With the air temperatures climbing back into the high 80’s and low 90’s, now will be a crucial time to monitor for white grubs.
The term “white grub” refers to a group of insects with a larval stage that damage turf. Subsurface feeding insects are of major concern in athletic fields because they feed on roots, cause turf to be easily dislodged, and result in poor footing. Know the life cycle of underground feeders such as grubs and anticipate when they may become a problem. The beginning of football season coincides with peak turf injury from white grubs. Masked chafers, Japanese beetles and May/June beetle are the most common grub species to attack Iowa athletic fields. Annual grubs such as masked chafers and Japanese beetles lay their eggs in the spring, and hatch in the summer. The larvae begin to feed on the root systems in August and these two species are commonly referred to as “fall grubs”, because a majority of damage occurs in the fall.
The damage is best diagnosed by grasping the blades of the grass and lifting. This process is known as a “tug test”. The grass will break away at the roots. Another option is to shovel or spade a three sided 1 sq. ft. piece of sod about 3 inches deep. Slowly peel back the sod and expose the soil as was done in the picture below.
Figure 1. Several white grubs feeding on athletic field in Fort Madison, IA. Picture courtesy of Cody Freeman.
Fall grubs that sever the root system do not necessarily kill the grass. If it is properly watered via irrigation or rainfall, it will recover. The drought stress following grub damage, kills the grass. With the warm temperatures in the foreseeable future, it is the most likely time to see damage across Iowa, especially if the rain switch suddenly turns off.
Keep Dylox or another insecticide handy for preventative measures. It is important to remember that all products need to be watered in. Using nozzles that produce larger droplets will move the product further into the canopy. After application, irrigation or rainfall can help move the product down into the soil, where it can be most effective.