Aphids can be killed by unfavourable weather, including freezes, excessive heat, and rain. However, manipulating the temperature in the garden or greenhouse to freeze aphids, probably isn’t the best solution for plant health! There are chemical insecticide solutions to control aphids, however there are also eco-friendly solutions including using aphids’ natural predators.
We have begun using a parasitic wasp to control aphids on our greenhouse plants. When I first heard “parasitic wasp” I pictured something much more ominous than what it actually is. The wasps, called Aphidus colemani are very small, usually less than 3 mm long. Female wasps lay an egg in the body of an aphid. Once the egg hatches, the wasp larvae lives and feeds inside the aphid. As it grows, the aphid is killed and mummified. The wasp, now and adult chews its way out of the mummified aphid. The wasps have a good searching ability, and are able to find aphid colonies from far away. The wasps detect “alarm signals” from an infected plant, and also smell the honeydew secreted by the aphids. Not only do wasps detect the aphids, but the reverse happens as well. The presence of a parasitic wasp can cause panic in an aphid colony, and the aphids will let themselves fall to the ground, where they die on impact, or from starvation.
As ferocious as these wasps are to the aphids, they are completely harmless to people. You likely won’t even notice them unless you actively seek them out. You will notice small pots of oat grass throughout the greenhouse, which will act as their home-base. If you DO want to seek them out, that’s the place to look!
At home, the best solution for addressing an aphid problem is using an insecticidal soap, or even a soap and water spray. The spray penetrates the aphid body to kill it, so a certain degree of diligence is required, spraying the plant often, until ALL aphids are gone.
Enjoy your Spring planning, we all look forward to seeing you soon, and when you stop by, make sure you look out for this superstar!