Spider mite treatment - Ask Extension
To Whom It May Concern:
We have a Norfolk island palm plant which is plagued by spider mites (all the signs are there). We are seeking guidance on ho...
Knowledgebase
Spider mite treatment #790484
Asked May 12, 2022, 3:12 PM EDT
To Whom It May Concern:
We have a Norfolk island palm plant which is plagued by spider mites (all the signs are there). We are seeking guidance on how to remove/kill the spider mites. We have already washed the plant using the garden hose. On your website we read to use " insecticidal soap for houseplants or a houseplant insecticide that is labeled for spider mites and houseplants" or "horticultural oil and insecticidal soap". Could you please elaborate further, because there are many different products with various active ingredients on the market, and we are not sure which one to pick.
We are also worried that spider mites have possible migrated to adjacent plants but these plants show no signs of infestation. What could we do as a preventative measure, other than relocating the plants? Thank you.
Montgomery County Maryland
Expert Response
Spider mites are one of the only pests Norfolk Island Pine plants tend to get, fortunately, but multiple treatments (whether water, soap, or oil) will be needed to eliminate them. If possible, we recommend you grow the plant outdoors for the summer since they will enjoy the high humidity and better airflow. Put the pot in shade at first so it's not prone to sunburn (indoor bright light is still relatively dim compared to shade outdoors, even if it looks similar to our eyes). In fact, you can probably grow them mostly-shaded all summer, though eventually moving it into part sun would probably be fine.
A strong blast of water from a hose or shower might be sufficient if you want to stay chemical-free, but sometimes a pesticide is warranted, especially if mite populations are large and webbing is extensive. Use either insecticidal soap or horticultural oil; while you might be able to alternate, there probably is no need unless one doesn't work well (after several tries), and they should not be applied in combination. For plants with a bluish or hairy leaf coating, hort. oil can permanently alter the appearance of treated foliage, but in the case with this particular plant, it's probably a non-issue. (If you wind-up needing to treat other houseplants, keep this in mind for any blue-leaved succulents, fuzzy-leaved trailing plants, etc.)
We don't recommend any particular brand or product, but as you mention, you'll have a lot of options since these are common ingredients for organic or reduced-risk pesticides.
Insecticidal soap usually works best when diluted with distilled or purified water, which will probably be mentioned on the product label. Tap or well water might suffice, but sometimes the natural mineral content interferes with how well the ingredients remain dissolved. If you're using a ready-to-spray product (as opposed to a concentrate you have to dilute yourself), then don't worry about this. The active ingredient for an insecticidal soap will be listed as potassium salts of fatty acids.
Horticultural oil can include a range of possible active ingredients (presented on that linked page) because current refinement techniques can allow different oil sources to be used as a pesticide with little risk to plant health.
Due to differences in ingredients and refinement, don't substitute any household soap, detergent, or oil products because they either won't work well or will carry a higher risk of damaging the plant. Having said that, many pesticides inherently carry some risk of phytotoxicity (plant tissue damage from chemical exposure), so test a portion of the foliage first and wait one or a few days to see if any "burn" symptoms develop before spraying fully, in case this particular species happens to be more sensitive than most. You can also check the product label, as some will list plants with known sensitivities to that product. As a generalization, plant sensitivities tend to be more common for insecticidal soap compared to horticultural oil. If you spray the plant outside, don't apply either product while temperatures are above 85 degrees, as most pesticides have an increased phytotoxicity risk in hot weather.
Norfolk Island Pine can be challenging to grow indoors long-term due to their preference for high humidity and relatively cool conditions. (Plus, old plants grow quite tall and can't be kept significantly smaller through trimming.) Household air tends to be dry enough that a humidifier may be needed where plants are grown. Since mites thrive in drier air and on stressed plants, this should also reduce the likelihood of a recurring infestation in the future.
The simplest preventative measure for your other plants is just to keep inspecting them for mite feeding or webbing and using the same water-blasting approach to remove what mites may be present undetected. You might also be able to treat them with either of the above pesticides if they are species that should tolerate the ingredients. (If too sensitive, resort to water sprays alone and perhaps moving them outside to a shady spot for the summer as well. Predatory mites and other beneficial insects sometimes find pest-infested houseplants put outside and can "clean" a plant pretty well by the time they come back inside.)
Miri
A strong blast of water from a hose or shower might be sufficient if you want to stay chemical-free, but sometimes a pesticide is warranted, especially if mite populations are large and webbing is extensive. Use either insecticidal soap or horticultural oil; while you might be able to alternate, there probably is no need unless one doesn't work well (after several tries), and they should not be applied in combination. For plants with a bluish or hairy leaf coating, hort. oil can permanently alter the appearance of treated foliage, but in the case with this particular plant, it's probably a non-issue. (If you wind-up needing to treat other houseplants, keep this in mind for any blue-leaved succulents, fuzzy-leaved trailing plants, etc.)
We don't recommend any particular brand or product, but as you mention, you'll have a lot of options since these are common ingredients for organic or reduced-risk pesticides.
Insecticidal soap usually works best when diluted with distilled or purified water, which will probably be mentioned on the product label. Tap or well water might suffice, but sometimes the natural mineral content interferes with how well the ingredients remain dissolved. If you're using a ready-to-spray product (as opposed to a concentrate you have to dilute yourself), then don't worry about this. The active ingredient for an insecticidal soap will be listed as potassium salts of fatty acids.
Horticultural oil can include a range of possible active ingredients (presented on that linked page) because current refinement techniques can allow different oil sources to be used as a pesticide with little risk to plant health.
Due to differences in ingredients and refinement, don't substitute any household soap, detergent, or oil products because they either won't work well or will carry a higher risk of damaging the plant. Having said that, many pesticides inherently carry some risk of phytotoxicity (plant tissue damage from chemical exposure), so test a portion of the foliage first and wait one or a few days to see if any "burn" symptoms develop before spraying fully, in case this particular species happens to be more sensitive than most. You can also check the product label, as some will list plants with known sensitivities to that product. As a generalization, plant sensitivities tend to be more common for insecticidal soap compared to horticultural oil. If you spray the plant outside, don't apply either product while temperatures are above 85 degrees, as most pesticides have an increased phytotoxicity risk in hot weather.
Norfolk Island Pine can be challenging to grow indoors long-term due to their preference for high humidity and relatively cool conditions. (Plus, old plants grow quite tall and can't be kept significantly smaller through trimming.) Household air tends to be dry enough that a humidifier may be needed where plants are grown. Since mites thrive in drier air and on stressed plants, this should also reduce the likelihood of a recurring infestation in the future.
The simplest preventative measure for your other plants is just to keep inspecting them for mite feeding or webbing and using the same water-blasting approach to remove what mites may be present undetected. You might also be able to treat them with either of the above pesticides if they are species that should tolerate the ingredients. (If too sensitive, resort to water sprays alone and perhaps moving them outside to a shady spot for the summer as well. Predatory mites and other beneficial insects sometimes find pest-infested houseplants put outside and can "clean" a plant pretty well by the time they come back inside.)
Miri
