Chemical sprays will upset the ecological balance in your garden and result in a cascade of further problems. Beneficial predators will also be wiped out so that pests previously under control may take over.
Some low growing herbs have very small leaves and flowers, thus picking them separately would be an extremely laborious task. These herbs therefore are dried whole, including the stem.
The aim in drying herbs is to remove the water content only, thus changing them as little as possible.
The old way was to hung the bunches of the herbs upside down
Herbs have been valued for their medicinal and cosmetic properties for centuries. In more recent times, the artifices of modern science made these uses seem outmoded for a while.