Effective and sustainable pest control for the garden.
It is only within my lifetime that consumer standards have changed so dramatically to the point where there is currently an expectation that all fruit and vegetables should be perfectly shaped, unblemished and of a specified colour. In order to achieve this level of ‘perfection’ commercial producers are forced into using a significant amount of chemicals. Luckily this is not the case for the home gardener, who can retain a sense of realism and common sense about the appearance of fruit and vegetables. Our gardens are all highly complex and interactive ecosystems, the actions we take have both short and long term effects. Listed below are a wide variety of pest management methods which you can use in your garden. All the recommended methods have a relatively low environmental impact but are effective.
Integrated pest management.
Gardeners looking for an environmentally responsible approach to pest management are adopting principles of Integrated Pest Management (IPM). This enables them to use multiple compatible tactics to control pests. The environmental and economic effects of widespread synthetic chemical use have led to the development of IPM where the problems of insect resistance, toxicity to humans and beneficial insects, and harm to the environment are addressed. Techniques including biological control, trapping and monitoring, highly specific microbial pesticides and selective and timed spraying are all part of IPM.
Beneficial insects and mites
A beneficial insect or mite acts as a predator, parasitoid or competitor of pest insects i.e. they are natural enemies of the pest species. Unlike insecticides which generally result in an immediate knockdown effect, the release and use of beneficial insects and mites takes longer to have an effect. Also the effect is to reduce the damage, often to a completely acceptable level but not completely eliminate damage (as needed in some ornamental flower crop production).
Predators
Usually as big or bigger than their prey, predators are predaceous as larvae and or as adults. They may be generalists, feeding on a wide range of prey, or specialists, selectively feeding on a narrow range of prey.
Ladybeetles (also called Ladybugs and Ladybirds) (pictured above) are beneficial as both larvae and adults, feeding primarily on aphids, but will also feed on mites, scale, thrips, small insects and insect eggs. Voracious feeders, they are effective predators and their numbers will build up with the food supply if broad spectrum pesticide use is limited.
The Mealybug Destroyer (Cryptolaemus montrouzieri), is a native Australian lady bird, black with an orange ‘head’ (pronutum), the larvae look very similar to its mealy bug hosts being covered with shaggy white waxy material. Another voracious feeder, where both larvae and adults are predaceous, each ladybeetle may eat up to 250 mealybugs during its development.
The Green Lacewings
With delicate pale green bodies and large transparent wings, the adult lacewings are only rarely predacious; it is their larvae which are the generalist predators. Sometimes referred to as ‘aphid lions’ they are voracious feeders of aphids, but will also eat other soft bodied insects, mites and insect eggs.
Typhlodromips montdorensis: This Australian predatory mite feeds on larval stages of thrips, whitefly and other small insects.
Parasitoids: These are parasite like insects, often the same size as their hosts and always killing their host (unlike true parasites which are often smaller and rarely kill their host). The parasitoid will develop on or within a single host during their development. Most parasitoids are highly host specific, and the vast majority are small to minute wasps. Example: Encarsia formosa a tiny wasp which parasitises the larval stage of whitefly.
All the following Cottony Cushion Scale, Black Aphid, Mealybugs, Citrus Leafminer have commercially available natural predators.
Suppliers of Beneficial insects and Mites
Biological Services in South Australia
Bugs for Bugs in Queensland
Lures, physical barriers, exclusion and traps
These range from netting trees to simple yellow sticky traps to the pheromone traps requiring some knowledge of the correct timing and correct lures for targeted pests.
Sticky traps and Glues
Horticultural glues and sticky bands or tapes are used to prevent insects crawling up tree trunks and into the tree canopy to feed on the leaves and or fruit. Good for codling moth, tent caterpillars, procession caterpillars and ants. Ants protect aphids, scale and mealy bugs, so reducing ant numbers aids in reducing these pest numbers. Yellow sticky traps are useful in greenhouses but also can be used for specific pests such as citrus gall wasp. Effective until trap is full of insects and no sticky surface is available. Non-discriminatory – will trap predators as well as pests.
Netting
A variety of nets are available which surround the plants to be protected and provide a physical barrier against the pest. Fine netting allows water and light to penetrate but prevents insects from entering and causing damage.
Advantages: No chemicals, no toxicity, can also aid in preventing hail damage and bird damage.
Disadvantages: If insects are already present, they will be included inside the barrier, and will need to be treated. See our cabbage white butterfly fact sheet.
