Turfgrass & Beetles

Japanese beetle is an insect that creates problems for turfgrass.

Beetles and their larvae, which are known as grubs are among the most serious pests that affect turfgrass. The pests are present in many lawns, yet go unnoticed until they reach threshold levels. If your turf seems dead and may be pulled up like a carpet, you may have a serous problem with grubs. But sound cultural practices generally help to keep beetle and grub populations down in turfgrass.

Damage

Both beetles and grubs can cause damage in turfgrass. The grubs feed on roots below the surface as they mature, while the adults feed on the leaves of plants prior to laying eggs. An adult beetle will leave large, irregular holes in turf grass blades. There are over 300 types of plant that beetles may feed on Each beetle will lay between 40 and 60 eggs. Female beetles will lay between 3 and 5 eggs, then feed and mate before laying another 3 to 5 eggs. The cycle of egg laying will extend from late June through August.

Damage Cycle

Beetles and grubs do damage to turf in cycles. In June the beetles emerge from the ground. They feed on foliage and lay eggs from June through August. Beetle eggs hatch into grubs in august and feed on grass roots through late September. They burrow deeper into the soil until March. In April, grubs return to the soil surface and begin feeding on grass roots until they turn into beetles in late May. At that point they emerge from the soil and the cycle begins again. Some beetles, such as June beetles may remain grubs for 3 years before emerging from soil.

Hiding Damage

Replacing turf grasses that are susceptible to grub feeding such as Kentucky bluegrass with less tolerant varieties such as fescue can help to reduce signs of grub damage. Additionally, irrigating a lawn in August and September will help to hide signs of damage by providing stressed lawns with root damage the additional water they need to thrive. Fertilize lawns with moderate amounts of nitrogen in fall to increase root development and help lawns recover from grub damage. Avoid heavy fertilization in spring. This can stress lawns and contribute to grub damage among roots in fall.

Beetle and Grub Control

Reducing irrigation in June and July can play a factor in grub populations as well. Female grubs are more attracted to well-watered soil because it is loose and easy to dig through and increases egg survival. Encouraging natural predators such as parasite wasps or nematodes can help decrease grub populations in the soil. When beetles enter the mating season, pheromone traps can capture the insects and gradually decrease overall populations. Insecticides must typically be applied when beetles are in the grub state and are near the surface of the soil. When grubs burrow deeply into soil for winter, the insecticides typically won't work, as well.

References

• Ohio State University Extension; Identification of White Grubs in Turfgrass; David J. Shetlar
• Missouri State University Extension; Turfgrass and Insects; Brad Fresenburg et. al; June 2003
• University of Minnesota Extension; Japanese Beetle Management in Minnesota; Vera Krischik et. al; 2001

Resources

• NC State Univeristy Extension; Sugarcane Beetle in Turf; Amy Lockwood et. al; November, 2009
• NC State Univeristy Extension; Pest Management; Stephen B. Bambara et. al; May 2003
• University of Kentucky Extension; Controlling White Grubs in Turfgrass; Michael F. Potter et. al