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• Issue 73 »
• Spring Activities

Spring Activities

Lantana leaf rust.

Most biocontrol agents become active during spring, making it a busy time of year to check release sites and move agents around.

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

• Check release sites for feeding shelters made by caterpillars webbing together leaves at the tips of stems. Also look for “windows” in the leaves and sprinkles of black frass. Small caterpillars are olive green in colour and become darker, with two parallel rows of white spots as they mature.
• 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.

Broom gall mites (Aceria genistae)

• Check release sites for galls, which look like deformed lumps and range in size from 5 to 30 mm across. Heavily galled plants may be dead or dying.
• If galls are present in good numbers, late spring – early summer is the best time to undertake harvesting and redistribution. Because the mites are showing much promise but are expected to disperse quite slowly, it will be important for all regions with a major broom problem to plan a comprehensive redistribution programme. Aim to shift at least 50 galls to each site and tie them onto plants so the tiny mites can shift across.

Broom leaf beetles (Gonioctena olivacea)

• Check release sites by beating plants over a tray. Look for the adults, which are 2–5 mm long and goldish-brown (females) through to orangey-red (males) with stripes on their backs. Look also for greyish-brown larvae that may also be seen feeding on leaves and shoot tips.
• It is probably still a bit soon to begin harvesting and redistribution.

Broom shoot moth (Agonopterix assimilella)

• Late spring is the best time to check release sites. Look for the caterpillars’ feeding shelters made by webbing twigs together. Small caterpillars are dark reddish-brown and turn dark green as they get older. We have found reasonable evidence of establishment only at one site in Southland to date, so we will be interested to hear if you find any sign of the caterpillars.
• We would not expect you 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 a protective covering of old moulted skins and excrement. You may also see brownish clusters of eggs on the underside of leaves.
• It should be possible to harvest beetles at many of the older sites. Use a garden-leaf vacuum machine and aim to shift at least 50 adults from spring throughout summer and into autumn. Be careful to separate the beetles from other material collected, which may include pasture pests.

Lantana blister rust (Puccinia lantanae)

• Check sites where lantana plants infected with blister rust were planted out last autumn, especially after a period of warm, wet weather. Signs of infection include leaf and stem chlorosis (yellowing) accompanied by large, dark pustules on the undersides of leaves and on the stems. Once infection is well-established, stunting, defoliation and die-back may also occur.
• Once established this rust is likely to be readily dispersed by the wind. If redistribution efforts are needed the best method will likely involve placing small potted lantana plants beneath infected ones and then planting these out at new sites once they have become infected. However, to propagate and distribute lantana in this manner an exemption from the Ministry for Primary Industries will be required.

Lantana leaf rust (Prospodium tuberculatum)

• Check sites where the leaf rust was released last autumn, especially after a period of warm, wet weather. Look for yellowing on the leaves with corresponding brown pustules and spores, rather like small coffee granules. A hand lens may be needed to see the symptoms during early stages of infection.
• Once established this rust is likely to be readily dispersed by the wind. If redistribution efforts are needed the best method will likely involve harvesting infected leaves and brushing the spores onto young leaves.

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 the moth is present in good numbers, the best time to shift it around is in late spring. Dig up damaged plants, roots and all. Pupae may be in the surrounding soil so retain as much as possible. Shift at least 50–100 plants, but the more the better. Place one or two infested plants beside a healthy ragwort plant so any caterpillars can crawl across.

Tradescantia leaf beetle (Neolema ogloblini)

• Check release sites, especially the older ones. Look for notches in the edges of leaves caused by adult feeding or leaves that have been skeletonised by larvae grazing off the green tissue. You may see the dark metallic bronze adults sitting on the foliage or the larvae, which have a distinctive protective covering over their backs. The white, star-shaped pupal cocoons may also be visible on damaged foliage.
• Redistribution has begun at some of the older sites. If you can see plenty of beetles sitting about then harvesting can begin. Aim to collect and shift 50–100 beetles. Collect the beetles either using a suction device or a small net.

Tradescantia stem beetle (Lema basicostata)

• Check release sites, especially the older ones. The black knobbly adults tend to drop when disturbed, and can be difficult to see. Look for their feeding damage, which consists of elongated windows in the upper surfaces of leaves or sometimes whole leaves consumed. The larvae inside the stems will also be difficult to spot. Look for stems showing signs of necrosis or collapse and brown frass.
• If you can find widespread damage at the site then you may be able to begin harvesting and redistribution. We still need to identify the best possible method to do this. If it proves to be too difficult to collect 50–100 adults with a suction device, then another approach to try would be to remove a quantity of the damaged material and put it in a wool pack or on a tarpaulin and wedge this into tradescantia at new sites. However, to distribute tradescantia in this manner an exemption from the Ministry for Primary Industries will be required.

Tradescantia tip beetle (Neolema abbreviata)

• Check release sites, especially the older ones. The adults are mostly black with yellow wing cases, and you may see them sitting about on the foliage. Look also for their feeding damage, which looks like elongated windows in the leaves, similar to the stem beetle. Larvae will also be difficult to see when they are feeding inside the tips, but brown frass may be visible. When tips are in short supply, the slug-like larvae feed externally on the leaves.
• We expect it is probably still a bit soon to begin harvesting and redistribution just yet.

Other agents

You might also need to check or distribute the following this spring:

• Gorse soft shoot moth (Agonopterix umbellana)
• Gorse thrips (Sericothrips staphylinus)
• Gorse colonial hard shoot moth (Pempelia genistella)

National Assessment Protocol

For those taking part in the National Assessment Protocol, spring is the appropriate time to check for establishment and/or assess population damage levels for the species listed in the table below. You can find out more information about the protocol and instructions for each agent in the Biocontrol of Weeds book.

Send any reports of interesting, new or unusual sightings to Lynley Hayes: hayesl@landcareresearch.co.nz, ph 03 321 9694.