Number 21 May 2002

What’s New In Biological Control of Weeds?

A Miner Triumph against Old Man’s Beard What’s Inside?

A Miner Triumph against Recently our confidence in the one or two mines per leaf Old Man’s Beard 1 old man’s beard leaf miner pretty much anywhere you (Phytomyza vitalbae) and leaf look. Laboratory studies have German Allies 2 fungus (Phoma clematidina) suggested that one mine per has been given a large boost. leaf can reduce the growth of Hot Gossip 4 After a tip-off from Ben small plants by about 17%. New contact details 4 Minehan (Marlborough District Extrapolation of these results Council) Simon Fowler paid a indicates that two or three The Coast special visit to Marlborough to mines per leaf might reduce takes charge 4 check on reports of growth of small plants by as Craig counts for spectacular damage. He was much as 50%. How these a good cause 5 not disappointed. results might translate to large Another international plants in the field has opportunity 5 In the short time since the leaf remained a mystery until this miners were first released autumn, when we have had our Still Searching! 6 (1996) they have spread well first insight into what might be and colonised old man’s beard possible. Aloha from Hawai’i 10 ( vitalba) infestations up and down the country. It “Higher than usual levels of Winter and Spring has become quite usual to find leaf miner attack, around 10– Activities 11

Tell Me More… 12

Manaaki Whenua Landcare Research

Heavily mined leaves at Para Swamp. What's New in Biological Control of Weeds? Number 21 May 2002

15 mines per leaf, have been pretty stunted and sorry for widely soon) and we are noticeable throughout itself and opportunistic native renewing investigations into Marlborough this season,” plants were already beginning the potential of the bark reports Ben. However, one to take advantage of its (Xylocleptes bispinus). site on the main road between reduced vigour.” Blenheim and Picton, known as Para Swamp, has been We now eagerly wait to see outstanding. “There were so what happens at this site next many mines on the leaves that year, and whether other sites it was hard to count them, but I begin to follow suit. It is would estimate that there were heartening to know that we have about 20–30 mines per leaf,” been able to achieve useful enthused Simon. Any green results at one site already with material not attacked by the only two agents. We still have miner was getting walloped by the saw fly (Monophadnus the fungus, which was spinolae) up our sleeve (which So, watch out old man’s beard released here in 1999. “The old we are still hopeful of being – you might just have to go man’s beard was looking able to release and establish after all!

German Allies

Over the last 6 months we gall wasp (Aulacidea with weaker root systems than have had a German student, subterminalis) to perform undamaged plants (gall Matthias Klöppel, working here. The gall wasp is a formation uses up valuable with us at Lincoln. Matthias is European species and, since nutrients, reducing the amount studying for a Diploma in our population originates from available for plant growth). Landscape Architecture the Black Forest in Germany, The wasps had the biggest (focusing on plant ecology) at it seemed fitting to have impact on mouse-ear the University of Applied Matthias work on it. hawkweed plants grown under Science, Wiesbaden, near ideal conditions. The main Frankfurt. “I really wanted to The gall wasps attack the stolons of these galled plants go somewhere I could stolons of mouse-ear were only a quarter the length practice my English and hawkweed (Hieracium. of those produced by plants escape the German winter,” pilosella) and orange not exposed to the wasps. confided Matthias. We were hawkweed (H. aurantiacum) However, mouse-ear keen also to get an extra pair and reduce their ability to hawkweed rarely grows under of hands. Matthias carried spread vegetatively by optimal conditions in the field. out some glasshouse producing daughter plants at More typically it is found in experiments to give us an the tips. In the glasshouse arid, nutrient-poor grasslands idea of how we might expect experiments galled plants and is usually under some the newly released hieracium tended to be slightly smaller kind of stress. 2 What's New in Biological Control of Weeds? Number 21 May 2002

