|Is it O.K to apply crabgrass and grubworm preventer at the same time
|You would not want to apply these at the same time. Crabgrass preventer needs to go down very early in the spring before the crabgrass begins to germinate, roughly when the forsythia bushes bloom in your neighborhood.
If you have had problems with grubs and there is a need to treat the lawn for them, the correct time to apply ost grub control products would be later in the summer when it will be most effective. If you apply it now it is too early and will not do the job. The exception to this would be milky spore disease which can be applied any time of year (as long as the ground is not frozen.)
Your local county extension should be able to tell you the right time to apply that for the best results, based on the weather conditions this summer.