Potential for Biological Control Agents for the Nursery Industry

James Altmann, Biological Services, PO Box 501, Loxton SA 5333.
Ph: 08 8584-6977; Fax: 08 8584-5057.

Good pest management relies on many forms of control to be successful. A control program which relies on pesticides alone will ultimately fail nearly every time. Many pests have developed resistance to the commonly used pesticides (eg. Mites, thrips, whiteflies). Another problem engendered by dependence on pesticides is the inducement of secondary pest outbreaks. Many two spotted mite outbreaks are the result of chemical applications applied to control other pests.

To minimise the activities of pests, all forms of control need to be implemented into a management program. This concept is know as Integrated Pest Management (IPM). The types of controls utilised include:

Exclusion (quarantine)
Varietal control
Physical control
Cultural control
Hygiene
Chemical control
Biological control

Biological controls include parasites, predators, insects, mites, nematodes, fungi, viruses, and bacteria. They are or can be:

Naturally present (lacewings, ladybirds)
Introduced beneficials
- mass released
- inoculation
usually pest specific
can be self perpetuating
can be slow
require monitoring and a good understanding of pest and beneficial biology

Biological Controls Available for Nursery Environments

Three key pests in the nursery environment can now be successfully managed:

Two spotted mite (or red spider mite)

Phytoseiullus persimilis, a predatory mite, has been available for over 10 years now, and has been used very successfully in many situations. To help establishment and aid control consider the following:

Release immediately predators are received
Introduce at the early stages of pest infestation
Mass release into hot spots, this can create a breeding area for predators which will move through the crop when pest mites are controlled in the hot spot area
Release small amounts regularly (monthly) into susceptible varieties or into areas within the greenhouse where infestations regularly start.
Mark a few places where predators have been released to check establishment
Persimilis prefers warm/humid conditions. Conditions that are very hot/dry will favour two spotted mites. In hot/dry situations overhead watering or misting will help establishment.

Typhlodromis occidentalis is another predatory mite able to control two spotted mite. It is mostly used in perennial outdoor horticultural crops. It is able to tolerate high temperatures and low humidity, and has tolerance to some organophosphate insecticides.

Greenhouse whitefly

Encarsia formosa has been successfully used for more that 50 years in Europe to control greenhouse whitefly. It has been available commercially in Australia for 4 years and its use is increasing every year. Encarsia is a tiny wasp parasite – approx. 0.6mm in size, black and yellow in colour.

To maximise levels of control consider the following:

Introduce at the first signs of whitefly. Alternatively for crops which constantly have whitefly problems, introduce parasites at the start of the crop
Release small numbers on a regular basis (eg. weekly), increasing numbers during cold weather, short day lengths, or under moderate whitefly pressure
Encarsia will be active at temperatures above 13 C but will be most effective when average daytime temperatures are 27 to 30 C. An average temperature of 23 C (with 15 C or higher at night) is the minimum for good control of whitefly. Temperatures around 18 C will maintain an equilibrium between the parasite and pest
Humidity is best maintained between 50 to 80% and parasites need a minimum of 10 hours of light to be fully effective.
In winter months some artificial heating and lighting may be needed for parasites to remain at their most effective. Otherwise higher release rates can be used.

Fungus gnats (or sciarid flies)

Hypoapsis miles is a soil dwelling, predatory mite which feeds on fungus gnats, thrips pupae and other small insects in the soil. Females are up to 1 mm in size and are light brown colour. Very successfully use in Europe, U.K. and North America – Hypoapsis is now available in Australia for the coming season.

Predators will tolerate most greenhouse conditions but are less active in cool conditions below 13 C. They will not work in water logged conditions, but can tolerate quite hot conditions.
Most effective when applied before fungus gnat populations become a problem. Predators feed on fly eggs and young larvae. Mites are long lived and will survive up to 7 weeks even in the absence of prey in many situations.
Mites are best applied to the soil surface which they then penetrate to commence feeding. They are most active in the top 2 to 3 cm of potting media. If mixed into the media prior to potting up many predators will be wasted.
Hypoapsis moves well on soil surfaces so it is not critical to apply to all flats or pots. However it should be applied prior to problems developing and as evenly as possible, at a full rate to allow time for it to spread.
If ground or under benches is conducive to the breeding of fungus gnats, mites can be released on the floor of the greenhouse.

Steinernema feltiae is a predatory nematode also commercially available for fungus gnat control. It is available in a powder like formulation which is mixed with water and applied by watering into the planting media. It can also be applied by irrigation systems. These nematodes can also be very effective if used in conjunction with Hypoapsis predators.

Apply nematodes when fungus gnats are at moderate levels before a problem exists
Re-treat hot spots or susceptible varieties on a regular basis
Are less effective during periods of hot weather
Apply immediately nematodes are received

Other beneficials available that could be used in nursery situations

Cryptolaemus – a predatory ladybird for mealybugs and soft scale
Lacewings – general predators for many soft bodied pests
Trichogramma – minute wasp parasites of moth eggs

Use of pesticides and beneficials

Most fungicide and nutrient sprays are of low toxicity to beneficials. Many miticides are also safe to use. Not all pesticides have been tested against all beneficial organisms, but generally most broad-spectrum insecticides will have a detrimental impact on beneficials. The suppliers of the organisms can usually give more detailed information on which chemicals are compatible or not.

In situations where pests are in high or damaging numbers, try and control the pests as completely as possible with a range of control options. After this has been achieved, recommence beneficial release program. Some chemicals may be residually toxic for 6 to 8 weeks after application however, so where possible try to avoid their use, or only use in times of high pest pressure.

Further research

Research at present is mostly focussed upon trying to identify and commercialise predators of Western flower thrips. Some promising candidates have been identified by NSW Agriculture but at this stage commercialisation may be several years away as much trial work will need to be assessed. A r ange of products is required to provide growers with alternative controls for all their pest problems. Research into developing commercially available beneficial organisms should be high on the R&D list for the nursery industry. The industry must understand that this research is long term and ongoing, therefore needing continual funding.