The good news is that the wasps can also perform quite nicely on stressed plants. Although each plant was exposed to only eight of the tiny wasps, their developing offspring interfered with nearly three-quarters of all the daughter rosettes that these experimental plants were attempting to produce. This suggests that even small Mouse-ear hawkweed plant attacked by gall wasps (right) compared populations of wasps could with a plant not attacked by gall wasps (left). shut down much of the vegetative reproduction that goes on in the plants. Plants statistically significantly. thinner stolons. Both under stress (e.g. low water, Nutrient- or water-stressed branched and thin stolons low nutrients, or competition) plants produced fewer, shorter tend to result in weaker produced slightly fewer and and more highly branched daughter plants. Branching smaller galls than unstressed stolons. Plants fighting to could also be advantageous to plants, but the difference was compete with other pasture the wasps by providing them not large enough to be plants produced longer, with more areas to attack.

Matthias’ study leads us to expect that the hieracium gall wasp is likely to be a successful control agent. Matthias commented that he “really enjoyed the opportunity of tramping around the South Island and the cheap cost of living in New Zealand.” We can also report that he did achieve his goal of improving his English although we can’t say that our summer was too hot weather-wise. Matthias has now returned home to complete his studies. He thinks he might like to do either further ecological research, landscape planning, or perhaps even a doctoral study. We wish him the best Matthias working on his experiments. for the future! 3 What's New in Biological Control of Weeds? Number 21 May 2002

Hot Gossip

New contact details We have changed our email domain name to make it easier for people to contact us and understand the difference between Landcare Research and other similarly named groups like the New Zealand Landcare Trust and landcare groups. So from now on if you want to send us an email please use the following format: surname+first [email protected] (eg. [email protected]) and if you want to visit our newly revamped website type in www.landcareresearch.co.nz. The old addresses will continue to work indefinitely until all stocks of printed items such as the pages for “The Biological Control of Weeds Book” have been used up and are ready to be reprinted. Speaking of websites, we are planning to put considerably more information about weeds and biological control methods on our website over the next couple of years.

One of our staff, Helen problem area seems to be flavicornis) have been released Harman has relocated from along the West Coast of the and, although conditions there Lincoln and is now based at South Island, where it may just are quite similar to parts of our Mt Albert Office, be too wet for the to New Zealand, “our beetle” has Private Bag 92170, Auckland do well. Fortunately there are been vastly outperformed by (Ph 09 815 4200 ext 7167, fax other ragwort agents out there the other one. Over the past 09 849 7093, email that we could call on if need year we have been working [email protected]). be. For example, another with the New Zealand similar flea beetle Landcare Trust to By all accounts the ragwort (Longitarsus flavicornis), a encourage the formation of a flea beetle (Longitarsus plume (Platyptilia community ragwort jacobaeae) is getting stuck in isolodactyla), and a leaf and action group on the West to ragwort (Senecio jacobaea) crown-boring moth Coast to champion the cause and reducing it to low levels in (Cochylis atricapitana) have all of bringing in additional ragwort many areas. However, we been released in Australia and agents. Public meetings were have a growing suspicion that are showing promise. In held in April, a group has been the beetle is not able to thrive Tasmania,Before both ragwort flea formed, and a number of everywhere. One such beetles (L. jacobaeae and L. organisations have pledged financial or other assistance to the project (West Coast Regional Council, Westland Conservancy of the Department of Conservation, Federated Farmers, Westland Dairy Company, Timberlands West Coast, and DEXCEL). We are helping this group to submit proposals to

D. McLaren, Keith Turnbull Research Institute Research Keith Turnbull D. McLaren, AGMARDT’s Progressive Farming Grants and MAF’s Sustainable Farming Fund, and we will keep you posted on the success of these Ragwort leaf and crown-boring moth applications in future issues. 4 What's New in Biological Control of Weeds? Number 21 May 2002

