As much as it might appear that an inconsiderate passerby spat on your grass, the frothy, foamy masses you see in a lawn are not spitwads, but a protective covering of a minor insect pest called the spittlebug. Though minor infestations generally cause no more than an unsightly nuisance, a dense population of spittlebugs can be problematic in a lawn. Spittle masses are easy to remove and chemical control of spittlebugs is usually unnecessary.
Spittlebugs include more than 3,000 distinct species in more than 300 genera. Also sometimes called froghoppers, the most common species include the two-lined spittlebug (Prosapia bicincta), meadow spittlebug (Philaenus spumarius), pine spittlebug (Aphrophora parallela), dogwood spittlebug (Clastoptera proteus) and alder spittlebug (Clastoptera obtusa). All resemble leafhoppers -- about 1/3 inch long with wings tented over the body in a V shape. Adults feed on a range of host plants, including ornamental perennials.
Nymphs hatch in spring from eggs that have overwintered in plant debris, and it is these nymphs that create the distinctive foamy spittle mass in lawn grass and other plants. The nymphs extrude the foam for protection from predators, and create it as a byproduct of the large amounts of sap they suck from their host plants. Adults and nymphs are most evident in the morning and evening hours, and both usually retreat lower on their host plants for protection in the midday heat. Nymphs mature into adults several weeks after hatching, and there is usually one generation per year in cooler areas, while warmer areas have two generations per year.
Spittlebugs rarely cause problems in most yards, as they are generally only present in low numbers. Adults and nymphs are neither aggressive nor poisonous to people, although the spit masses may fascinate children. They do pose more of a problem in the humid southern states, especially on centipede grass (Eremochloa ophiuroides), which grows in U.S. Department of Agriculture plant hardiness zones 7 through 10. Heavy infestations can cause a squishy feeling underfoot where the nymphs have retreated deep into the grass for shade, and badly affected areas may turn yellow and then brown before dying. Tree damage by adults is generally limited to minor speckling or discoloration of leaves and stems, though the adults’ feeding may lead to bacterial and fungal diseases.
Remove spittle masses by smearing them away by hand, or by shooting them with a strong stream of water. Proper turf care is the best defense against heavy lawn infestations, and includes a regular mowing and dethatching schedule. Avoid over-watering, as nymphs require high levels of humidity to survive. Though natural predators are effective in controlling spittlebug populations, heavily infested yards may benefit from horticultural oil or insecticidal soap. Though some products come ready to use, many products are concentrated. Mix 1 to 4 tablespoons of horticultural oil per 1 gallon of water and spray to distribute while continually shaking the spray bottle. Dilute 5 tablespoons of insecticidal soap per 1 gallon of water and spray to distribute. After treatment, yards rarely need treating again as long as the grass is properly maintained. Follow the directions on the label as rates may vary by brand.