Help & Advice

Integrated Pest Management for Interior Atriums and Office Plants

INTRODUCTION

All plants can suffer with pest or disease outbreaks, particularly those under stress due to their environment or positioning. Beneficial organisms can be used for control of common sucking pests such as aphids, spider mites, scale insects and mealybug. There are also several pesticides with activity against these pests, some of which can be integrated while others have a much broader range of activity, killing most natural enemies as well as (hopefully) the pest. However, once a plant is taken into an atrium or office area it falls into a unique category as far as the UK Pesticides Safety Directorate (PSD) are concerned. These are plants maintained by a professional team that can use professional feeds and biological controls but usually only amateur pesticides approved for use on household plants. There are a few professional pesticides such as Deleet containing deltamethrin that can be used by trained and certified operators after a full COSHH / Risk Assessment has been done.

Integrated Pest Management (IPM) uses cultural techniques, biological control agents and selective or short persistence pesticides to provide long term pest management. It is quite practicable to use a fully sustainable IPM programme that can run from year to year with just minor adjustments and without the need to resort to total area sprays should there be a pest outbreak. This article will look at the main pests, their biological and integrated pest management options.

Pest Identification

It is essential to be able to identify pests before they are able to proliferate and a knowledge of basic biology is also useful if an IPM programme is to be fully effective. Sap sucking pests such as aphids, mealybug and soft scale insects can excrete vast quantities of sticky, sugar-rich honeydew that, in addition to direct plant damage will further disfigure plants with associated growths of sooty moulds and loss of plant vigour. Spider mites are also an extremely common and severely damaging pest with a rapid rate of reproduction when conditions are hot and dry. Predatory mites are available that can frequently eradicate the pest completely. Various species of thrips can cause differing types of leaf damage as well as transmitting plant viruses to a wide range of plants. The book: A Colour Handbook of Biological Control in Plant Protection written by myself and Kevin Brown with excellent colour photos by Nigel Cattlin describes the majority of pests and their biocontrols that can be found on interior plantscapes.
Clumps of mealybugs. Species identification is useful for best control.

PESTS AND THEIR CONTROL

For any plant holding units or areas where newly potted plants are kept, even for a short while the predatory mite Hypoaspis miles should be introduced. This mite lives in soil, compost or capillary matting and feeds predominantly on Sciarid fly larvae. They will also eat thrip larvae/pupae, springtails, mealybug nymphs and other organisms in or close to the compost. The mite is best introduced as a preventative
treatment to all plants, ideally within 2 weeks of potting or installation to a site or at the very first sign of Sciarid fly adults or larvae on the compost. Excellent results have been obtained by using Hypoaspis at 100 - 150 mites per m² with repeat applications at 10 - 12 week intervals. In this way the predators will maintain an active population to control a range of soil borne pests.

Colony of citrus mealybug nymphs showing protective grey wax covering.

Mealybug and Scale Insects

Mealybug and scale insect can establish on many plants, particularly woody ornamentals, slow growing ornamentals and even commercial crops such as tomatoes. An unmated female mealybug can survive on an inert surface such as pot rims, cracks in containers, behind plant ties etc. for 6 months or more before mating with a winged male and returning to a plant to reproduce. Biological control with the Australian ladybird Cryptolaemus mon-trouzieri works well on egg laying species of mealybug such as Planococcus citri and some Pseudococcus species but these ladybirds can be slow to establish on long-tailed mealybug. Citrus mealybug (P. citri) is easy to identify by having a short fringe of waxy hairs and a darker bar along their back. 
A woolly white Cryptolaemus larva. Very useful but can be visible on plants.