Craig Sixtus has begun studying the two gorse seed feeders as he works towards a Masters degree at Lincoln University. Craig will be measuring the amount of seed that the gorse seed weevil (Exapion ulicis) and the gorse pod moth (Cydia succedana) are destroying at various sites The opportunity to take part in look at weed issues on Banks around the South Island another international Peninsula is being organised where both agents are now conference is coming our way. for the following day. This will well established. The study The 8th International be another great opportunity to sites are East Takaka and Congress of Plant rub shoulders with some of the Wainui Bay (Tasman), Pathology is being held in world’s leading scientists in McLeans Island Christchurch 2–7 February this field. For further (Christchurch), Hinewai 2003. Please note that a information about the (Banks Peninsula), Twizel workshop on biological control “Biocontrol of Weeds with (South Canterbury), and of weeds using pathogens will Pathogens” workshop check Wainakarua (North Otago). be held immediately prior to out the website http:// The results should be the conference (Saturday 1 events.lincoln.ac.nz/icpp2003/ extremely useful, as so far February) and a field trip to workshop.htm. we have only measured the impact of both agents at Have you found a new weed? one site near Darfield (where The Department of Conservation the amount of seed (DOC) has recently published two destroyed varied enormously free weed fact sheets for the within the site), and will help Wellington Conservancy entitled to build up a much clearer “Have you seen these plants in the picture of how useful these Wellington Conservancy?” and seed feeders are likely to “Have you seen these aquatic be. Craig is also going to plants?”. The species included in these fact sheets are not study aspects of the life known to occur in the region, and could present a huge problem history of the gorse pod for native plant and communities if they established moth that are not well there. Each fact sheet has photos of the species, and lists understood, such as the some of their characteristics to aid identification. DOC would temperature threshold for like people to look out for the species during their travels, and egg development and how inform them immediately if they think they have found one. This many larval instars there are, will greatly help DOC to prevent these from plants colonising as well as its phenology (i.e. and stop them before they become a major problem. If you the timing of its life cycle would like a copy of either free fact sheet please contact DOC, here in New Zealand, how Technical Support Team, Wellington Conservancy, P.O. Box many generations it 5086, Wellington (Ph 04 472 5821). completes etc.). 5 What's New in Biological Control of Weeds? Number 21 May 2002

Still Searching!

Californian thistle (Cirsium disaster for the gall flies! Siberia, China, Mongolia, and arvense) is the most common Obviously more agents are Tibet, as well as revisiting thistle in New Zealand, and so urgently needed to add pressure Pakistan and Turkey. far it has proven to be one of to the plant, and researchers the most difficult biological are still working on it. Over the four decades that control targets. Only one of the researchers have been released to attack the The native range of Californian looking, quite an assemblage plant, the gall fly (Urophora thistle is believed to include of insects have been found on cardui), is showing any most of Europe, northern Californian thistle, but most promise at all, and it is not yet Africa, and large areas of Asia have not been sufficiently host widely established. On the (including Afghanistan, Iran, specific or damaging enough, pathogen side of things, there Pakistan, and eastern China), or have been just plain too is still a good chance that a but this has been difficult to difficult to work with. mycoherbicide may become ascertain with any certainty Specificity is particularly available in future. since human migration and critical for agents intended for agricultural practices have areas like North America that Back in 1999 a group of allowed the plant to become a have native thistles to contend concerned farmers and widespread weed throughout with, and it is not looking too regional council employees in most of temperate Europe and hopeful that additional the Otago/Southland area Asia. Californian thistle also acceptable species can be formed The Californian Thistle grows under a wide range of found for that region. Action Group*. This group has environmental conditions so Fortunately we do not have made a concerted effort to rear there are lots of places to look any native thistles here in the gall flies in special cages for potential control agents. New Zealand and so we have outdoors to enable widespread However, some places have not many more options open releases to be made. However, until recently been (or still to us. it has proven to be easier said aren’t) safe or easy to visit so than done with quite variable only western Europe has been Leading contenders results – at the end of the day thoroughly surveyed for Experience has also shown rearing insects is often not easy! potential control agents. Areas that, with its extensive There are also some question of central and western Asia are creeping root system, the marks about whether the gall now being targeted, with plant can be quite hard to flies will ever be able to central Russia visited in 1999, knock back and is not too establish widely in New Zealand. Uzbekistan in 2000, and troubled by a bit of damage to Experience has shown that Armenia in 2001. André its leaves. Researchers are sheep make a beeline for Gassmann, of CABI Bioscience, now mainly focusing their galled plants and particularly Switzerland, is leading the team attention on finding potentially seem to enjoy this special of researchers looking for new more harmful root and stem added-protein snack—nice agents on our behalf. They feeders that may have the maybe for the sheep, but a are still planning to survey added bonus of allowing

