Dandelions may indicate a potassium deficiency. Most weeds need light to germinate and taller grass will shade them out. Remove dandelions and thistle with a dandelion digger. As with weeds, a healthy, properly maintained turf will minimize most insect problems. Two common insect pests in lawns are white grubs and chinch bugs.
White grubs are the larval stage of several types of beetles.
Grubs chew on the roots of turf and can sometimes kill entire sections of lawn. Apply Milky Spore, a bacteria, or Grub Guard, beneficial nematodes, to control. Chinch bugs appear during the summer months. They suck the grass blades to withdraw the moisture and inject a toxic saliva that can then kill the grass. Severe infestations can be controlled by spraying a quart of premixed Insecticidal Soap with a tablespoon of isopropyl alcohol.