes move in response to changes in local food resources.
This explains the sudden influx in places such as Batemans Bay where preferred food suddenly becomes abundant. But it also highlights the importance of a national approach to flying-fox management and conservation.
Intense local flowerings of Eucalypts, such as spotted gums, produce copious amounts of nectar and pollen, which attract large numbers of flying-foxes and other species for several weeks. When a relatively small local flying-fox population that is tolerated by its human neighbours suddenly increases tenfold, it can place severe pressure on the local community.
Despite their transient nature, these influxes are often wrongly interpreted as population explosions, leading to calls for culling. In comparison, more humane tactics – such as using loud noise or vegetation removal to disperse the flying-foxes – can seem like a more balanced response. But does dispersal actually work?
Shifting the problem elsewhere
There is now ample evidence to show that dispersals are extremely costly and can exacerbate the very human-wildlife conflict that they aim to resolve.
Most dispersals result in the flying-foxes returning the original roost as soon as the dispersal program ends, because naïve new individuals continue to arrive from elsewhere. Overcoming this can take months or years of repeated daily dispersal.
Other dispersals result in flying-foxes establishing new roosts a few hundred metres away, typically within the same urban environment in locations that we cannot control. This risks shifting the problem to previously unaffected members of a community and to other communities nearby.
While flying-foxes are often portrayed as noisy pests, they serve our economic interest by providing irreplaceable pollination and seed-dispersal services for free. What’s more, those same bats that annoy people during the day work tirelessly at night to maintain the health of our fragmented forests and natural ecosystems.
So it is in our national interest to manage conflict at urban roosts, by using approaches that balance community concerns with environmental considerations.
To be considered “successful”, a dispersal should permanently reduce conflict to a level that is acceptable to the community without causing significant harm to the animals. However, dispersals are currently implemented at the local council level with little or no monitoring of the impacts in or outside the immediately affected area. This makes it hard to assess whether they have been successful.
For example, it is not uncommon for flowering to cease and flying-fox numbers to decline naturally during the period of active dispersal. This gives the community a false sense that a permanent solution has been achieved, when in fact the issues will recur the next time the trees blossom. There is thus an urgent need for urban roosts to be managed with properly defined and applied criteria for success.
Unfortunately, lack of research effort directed at “ugly” and “less popular” Australian animals means that very few evidence-based management tools are available to deal with contentious roosts.
Research targeting a few key areas would greatly help efforts to improve urban roost management. For instance, we do not know how flying-foxes choose their roost sites, which leaves us unable to design “carrot solutions” by creating more attractive roost sites elsewhere.
Intensive tree-flowering events are relatively infrequent and hard to predict. This means that it is difficult to prepare communities for a sudden influx of flying-foxes.
Furthermore, the acceptability of various flying-fox management options differs between sections of the community, so it is difficult to find optimal solutions. Social scientists are currently trying to help identify priority areas that promote long-term viability of flying-foxes while also easing conflict with humans.
Local, state and federal governments continue to allocate considerable funds for dispersal responses, even though such actions are high-risk activities for local communities and are unlikely to provide long-term solutions. We argue strongly that targeted research is needed to better inform land managers and affected communities of flying-fox ecology and provide them with low-cost, low-risk, evidence-based tools for dealing with urban roosts.
Flying-foxes don’t care about legislative borders, and state-based responsibility for wildlife management leads to discontinuity in approaches between jurisdictions. While flying-foxes are being monitored at the national scale, this initiative needs to be combined with a uniform federal approach for managing flying-foxes in our human landscapes. Otherwise, conflicts such as those faced by the residents of Batemans Bay will continue unabated.
I’ve posted before about the unsuitability of Adare Road for large amounts of traffic.
There’s more to that issue and I’ll come back to it in another post.
There are unsuspected losses associated with traffic on Adare Road that we face if the proposed motocross development is allowed to go ahead.
