Lawn grubs, often called white grubs, can be quite damaging to lawns. These white, C-shaped creatures have soft bodies with legs near the head and feed on grass roots causing sections of the lawn to die. Once grubs reach maturity as adult scarab beetles, they will emerge to mate and lay eggs, resulting in more grubs. This is why identifying them early on and controlling them is so important. If ignored, you could be left with an infestation that will kill your entire lawn.
Depending on the type, scarab beetles can have anywhere from a one to a three-year life cycle. This is what a typical cycle is like:
- Spring: grubs awaken from the winter, feed on grass roots and then change into pupae that will later become beetles.
- Summer: pupae turn into beetles that feed on foliage and flowers and then lay eggs.
- Fall: eggs hatch into new grubs that feed on grass roots.
- Winter: grubs are burrowed deep (up to 8 inches depending on the region) into the soil until spring arrives.
As you can see, the cycle is continuous and very destructive if left ignored.
Symptoms of Grub Damage
Although not every yard will suffer from the same symptoms, here are four common ones to look for:
- Obvious brown patches in a greening spring lawn.
- Irregularly shaped dead patches in late summer or early fall.
- Animals like birds, skunks, armadillos, raccoons or moles tearing up your lawn.
- Turf looks or feels spongy.
It’s important to remember that not all infestations or damages are grub-related, so check your turf before treating. If your lawn rolls up like carpet or has no roots when pulled up, then you may have a grub problem.
It’s also important to remember that not all grubs are a threat. A healthy lawn can usually support a grub population of at least zero to nine grubs per square foot. Scout your lawn for grubs by digging several sections of sod (approximately 1 foot square and 2-4 inches deep) during late summer and count how many grubs you see. As mentioned earlier, a healthy lawn can support up to 9 grubs per square foot. An unhealthy lawn cannot and would therefore need treatment. As a general rule, if you see 10 or more grubs, it’s time to treat no matter what the condition of the lawn is.
When it comes to treating a grub infestation, timing is crucial. Immature grubs are most susceptible to pesticides while young, so it is best to treat in mid- to late summer and early fall while newly hatched grubs are feeding.
There are two main approaches to pesticide treatments: preventative and curative. Preventative pesticides kill grubs over a longer period of time (existing to soon-to-be hatched), while curative products kill existing grubs on contact. Whichever treatment you choose, be sure to keep the lawn well irrigated to move pesticides down and also to avoid grass burn.