Question
I have little white(off-white)microscopic bugs, tons of them, on my annuals.  They are leaving a cob-web like covering on the flowers and my plant stand.  The leaves are turning purplish and they are dying.  I have sprayed with sevin but they are still here.  Maybe I need to spray more often but how much?  Or is there something better?

Answer
Denise,
Microscopic?  Do you really need a microscope to see them?  Without a photo I'm stumped.  There are very tiny white insects called whitefly, but they don't make webs and they are underneath the foliage.  Also, I know if no insect that turns foliage purple...did the foliage turn purple before or after using the Sevin?  I'd suspect that the change in color might be due to something other than insects.

Sevin is a pretty heavy hitting insecticide, so I can't imagine that it isn't effective unless you only sprayed once. Many insects have repeated generations and the eggs hatch every seven to ten days or more, so repeated use of a control method is necessary.  But I wouldn't recommend that you spray ANYTHING unless you have an accurate identification of the problem, which I can't make unless I see the insects, webs and plant.  I'd recommend that you snip a sample, insects webs and all, into a jar and take it to your local garden center or cooperative extension service for diagnosis.  

Sorry that I can't be of more help, but without a photo of the bugs, webs and plants I'm at a loss and wouldn't want to guess and possibly lead you down the wrong path.

all the best,
CL