One of these relates to the Gatton Light Horse Troop. You might be familiar with their role in the Anzac Day celebrations in Gatton and other localities in the Lockyer Valley.
The Gatton Light Horse Troop in the Anzac Day parade in 2012. A friend in Germany sent this to me, which shows how far the knowledge of our Light Horse Troop has spread.
What you wouldn’t know, unless you are out toward the end of Adare Road early on a Saturday or Sunday, is that the Horse Paddock beside Adare Road,on the right just before the Redbank Creek Crossing, is one of their training grounds.
It’s a stirring sight to see them practising mounted military manoeuvres at full speed.
If there are up to 150 vehicles travelling down Adare Road on a Saturday or Sunday morning, the Horse Paddock will become unsuitable for Light Horse training exercises.
There’s another group in the community (this time a much wider community) who know of the Adare Road Horse Paddock. They are the birdwatchers, and the trees and bushes around the edges of the Horse Paddock are one of several regular birding spots for many visitors.
Adare road has been visited with increasing regularity by local, Brisbane, interstate and overseas birders over the last 20 years. The location features regularly in online lists of the interesting or rare species which have been seen there.
Two of the visitors in this group were from Japan
It continues to be something of a ‘hot-spot’ where visitors can find a selection of scarcer species which can be difficult to locate elsewhere in the region. The combination of open woodland, riparian vegetation where Redbank Creek crosses the road, open paddocks, and the dams along the road provides for a range of habitats and therefore bird species that isn’t easily found in a situation where it is easily viewable from the road. And there’s always the possibility of seeing a koala, especially at the Redbank Creek crossing.
There are many birdwatchers who visit Adare Road regularly, some every couple of months, some every week. There are also bird clubs which make annual trips to the area.
A lot of the most interesting birding is done along the road verges, including along the sides of the Redbank Creek crossing. Motocross traffic in the mornings and evenings (when most birders visit) is going to turn birdwatching along Adare Road into an extreme sport – not to mention being extremely unpleasant with all the dust and noise. It can be pretty confidently predicted that the beginning of motocross traffic will be the beginning of the end of birdwatching on Adare Road.
Koalas are probably the most environmentally significant species that would be impacted by the establishment and operation of a motocross track on the Adare property. Impacts will come from noise, vehicle strike and possibly vegetation clearing in Stage 2 of the development.
It’s funny how members of a community can individually recognise that they have an unusual number of koalas in their vicinity, but no one actually comes to the conclusion that there is an unusually large koala population in the local area. This is another aspect of our environment/community that dealing with the motocross proposal has brought to the fore.
For the last few weeks our group has been collecting incidental records of koala sightings in the area of bushland which is contiguous with the vegetation in the vicinity of the proposed Adare motocross track.
We now have 66 records of koala sightings for this area. It may not look like 66 “pins” on the map, but that’s because at this scale many pins are hidden behind others.
These sightings are all within 5km of the motocross track, and almost all are within less than 4km. The nearest is only 950 metres from the track.
All of these sightings are in vegetation types that occur on the motocross property and within 20-70 metres of the track. These vegetation types are classified as Bushland Koala Habitat or as Essential Habitat for koalas.
Remember, these are incidental sightings. They are not the result of targeted surveys for koalas. They are sightings that people happened to make while they were doing other things, and which they have some record of. People don’t tend to look up in trees when they are working on their land. Even if they do, koalas are pretty cryptically marked. They have colours which tend to blend with the bark of trees and the dark shadows in thick foliage, and they even have lighter patches around their rear ends, so that their silhouette is broken up when seen against the sky from below. Most people never see a koala when they are walking through the bush.
Our data collection is not yet complete. The properties where there are no koala records are almost all ones where we haven’t yet tried to collect information or where we don’t have access.
The Road-kill Threat
Death by vehicle strike is among the three greatest threats to koala populations in Southeast Queensland.
