Seed treatment

In agriculture and horticulture, seed treatment or seed dressing is a chemical, typically antimicrobial or fungicidal, with which seeds are treated (or "dressed") prior to planting. Less frequently, insecticides are added. Seed treatments can be an environmentally more friendly way of using pesticides as the amounts used can be very small. It is usual to add colour to make treated seed less attractive to birds, and easier to see and clean up in the case of an accidental spillage. Specialist machinery is required to safely and efficiently apply the chemical to the seed.
A seed coating is a thicker form of covering of seed and may contain fertiliser, growth promoters and or seed treatment as well as an inert carrier and a polymer outer shell. 
The term "seed dressing" is also used to refer to the process of removing chaff, weed seeds and straw from a seed stock.
History.
The earliest seed dressings were of organo-mercurials used to control pests such as oat smut and bunt of wheat. These were available from the 1930s but were ineffective on "Pythium" and "Fusarium" species which are pathogens of many crops including cotton, maize and soya. Thiram was therefore developed as a seed treatment in the 1940s to extend the spectrum of diseases that could be controlled.
In 1949 ICI commercialised a seed treatment with trade name Mergamma A, containing 1% mercury and 20% lindane, an early example of a product designed to protect the seed from both fungal and insect attack.
Modern seed treatments.
One seed treatment, imidacloprid, from the neonicotinoid family of insecticides, is controversial and was banned in France for use on maize, due to that government's belief that the chemical was implicated in recent dramatic drops in bee counts, and possibly in Colony Collapse Disorder. Dust from treated seed is known to have caused at least some problems particularly from crops such as maize drilled during the main honey flows. Improvements to pneumatic drills to reduce dust release, and improvements to seed treatment compounds to prevent the compound breaking up into dust have been introduced in Europe led by Germany and the Netherlands from 2009 to 2012. Information on seed treatments including the information above can be seen on the registration authority databases.
In order to qualify for the United States Department of Agriculture Organic certification, farmers must seek out organic seed. If they cannot find organic seed, they are allowed to use conventional, untreated seed. Treated seed however, is never allowed.