White grubs are the larval stage of many common beetles. These grubs feed on the turfgrass roots, destroying connective tissue and killing the grass plants themselves. Most white grub damage appears in the fall of the year. The grubs causing this damage hatch from their eggs in early to mid- July and begin to feed on the turf roots almost immediately.
Damage to the roots of the turf will cause large areas of turf to become unstable. With no roots connecting the turf to the soil, these areas of turf slide and move around like carpet that is not connected to the floor. Injuries to players can occur in this situation. Imagine a big linebacker running full speed, then suddenly planting his feet for a quick stop to change direction, only to have the turf come out from under him. Ankles can be turned, and knees can be injured. Also, birds, skunks and even raccoons will dig up the turf, looking for grubs to eat and causing further damage.
One of the biggest challenges the athletic turf manager faces in dealing with white grubs are the lights found around athletic fields. Most of the adult beetles are night flyers that are strongly attracted to lights. Of all of the species of white grubs that we deal with in turf, only two of the adults are active during the day: Japanese beetle and green June beetle. All of the other species are active at night and are attracted to lights. Northern masked chafer, Southern masked chafer, European chafer, oriental beetle, Asiatic garden beetle, black turfgrass atenius and May June beetle are all attracted to the lights, and they will then find the well-maintained turf below, where they will then lay their eggs.
Using a black light trap, you can easily observe the populations of these night-flying adults as they appear in mid- to late June. You can then watch their numbers begin to climb and, eventually, peak. When peak populations are reached, you know that the most adults are out, mating and laying eggs.
The labels of preventive grub controls recommend that you apply them prior to egg hatch. So, when these adults peak in your light traps, this is a good indicator that they are laying eggs, and now is the perfect time to apply, ensuring that you are making your application prior to egg hatch.
You can also catch the day-flying Japanese beetles. For trapping Japanese beetles, you use a pheromone trap. These traps use two different baits: a floral lure for attracting females and a sex pheromone lure for attracting males. These traps attract a lot of adult beetles each day, and you can destroy these adults, which can help reduce your grub populations. But you really want to use these traps to watch the numbers peak.
Green June beetles are much larger than their Japanese beetle cousins. You can easily spot these erratic day flyers. You find them out and about on warm, sunny late June through early July days. The larval stage of this species causes damage not so much from feeding but from tunneling. The tunnels allow air into the turf roots, drying them out and causing damage. The larvae also leave large mounds of soil when they dig their way to the surface. These casts could cause players to trip and could cause damage to mowing equipment. All of these larvae or grubs have a series of spines, hairs and open spaces on their posterior ends. These raster patterns allow you to identify one species from another when they are in the larval stage. For example, a Japanese beetle has a V-shaped raster pattern, while a northern masked chafer has a random raster pattern. These grubs go through three molts or instars. You can determine what instar the grub happens to be in by measuring the width of its head capsule. These clues become important when making control decisions.
The easiest and surest way to take care of your grub problem is by using preventive controls. Preventive controls include the neonicotinoids, like Merit, Arena and Meridian, as well as anthranillic diamides, such as Acelepryn, and insect growth regulators, like Mach 2. Neonicotinoids and anthranillic diamides are systemic products. The plant takes up these products, so that any insect that feeds on the plant will also ingest the product. These products need to be irrigated in. Please follow the label recommendations when deciding on how much irrigation water to put on after an application. These products also have long residuals and, when applied at the proper timing, will give you good control from mid- summer through fall, when the remaining white grubs begin to dig down into the soil to survive winter.
The insect growth regulator Mach 2 can also be applied prior to egg hatch. Mach 2 mimics the hormone ecdysone, which causes an insect to molt. Mach 2 causes the insect to molt continuously until it dies of exhaustion.
All of these products will give control well into the 90% range. Mach 2 can be put down somewhat later, up until grubs reach 2nd instar size. And Acelepryn can be put down from early April till early September. Since black turfgrass atenius grubs appear in April, you would need to treat much earlier for this grub than for the other species.
If you have a breakout in late summer or early fall, and you need to apply a curative or rescue treatment, you can use Dylox or Sevin. These can be spot sprayed to stop the damage and allow the turf to begin to heal. Please refer to the label before applying any product.
By paying attention to the emergence of the adult beetles during the summer, and using that knowledge to time your preventive applications, you can effectively control white grub populations in your athletic turf.
Danny Kline is a research technologist in turfgrass entomology at Penn State. This article was originally published in Pennsylvania Turfgrass, the publication of the Pennsylvania Turfgrass Council, www.paturf.org.