Adare Road runs from the big dam just to the right of bottom centre in the map vertically (north) to the entrance to the motocross track. There are more than 30 records of koalas within 250 metres of Adare Road (four of these are of koalas crossing the road, and one is of a dead koala on the road).
Koalas are active at night, and that’s when they will be crossing the road. Imagine the number of road-killed koalas there will be if there is motocross traffic on Adare Road four to six nights per week!
Comparison Between Our Data and the Government Database
The WildNet database has been built up by the State government over a number of years. It contains records of wildlife sightings and listings of plants, mammals, birds, amphibians, reptiles, freshwater fish, sharks and rays, butterflies and other priority invertebrates in Queensland.
The wildlife lists are based on collated species lists and wildlife records from Queensland Government departments and external organisations. The data sources include:
research and monitoring programs;
inventory programs including extension activities;
wildlife permit returns; and
community wildlife recording programs.
WildNet at present has 65 records of koalas within 10km of the motocross track. In only a few weeks members of our group, with the cooperation of the local community, have gathered 66 records within 5km of the track. That’s a fantastic effort, and it’s not finished yet.
It’s not that the koalas weren’t there before – just that this is a big State and there has never been sufficient resources to carry out the necessary surveys at the scale we need for dealing with local government planning applications.
Ultimately our records will go into the WildNet database and into the privately funded Koala Tracker database.
One of the things that really depresses me when I think seriously about the mangement of our 33 hectares of native bushland is the problem of pasture grasses gone feral. Green Panic is the major problem here, but we have a number of others, including Rhodes Grass. Both were introduced into Australia as pasture plants.
The Green Panic (Panicum maximum var. trichoglume) is still touted as a good pasture grass. The story when it was introduced was that it would not spread and become a pest because it needs plenty of moisture and will not grow under shade. Did the agronomists not know about evolution? Did they not know that a grass often has weedy characteristics because it is inherently capable of rapid adaptation to different environments.
Just in case there are agronomists or botanists who were involved in the introduction of this wonder grass among my readers: We have a new variety of Green Panic – Lockyer Valley Green Panic. It has adapted and evolved (surprise!) and now grows even on dry ridges and under semi-closed woodland trees. And, like all Green Panic, it grows dense and tall when it isn’t grazed, so that it crowds out the native grasses and by the middle of summer when it has dried out it forms a near explosve compact mass of cellulose that will send flames into the tree canopy. Where previously there was a carpet of low green Kangaroo Grass on the woodland floor, now in parts of the Lockyer Valley Region we have dense tall brown monocultures of Panic. Kangaroo Grass is unusual because it has green growth at the height of summer, and with this and its short tussocks it not only makes for some of the most beautiful Australian woodland that I know of, it also burns cool and recovers fast. [sorry for the lack of photos, for the moment I can’t find any pics of our Kangaroos Grass areas].
One of my fondest dreams is that I will see the day when communities across Australia come together in a class action against government agencies and agricultural companies, claiming massive damages for the harm done to the Australian environment by non-native pasture grasses. So you can see why I was very heartened to see an article in todays Australian edition of The Conversation about the harm pasture grassed do.
Here’s an excerpt:
Feed or weed? New pastures are sowing problems for the future
Weeds cost Australian farmers around A$4 billion every year — and they are likely to do a similar amount of damage to the environment.
Similarly, Gamba grass was widely promoted by the cattle industry and government in northern Australia, but is now listed as a Weed of National Significance. Gamba grass increases fire intensity five-fold, which transforms native woodlands into exotic grassland and increases the cost of fire management by an order of magnitude.
Introducing these pasture species was a big mistake that Australians will continue to pay for indefinitely. We face increased fire risks, increased management and weed control costs, as well as ongoing loss of our natural heritage.
Have we learned our lesson?
Not yet. Agribusinesses still develop and promote new varieties of species, which are known invasive weeds.
Our new survey of pasture plants reveals that over 90% of taxa developed and sold by agribusinesses are weeds somewhere in the world, and on average 30% are weeds in the country in which they are promoted.