Lures
Pheromone lures are used at specific times to lure the pest to a trap, usually before breeding to interrupt the breeding cycle. See our codling and oriental moth fact sheet
Microbial Insecticides
Microbial insecticides are composed of microscopic living organisms (viruses, fungi, bacteria, protozoa, nematodes) or the metabolites produced by these organisms. They are formulated as conventional insecticidal dusts, sprays or granules.
Advantages: Essentially nontoxic and nonpathogenic to wildlife, humans, and other organisms not closely related to the target pest. The toxic action of microbial insecticides is often specific to a single group or species of insects. This means the natural predators and competitors of the target insect remain unaffected by the insecticide. Most microbial insecticides can be used in conjunction with synthetic chemical insecticides because in most cases the microbial product is not deactivated or damaged by residues of conventional insecticides. As the residues are considered harmless, can be used on crops close to harvesting. In some instances the microbe can become established in the pest population and provide ongoing control over the season and possibly subsequent seasons.
Disadvantages: They are specific to only a well defined range of target species, this means that only those pests are treated, other damaging pests are untreated, this is also true with other pesticides, but is more noticeable with microbial insecticides. Heat, desiccation (drying out), or exposure to ultraviolet radiation reduces the effectiveness of several types of microbial insecticides. This means correct application processes are more important with these insecticides. Special formulation and storage procedures are necessary for some microbial pesticides.
On the shelf: Bacillus thuringiensis (abbreviated as Bt): A bacterial pathogen occurring commonly in soils. Must be eaten by the target pest to be effective. Although the target insect may take a few days to die, it will stop eating rapidly after ingesting Bt treated foliage. Bt does not reproduce and infect subsequent generations of the target pest so must be re-applied as necessary. The most widely known and used Bt is Bacillus thuringiensis var. kurstaki, these are toxic only to larvae of butterflies and moths and have proved invaluable in controlling damage done to many crops, including the brassica crops (cabbage, cauliflower, kale, Brussels sprouts). Bt degrades rapidly with UV, and may need to be applied twice a week if the pest problem is severe. Can be found on the shelf as Dipel Spinosad is an insecticide derived from naturally occurring soil bacteria Saccharopolyspora spinosa. Spinosad is highly active by both direct contact and by ingestion to numerous pests. It will move into the leaf giving it residual activity and some resistance to sunlight and rain (although any spinosad remaining on leaf surface will be rapidly broken down by sunlight and rain). Spinosad affects some insects at multiple life stages and others only in the adult stage. Considered a natural product, spinosad is approved or use in organic farming by numerous nations. It has high efficacy, a broad insect pest spectrum, low mammalian toxicity and a good environmental profile. Various studies have concluded that spinosad offers a negligible risk to honeybees.
Insecticidal soaps
Insecticidal soaps are selected and formulated for their insecticidal properties (contain the potassium or sodium salts of insecticidal fatty acids). Despite many years of use the exact manner of action of insecticidal soaps is unclear. Some physical disruption of the insect cuticle is known to occur, but other toxic activity is assumed. There is some evidence that the cell membranes are broken down and call metabolism disrupted.
Uses: Useful for controlling soft bodied pests such as aphids, thrips, scale (at the crawler stage only), whitefly, leaf hopper nymphs and mites. Effective only when wet spray comes into direct contact with the insect. Adult forms of beneficial predators are generally safe from the soap spray – but their immature forms may be susceptible.
Advantages: Rapidly broken down by enzymes and degrade rapidly in sunlight, moisture and air. This is considered advantageous as it is less persistent in the environment and non – target organisms are less likely to be at risk Rapid action – insect stop feeding almost instantly, even if death occurs days later. Often (but not always) low toxicity to mammals
Disadvantages: The rapid breakdown means more frequent applications may be needed and more precise timing of application Whilst mild, still has some degree of toxicity (like any soap) and care needs to be taken
Botanical insecticides
Sometimes just referred to as ‘botanicals’ are naturally occurring insecticides derived from plants.
Background: In common use from the late 1800s until mid 1940s. The development of synthetic insecticides led to the wholesale abandonment of botanicals in commercial agriculture and horticulture. Since early 2000 the resistance of key pests to synthetic insecticides has led to the re-introduction of some botanicals into commercial use, and a general increase of interest in their use. Concern about environmental contamination and pesticide residues has also fostered renewed interest in botanicals. The increase of certified organic production has also led a resurgence in the use of botanicals and increased research and development of new botanicals.
