We lost all our roses last summer, due to greenfly. The only solution we have so far found was highly toxic. Are the more sustainable alternatives?
- Make sure your roses are not in a location with strong winds, if so relocate them. The best place is a sunny area with at least 4 hours of sun and only slightly windy.
- Use an organic fertilizer so the roses have enough nutrients. Usually you need to do this twice a year (early spring and after the first flush of bloom) but check the instructions on the fertilizer for more information.
- Once the greenflies appear spray the roses every day with water, preferably early in the morning so the plant can dry during the day. If there are lots of greenflies add some soap and/or vinegar to the water before spraying.
- Alternatively you can try to attract or buy ladybugs that eat the aphids and/or try to get rid of any ants that feed on the greenflies and fend of ladybugs.
I've also read somewhere that lavender, thyme, sage or garlic plants planted between the roses may also help. I've tried lavender last year myself but didn't notice any effects.
Sticky Fly Traps are great in greenhouses, but rapidly overwhelmed outdoor. And ladybirds are inefficient in face of an herd of green flies protected by ant shepherds (the ants protect the greenflies from which they eat some secretion). Having tried several solutions, the best thing for me is to spray a mix of black soap and water.
The basic recipe is to pour 5-10 % of liquid black soap (pure, made of potash, without perfume, then totally biodegradable. You should be able to find it in garden store or drug store) in tepid water. Let it cool down and then spray the plant (especially under the leaves). Be careful to do this in the morning, so the plants are dry when the sun is high up in the sky.
I personally add an arbitrary amount (+- 2 teaspoon in 1l water) of linseed oil. This to have a quite thick mixture (not too thick unless you want to clog your spray). Be careful to spray even the back of the leaves, and the mixture cover insects body and asphyxiate them.
In addition, you should tie glue tape around the base of the trunk to avoid ants bringing back flies (see above).