In Australia, these species include Orchardgrass (Dactylis glomerata), Canary-grass (Phalaris species), Tall fescue (Schedonorus arundinaceus), and sub-terranean clover (Trifolium subterraneum). These species are all recognised weeds in Australia, and all promoted by agribusiness for pasture.
Inadvertently breeding super-weeds
These species have already spread throughout much of Australia. But new varieties of the same species can be just as bad, if not worse.
Although they belong to the same species, these varieties can be quite distinct from their parents – just think of the differences between dog varieties like Chihuahuas, Dalmatians and wolves.
The impacts of new pasture varieties in the environment can be substantial, as emphasised in a report “Weed risk set to rise”, to be published this week by the Ecological Society of Australia.
New varieties can be created by cross-breeding different varieties or different species. Another trick to create better performing plants is to manipulate the symbiotic bacteria and fungi that live inside the plants. Engineering plants in any of these ways can lead to varieties with higher reproduction, higher growth rates, better resistance to disease and higher tolerance of environmental extremes.
Unfortunately (but perhaps not surprisingly), these are the same characteristics associated with invasive species. New varieties of pasture plants are bred to grow great pasture, but at the same time, they are inadvertently bred to be super-weeds, perfectly-matched to their environment and planted widely across the landscape.
Producing enormous amounts of pollen and seeds, these new pasture plants can spread quickly and over vast areas, making them very expensive to control if and when they become invasive. So it makes sense to nip the problem in the bud.
If you’ve been reading my blog for a while you will know that I’m very concerned about the encouragement of the use of invasive or potentially invasive species in permaculture (you can see where I’ve written on the subject here and here).
Typical effect of unchecked Madeira Vine [from Milkwood Permaculture blog]
As they point out, Madeira Vine is an already “adapted, perennial, zero footprint and highly nutritious food plant” with the following characteristics which are desirable in a food plant:
“It grows without much assistance, is hardy and produces prolifically.
It requires minimal cultivation.
It dominates an area where it is planted (meaning far less weed control is needed)
It is spread only* by humans and by water flows distributing the bubils – an easy factor to contain with good design.”
The Milkwood guys are planning on having it as a food plant in their garden. They recognise that it is a potential problem, and will manage it by eating it and stopping it from spreading.
So, should we incorporate Madeira Vine into our permaculture food production?
My first question would be: Just how weedy/invasive is it really?
Madeira vine grows prolifically at rates of up to 1 m per week in high-light environments. It produces large numbers of subterranean and aerial tubers that not only act as reproductive bodies, but also provide the plant with a carbohydrate source that enables it to survive through difficult times. As a consequence, Madeira vine can tolerate a range of adverse conditions including drought, snow and frost, and it has been found growing in areas as diverse as rainforests, riparian fringes, rocky outcrops and frontal dunes (source). This same ability to tolerate adverse conditions also means that the tubers can survive for very long periods of time in suspended animation, before they experience the right conditions to shoot (source).
The vine reproduces through the proliferation of aerial tubers and also from rhizome (subterranean tuber) fragments that may be broken off (source). The aerial tubers can persist for two to 15 years and rhizomes for five to 10 years, with tuber germination rates of up to 70 per cent (source). Although Madeira Vine is widely believed not to set seed in Australia, up to 5% of dried flowers collected from southeast Queensland were found to contain germinable seed (see #Vivian-Smith et al, below).
Dispersal is believed to occur primarily* via human spread (cultivation for ornamental purposes, disposal of vegetative material and tubers, e.g. in green waste (source), or being spread by machinery and/or gravel during road construction). However it also spreads downslope under the influence of gravity and water movement from ridges and down watershed, and via floods (source).
Saying that it is spread primarily by humans needs to be considered in relation to just how widespread it is, what a significant destroyer of habitats it is once established, and how extremely difficult it is to eradicate once established. Here is how the Environment Australia weeds database summarises the facts about Madeira Vine:
Madeira Vine is a Weed of National Significance (WONS). It is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts.
