Growing Heritage Roses in WA, Including managing Chilli Thrips & Quarantining

The Perth region of Western Australia is quite extensive, and has a diverse mix of soil and climate types, from the sandy suburbs, coastal plains, rich soils of the Swan Valley, and the clay rich soil of the Perth Hills. Di Durston, Tea Bag and PRHRiA member, gives some excellent tips on how to grow your heritage roses in your garden or in pots (read on!).

We also take a brief dive into the world of Quarantine. New WA quarantine regulations have made it expensive to import roses from interstate and fewer nurseries are willing to post roses to WA. It is therefore important that WA becomes as self sufficient as possible in supplying budwood from within our own state. The more varieties of heritage and early modern roses we can grow here the better it will be for the future of WA rose conservation in Western Australia.

Growing roses does present some problems, and the Department of Primary Industries and Regional Development WA give crucial advice on Chilli Thrips on roses, how to identify and monitor this, and how to manage them. Read more below.

Growing Roses in Perth, WA

To grow roses in home gardens is one of life's great pleasures. They keep blooming for up to nine months each year in Perth's warm Mediterranean climate. When the cooler months arrive the plants become dormant and then winter pruning can begin. Tea Bag Di Durston has compiled an overview of Growing Roses in Perth.

We need to prepare the soil several months ahead of the time before planting. Some say that April is a good time to plant to allow for root growth before the Spring flowering.

After listening to a lecture with a ‘Mottisfont’ Headgardener, I have taken up his growing tip of adding Mycorrhizal Fungi in the hole to help with root development. I also recall one of my Horticulture lecturers telling our group to put a good handful of slow release fertiliser in the bottom of the hole and cover with about 10 cm of soil. His reason was to develop a good root system.

Once planted the rose will need deep watering several times a week in warm weather and I also like to use seaweed saver in a bucket of water to keep the plants healthy. When fertilizing, it is best not to over do the nitrogen and this year I plan to try Yara Mila after seeing the fabulous results at Mostly Roses, at Newlands.

Roses grow happily in pots and I first came across Tea Roses in pots at the Fremantle Conference when Bob Melville decorated the lecture hall with the most beautiful pots of healthy flower laden Tea Roses. I don’t use granulated fertilizer in pots, slow release and liquid only, to prevent the build up of salts in the pot.

To conclude, we need sun, good soil, and deep watering with a whole lot of passion to grow the queen of the flowers, Old Roses.

As with growing any plant, soil preparation is the first step, with lots of added organic materials to break up the soil and protect the plant from drying out in summer. We are blessed with abundant sunshine in Perth, and roses love to grow in the sun. It is best to have about six hours a day of sunshine for the rose garden.

Quarantine

Quarantine Requirements for Importing Budwood to Western Australia

The movement of plant goods from one State to another and importing plant stock from overseas gardens requires you to check that the relevant quarantine conditions are met, and in the case of rose stock this entails a period of quarantine once it has arrived in Western Australia.

Rose growers looking to import budwood from the Eastern States are required to adhere to strict import requirements under the Biosecurity and Agriculture Management Act 2007.

The requirements are designed to help protect Western Australia’s valuable agriculture industry, environment and lifestyle from the risk of an exotic pest or disease. WA Quarantine has advised of the following requirements for home growers for budwood imports.

Importing rose budwood into Western Australia

All plant species that have been assessed for import approval status are listed on the Western Australian Organism List (WAOL). If a species isn’t listed, it needs to go through an extensive assessment process. Rose budwood has been assessed and approved for import into Western Australia, provided it meets the import conditions in place for each state.

To import large quantities or plants in potting media, you need to meet the conditions for the state from which you are importing the material. For small amounts of fewer than 20, budwood, bare rooted plants (with the exception of those from Victoria) and cuttings need to be able, as a minimum, to meet the alternative conditions as listed below.