Advantages: Rapidly broken down by detoxification enzymes and degrade rapidly in sunlight, moisture and air. This is considered advantageous as it is less persistent in the environment and non – target organisms are less likely to be at risk Rapid action – insect stop feeding almost instantly, even if death occurs days later. Often (but not always) low toxicity to mammals Some need to be ingested, hence only the chewing/sucking insects are affected and their natural predators remain unaffected. Almost never phytotoxic (Toxic to plants)
Disadvantages: The rapid breakdown means more frequent applications may be needed and more precise timing of application Whilst most botanicals pose fewer hazards than synthetic insecticides, some degree of toxicity exists and some botanicals (e.g. nicotine) are highly toxic, so care always needs to be taken. ‘Natural’ and ‘botanical’ does not necessarily equate to ‘safe’ or ‘non-toxic’.
Botanical insecticides for garden use include:
Pyrethrum and Pyrethrins Easily confused with pyrethroids which are synthetic compounds based on the chemical structure and physiological action of naturally occurring pyrethrins. The pyrethroids are often much more persistent in the environment and toxic to insects. Pyrethrum is the dried powdered flower head of the Pyrethrum Daisy (Chrysanthemum cinerariaefolium). The pyrethrins are the 6 related insecticidal compounds that are derived from this raw material. Their mode of action is disruption of the sodium and potassium ion exchange in insect nerve fibres and interruption of normal transmission of nerve impulses causing almost immediate paralysis (the knockdown effect). This effect is often very short lived and the insect commonly can recover. To prevent this pyrethrin insecticides generally contain a synergist PBO which prevents the insect from degrading the pyrethrin and recovering. PBO is low in toxicity, has no inherent insecticidal activity and is not persistent in the environment. Toxicity: Pyrethrins are low in mammalian toxicity – one notable exception is cats which are highly susceptible to poisoning by pyrethrins. Uses: Effective against a broad range of insect pests. They are contact poisons (spray must land on the insect) and have almost no residual activity, so repeated applications may be needed.
Rotenone An insecticidal compound found in the roots of several plants from the Fabaceae family and in the stems and leaves of several other species of plants including the roots of the Lonchocarpus nicou species in South America and the Derris elliptica species in Asia In insects rotenone acts at the cellular level, primarily on nerve and muscle cells, resulting in almost immediate cessation of eating, although death may take several hours or days. Toxicity: Extremely toxic to fish, used as a fish poison in water management programs. One of the more acutely toxic botanicals, care needs to be used when applying this compound. Uses: A broad spectrum contact and stomach poison, very effective against leaf feeding beetles and certain caterpillar pests. Has some residual effect and when applied as a dust, will remain active for approximately 6 days. On the shelf: Found in Derris Dust
Sabadilla First used in the 16th Century, the insecticidal dust is derived from the ripe seeds of
Schoencaulon officianale, a tropical lily plant from Central and South America. The toxic alkaloids cause immediate paralysis of insects, in some cases immediate death, in others death may occur several days later. Toxicity: Highly toxic to honey bees. Low mammalian toxicity. Uses: A broad spectrum insecticide, effective against certain bugs from the Hemiptera family (e.g.Harlequin bugs, leaf hoppers, aphids). Rapidly degrades leaving little residual activity.
On the shelf: Natural Pyrethrum (pyrethrins, PBO) Sharp Shooter Beat a bug (garlic/chilli/pyrethrins/PBO) Richgro Derris Dust (Rotenone) Amgrow
Using oils as a pesticide.
Nerdy background stuff
Oils are distilled from petroleum, plants or animals.
Those oils distilled from petroleum in horticultural use are highly refined paraffinic oils often referred to as ‘white oil’ or ‘horticultural oil’. Regardless of where the oil is sourced from, the mode of action is similar: Insecticidal oils kill insects on contact by disrupting gas exchange (respiration), cell membrane function or structure. They also kill them by altering their behaviour such as disrupting their feeding on oil covered surfaces or reducing egg laying. Their toxic action is more physical than chemical and is short-lived. Fungicidal oils smother fungal growth and reduce spore germination on treated surfaces. They are mostly fungistatic, stopping fungal growth rather than killing the pathogens. Some plant oils that contain sulfur compounds, such as neem oil, may possess additional fungicidal activity compared to petroleum oils. Stylet oils are highly refined oils and may control insect-vectored plant viruses in addition to insects, mites and fungal pathogens. These oils reduce the ability of aphids to acquire the virus from an infected plant and transmit it to healthy plants. Stylet oils may interfere with the virus’s ability to remain in aphid mouthparts (stylets).