* The Californian Thistle Action Group gained a 3-year grant from the Agricultural and Marketing Research and Development Trust (AGMARDT) in 1999. The overseas work that they have helped to support has also received funds from The North American Canada Thistle Consortium (including Agriculture and Agri-Food Canada, South Dakota Department of Agriculture and Maryland Department of Agriculture). 6 What's New in Biological Control of Weeds? Number 21 May 2002

Table 1. The top five current prospects under consideration for Californian thistle control

Aceria anthocoptes Potentially very specific and damaging. Common in the Balkans and Gall-forming mite recently found in the USA (Maryland). Need to determine the host range of the mite in the field, and carry out molecular studies to compare mites from Europe with those discovered in the USA.

Altica carduorum Has been released in New Zealand and failed to establish. There may be Foliage-feeding better strains available in Armenia or Asia (Uzbekistan, China). Need to beetle collect and import better strains and obtain permission to release.

Apion onopordi Can vector the fungus, Puccinia punctiformis, but the weevil is uncommon in Root-feeding the thistle’s native range. Need to check if host races exist on different weevil species of thistles and begin preliminary host range testing.

Cleonus piger May contribute to Californian thistle control in some places in Canada. Not Root- and crown- originally considered sufficiently host specific for us. However, there may be feeding weevil a more specific strain in Armenia, which has unusual larval behaviour, and is worth more attention. Weevil larvae were found in roots >15 cm below the ground and such deep root-mining has not been described before. Need to clarify and begin preliminary host range testing.

Luperus nr. altaicus Several chrysomelid beetles have been collected in Armenia, including this Foliage-feeding locally common and damaging one. Need to clarify taxonomy and begin beetle preliminary host range testing. naturally occurring pathogens associated with the plant. not appear to support the to gain entry to the plant. A Despite digging up plants to either so the true host is shortlist of what are currently examine the roots, researchers still a mystery. believed to be the most found no sign of the moths. promising insects and what Pheromone traps were also Fungal forays needs to happen next is used, including in areas where As well as looking for suitable summarised above in Table 1. the moth had previously been biological control agents with Negotiations are currently collected (no Californian six legs there has been underway regarding what work thistles could be seen nearby considerable effort both here will be funded in 2002/03. but there were large stands of and overseas to find fungal slender-winged thistles solutions to the problem. One agent that featured was (Carduus pycnocephalus)), but Graeme Bourdôt, of AgResearch amongst the top prospects only a small number of moths (based at Lincoln), has been this time last year has since collected in one trap. Eggs working for a number of years been ruled out. A root-boring were obtained from two with a pathogen known as moth (Euhagena palariformis) trapped females but the Sclerotinia sclerotiorum. “This that was believed to attack resulting larvae did not survive fungus has a wide host range Californian thistles in Turkey is when placed on Californian and, amongst other things, can no longer thought to be thistle. Winged thistle does make your lettuces to go brown 7 What's New in Biological Control of Weeds? Number 21 May 2002

