Question
I live in UK. In my garden an elm tree and a shrub have developed many small fluffy white spots on the branches and trunks.  The spots are approx. 5mm diam. with a roundish-oval, scale-like, brown 'thing' (looks like a flat barnacle) on top of each white fluffy spot.  Also a large laurel bush which was recently trimmed has developed much smaller leaves than usual where it has been cut, each having leaf curl with whitish mold-looking powder on the leaves. None of this has happened before, and I wonder if it is because of the weather which has been unusually dry for a spell, but with bursts of heavy rain. It has also been hot one week and then really chilly the next and so on - very changeable. Please do you know what may be the cause, and if you do how I can treat it, and whether it is infectious to other woody plants.
Hoping you can assist.  Thanks.
Mary

Answer
The scale description is correct and can move to other plants if left untreated.  A product called Bayer Advanced Tree and Shrub Insecticide works very well against the scale.  It is mixed with water and poured around the base of the plant and is taken up systemically.  It will kill most bugs within a week or so.  It also provides protection from reinfestation for up to a year.  Good Stuff.

The other problem sounds like powdery mildew, which is a fungal disease.  Several products work pretty good.  Wettable sulfur powder mixed with water will control the mildew pretty good.  If it is warmer than 90F (35C?) then it may cause phytotoxicity.  In this case I would not use this product.  Another mixture made of one tablespoon baking soda and one tablespoon cooking oil mixed with 4 liters of water will also work pretty good.  The latter mixture will have to be sprayed every 5-7 days and will need to be mixed fresh each time, but it is cheap.  

I hope this answers your questions.  Thanks.