Condition C71 – Alternative conditions

Subject to prior approval by an inspector, inspection upon arrival of bare rooted plants (except Victoria) and cuttings/budwood is permitted in lieu of other measures prescribed in this condition.

The inspector must be satisfied that any prescribed pest or disease of concern is able to be detected by inspection and that it is feasible to 100% inspect the volume of material proposed to be imported. The approval may be for a consignment to a maximum of 20 individual plants/cuttings/budwood, and must be issued by an inspector in writing with the following conditions:

All consignments must be imported into Western Australia in a manner that prevents the escape of pests and diseases and remain so until on-arrival inspection and/or treatment is undertaken.
Consignments to be free from pests and diseases of quarantine concern on arrival in Western Australia.
To be 100% inspected by an inspector on arrival in Western Australia at the gazetted fee for service in some instances. More information can be obtained on the fees by calling 9334 1800.
All importation requirements, including labelling, other than those specified as exempted by an inspector, to be met.
An inspector's approval may be cancelled or not approved for future consignments if a consignment is found not to meet the above requirements.

Additional conditions may be imposed by the inspector. Inspections are carried out to detect any risk material. If risk material is found, the importer may opt for treatments or destruction.

Requests for approvals should be forwarded to Quarantine WA at followup@agric.wa.gov.au

You can check the import status of other plants by searching the database at https://www.agric.wa.gov.au/organisms

New WA quarantine regulations have made it expensive to import roses from interstate and fewer nurseries are willing to post roses to Western Australia, so it is therefore important that WA becomes as self sufficient as possible in supplying budwood from within our own state. The more varieties of heritage and early modern roses we can grow here the better it will be for the future of Western Australian rose conservation in WA.

Chilli Thrip on your Roses

Although roses are such a joy to grow, and in most cases not difficult to grow at all, they are subject to several problems, and Chilli Thrip is one of them that is so important to keep a watch for.

Their website is very comprehensive and a fantastic resource for all growers. It is a good idea to check in from time to time to see what they have discovered or are testing, in the Horticulture Section.

Their most recent advice, after testing of damaged rose samples from the Perth metropolitan area, determined that Chilli Thrip has been very active in Perth gardens, after migrating from the north of WA down to the southern part of the state.

Chilli Thrips are a pest that needs quick attention to prevent the spread throughout the state, and the decimation of countless roses.

Please read the following information and advice published on the DPIRD website on 20 May 2021 HERE, or continue to read the info from their site reproduced below.

Chilli Thrip on Roses

Chilli thrips (Scirtothrips dorsalis) are found throughout the world and were first reported in north Western Australia about 20 years ago. Chilli thrips are sap-sucking insects that can cause deformities in ﬂowers, leaves, stems, and shoots. Also known as strawberry, and tea thrips, chilli thrips feed on roses, all citrus and their hybrids, as well as a range of fruit and vegetable hosts.

Thrips are most active during spring, summer and autumn. In Perth, recent rainfall and humidity has created conditions that are conducive to chilli thrips, which feed on the sugars in new shoots.

Damage to rose plant caused by Chilli Thrip (image credit DPIRD 2021)

In brief

Similar to: Western flower thrips (Frankliniella occidentalis), Plague thrips (Thrips imaginis)

Habitat: Deep in the ﬂower or on the undersides of the leaves, and on the ground or lower leaves when pre-pupal or pupal stages

Hosts: Roses, all citrus and their hybrids, and a range of fruit and vegetable hosts

Monitoring: Look for chilli thrips when they are most active; in spring, summer and autumn

Damage: Distinctive brown scarring along the leaf veins, flower buds and the calyx or outer casing of fruit, light brown spots on leaves, curled and dried leaves, and deformed shoots or flowers

Lifecycle

The thrips lifecycle, comprising egg, larva, pre-pupa, pupa, and adult, lasts several weeks.