Glasshouse mealybug (P. affinis) has a similar fringe of hairs but also a couple of waxy tail filaments that are approximately half its body length protruding from is posterior end. The long tailed mealybug (Pseudococcus longispinus) is commonly found on a wide range of plants and easily identifiable by having a narrow body with tail filaments that are slightly longer than its main body. Cryptolaemus also feed on scale insects but will not establish without mealybug. The woolly, white Cryptolaemus larvae can be very noticeable on display plants. This has led to the preferred use of lacewing larvae for mealybug control where visual appearance is of paramount importance. Lacewing larvae (Chrysoperla carnea) are small predatory insects with pincer mouthparts that can penetrate most soft bodied insects such as aphids, mealybug, young caterpillar, thrips, spider mites etc. Chrysoperla are much less noticeable to the public than the white Cryptolaemus larvae but their big advantage is that they will remain close to their release point, unlike Cryptolaemus adults that can easily fly away. I suggest a rate of 10 - 15 larvae per m² on a 2 - 4 weekly cycle if needed. Specific parasites are seasonally available (usually May to September) for mealybug and scale insect; contact Fargro for availability and advice. SB Plant Invigorator has given excellent control of mealybug and scale insects when applied as contact spray with a second follow up spray 2 - 3 days after the first. This works by allowing the first application to remove the waxy protective coating on mealybugs while subsequent sprays stick and suffocate the pest.
Lacewing larvae feed on most soft bodied prey are less noticeable on plants.

Aphids

Aphids can be a seasonal pest problem when winged adults fly-in from their over wintering sites, they can build up to high numbers in a short period of time causing sticky residues on leaves and below plants. The parasite Aphidius and predator Aphidoletes will easily control most aphid species. These should be introduced fortnightly at the first sign of aphids at a rate of 2 5 per m² while aphids are a threat. Aphidoletes adults are nocturnal and will not establish in areas where 24 hour lighting is used. Lacewing larvae (Chrysoperla carnea) will devour most aphid species and can be used to control quite large infestations. They will feed on other soft-bodied organisms including leafhopper nymphs, mealybug, scale insects, spidermite, thrips and developing whitefly. Lacewing larvae can also be introduced to hedges and external borders in late April to May and again in June to provide a population of natural enemies that can control a wide range of pests and help prevent pest migration into atriums. Lacewing larvae can be cannibalistic if food supplies run short; so they need to be distributed thinly, rather than many in one place. SB Plant Invigorator may be used to control 'hot spots' of Aphis fabae (black bean aphid) was effectively controlled aphids and other pests when applied as a contact after 1 treatment. spray, it works by physical means rather than poisoning, i.e. smothering and sticking. The photographs show a before and after shot of a rose stem but the product works equally well on all other plants.

In depth details of this product are given further in this article.

Aphid parasite Aphidius inserting egg into live aphid.

Before          After

Aphis fabae (black bean aphid) was effectively controlled after one treatment.

Spider mites

Spidermites can survive throughout the year on a wide range of office plants producing their characteristic yellow speckling feeding damage. A new development in spider mite control / prevention is the predatory mite Amblyseius andersoni. This UK sourced and produced mite is available in controlled release system (CRS) sachets that hang on plants and release mature mites continuously over a 6 - 8 week period. A. andersoni can also provide control of fruit tree spider mite, russet mites and other small prey but do not perform well on severe outbreaks due to spider mite webbing. However, they survive well in surrounding areas often ambushing straying spider mites and limiting their spread. Due to their ability to survive on other food sources such as pollen, other mites and small prey they are ideal to 'seed' a susceptible
crop before spider mites appear. The more voracious predator Phytoseiulus persimilis can be used as a stand alone predator for curative use as and when needed or alongside Amblyseius species to boost their activity. The licensed predatory mite Amblyseius californicus is tolerant to high temperatures and lower humidities, but is only allowed to be released on plants in production within a protected structure. Unfortunately plants in an office or atrium fall outside the license approval for A. californicus however; A. andersoni being native to the UK does not require a license and can be used in any suitable situation.

Spidermite predator Phytoseiulus eats all stages of spidermites.

