Hello Master Gardeners,
I am writing with an indoor plant question. I am in Toronto but have planted a bird of paradise plant indoors which lives in a bathroom with a shower so is subject to some steam and flourishing. It lives in a giant plastic pot which has space for drainage at the bottom where we suspect water has been collecting (though in a designated space below the roots, so not soaking the roots). We’ve stopped watering it, suspecting it doesn’t need much from us that it is t already getting from the pot below/air around.
Over the past few months I’ve noticed a fair number of flies that looks like fruit flies around the house and concentrated in the bathroom near the plant. Do I need to spray/treat it with something to address the issue?
Thank you for contacting Toronto Master Gardeners, and congratulations on what must be a spectacular Bird of Paradise (Strelitzia reginae). You don’t mention if it gets any direct sun, but since it is “flourishing” I presume that it does.
I think the first step should be to confirm what kind of pest you are dealing with. White flies are the most likely culprit, but they are very small and distinctly white, whereas “fruit flies” are a little bigger and usually black. So inspect the plant closely. White flies will cluster on the underside of leaves (but scatter in flight when the plant is touched), and lay tiny eggs there. They suck sap from the plant, which then exudes a sticky substance which can make black spots on leaves below. They cause tiny pits on the leaves and stems. If you don’t see any whiteflies, check other places: is there any bug or burrowing activity in the soil? are there little nodules on the stems, which might be a scale insect? Are the leaves damaged severely or seriously discoloured?
If you do find whiteflies the easiest course of action — especially given that your plant is near the shower — is to use a strong blast of water to clear most of them off. Then you can follow up with sprays of an insecticidal soap. This will have to be done repeatedly, as the eggs will continue to hatch. Neem oil and sticky traps can also be useful, and if the infestation is severe enough, you can vacuum the worst spots. A particularly bad leaf or two could just be removed.
The following article in our online library discusses thrips on a different houseplant, but many of the symptoms and treatments are the same, so check it out:
https://www.torontomastergardeners.ca/askagardener/coaxing-a-stephanotis-plant-to-flower/
There are also some useful links in this article:
https://www.gardeningknowhow.com/plant-problems/pests/insects/control-whiteflies-houseplants.htm