Madeira Vine has aggressive vegetative growth which competes with and replaces other vegetation, and is difficult to control once established. Its aggressive nature gives it the potential to smother other desirable plants. Its sheer weight is capable of breaking branches off trees, thereby reducing them to poles, potentially causing collapse of the rainforest canopy (ISSG 2006). It restricts light and thereby prevents germination of desirable native species (Harley undated).
Should we then include Madeira Vine in permaculture food production? I think there are two things to take into account before making a decision on this.
First, the permaculture ethics of care for the Earth and care for people. The potential impacts on the Earth from Madeira Vine escapes are obvious (see the sources and photo above) and well documented, as are its impacts on the people whose properties and amenity are impacted.
Second, based on an assessment of invasiveness and impact, Madeira vine was ranked 5th worst of1060 naturalised south-east Queensland plant species (#Batianoff & Butler, below). How are you going to ensure that:
no seed is set, and neither seed nor tuber material is distributed by animals, or other agents of dispersal, including water (i.e. the area where you will grow it will never flood or be exposed to high volumes of water runoff;
everyone who works on your garden or caretakes for you while you are away is as careful as you would be not to allow any dispersal of aerial tubers, (fragments of) rhizomes or seeds;
before you move on, you will have somehow removed all aerial tubers and every last fragment of rhizome before you leave, or failing this, you have some guarantee that the next landholder is going to take the same careful management approach as you?
– – – – – – – –
*I consider the statement that it is spread “only by humans and by water flows distributing the bubils – an easy factor to contain with good design” to be dangerously simplistic for a number of reasons. First, once a Madeira Vine has established itself in a vegetated area it does not sit and wait for humans or water flows to come along and move its tubers or rhizomes. The tubers are spread naturally when they fall from the adult plants where they have climbed up and across the canopy (often a considerable distance) from where they originally grew. Second, anywhere that an established population of Madeira Vine grows over a waterway that even only occasionally flows, this will distribute the plant to any and all areas downstream. Third, saying that it is spread “by humans” without mentioning the many ways in which human activity can spread the plant, or the very long viability period of the tubers, gives a very misleading impression of the ease with which human activity can (even unwittingly) result in spread.
Here is a rather more informative account of how it is spread:
The most common means of reproduction and spread is via asexual tubers formed on the roots and stems. Prolific numbers of aerial tubers are produced throughout the year, which drop to the ground when mature or in response to stress. Research indicates that aerial tubers can persist for two to 15 years and subterranean tubers for five to 10 years, with tuber germination rates of up to 70 per cent. In areas of heavy infestation, soil tuber densities are up to 1500 per m2. Madeira vine is also capable of shooting from sections of severed vine.
Dispersal occurs primarily via human spread such as cultivation for ornamental purposes, disposal in green waste, or spread by machinery during road construction. It can also spread via gravity and water movement from ridges and watersheds or during floods. Mammals and birds may also play a minor role in localised spread.
While seed production is believed to be rare in Australia, research indicates that up to 5 per cent of dried flowers collected from southeast Queensland contain germinable seed. It is speculated that seed set and germination may only occur under ideal environmental and seasonal conditions.
Sources which aren’t linked above:
#Vivian-Smith et al, Alan Fletcher Research Station QLD Unpublished data (cited in this source)
#Batianoff, G.N. and Butler, D.W. (2002). Assessment of invasive naturalized plants in south- east Queensland. Plant Protection Quarterly 17: 27–34.
The use of “weedy” species, together with the use of non-local species of unknown weediness, incites very heated debate in permaculture circles, inspiring a lot of name-calling and pseduo-science. My own view is that the promotion of known invasive, or potentially invasive, species as part of the permaculture approach is highly irresponsible and arguments for their use are often couched in language that approaches the mysticism or spirituality that is supposedly “banned” in serious permaculture. (You can see my views on the use of Leucaena here.)
