Scale questions

ourarkaSeptember 20, 2012

I am based in the UK and have two small citrus, of an unknown variety, that I keep year round in my conservatory. I have a large Tahiti lime, Eureka lemon and Mandarin orange outside which have had a good summer.

The two small conservatory plants are riddled with scale. I have tried wiping off the worst, spraying with pesticide and using horticultural oil but am losing the battle at the moment. I have three questions:

1) Is the battel against the scale pointless .... or can I win out?

2) If I ditch these plants and get two new ones is the scale likely to return. No other plants in the conservatory seem to show any sign.

3) If I move my outdoor plants in briefly during the coldest part of winter are they also likely to develop scale.

Hope you can help - really want some small citrus in my conservatory but struggling.

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Hi, Ourarka. I had scale problem on some of my citrus in the past. At that time, it seemed a lost battal for the scale kept showing up after I cleaned, wiped the stem and leaves. But it eventually is gettting less and less. My citrus trees do not have scales now. So please keep up the hope and keep doing what you are doing. It is very important that you know what scale you have and keep the pesticide spray in fixed interval.
I did crazy thing once when dealing with the scales... I pick off all the leaves and just wipe off the scales on the stems every day which is much easier. And sprayed with some neem oil for period of time.

If you have scales in your citrus tree, very likely , you have scales somewhere in the conservatory... You just haven't see it in large quantity yet... You might want to isolate these citrus trees from the rest till they are scale free.
Good luck.

    Bookmark   September 20, 2012 at 10:40AM
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rhizo_1 (North AL) zone 7

Is there a chance that you could post some images so that we can see what kind of scale it is and how bad the infestation?

    Bookmark   September 20, 2012 at 12:20PM
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If they were my trees, I would opt for ISD (Imidacloprid Soil Drench)or bi-annual spray with Imidacloprid; it is topically active at the time of application, and then enters the plant as a systemic. The best part is it doesn't kill all your beneficials... very important outdoors; because the beneficials (birds, other insects) generally control scale. Indoors there are no beneficials so you have to do control by hand or by chemicals. If you opt for the spray application, try to time the first application to when you observe the scale "moving"/advancing; the crawlies are the most vulnerable to treatment. Horticultural oil also can control scale; but the timing of the application is critical. Here is a link that might help you.

Here is a link that might be useful: Citrus Scale

    Bookmark   September 20, 2012 at 12:21PM
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Thanks so far everyone. I will try to get a couple of pictures for scale identification later on but useful comments that I will take on board. I will see if that pesticide goes by any other name in the UK as I hadn't heard of it. As for leaf stripping, how much defoliation can I realistically inflict without serious consequences ...... as it does make 'wiping' much easier.

    Bookmark   September 21, 2012 at 4:28AM
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Here is the first picture I was able to get. Haven't worked out how to post two pictures so another one to follow!!

    Bookmark   September 21, 2012 at 5:44AM
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Picture number 2

    Bookmark   September 21, 2012 at 5:45AM
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rhizo_1 (North AL) zone 7

Ourarka, the active ingredient in the pesticide recommended by John is Imidacloprid. It may be extremely difficult to find in the UK, as banning is becoming more of a possibility. This chemical does translocate throughout the plants that it is used on and has been detected in pollen and nectar, making it an issue for pollinators such as honeybees.

Yours is one of the armored scale species. As a group, armored scale are poor candidates for effective control by imidacloprid pesticides. I'd keep up with the horticultural oil applications.

    Bookmark   September 21, 2012 at 7:13AM
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Thanks rhizo, for mentioning the problem with honeybees and imidacloprid. This might not be a major concern with indoor plants, but then again, most products containing imidacloprid also clearly warn against use on edibles anyway.

Finally, imidacloprid has to be reapplied regularly for scale, and it only kills the insect at certain growth stages. The next time you get an infestation, it could be much worse too. Periodic manual removal followed by horticultural oil has been the only solution for me, although certainly not enjoyable nor foolproof. My problems with scale have severely dampened my excitement for growing potted indoor fruit trees, especially citrus, which seem to be plagued the most.

Incidentally, I've found the following to be resistant and/or grow so quickly as to render the scale harmless:
-- Mango
-- Cactus
-- Papaya
-- Avocado
-- Passion Fruit
-- Most Ornamentals

    Bookmark   September 26, 2012 at 2:23PM
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jbclem(z9b Topanga, Ca)

Let me suggest a couple of easy things you can try. They don't involve using pesticides, and on such a small plant(s) it should be really easy.

