Then, if he says he loves you,
It fits your wisdom so far to believe it
As he in his particular act and place
May give his saying deed; which is no further
Than the main voice of Denmark goes withal.
Then weigh what loss your honour may sustain,
If with too credent ear you list his songs,
Or lose your heart, or your chaste treasure open
To his unmastered importunity.
Fear it, Ophelia, fear it, my dear sister,
And keep you in the rear of your affection,
Out of the shot and danger of desire.
The chariest maid is prodigal enough,
If she unmask her beauty to the moon:
Virtue itself 'scapes not calumnious strokes:
The canker galls the infants of the spring
Too oft before their buttons be disclosed,
And in the morn and liquid dew of youth
Contagious blastments are most imminent.
Be wary then; best safety lies in fear:
Youth to itself rebels, though none else near.
Shakespeare is clearly on a roll in Hamlet, cooking up new words as they come to him. Already in the play we have heard condolement and now blastment. I'll keep the Index entry on this family of words up to date whenever we meet a new one in the play.
Laertes finishes his speech to Ophelia with quite an involved set of botanical images - cankers, dews and contagious blastments all besetting the 'infants of the spring'. It's worth always bearing in mind that Shakespeare grew up in the country, and was deeply aware of the life of the seasons. No surprise that there are enough botanical references in Shakespeare to fill a book - and a lovely one, too - Gerit Quealey has put together "An Illustrated Compendium of All the Flowers, Fruits, Herbs, Trees, Seeds, and Grasses Cited" - you can find it here.