Not typically. Mosquitoes do not usually seek shelter in the grass. When first treating your property, our technician will do a pre-spray walk to seek out the areas where mosquitos might be resting. The most common areas to find mosquitoes during the day include: the underside of the leaves of dense/shrubby plants, under decks and in damp shady areas of the property. We do recommend that you keep your grass short during the mosquito season. In some cases such as special events like weddings and large outdoor parties, we will spray the grass where your guests will be.