Spraying is traditionally seen as the first line of defense for the PHC practitioner, however, these days it is also the most controversial.
Spraying can be applied to the leaves or to the woody (trunk and limbs) parts of the plant. The benefits of a spray program are fast efficacy (often spray insecticide formulations are “knock-downs”) and low product cost as they are diluted in large volumes of water. For some foliar fungal diseases spraying may be the only option for control.
The downsides of sprays include effects on non-target species, high equipment cost for modern spray rigs, drift and applicator exposure, difficulties of reaching high canopies, short residual, and, as mentioned, the increasingly controversial nature of spraying.
New laws and ordinances are restricting the use of spray on trees in urban areas as well heightened public sentiment against spray applications. That said, if sprays are used judiciously they still have a place in the PHC toolbox.