scale on saucer magnolia?

[saucer]

I have lived in my house for a year and a half and have two saucer magnolias (one shared with a neighbor). The trees have been sprayed with horticultural oil twice a year for many years, but they continue to produce honeydew/sooty mold.

One arborist told me that he didn't think it was scale, and didn't think there was anything wrong with the tree (to be fair, he saw it March of last year before the honeydew was dripping).

I'm wondering if there could be other insects besides scale that could be causing the problem (and if that is the case, if something other than hoticultural oil would be a better solution). I have never seen scale on the tree myself. Other than seeing the actual scale insect and honeydew/sooty mold, are there any other telltale signs to look for for diagnosis?

If the problem IS scale, how do you ensure that the spraying is done at the right time? Our spraying seems to be dependent on when they can schedule the truck. Last year, it was April and September.

Thanks for any insight.
Amy

 

[NYCHA FORESTER]

I don't think a systemic will do you much good in this particular case....the scale insect (in this particular case) is feeding in the phloem/cambium area of the twigs. Merit does not normally leave the xylem or leaf. The reason bidrin works for these critters is that just a little dab will do them....sort O speak.

 

[alanarbor]

I think the dormant sprays are doing some good. Your tree would probably be dying back, but they are just holding back the tide.

It is important to know exactly which scale is the problem. Merit is not especially effective on magnolia scale, but you may have tuliptree scale, european fruit lecanium, and a couple others on that tree. Down in PA I am dealing with a property which has magnolias with 3 different species on each tree. Merit is helping. I am also using a material called distance, an insect growth regulator mixed with oil.

Coverage is essential. The scales all congregate at the branch tips, as do the crawlers. If the spray is not THOUROUGHLY applied to the tips, control will be sub par.

A severe scale problem can take years to fully control. You are greatly outnumbered.

 

[saucer]

Thanks eveyone for the helpful responses and pdf file. I climbed up into the tree yesterday and found scale! (surprise!) I clipped some samples and with the help of the University of CA website and Google Images, I'm 99% positive it's tuplitree scale (Toumeyella liriodendri). An image can be seen here:

http://images.google.com/imgres?img...oumeyella+liriodendri&svnum=10&hl=en&lr=&sa=G

The only good news I can find is that it's a soft scale, which, according to what I've been reading, is usually not fatal to the tree. Any thoughts? I've also read sites that discourage spraying in order to encourage natural predators such as beetles and wasps. I do think my infestation is bad enough to warrant spraying, but just wondering if anyone has had success with natural predators?

Also, I was just talking to someone at a tree spraying company who said spaying for scale is ("unglamorous" - not sure if this means he doesn't want the job?) and that he usually recommends clients with scale infested magnolia to just remove them b/c they end up paying for 10 years of spraying and then the tree dies anyway and has to be removed. Thoughts?

Many thanks!

 

[alanarbor]

Try the soil treatment. Merit is usually effective on tuliptree scale. Combine that with a couple of timed sprays of soap or oil during the crawler stage. This straegy will limit impact to beneficial insects, and should clean the problem up in a season or two depending on how bad it is.

 

[Urban Forester]

Have a commercial co. try "Talus' IGR (insect growth regulator). We started using it thjis year on a MASSIVE outbreak of Calico and Lecanium scale and it has worked very well.