Trial formulations applied in the spring have proven to be capable of reducing thistles to low levels, but the results have CABI Bioscience been erratic. This is believed to be to due to a lack of adequate moisture at times for infection. For this reason Graeme has now turned his immediate attention to using S. sclerotiorum against other weeds that more commonly grow in wetter areas, e.g. ragwort (Senecio jacobaea) and Mite (Aceria acanthoptes) damage on Californian thistle. giant buttercup (Ranunculus acris). He is also supervising a and slimy,” explained Graeme. It 3–4 years after application so PhD study by Brenda Pottinger can also be extremely the withholding period for (Lincoln University) to gain a damaging to Californian planting susceptible crops would better understanding of the thistles (see picture below), not be too onerous either. infection process of this fungus but natural outbreaks in the so that improved formulations thistle do not occur very often The greatest challenge has can be developed. AgResearch or over large areas. Because turned out to be not around scientists are using new “bio- S. sclerotiorum is already here, safety but in developing a polymer” technologies to widespread, and not terribly suitable formulation – a common improve the reliability of specific, Graeme has taken the problem with mycoherbicides. biopesticides. mycoherbicide approach with this pathogen. Initially there were concerns that a mycoherbicide

using this active ingredient might G. Bourdôt cause damage to desirable neighbouring crops, like peas, through dispersal of the spores after the thistle had been killed. “However, trials designed to assess the level of risk showed that normal background levels of spores were achieved within 5 m, and dispersal models indicate that a 60-m safety zone would be adequate,” revealed Graeme. Background levels of the resting bodies produced by the fungus (sclerotia) were also A trial near Lincoln showing in the foreground how well S. sclerotiorum achieved in treated areas about can knock back Californian thistles under good conditions. 8 What's New in Biological Control of Weeds? Number 21 May 2002

Some unusually sickly looking Californian thistles were

A. Spiers noticed in the Manawatu in 1999. Adrian Spiers (Idein Technologies Ltd) isolated the pathogen Phoma exigua var. exigua from them. A Phoma sp. had previously been described as a weak leaf spot pathogen on Californian thistle, but the one found in the Manawatu was causing considerable damage and is likely to be a new record. Records of P. exigua damaging Young plant infected with P. exigua var. exigua showing marked yellowing. thistles (many species may be affected) are now starting to come in from all over the What is the cost of Californian thistle? country. Typically plants become chlorotic (yellow- The Californian Thistle Action Group contracted the Clutha looking) and then turn brown Agricultural Development Board to undertake a survey of as they die. The symptoms farmers in February 2000 to find out how Californian thistle are quite different from the affected them and what it cost them to control the plant. The other fungus (Puccinia survey found that the thistle caused problems for farmers punctiformis) that you finishing lambs (by increasing the likelihood and severity of the commonly see on Californian viral infection “scabby mouth”), and producing quality hay, thistles. Plants affected with winter feed, and grain crops. The farmers estimated that they this rust are usually covered in spent on average $1,200 a year chemically controlling the plant. brightly coloured spores Many commented that they were actively trying to reduce (yellow, orange or brown). In chemical usage, but nearly half of respondents said that the light of the new find, Graeme cost of chemical control was increasing. Most farmers also and Nick Waipara mowed and topped their thistles. The survey concluded that (HortResearch) are planning to the Otago/Southland Region probably spends annually about compare the potential of P. $6.6 million on chemicals, $18 million on mowing and topping, exigua with S. sclerotiorum and $2.4 million on scabby mouth vaccine, which comes to a against Californian thistle. We grand total of $27 million per year, or about $4,500 per farm. will keep you posted on the This seems like a reasonable estimate given that a 1989 survey outcome in future issues. of farms in the same region by Mitchell and Abernethy** estimated that Californian thistle cost the region, at that time, For further information about about $21 million or about $3,500 per farm, and a subsequent the pathogen work described survey of farmers near Gore yielded a figure of $3,100 per farm. above you can contact Graeme by email ** Mitchell, R.B.; Abernethy, R.J. 1993: Integrated management of California thistle ([email protected]) in pasture. Proceedings of the 46th New Zealand Plant Protection Conference. Pp. or phone (03) 983-3973. 278–281. 9 What's New in Biological Control of Weeds? Number 21 May 2002

Aloha from Hawai'i

are likely to be suitable for the bacteria and that our ginger populations are susceptible.

