Question
I have a 7 ft. jasmine that we move outside in the warm weather and overwinter in my sun room.  It has a shiny, clear, hardened residue on its leaves.  It appears to be coming from inside the plant, because it is also on the brick floor surrounding the plant, like it has fallen off.  I can scratch it off the leaves with my fingernail.  There does not appear to be any harm done to the plant, but I am also seeing it on a palm I have in my family room.  I can't find this in any of my books.  Help!

Answer
Shirlene,

The hard residue that you are seeing might just be a scale insect infestation.  If the hardened "residue" is about 3 mm to 5 mm (1/16 to 1/8 inch) in diameter, is oval to circular in shape, and ranges from light tan to dark brown in color, then you probably have a scale insect infestation.

Scale insects are closely related to mealy bugs, and they such the phloem (sap) from the plant tissues. The residue from these sugary saps appears as a sticky, sugary film on or near the plant that is infested.  These "honeydews" may drop from the tree onto surfaces adjacent the plant and create a very sticky film.

If these signs sound familiar, examine your jasmine tree for small white flecks (juvenile scale insects) on the branches (they may be alone or in small groups in the crotches of the branches.)  The adult scales affix themselves permanently to a feeding site, and they form a hard shell covering them.  

Adult scale insects can be removed with a little effort by hand (or with an old toothbrush) and mild soapy water.  The juveniles can be removed by saturating a Q-tip in 70% rubbing alcohol and drenching them.  

As long as the tree is inside, you will have to monitor closely for a renewed infestation because the natural predators that control them outdoors are not present.  This is one of the indoor pests that is rarely a problem outdoors, and once the plant is return outdoors, the scales will not be a problem.

If infestation is severe, there are horticultural oils that can be applied that with "smother" the adults and juveniles, but the use of these oils is highly temperature dependent; misapplication can cause severe burns to the plants.

I would suggest that if this is the problem that you try to remove the scales manually first, then try the chemicals when all else fails.  

Good Luck.