Nothing makes a homeowner and turf manager cringe like the word grubs!
Most of us have seen the effects of grub damage on our lawn, our neighbors lawn, or on the golf course. When you pull on a dead patch of grass and it comes up easy like pulling up carpet, you get a nauseous feeling. Seeing those ugly little “c” shaped critters with those two Tyrannosaurus Rex arms really makes your skin crawl.
Contrary to popular belief grubs are not worms, they are larvae of a beetle. There are over 350,000 different types of beetles worldwide and all of them have an immature life form called a grub.
In Iowa, chances are these little grubs are larvae of the Northern Masked Chafer “Cyclocephala borealis” . Other notable turf damaging grubs we look for in Iowa are the Japanese Beetle, Green June Beetle, May/June Beetle and the Black Ataenius. You can determine which grub you have by looking at the “Raster”, otherwise known as the tail end. The below diagram from the University of Purdue does a good job in illustrating the different identifying patterns
When controlling any living organism it is important to understand its life cycle. Grubs are no different. The diagram below illustrates when the grub is most vulnerable.
This diagram may be different depending on what growing zone you live in.
Once the eggs are laid they can take as little as 14 days to hatch. From hatching to its second instar, the grub goes through several molting processes. This is when the grub is most vulnerable. Products like Imidacloprid (Merit) make the young grub molt (shed skin) too quickly, therefore killing the grub. Timing is critical when preventing grub populations. If you put your grub prevention down too early it may wear off before all the grubs have hatched. Putting it down too late will cause you to miss some early hatched grubs. As grubs becomes mature in late August/early October they becomes more aggressive eaters. This is when you will start to notice the damage. You may assume the patches are left over heat and drought stress from the summer months, but the best way to check is to grasp the grass in your hand a pull upwards. It does not take much effort for the turf to come up and you will most likely expose the culprits of the damage in the process.
As the season progresses into winter, the grubs overwinter deeper into the soil. Once spring comes around we start seeing these critters as we dig in our flower gardens and landscapes. This is a good indicator you may need to apply grub prevention. In Iowa, late June or early July is the recommended time. You may want to check with your local county extension to see when egg hatching is most prevalent.
It is hard to predict if you will have an outbreak of grubs in your lawn, but over the years I have learned some things to look for as you consider grub prevention.
- In the evening hours just after the sun has set, take some time to walk your lawn and look for flying beetles hovering just inches over the turf. Pay close attention to areas that are illuminated.
- Many times on a nice evening we like to sit in our homes with the lights on and windows open. Pay attention to bugs hitting the screen. Are they beetles? If so you may want to go check the rest of your lawn for beetles hovering over the grass.
- Some people hate having the windows open to listen for beetles hitting the window screens. If this is you, use a coffee can or mixing bowl (or if your wife won’t let you use a mixing bowl, your pets water bowl) to fill with water and leave your outdoor light on. Check the bowl in the morning for floating beetles. (Kiddie pools are also great to use.)
- Pay attention to your neighborhood. If your neighbors have had grubs in the past, chances are they are still hiding around somewhere.
Grubs can cause lots of damage and in some cases it can take a full year to repair. When considering the cost of removing the damaged turf, adding seed, water, and the unsightly damage, everything adds up pretty fast. This is one reason my 5-step program automatically gets you grub prevention, it is a good insurance policy that lets your mind rest easy all season long.