Hugh has been undertaking host range tests for a number of years on various gorse agents for the Tasmanian Institute of Agricultural Research. Lately, he has been testing the gorse soft shoot moth (Agonopterix ulicetella), but lab tests have not clearly demonstrated the safety of this agent. “The gorse soft shoot moth is abundant at Hugh examining banana passionfruit (P. tarminiana) in Hawai’i. a site on the Mauna Loa volcano, so I was able to plant out a Hugh Gourlay recently travelled hoping to co-fund (with our couple of the problematic to Hawai’i to help further the Hawai’ian colleagues) a survey in species that I was still a bit cause of biological control of South America in 2004 to look unsure about,” said Hugh. These gorse (Ulex europaeus), banana for additional new agents and plants will later be checked for passionfruit (Passiflora spp.), collect colonies of agents that damage by our gorse and wild ginger (Hedychium the Hawai’ians have worked on colleagues, Patrick Conant spp.). Before he left, Hugh sent previously and warrant further and Clyde Hirayama (USDA). over some New Zealand banana study,” explained Hugh. The site at Mauna Loa is also passionfruit plants*, so they home to good numbers of would be ready for him to Kahili ginger (Hedychium gorse thrips (Sericothrips begin initial testing of the fruit- gardnerianum) has also invaded staphylinus), so Hugh feeding fly Zapriothrica nr. thousands of hectares of collected some more of the nudiseta upon his arrival. He Hawai’an forests. Researcher Portuguese strain to boost our also checked on progress with Rob Anderson is developing a rearing colony here. Finally other banana passionfruit agents bioherbicide for kahili ginger Hugh touched base with a including the leaf spot fungus using a bacterium (Ralstonia major project on the integrated (Septoria passiflorae) and the solanacearum). “I have put the management of gorse that has shoot- and flower-feeding moth wheels in motion to get Rob out just begun at this site (funded (Pyrausta perelegans). The here on an exchange scheme by Parker Ranch). Hugh will be fungus is doing well (see next January,” revealed Hugh. involved in this project by “Honey I shrunk the weed”, There is a lot of interest in testing, and hopefully later Issue 19) but the moth is whether the technique might be establishing, the gorse pod struggling, possibly due to appropriate for use here too, so moth (Cydia succedana) in heavy parasitism. “We are we need to check that conditions Hawai’i.

* A recent taxonomic revision now lists four Passiflora spp. under the collective heading of “banana passionfruit” in New Zealand. They are: P. tripartita var. mollisima (was P. mollisima), P. tripartita var. azuayensis (was probably also known as P. mollisima, quite rare), P. tarminiana (was P. mixta) and, P. mixta (was also known as P. mixta, quite rare). Our only native species (P. tetandra) and commercially grown passionfruit (P. edulis) are in different subgenera to the weedy ones. 10 What's New in Biological Control of Weeds? Number 21 May 2002