SB Plant Invigorator is also useful in situations where the predatory mites have been introduced and require additional help to control a severe outbreak. It is worth remembering that the spider mite lifecycle from egg to egg-laying adult is no more than 7 days at 30^o C and under the same conditions Phytoseiulus becomes less active, preferring to stay lower in the crop canopy where it is cooler. Under conditions of high pest density the predatory mites can be quickly over-fed and will take time before their numbers increase to provide the necessary degree of control. All predatory mites struggle to move between well-spaced leaves and plants, the carrier (vermiculite) can also easily fall off leaves losing mites and making a mess on the ground. To improve their activity and prevent messy loss of predatory insects and mites that are distributed in an inert carrier, strips of fleece or small fleece bags can be hung discreetly within the plant canopy.

Fleece bag in palm holding bio controls in inert carrier.

SB Plant Invigorator

A spray with SB Plant Invigorator has minimal effect on predatory mites but will kill most stages of this pest and other small or slow moving organisms. SB Plant Invigorator is a mix of foliar feed (chelated iron, urea etc.) Linear Sulphanate and Folia Lattice that effectively act as a tonic for the plants while killing various pests by its physical mode of activity. The insecticidal activity is by de-waxing insect cuticles
while the long chain molecules of the surfactant smother and stick the now unprotected pest bodies. There is no harvest interval for edible crops and no reported phytotoxicity, its light brown colour and faint smell of soapy ginger ale makes it suitable for use in atriums.

Mealybug colony before treatment.

The UK PSD has stated that treatment with SB Plant products acting by a non-chemical or non-biological means fall outside the European Pesticide Directive. Since SBPI has treatment with SB Plant been shown to act purely by physical means, it was exempt Invigorator turn an orange colour after protective wax from the legislation and therefore does not require registration as a pesticide. Trials is stripped off with Invigorator have demonstrated that the product can reduce certain fungal problems on plants, such as powdery mildew, through a washing and cleaning effect. As with the insect and mite control activity, this action is by physical means. Studies with aphids revealed that those that had not drowned before the treatment air-dried, recovered, so thorough spray coverage is essential. These observations confirmed the mode of action of SBPI as being physical.

Mealybug colony after treatment.


Many countries have now approved the marketing and use of SBPI due to its excellent activity, crop and environmental safety. These include the UK and Republic of Ireland. An extract from the safety data package sent to PSD states "None of the constituents are toxic, harmful, corrosive, sensitizing, carcinogenic or mutagenic. The preparation is non-irritant and does not present a danger to the environment". There is no residual effect and therefore treatment applications need to be thorough to optimise the effectiveness of SBPI. Tests have shown that heavily infested plants will require spraying two or three times at two or three-day intervals before routine maintenance sprays or a biological programme commences. It will also ensure that the large amounts of protective wax produced by some of the pest species is overcome (e.g. mealybug, woolly apple aphids, mealy cabbage aphids, bay sucker, psyllids etc). Similarly, heavy infestations of spider mite will require two or three repetitive treatments in order to overcome the protective webbing and the difficult to control eggs. Parasitoid wasps developing within host 'mummies' are not affected by Invigorator, nor are Hypoaspis mites in soil or compost. Robust predators such as lacewing larvae, ladybirds, hoverflies etc. are also not affected. However, most leaf dwelling mites (Amblyseius species and Phytoseiulus) may be affected by multiple applications.

Thrips

The other major pest of protected plants is thrip; usually Western Flower Thrip (WFT) and Onion Thrip although cereal thrips can cause widespread plant damage in late summer. The recently identified black 'T' thrip Echinothrips americanus may be found on many houseplants and in interior landscaped atriums. Several thrip species are able to transmit plant viruses to a wide range of plants, potentially causing severe infection symptoms on the whole plant. Thrips feed by rasping the leaf surface causing distorted growth and loss of colour from flowers, followed by early death. This insect is best tackled preventatively by introducing the predatory mite Amblyseius cucumeris, particularly to flowering plants such as Spathiphyllum.

Predatory Amblysieus mite feeding on young thrip.