Eggs are laid within plant tissues (eggs hatch more quickly in higher temperatures)
Larvae emerge from the eggs feed on surrounding tissues
Larvae fall to the ground or lower leaves when they reach the appropriate stage of development. They live there during the pre-pupal and pupal stages until a reproductive adult appears with fully developed wingChilli thrips can have many generations in a single year and populations can build up over time.

Identification

About two millimetres long
Elongated, flat ‘torpedo’ shaped body
Coloured pale or translucent to black
Adult thrips have four feathery wings
Very difficult to distinguish from other thrips species with the naked eye

Chilli thrips are difﬁcult to see because they are small and hide deep in the ﬂower or on the undersides of the leaves, which become silvery on the upper surface.

Damage

Thrips larvae feed on plant tissues and are responsible for the majority of plant damage.

Early symptoms include a clear discoloration of the leaf with black dots (faecal secretions).
Light brown spots on leaves, which may curl.
In cases of very severe infestation, the leaves may entirely dry up.
Wrinkled leaves with distinctive brown scarring along the leaf veins, flower buds, and the calyx or outer casing of fruit.
Mosaic patches on plants, in which the top layer of the tissue is undisturbed and a window or clear tissue in evident. Chilli thrips cause this sucking up the liquid from plant cells; mainly from the leaves, but also the petals, shoots and fruits.
Adult thrips also feed on the underside of leaves.
Deformed shoots or flowers of affected plants, caused by toxic substances in the saliva of the pest.

Chilli Thrip's damage to a rose leaf (image credit DPIRD 2021)

Monitoring

Inspect plants regularly for evidence of thrips to enable early detection and minimise impact by the pest.

Monitoring is vital to enable the implementation of preventative measures when thrips are detected, because they are difficult to control once plant damage is evident.

Use an adhesive trap (ideally blue since it attracts chilli thrips). Examine every few days using a magnifying glass to check whether chilli thrips (usually winged adults) have stuck to them.
Tap flowers over a sheet of white paper and examine the black, torpedo-shaped 'specks' beneath a magnifying glass.

Management

Chilli thrips are difficult to control and public reporting indicates chilli thrips and other thrips species are prevalent across the Perth metropolitan region. The use of an Integrated Pest Management System is the most effective way to prevent chilli thrips infestations. DPIRD recommends the following management activities:

Undertake a hard prune of infested plants to remove damaged plant material
Dispose of cuttings as most practicable.
There are no mandatory disposal requirements for this pest but good biosecurity practices when inspecting and treating plants will limit pest and disease spread:
- Bag smaller volumes of cuttings to help reduce local spread to sections of the property that are not showing signs of the pest.
- Clean tools between plants, especially if cutting plants that looks diseased.
Small populations may not cause sufficient damage to warrant chemical control but large infestations can seriously weaken plants.
A range of products registered to treat other thrips species may be used.
- Preventative sprays may be required in some situations, such as to negate even small amounts of damage to blossom stems for show roses. Time preventative spraying to correlate with bud initiation.
- Products that contain active ingredients such as imidacloprid, acetamiprid, spinetoram, or pyrethroids are effective against thrips, and may be available to home gardeners.
- Horticultural soap, oils, and other products may be available as organic controls.

Always use products purchased for management of thrips according to label directions.

DPIRD recommends thoroughly spraying plants all over because the thrips take refuge under the veins of the leaves, making it difficult for the insecticide to contact all the insects. It may be difficult to kill the pests when they are hidden deep within the flower petals.

Multiple applications of treatments, whether organic or not, may be required and it may be wise to apply treatments to other nearby host plants to protect them from the pest. Take care when applying insecticides to conserve the beneficial predators that will help with thrips control.

Reporting

Report unfamiliar and damaging pests for identification and distribution mapping.

The Department of Primary Industries and Regional Development is proactive in providing up to date information on anything related to agriculture and growing plants, including growing roses. They have produced a comprehensive page on their website about the very menacing Chilli Thrip that sends a chill down the spine of most Rosarians.