Winter and Spring Activities

Winter is the time when many thistles, so look out for spartiophila), gorse pod moths of you will be able to have a damage to these plants too. (Cydia succedana), and gorse bit of a breather on the Crown weevils can also thrips (Sericothrips biological control front as usually be harvested and staphylinus). Spring is also many of our bugs will shut shifted around as late as June. the best time to check mist down for the duration. flower fungus (Entyloma However, winter can be a We suggest that you use the ageratinae) and gorse colonial good time to check nodding off-season to make plans for hard shoot moth (Pempelia thistle crown weevil the coming spring, and get up genistella) release sites. The (Trichosirocalus horridus) to date on the paperwork. If colonial hard shoot moth release sites. Some weevils you have any outstanding caterpillars remain tiny lay eggs all year round, but release or recovery forms, then throughout the winter and put the bulk of them begin to lay please send them in without on a growth spurt in the in the autumn and the delay so we can ensure our spring as they forage on damage to the rosettes nationwide databases remain young buds, shoot and becomes more noticeable as as up to date as possible. flowers. Look out for the the winter progresses. As the Also start thinking about communal webs (which can grubs feed in the crown, they suitable release sites for any get up to 20 cm across) with produce a black waste new agents that you may be green-and-brown striped substance (frass), and the receiving from us next season, caterpillars inside. The ribs of the surrounding leaves and planning harvesting caterpillars' feeding damage take on a reddish-brown operations and field days for and balls of frass should also colour at the base. The things like broom seed beetles be quite obvious and help leaves of damaged rosettes (Bruchidius villosus), broom you to distinguish these webs become less prickly and start psyllids (Arytainilla from spider webs. to look a bit like dandelion leaves. You may see rosettes that look like this at any time of the year, but the damage is usually most obvious later in the winter and in early spring. If you dig a damaged rosette out of the ground and cut it in half with a pocket knife, you should be able to see the white grubs feeding inside. As well as nodding thistles (Carduus nutans) the weevil attacks cotton (Onopordum acanthium), marsh (Cirsium palustre), plumeless (Carduus acanthoides), Scotch (Cirsium vulgare), slender-winged (Carduus pycnocephalus) and Typical gorse colonial hard shoot moth web, note caterpillars, webbing winged (Carduus tenuiflorus) and frass (at bottom). 11 What's New in Biological Control of Weeds? Number 21 May 2002

Tell Me More…

Question: My ragwort has populations are kept low by a What can I do to help? come back. What has gone small resident flea beetle • Avoid activities that wrong? Has the ragwort flea population, can continue for promote ragwort growth – beetle stopped working? some time. However, if basically anything that something happens to suddenly opens up pasture. No, don't hit the panic button, as promote ragwort growth (e.g. • Avoid activities that harm this is to be expected! Even drought, overgrazing, or the agents, e.g. spraying the though the ragwort flea beetle pugging, which opens up rosettes when the agents are (Longitarsus jacobaeae) has gaps in pasture) you can developing inside and are been doing an excellent job in suddenly have a bumper crop unable to escape. If you must recent years at taking out ragwort of ragwort on your hands. The spray your ragwort then use plants (Senecio jacobaea), small resident flea beetle one of the more beetle- there is still a huge seed bank population is suddenly spoilt friendly products, such as in the soil just waiting for the for choice and unable to attack metsulfuron methyl (Escort®) right conditions to grow. all the plants available. However, when mobile adults are the now that its host is again dominant life stage (see the When flea beetles are released abundant the flea beetle “The Biological Control of on to ragwort it usually takes a population can grow accordingly Weeds Book” for more details few years for their numbers to and eventually bring the about using herbicides with build up to the stage when they ragwort back under control ragwort flea beetles). start to make a dent in their again. This boom/bust cycle is • Check that the beetles are host. As the beetles become likely to be repeated many indeed still present and if numerous the ragwort usually times before the seed bank is necessary arrange for a top- begins to decline quite rapidly exhausted. Even then there may up release. to low levels. When there are be some years when ragwort only a few plants left for the temporarily becomes bad again NB. Ragwort flea beetles are beetles to utilise, their numbers if conditions favour the growth not able to control ragwort also take a nosedive. This of this weed and/or do not suit growing in all situations. See state of affairs, where ragwort the control agents. Hot Gossip page 4.

This newsletter is produced three times a year by: Website: www.landcareresearch.co.nz Landcare Research NZ Ltd PO Box 69 Editor: Lynley Hayes Lincoln 8152 Email: [email protected] New Zealand Layout: Kirsty Cullen Ph +64 3 3256 700 Cartoon: Susan Marks Fax +64 3 325 2418

This newsletter is now available online! Check out our website! Manaaki Whenua. Manaaki Tangata: Care for the land. Care for the people ISSN 1173-762X This information may be copied and distributed to others without limitations, provided Landcare Research and the source of the information is acknowledged. Under no circumstances may a charge be made for this information without the expressed permission of Landcare Research. 12