Some herbicides are available both as liquids and granules. Granules are usually quicker and easier to apply. Liquids can be more accurately controlled, but they can also be affected by the wind and spray drift. Dry fertilizers can be spread by hand, by a shaker or a lawn spreader. Drop spreaders are more accurate than broadcast spreaders.
Liquid fertilizers require a sprayer.
Almost all sprayers have plastic parts that will absorb the herbicides, and when used later with insecticides or fungicides, may cause damage to your plants. There are dangers with all chemicals to pets as well as people, but if you use them according to directions at recommended rates, you can use them safely. Some herbicides are very residual, affecting plant growth for years. Others break down quickly and cannot even be detected. Read your labels carefully.