Of course, the topic of invasive species overlaps with the consideration of “weeds” as an element of food productions activities. I’m not going to go into that here, but the eXtension website has an excellent article on weeds in agriculture (An Ecological Understanding of Weeds) that incorporates both the negative and positive aspects of weeds in agriculture. Well worth reading – much of it reads as if it was written by an well-informed permaculturist. In fact the author, Dr Mark Schonbeck, is credited by the the Virginia Association for Biological Farming as combining “deep scientific knowledge, practical farming technique and policy smarts”. I recommend googling his name – it will turn up a plethora of interesting and informative articles.
Dr Schonbeck’s article also deals with invasive species, under the heading of Imported Weeds and Invasive Exotic Plant Species. Among other things this part blows out of the water the permaculture argument that for a species to become invasive in an ecosystem there must have been a vacant niche in the ecosystem.
Below is the text of that part of the article (with what I think are the really telling points underlined by me), but I really recommend you read the whole article for its information about the place of weeds in food production systems. Remember that the weed/invasive species referred to are in relation to the US, though it is interesting how many are familiar to us in Australia.
Many of a region’s most problematic weeds are those that are not native to the region, or even the continent. These exotic plant species often grow more vigorously in their new habitat than they do in their area of origin, where certain soil organisms, herbivorous insects, climate patterns, and/or competing vegetation keep them in check. Kudzu (Pueraria thunbergiana), imported from Japan as a forage crop, is one dramatic example whose enormous vines can cover and kill large trees in the southeastern US. However, a small (4–18 inches) perennial weed called purple nutsedge (Cyperus rotundus), which has invaded the southern United States, causes much greater losses in cultivated crops (even sugarcane and coffee trees), and is considered the world’s worst weed (Holm et al., 1991).
Some of our major agricultural weeds were intentionally brought to the United States from overseas to provide food or forage. European colonists carried common lambsquarters (Chenopodium album) to the New World as a vital source of early season greens that prevented scurvy and other nutritional deficiency conditions. Common lambsquarters has spread around the globe and is now listed as the world’s 10th worst agricultural weed. Livestock farmers imported bermudagrass (Cynodon dactylon, 2nd worst weed), johnsongrass (Sorghum halapense, 6th worst), and quackgrass (Elytrigia repens, a major weed of vegetable crops in the northeastern US) to this country for their utility as forages. Other serious exotic weeds were first planted as flowers and other ornamentals, and subsequently spread from cultivated gardens into surrounding farmland and/or natural ecosystems. Still others arrived by accident as a seed contaminant in imported crop seed, feed grain, foods, bedding plants, or other materials.
Many exotic weeds have become “naturalized” over time, and are now part of a region’s agricultural weed flora that must be managed (not necessarily eradicated) to protect crop yields. However, some newly introduced plants growing in the absence of the natural enemies with which they evolved may spread unchecked, choking out native vegetation as well as invading pastures or cultivated fields. Imported weeds that threaten natural ecosystems and/or rangeland over wide geographic areas are designated invasive exotic plant species or invasive exotic weeds, and often become the focus of regional or nationwide coordinated eradication efforts. Examples include water hyacinth (Eichhornia crassipes) and purple loosestrife (Lythrum salicaria) in wetlands; Canada thistle (Cirsium arvense), musk thistle (Carduus nutans), spotted knapweed (Centaurea maculosa), and St. Johnswort (Hypericum perforatum) in rangeland; and autumn olive (Elaegnus umbellata) and tree-of-heaven (Ailanthus altissimus) in eastern deciduous woodlands. Classical biological control—the introduction of herbivorous insects or microbial pathogens that are natural enemies of these weeds in their native lands—has been used with considerable success to combat some invasive exotic weeds.
Arrival of a new invasive exotic weed on an organic farm is one instance that may justify efforts to eradicate the new arrival. Early detection—combined with an understanding of the ecology of the weed—is vital for successful elimination of the invader.