An organic remedy for aphid infestation

Aphids may cause considerable damage to organic vegetable, vine, fruit, and selected flower species. The damage may be a direct weakening of plants through feeding or indirectly through transmission of viral and bacterial pathogens. Plant derived insecticides have resulted in limited success however the short lifespan of common aphid species points to their natural adaptability and tolerance against such measures.

An important biological control for many aphid varieties is Aphidius Colemani, a species of parasitic wasp native to North America but now common throughout many regions of the world.

Mature Aphidius wasps are approximately 3mm in length and dark reddish brown in colour. The female wasp lays its eggs into selected aphids. The larvae then pupate and develop destructively within the aphid, causing it to swell and assume a mummified appearance. Female wasps can parasitise several hundred aphids during their two week lifespan.

Aphidius Colemani can be purchased as adult specimens or emergent pupae attached to cards. The recommended release rates for commercial growers are 5000 wasps per hectare for high level aphid infestation. This figure would be suitable for most organic setups however it is strongly recommended that all growers should discuss their specific situation with suppliers.

Upon release the highly mobile wasps should disperse to search for aphid colonies. An assessment should be conducted after approximately four weeks. Serious infestations will require regular release of Aphidius Colemani throughout the growing season. Organic growers seeking to maintain a working population of wasps will need to plant sacrificial crops to encourage a ready supply of aphid hosts. In vegetable and fruit crops, the sacrificials might consist of suitable winter grains or weeds.