I overwintered my lemon tree at a greenhouse here and when I picked it up it was covered with mildew and had scales everywhere.Seems it was in poorly circulated area.I have had it in full sun since may 24 and the scales are just getting worst,I am wanting to spray with horticultural oil but am worried what will then happen when the sun hits it.Is there something out there specificaly for scales outdoors.Last year had a bit of scales but when I put it out the wasps were around that tree eating the scales but this year no wasps.Thanks for the help everyone!!!

There are a few posts that have been answered on this.
The search functions great, I'll post what I found.

Posted: Thu Feb 04, 2010 6:43 pm    Post subject:
Bonnie is correct --- UltraFine Horticultural oil. You can find UltraFine at most Home Depots, and garden centers. Make a solution of 1 percent oil /99 percent water. Spray early in the morning, or at dusk. Never spray during the heat of the day. Spray both sides of the leaves, and all twigs and trunk. - Millet (1,080-)

Ultra Fine horticultural oil has a quick rate of evaporation, which makes it very safe on citrus when properly applied. Therefore, if you spray your tree near dusk, the tree will not have a problem the next day. I have done it time after time. You can also spray on any cloudy/raining day. Be sure you spray the upper and lower surface of the leaves along with the trunk and branches. Some people spray with a soap and water solution, but it might take 3 to 5 spraying to get complete control of scale. Personally, I only use UltraFine. - Good luck to you and your tree. - Millet (923-)

My experience with horticultural oil was a disaster. I almost killed some of my favorite trees. I mean, yes it has helped me dispose of 90% of the scale but also 90% of the leaves.
I used a systemic insecticide. I know that in your country you don't have a lot of insecticides available in stores but if you go in a specialized store I am sure you will find something.

covrig, what was the type of horticultural oil that you used? It is the evaporation rate of a horticultural oil that determines it quality and its safety. For the control of many insects, including scale, UltraFine horticultural oil has become one of the standards of the US Citrus Industry. Its safety is certainly unmatched. I am not familiar with the horticultural oils available in Romania, therefore I cannot comment on your misfortune. - Millet (922-)

I know Millet. I am not arguing with you.
I agree that some types of oil are very good, but in other countries than US it is pretty hard to find the same products and even if you can find is in most cases you find it at a lower quality.
So it is better to try a insecticide first and after that the oil as the last resort.
In my case the oil didn't evaporate fast. After a couple of days I wiped it with a cloth but it was too late.
If he can find UltraFine I would say he can go ahead and use it.

I couldn't find ultrafine but I use Dormant oil, which is a horticultural oil as well.
It's been a godsend for scale, mealies, and sooty mold. I was a bit afraid to use it in the summer, as the name is DORMANT oil, but I used it the end of May on some sooty mold and it worked great and no problems with the plants. I spray in the early evening, and let it work all night. I don't think you're supposed to use it when the temp is above a certain degree, which is why I used it in the evening.
Horticultural oils are not supposed to be used on certain plants, like Hibiscus, and Eucalyptus.

I've always been afraid to use a systemic, doesn't it stay in the tree and go into the fruit?

Millet,

What do you think of the horticultural oil in the link below? Do you have any experience with it?

http://www.amleo.com/index/item.cgi?cmd=view&Words=pur25

I have never heard of it, but from the literature it sounds fine. In fact the information given is much the same information given for UltraFine. Just to be careful, test it on a branch or two before doing a major spray. But I think it should be fine. - Millet (915-)

I tried Neem Oil (I could not find UltraFine) and it did nothing to the scale.

The only way I could eliminate scale was with Malathion. I found this made by Bonide at a hardware store:
http://www.amazon.com/Bonide-Malathion-Pints-Model-992/dp/B001WPIQ62

The problem is, its really toxic, so I don't think you should use it when expecting fruit. But for me, it was either do it, or the plants die (I was losing entire branches daily!). The choice was abvious. And take your plants outside for a few hours to spray (if they are indoor).

ONE application knocked all scale dead - small and large. I would try oils first, but use this as a last resort.

BTW, this is known and recomended for killing scale on citrus (safe for citrus if applied correctly) but again, be aware of the toxicity and damage to beneficial insects, etc.

By the very definition, an insecticide is toxic. Their are toxic insecticides, and then their are toxic insecticides. Malathion is not among the list of highly toxic insecticides. Malathion's label allows its use on a wide variety of fruits and vegetables, with a very short re-entry time. It is not a systemic insecticide, so is not taken up by the plant. I would consider malathion a valuable tool, when the situation calls for it use. - Millet (9120)