Advantages of oils over synthetic broad-spectrum pesticides
- Many pests can be controlled simultaneously.
- They have less harmful effects on the natural predators of the pests
- They do not stimulate other pest outbreaks.
- Pests are not known to develop resistance to them.
- The oil deposits are broken down within weeks to form simple, harmless molecules.
- When using oils only minimum protective clothing needs to be worn.
- They are suitable, depending on the emulsifiers and additives used to formulate products, for use in organic farming.
- They are not toxic to humans or other animals.
Using oils
Phytotoxicity: This simply refers to the damage that may occur to the plant by the oil. As the quality of oils has improved, instances of phytotoxicity have reduced, none the less some oils can injure plants (leaf scorching and browning, defoliation, reduced flowering and stunted growth) and as a general rule do not use oils on stressed plants. Do not apply on hot days, very cold days or days of high humidity. All oil products have emulsifiers added to enable them to be mixed with water and used as a spray. When sprayed onto a leaf, the oil tend to stay on (or be absorbed by) the leaf, while the emulsifier and water runs off the leaf. Always use oils as indicated on the label. Spray immediately after mixing, and agitate the mix as you go along. Some oils are incompatible with other products, it is essential you check the label for this, for example do not apply an oil spray within 1 month of a sulphur spray.
Neem oil
Neem or neem oil is extracted from the seeds of the Neem tree, Azadirachta indica, a native of India and has recorded use in India for many hundreds of years. In the mid 20 century serious academic research began on neem oil and its properties. As a result a number of Neem based commercial products have come on to the market. The oil is made from many components, with at least 3 compounds known to have insecticidal properties: azadirachtin, meliantriol and salannin.
Horticultural uses
The best understood and active component of neem oil is azadirachtin. The azadirachtin must be ingested by the insect eating the treated plant for it to work (remaining active on the plant for 1 to 2.5 days). It acts as both an insect feeding deterrent and as an insect growth regulator. Azadirachtin prevents the treated insect from moulting and transitioning to the next life stage, it subsequently dies, thus preventing it reaching maturity, mating and reproducing. Consequently Neem is most effective against sucking and chewing insects in their actively growing immature stages (e.g. caterpillars, mites, curl grubs, aphids, leaf miner, whitefly). Death may occur in 2 or more days, but damage to the plant stops immediately. A significant advantage of neem oil is that it does not harm beneficial insects such as lacewings and other predators in the garden, hence is excellent to use when using Integrated Pest Management (IPM) as a way of controlling problem insects. Further it does not appear to harm pollinating insects such as bees, and is safe around pets and people. Azadirachtin acts as an insect repellent when applied to a plant and it also has some systemic activity. It is known to repel and reduce the feeding of nematodes. Other components of neem oil kill insects by hindering their ability to feed. The exact mode of action of all the components of neem oil is yet to be fully understood.
Safety: Neem has extremely low mammalian toxicity and in most forms is non-irritating to mucus membranes and skin.
Mineral based pesticides
Sulphur (syn sulfur) Sulphur probably is the oldest known pesticide in use. Sulphur is formulated as a dust, wettable powder, paste or liquid. Primary used to control powdery mildews, certain rusts, leaf blights and fruit rots, it can also assist in controlling Spider mites, psyllids and thrips. Most pesticidal sulphur is labelled for vegetables such as beans, potatoes, tomatoes, peas and fruit crops such as grapes, apples, pears, cherries, peaches, plums and prunes. Sulphur has the potential to cause plant injury in dry hot weather. It’s also incompatible with other pesticides. Never use sulphur on plants within 30 days of applying spray oils. Sulfur is non-toxic to mammals, but it may irritate eyes and skin.
Lime Sulphur Lime sulphur is made by boiling lime (calcium hydroxide) and sulphur together with a small amount of surfactant. The mixture is used as a dormant spray on fruit trees to control diseases such as blight anthracnose, powdery mildew, black spot and some insects including scales, thrips and eriophyid mites. Its drawbacks include its rotten-egg smell, its potential to burn exposed skin and eyes and to injure plants if applied when temperatures exceed 27degrees C.