Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Spring Activities

Broom gall mite galls.

Broom gall mite galls.

Most biocontrol agents become active during spring, making it a busy time of year. Some activities that you might want to fit in over this time include:

Boneseed leafroller (Tortrix s.l. sp.“chrysanthemoides”)

  • Check release sites from mid-spring for feeding shelters made by caterpillars webbing together leaves at the tips of stems. Small caterpillars are olive-green in colour and become darker with two parallel rows of white spots as they mature. We would be very interested to hear if you find any severe damage to boneseed foliage.
  • Caterpillars can be harvested if you find them in good numbers. Cut off infested boneseed tips and wedge them into plants at new sites. Aim to shift at least 500 caterpillars to sites where scale insects and invasive ants are not known to be present.

Bridal creeper rust (Puccinia myrsiphylli)

  • Check bridal creeper infestations for bridal creeper rust, particularly sites where it has not been found before. Plants infected by the rust have yellow and black pustules on the undersides of leaves and on stems and berries. They may look defoliated and sickly.
  • If you need to redistribute bridal creeper rust see detailed instructions at CSIRO: Bridal creeper rust fungus.

Broom gall mite (Aceria genistae)

  • Spring and summer are the best times to check plants at release sites for galls, which look like deformed lumps and range in size from 5 to 30 mm across. They will probably be fairly close to the release point. Occasionally galls can be found on broom that are not made by the gall mite, but these are much less dense. We are happy to help confirm the identity of any galls you find.
  • If galls are present in good numbers you may be able to begin harvesting and redistributing them in summer when they are mature. Aim to shift at least 50 galls, and tie them onto plants at the new site so the tiny mites can shift across. Because the mites are showing much promise but are expected to disperse quite slowly it will be important to plan a comprehensive redistribution programme.

Broom leaf beetles (Gonioctena olivacea)

  • Check sites where beetles have been released for three or more years for signs of establishment. The adults are 3-5 mm long and females tend to be goldish-brown while males have an orangey-red tinge – although colouration can be quite variable. Look for larvae in late spring – they are a greyish-brown and feed on leaves and shoot tips. Use a beating tray to help find this agent, and don’t be surprised if you only find one or two beetles at this stage.
  • It is probably still a bit soon to find enough beetles to be able to begin harvesting and redistribution just yet.

Broom seed beetles (Bruchidius villosus)

  • Look for adult beetles gathering together on broom flowers or for eggs on the pods.
  • If need be the beetles can be moved around fairly easily. Use a beating tray and a pooter to collect adults or put a large bag over a branch of flowers and give them a good shake.

Broom shoot moth (Agonopterix assimilella)

  • Late spring is the best time to check broom shoot moth release sites. Look for the caterpillars’ feeding shelters made by webbing twigs together. Small caterpillars are dark brown and turn dark green as they get older. We have not yet seen any good evidence of likely establishment at any of the release sites so we will be especially interested to hear if you find any sign of the moth.
  • We would not expect you to find enough caterpillars to be able to begin harvesting and redistribution just yet.

Green thistle beetles (Cassida rubiginosa)

  • Check release sites for adult beetles, which emerge on warm days towards the end of winter and feed on new thistle leaves making round window holes. The adults are 6–7.5 mm long and green, but are quite well camouflaged against the leaf. The larvae also make windows in the leaves. They have prominent lateral and tail spines and a protective covering of old moulted skins and excrement.
  • The beetles may have built up to harvestable numbers at some of the oldest sites so it may be possible to begin redistribution. Use a garden-leaf vacuum machine and aim to shift at least 50 adults in the spring. Be careful to separate the beetles from other material collected during the vacuuming process, which may include pasture pests.

Ragwort crown-boring moth (Cochylis atricapitana)

  • No signs of establishment of this moth have been seen yet so it would be good to check release sites one last time. Look for rosettes with damaged centres and black frass or thickened stems and bunched leaves. If present the caterpillars should be most easily found by pulling apart damaged plants during August–September. They are creamy-white, with black heads that become brown when they are older, and are quite short and fat. Please let us know if you find any.

Ragwort plume moth (Platyptilia isodactyla)

  • October is the best time to check release sites for caterpillars. Look for plants with wilted or blackened or blemished shoots with holes and an accumulation of debris, frass or silken webbing. Pull back the leaves at the crown of damaged plants to look for large hairy, green larvae and pupae. Also check where the leaves join bolting stems for holes and frass. Don’t get confused by larvae of the blue stem borer (Patagoniodes farinaria), which look similar to plume moth larvae until they develop their distinctive bluish colouration.
  • If this moth is present in good numbers the best time to harvest it is in late spring. Dig up damaged plants, roots and all. Pupae may be in the surrounding soil so retain as much as possible. We recommend shifting at least 50–100 plants but the more you can shift, the greater the chance the moth will establish. Place one or two infested plants beside a healthy ragwort plant at the release site so any caterpillars can crawl across.

Tradescantia leaf beetle (Neolema ogloblini)

  • Although most release sites are still less than 18 months old some people have already been able to fi nd signs of the beetles early on so it is probably worth taking a look. The dark metallic bronze adults may be hard to spot as they tend to drop when disturbed. Look instead for the slug-like larvae in areas where there is damage to the leaves. Adults chew holes around the edges of leaves, and may consume entire leaves. The larvae graze the epidermal tissue off the leaves, mostly on the undersides, and can skeletonise them.
  • We would not expect you to find enough beetles to be able to begin harvesting and redistribution just yet.

Tradescantia stem beetle (Lema basicostata)

  • Given that the first release only went out last autumn it may well be far too early to find the stem beetle at release sites this spring, but there is no harm in taking a look! The shiny black knobbly adults may be hard to spot as they also tend to drop or fly away when disturbed. They chew elongated windows in the upper surfaces of leaves and sometimes consume entire leaves. The larvae are inside the stems so look for signs of their feeding (collapse and necrosis of stems) and brown frass.
  • We would not expect you to fi nd enough beetles to be able to begin harvesting and redistribution just yet.

Woolly nightshade lace bug (Gargaphia decoris)

  • Once the weather warms up look on the undersides of leaves at release sites for the adults and nymphs, especially on leaves showing signs of bleaching or black spotting around the margins.
  • We expect the lace bugs might also be slow to disperse so if good numbers are present it would be worth collecting some to release in other areas. Always wear gloves when handling woolly nightshade foliage to avoid any health issues. Cut leaf material that is infested with adults and/or nymphs and wedge or tie this material fi rmly into new woolly nightshade plants so the lace bugs can move across. We recommend that you shift at least 1000 individuals to each new site at any time during the warmer months.

Other agents

You might also need to check or distribute the following this spring (for further details see The Biocontrol of Weeds Book):

  • Gorse soft shoot moth (Agonopterix ulicetella)
  • Gorse colonial hard shoot moth (Pempelia genistella)
Send any reports of interesting, new or unusual sightings to Lynley Hayes.