How to treat soft scales infested conservatory plants?

February 24, 2007 11:50 AM

Strelitzia reginae and other conservatory plants seem to suffer with soft scales...more inside

I have a strelitzia reginea and a couple of ficus benjaminum on my hands which appear to suffer with soft scales.

These aren't my plants - I was asked to water a conservatory full of plants for about six months whilst the owners are off in their motorhome...Being somewhat ignorant about plants I googled the problem and soft scales seems to fit all the symptoms I have noticed.

A lot of the products recommended seem to kill things like aphids, too. In the past I have successfully treated aphid infestations with a light solution of washing up liquid and cold whater which I sprayed on the infested plant.

Would that work for soft scales, too, or should I get the specialist stuff?

The plants are quite large and buying the specialist stuff would work out very expensive to treat all three! Thanks.

posted by koahiatamadl to home & garden (11 answers total)

Superfine or Ultra-fine horticultural oils. The oil suffocates the scale. You must be dligent. Spray daily for two weeks, and reassess.
posted by LoriFLA at 12:11 PM on February 24, 2007

re-assess.

Also, I don't know what part of the world you're in, but I would seem to think superfine horticultural oil would be readily available. I am in the United States and it can be easily be found at garden centers. You will need a garden sprayer, but you're probably aware of this requirement.
posted by LoriFLA at 12:19 PM on February 24, 2007

Mild soap and water applied diligently fixed a severe infestation on a Hoya for me. It took several applications, but it worked.
posted by kuujjuarapik at 12:29 PM on February 24, 2007

Mineral oil, which is probably similar to the ultra-fine stuff linked above (in NZ it's called Conqueror Spraying Oil), but don't spray it on. Mix with water following the instructions and carefully wipe the plant. You should wipe both sides of the leaves and the stems, although can focus on the scaly bits if you get bored. This will clean the leaves and make them pretty and will coat the scale with the oil as well as physically bumping many of them off. You need to be gentle with fleshy plants so you don't scratch them and also be careful not to knock the ficus leaves off, but none of this is too difficult.

I have several really large Ficus trees and a bunch of other plants and have found spraying a waste of time for scale (this was the same when they were very small). Wiping is more arduous but it works. You should only need to do this once in six months. There are insecticides for scale too, but they're nasty and not really necessary if you do a careful all over wipe with the oil.
posted by shelleycat at 2:16 PM on February 24, 2007

The plants are quite large and buying the specialist stuff would work out very expensive to treat all three!

I have two giant tree sized ficus and one medium waist high one, plus a tree sized palm tree that gets scale. One bottle of spraying oil lasts for a couple of years and costs maybe $5-10. Wiping three trees should only use maybe fifty mL of the oil (make it in smaller batches, 5mL per litre I think, because it gets dirty) even if you're being generous. There's no reason for this to be expensive, although it is going to be time consuming. Spraying is more wasteful but even then a 250mL bottle will be plenty.

It's also better to get on to it earlier rather than later. Ficus have a tendency to drop most of their leaves if they get stressed and this can take a long time to grow back (and the owners will notice, it's ugly). It can also kill the tree if it's really unhappy.
posted by shelleycat at 2:22 PM on February 24, 2007

Thanks for the advice! I'll have to see about getting some oil. The only products my googling had highlighted were soaps which seemed to be quite expensive per spray bottle.

The ficus have been dropping leaves...but I am convinced the scales were there before I was left in charge, so I shall deny all knowledge!

As for wiping leaves with oil - there a many parts of the strelitzia leaves that are kind of folded in and cannot really be reached with a cloth - any thoughts on how to get to those bits? Presumably the oil only works if you manage to cover the whole plant - otherwise the scales will just stick to the parts that aren't treated?
posted by koahiatamadl at 3:04 PM on February 24, 2007

As for wiping leaves with oil - there a many parts of the strelitzia leaves that are kind of folded in and cannot really be reached with a cloth - any thoughts on how to get to those bits? Presumably the oil only works if you manage to cover the whole plant - otherwise the scales will just stick to the parts that aren't treated?

Hmm, I would go with the mixing of the horticultural oil with water in a hose end sprayer and sticking with that.

You can also mix in malathion if you are really determined. Of course, malathion isn't as nice to the environment as the oil is, but it's sure to kill the scale. You can mix the malathion with the oil and water.

I spray enough oil and water on the plants to coat. There's not a lot of drip and not a lot of waste.

There's been a terrible problem with Asian scale attacking sago palms in the southern US and Caribbean Islands. Ultra-fine horticultural oil was recommended by our local Master Gardener, radio shows, and just about every website. I found that it worked quite well.
posted by LoriFLA at 5:07 PM on February 24, 2007

Be careful with the horticultural oils, and follow directions. If applied during the wrong season or at the wrong time of day, they can severely damage plants due to their phytotoxicity.
posted by oneirodynia at 5:21 PM on February 24, 2007

Actually the point of mineral oil is that it penetrates the insect's exoskeleton and kills it, not that it stops the insect sticking. So it's the rubbing oil on the insect that's relevant. For the folded parts I'd just squirt some in there if you can and then not worry about it too much, focus as much as you can on the scale itself. I've never had issues with phytotoxicity (and there are no warning in the literature from the manufacturer) but maybe it's because I'm using straight mineral oil and not fancy horticultural something or other? Or maybe I've just been lucky.

Spraying a large ficus tree comprehensively is hard work, drippy and difficult. Wiping it gives much better coverage, uses a fraction of the liquid (half a litre water with 5mL oil will do the whole tree) and takes probably about a third more time. And the physical rubbing off of the scale is way more effective than anything you get from spraying. Since I started wiping the plants I can clear the entire infestation in one go and not need to do it again for at least six months, whereas before I was spraying every month or two. Here's a picture of me cleaning one of them, although it's grown a lot since then.

If yours are already losing leaves and you can already see plenty of scale on there (they tend to be at the base of the leaf bottom where it attaches to the stalk) then it's been growing for a while. So yeah, probably not your fault at all. FWIW scale tends to be more common if it's humid, which is why I have ongoing problems with it.
posted by shelleycat at 5:57 PM on February 24, 2007 [1 favorite]

I've never had issues with phytotoxicity (and there are no warning in the literature from the manufacturer) but maybe it's because I'm using straight mineral oil and not fancy horticultural something or other? Or maybe I've just been lucky.

Maybe because your trees are kept indoors? If you spray oil in the dead of summer, or anytime the sun is strong it can burn.
posted by LoriFLA at 8:10 PM on February 24, 2007

Good point. All my scale-troubled trees are indoors and get even filtered sunlight. I can also see how coating leaves in oil then putting it in the sun would cause problems, regardless of the kind of oil used. I'll store this information away for the future as I can see it being useful at other times (I have outside trees too), thanks.
posted by shelleycat at 9:01 PM on February 24, 2007