European Crane Fly (Tipula paludosa) and, more recently, the Common Crane Fly (Tipula oleracea), are the most widely spread turf insect pests in the Pacific Northwest. In low numbers, they do minimal damage to lawn. In high concentrations, lawns can be severely affected, with new lawns tending to be more affected than established lawns.
Adult Crane Flies do no damage, it is the larvae that destroy lawns by eating the roots. If you suspect Crane Flies, begin monitoring your lawn in December or January. Remove a 1’ by 1’by 3” deep area of sod and count the Crane Fly larvae – if your population is above 30-50 larvae per square foot, and the lawn in thinning or looks to be in poor health, it is time to treat your lawn. Treatment should occur in early spring. If you find the same number of larvae and the lawn looks to be in good health, wait to apply treatment, as none may be required. A healthy lawn can typically withstand an average Crane Fly infestation with little to no damage.
One sign of Crane Fly infestation is heavy bird or insectivore (mole, gopher) activity in your lawn – these animals love to feast on Crane Fly larvae. In addition, nematodes, parasitoids, wasps and other beneficials will do their part in helping to control an existing Crane Fly larvae population. Applying a chemical Crane Fly control could cause harm to these critters if they eat contaminated larvae, so be sure your lawn actually requires treatment (is thinning or yellowing) before applying any chemicals.
The best prevention for Crane Fly damage is maintaining a healthy lawn. Thatch and aerate as required by your lawn and soil types; fertilize three to four times during the growing season; water your lawn deeply and infrequently, applying about 1 inch of water per week.
If a chemical control is required, you will find most Crane Fly treatments are granular formulas that are applied to lawn areas and kill only Crane fly larvae. Follow manufacturer’s instructions as to proper quantity and frequency of applications. Most treatments are applied in late fall (October through November) and in the early spring (March through April) with repeat applications taking place as needed, based on your observations.