The controlled release system (CRS) is actually a breeding population of predatory mites in a sachet and is also the cleanest and most suitable method for use on atrium or office plants. CRS sachets last about 8 weeks and release mated females that distribute themselves over an area of about 1 m². The parasitic nematode Steinernema feltiae, as Nemasys, has given excellent and reliable pest control of WFT, scale insect and other pests on a range of plants. Nemasys is formulated in a clear gel that does not mark leaves, whereas other nematode products are formulated in a fine vermiculite carrier that can leave a light brown deposit on plants.
Nematodes should be applied weekly for up to four weeks as a high volume spray to leave a wet residue that remains on the plant surface for as many hours as possible. Nematodes swim through this film of water to attack and kill various prey insects. Once the spray has dried the nematode activity ceases so the application should be timed to allow a film of water to remain on the leaf for as long as possible.

Sciarid flies

The small black flies known as fungus flies are Sciarids, and can be found on compost surfaces. One feature of these flies is the nuisance they cause when they fly around peoples faces, however they can not bite. Hypoaspis, as mentioned earlier are ideal to use as a preventive measure against Sciarid flies and several other pests. Nematodes formulated as Nemasys, will provide excellent curative activity against
Sciarid fly larvae living in compost. They should be applied at the first sign of adult flies to moist compost, the moisture content is critical as an over wet compost will drown the minute nematodes and a dry compost will inhibit their movement. Yellow sticky traps laid horizontally with the sticky side up will trap the adult flies and should be used as an indicator as well as positive reduction of adult flies.

Vine weevil

Vine weevil can devastate outdoor beds and can easily find their way into buildings where they establish an active population. All adult vine weevils are female, each can produce 800 - 1,000 eggs and they can live for up to 1 year. Adults feed by notching around the edge of leaves and can be found on ground floor beds right up to roof gardens several floors up. Their main natural predators are ground beetles (Carabidae) but these insects are restricted to open ground areas, being unable to climb the sides of most containers and certainly any building. If vine weevil larvae are found on any plants the insect parasitic nematode Heterorhabditis megidis as Nemasys H is the fastest, curative treatment when soil / compost temperatures exceed 14^o C and is ideal to use on internal beds. These nematodes can enter through the host cuticle as well as 'natural body openings'. After entering the weevil larvae they release a small pellet of bacteria that kills the Vine weevil grubs insect changing them from creamy/white to pinkish red. Steinernema krausseii as can decimate plant roots.

Vine weevil grub     Vine weevil adult

Nemasys L can provide excellent preventative as well as curative activity from 5^o C up to 25^o C both types are applied as a drench to the compost, this species is best on colder outdoor beds. Nemasys L is slightly slower acting but can be longer lived in soil or compost, providing good protection even when conditions are cold. Routine treatments of nematodes have been shown to provide a reliable, safe method to control and prevent outbreaks.

Caterpillar

Caterpillar, in particular Tortrix can be controlled with routine sprays of Bacillus thuringiensis as DiPel DF, which has given excellent results. Pheromone lure traps are a very useful addition to the IPM programme they are specific for each species of moth to be caught and will attract moths from a wide radius, indicating when to begin a spray programme and often providing a degree of pest control. The parasitic wasp Trichogramma will give reasonable parasitisation of eggs from most moth species. These are introduced on cards when moths are flying i.e. mid spring to later summer depending on weather conditions. The insect growth regulator insecticide Nemolt (teflubenzuron) has amenity approval for control of several caterpillar species including Oak Processionary Moth and can be used on all ornamental plants in most situations.

Tortrix moth caterpillars normally hide within a folded leaf.

Caterpillars can devastate most plants.

CONCLUSION

The key points to a successful, sustainable IPM programme is to use cultural techniques to keep the system clean; biological control will keep a pest population low and can frequently eradicate pests completely. Selective pesticides can be integrated to control troublesome outbreaks.

November 2007
Registered trade-marks are acknowledged.
some photographs supplied courtesy of Holt Studios