Ireland 
why are my nastersions being infested with black fly I save my seeds every year then grow them but this is the third yaer in a row they have been really badly infested can the fly stay in the seed and hibrenate until I grow them again or is it something else thank you
21 Jul, 2010
Answers
Andip's right - these plants are on the top of the list for favourite foods for aphids, along with English marigolds.
21 Jul, 2010
I swear the aphids can smell them a quarter mile away!
21 Jul, 2010
Thank you very much
27 Jul, 2010
I have the same problem. A quick search elsewhere online shows:
"...very prone to aphids and are sometimes used as a trap crop in vegetable gardens. A strong blast of water is usually enough to get rid of the aphids."
Perhaps it's something to do with the plants components being edible?
21 Jul, 2010