Spraying vegetables or ornamentals for insect and disease control can be an act of fatal kindness, especially if the sprayer being used has had other types of chemicals sprayed through it.
The weed killer, 2,4-D, is one that most times is involved in damaged or has killed non-target plants. Once this chemical is placed in a spray tank it is very difficult for the average user to ever wash the chemical out completely. While some plants have a degree of tolerance to very small traces of 2,4-D, others are super sensitive. Tomatoes will not tolerate 2,4-D at any level without showing some damage.
If herbicides such as 2,4-D are to be used, it is recommended that two separate sprayers be available and the one in which 2,4-D or other herbicides are used be marked or painted to inform anyone of this fact. Another safety factor would be to store the regular garden sprayer in a convenient place for ready use and store the herbicide sprayer in a separate location more difficult to reach.
After using weed killers in their sprayer, some people attempt to control insects with insecticide dusts rather than buying another sprayer. This may work in some cases, but many insects cannot be controlled with dusts because there is no way a dust can give you the thorough coverage that can be achieved with a sprayer. It is difficult to coat the undersides of leaves with dust. Quite often, this is where the majority of the insects are located. Another advantage of the sprayer is that it gives you more choices.
There is a wider selection of liquid or sprayable insecticides than dusts.
Please remember to follow label directions whenever you are using a pesticide.
Under or over application may not give the results you desired. Using pesticides according to label directions protects you and our environment.