In foliar spraying, the herbicide is diluted with water or diesel at a specific rate, and sprayed over the foliage to point of run-off (until every leaf is wetted, but not dripping).
The method is most suited to shrubs, grasses and dense vines less than 6 m tall so that complete coverage is achieved. Advantages include quickness and economy. Disadvantages include the potential for spray drift and off-target damage.
Foliar spraying can be done a number of ways depending on the size of the weed plant and/or the infestation. Blanket spraying using a boom spray from a tractor can be used to treat areas completely infested with weeds, especially with selective herbicides.
For large infestations that need targeted applications of herbicide, a hose and handgun can be used to spray solution from a herbicide tank and pump carried by a tractor or vehicle. Smaller infestations can be sprayed using a backpack/knapsack spray unit. Spot spraying is used to treat individual weed plants or areas that only have small clumps of weed infestations.