Annuals are generally trouble free under proper cultural conditions. However, there are some common pests to be on the lookout for. When this can't be done, fungicide treatment may be necessary. The most common are aphids, white fly or spider mites which are easily controlled by various pesticides. Mites and white fly are less of a problem when plants are frequently watered.
High temperatures increase insect populations necessitating more frequent pesticide treatment.
Use extreme caution with pesticides. These pests can feast on young bedding plants, especially marigolds, petunias and salvia. Place slug bait near new plantings in late afternoon and replenish as needed. Take care to prevent children or wild or domestic animals from eating bait. Weeds may appear, even though you used mulch and pre-emergent herbicide.