Dead patches in the lawn are typical signs of grubs
Andre has the most beautiful lawn.
It’s lush, it’s thick, it’s a lovely deep green …
So when Mark asked me to take some pictures of grubs in his lawn, I was really surprised.
But sure enough, when I went down, I saw several brown patches in the front lawn; one of the telltale signs of grub activity. Some of these patches were quite small and not very obvious but there were also some larger areas that were completely dead.
Damaged turf peels back easily revealing the grubs.
.
As is typical of turfgrass that has been fed on by white grubs, the grass in these damaged areas was very easy to peel up because the grubs had literally consumed most of the roots that held it in place. As the turf was rolled back, the soil underneath was littered with white grubs. I have seen pictures of this in books and online, but I’d never actually seen it in person. It was pretty impressive.
White grubs are the larval stage of scarab beetles, a large family of heavy-bodied beetles which include the Japanese beetle, June bugs, and European chafers. They are typically white or pale gray in color with brownish or orange heads and six legs near the head. When found in the soil, they are usually curled up in a characteristic C-shaped position.
White grubs are usually found curled up in their characteristic C-shape.
Japanese beetle grubs usually get blamed for a lot of the turf damage in our area but I think these grubs may be the larvae of one of the chafer beetles. There were thousands of these reddish brown beetles swarming around at night in July so I wouldn’t be surprised to find a lot of chafer grubs in the soil this fall.
The problem with grubs is that by the time you see the damage to the lawn, it is almost too late to get good control. Understanding the life cycle of these lawn pests is important in determining the optimal time for controlling them.
A heavy infestation was found beside a willow tree near the pond.
Fortunately, the timing of the life cycle is similar for most of the grubs that feed on grass roots. The cycle begins when the adult beetles emerge from the ground in late June and July, mate, and begin laying eggs in the grass.
Well, I don’t know – which comes first the beetle or the egg!
Anyway, in about 2 weeks or so, the eggs hatch and young larvae (grubs) begin to feed on the roots of the grass. From late August through October, the grubs grow, molt, and continue to feed heavily on the plant roots. This is when you will begin to see damage to the turfgrass.
The roots of the grass plant on the right were eaten by grubs. Undamaged grass plants have healthy roots (left).
Once the weather turns colder and the soil begins to cool down, the grubs stop feeding and burrow down deeper into the ground. At this point applying grub control products is pretty much a waste of time and money. In the spring when the soil warms a bit, the grubs begin to move up toward the surface again and feed on the roots for a short while before they pupate near the surface. Spring treatments are not as successful as late summer treatments because these larger grubs don’t feed much in the spring and the pupae are fairly resistant to insecticides. The adults emerge in early to mid summer and the cycle begins again.
The best time to go after these grubs is when they are small, close to the surface of the soil, and actively feeding on the grass roots. This usually means that most of August is the prime time to apply a grub killer. In September and early October, the grubs are bigger but are still close to the surface and actively feeding on the grass roots.
- From August through mid-October, control products containing the active ingredient trichlorfon (Dylox) such as Bayer Advanced 24 Hour Grub Control work well when applied according to the label directions.
. - From May through mid-August, grub control products such as Bonide Annual Grub Beater, Bayer Advanced Season Long Grub Control, or Scotts GrubEx Season-Long Grub Killer can be applied according to the label directions to control grubs in the lawn. (These pesticides may not be available in all states.)
Before deciding on a control strategy, it’s important to determine if chemical control is even warranted. Generally there is a threshold number of grubs (more than 10 grubs per square foot of lawn) above which it might make sense to consider applying a grub control product. There are specific sampling methods that can be used to estimate the number of grubs per square foot in your lawn. The results of this sampling will help you determine whether treatment is necessary. Healthy vigorous grass can usually withstand small populations without much damage and control measures are usually not needed.
Skunks further damaged the turf when they dug for the grubs by the willow.
A side effect of a heavily or moderately infested lawn is that critters like skunks, raccoons, and moles really love to eat these fat, juicy grubs and will often tear up the lawn digging for them. We saw evidence of this in one heavily infested area at the farm.
Looking at the numbers of grubs that we found in some sections of Andre’s lawn, I think he needs to get out there this weekend and spot treat with a grub control before it’s too late!
Until next time – Happy Gardening!