1. Put some rubbing alcohol in a spray bottle, I'm using 70% and it seems to work(I don't dilute it). Here in the USA there is also 90% which is just that much stronger. Spray it liberally on the scale, especially the branches themselves (they are the scale superhighway) It's easy to find the scale, just follow the ants. That may kill some or all, but after a while (or the next day) you'll find the scale will be easy to rub off with your fingers/thumb. And you can spray again next day with the alcohol, it doesn't seem to harm the leaves.

2. Deny the ants access to your trees, should be easy to do since the trunk(s) seem to be the only thing touching the ground. Watch this short video from Alex Silber (Papaya Tree Nursery). I'm using his technique on some full grown citrus trees, and on a container eggplant. He uses Tree Tanglefoot and flagging tape. It stops the ants cold.

You have to keep the leaves from touching the side of the container, or anything else...the ants will always find a way up the tree if they can.

The names may be different in the UK, but flagging tape is very cheap here ($2-3 a roll) and the Tree Tanglefoot about $8-10 for the tube, and I paid $9 for a tub of it.

    Bookmark   September 30, 2012 at 2:55AM
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rhizo_1 (North AL) zone 7

Jb, the original poster said nothing about an ant infestation in his indoor conservatory.

    Bookmark   September 30, 2012 at 3:26PM
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jbclem(z9b Topanga, Ca)

rhizo, you're right...there was no mention of ants at all, and none showing in the photos. I mentioned them because they are so obviously involved on my citrus trees, and Tanglefoot seems to work well in keeping them off of trees.

So my apologies to the poster, I wouldn't want to wish an ant infestation on anyone. And I was reading today that there are some scale varieties that don't secrete honeydew...perhaps he has one of those types also.

The key is to stop their reproductive cycle, and as Johnmerr noted, the crawlies are the most vulnerable. I've been successful that way with spider mites which reproduce like crazy. Killing them (crawlies and spider mites) isn't that hard to do, but you have to keep coming back at them until there are none left to reproduce. With spider mites that's every 4-7 days in hot weather. With scale I think it's dependent on temperature accumulation. On the University of Calif Integrated Pest Management website they say the crawler stage peaks at 555 degree days(accumulated above a 53 degree F threshold). In a conservatory with constant warmth, this might be different. One way to tell is to wrap double-sided sticky tape around some branches and when the crawlies are running they will accumulate on the sticky tape and be easier to spot.

    Bookmark   October 1, 2012 at 6:06AM
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number2(USDA 9b/Sunset 14)

I've dealt w two different scale prob in the past so i really can't hold back from sharing...

JB is right. If ant exists, step 1 is to put on the sticky tanglefoot. I did this to my outdoor kumquat tree (in container) last year, followed by pruning off a seriously infested branch and a single application of neem oil (make sure apply only in cool weather),plus some hand cleaning here and there. I never have time for additional application of neem oil but I ensure the plant gets sufficient water and nutrient with religious fertilizing schedule+sulphur+iron, once in a while organic spray of seaweed extract or ironite. Whenever I spray organic stuff over my other fruit trees like peach, apple or peach, I spray also all my citrus since I found citrus a super heavy feeder. Today I still find scale here and there on the tree but I think the plant just "outgrown" the problem(plant growth faster than scale growth). We finally have some fruits this year after 3+ yrs of experimentation and battling with the scale and spider mite.

Second scale problem is with my indoor Bay leave plant. I tried neem oil, insecticide soap, hand cleaning with alcohol, also clean the window area where the plant is. The scale just keeps coming back. I don't have the time to keep doing this weeks after weeks and any new leave growth just turns brown. As a last resort before dumping the plant, I put the plant out in the middle of the yard (no near any of my other woody or fruit trees) and let the nature deals with the problem. In no time, the ant climb up and extend the infestation. All the full grown leaves turned yellow from the edge (from scale sucking the plant juice). HOWEVER, the new leave growth is finally looking fine!! Now I just ensure the plant gets proper watering and clean only the new leaves (lot smaller and easier to clean). I'm hoping that one day the new growth will outpace the scale like what happened to my kumquat. And I will probably start controlling the ant also. To Ourarka's question, I believe bringing in the plant will make the problem worse. There are insects in the nature that help counterbalance the scale population. Bringing in the plant essentially help protect the scale from its natural enemy.

Sorry for the long story but good luck with your trees!

    Bookmark   October 1, 2012 at 9:25PM
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