Bug of the Month May GRUBS
What is a grub and why are they in my lawn?
What is a lawn grub?
Grubs, are the term given to larvae of scarab beetles. In Canada we deal with the Japanese beetle the May/June beetle and the European chafer beetle. These grubs are frequently found feeding on the roots of turf grasses.
People are often surprised to find out that the pesky beetles spent 11 months as a grub eating and destroying their lawn before turning into a beetle. In the case of the June beetle, they can spend as much as three years in your grass eating your lawn from the bottom up.
Many a Canadian lawn have suffered at the hand of these pesky critters
Most homeowners do not know that white grubs are present until they suffer significant turf loss from secondary pests, such as animals who feed on the grubs and cause damage. The key to success with white grubs is identifying that they are present before any turf damage is visible, so monitoring early and often is the best.
If we understand the life cycle, we will have a better chance at spotting the sign and symptoms of Grub damage.
Grub Life Cycle
Grub Life Cycle
EGG STAGE: Adult beetles dig shallow holes in the soil where they lay their eggs. Depending on the white grub species, the egg laying period occurs between June and August. Several factors – including soil moisture and temperature – determine how quickly the eggs will hatch. Under regular conditions the eggs hatch in about 2 weeks.
LARVAE STAGE: After the eggs hatch, tiny 1st instar larvae begin feeding on grass roots close to the surface. feeding continues for several months into late fall. As the larvae mature into 2nd and 3rd instar they grow and feed more aggressively. Turf damage can start to become visible if infestation levels are high.
Animal digging from skunks and raccoons is also common during an infestation, as the grubs are a great food source. The white grub overwinters as a 3rd instar larva and moves deep into the soil as the ground freezes. When early spring arrives, the larvae move back towards the surface and continue to feed on the roots. This feeding lasts for one to two months then the larvae stop feeding and turn into pupae.
PUPAE STAGE: The pupae life stage takes place after the larvae feeding has finished. The larvae transform into a pupa in the soil, where they then remain for several weeks. During this transformation process the pupae becomes an adult beetle, the last stage of its life cycle.
ADULT STAGE: This transformation to adult beetle takes place in early summer, lasting for about a month. After the completion of their transformation the adult beetles emerge. The adult beetles dig their way out of the soil and move up to the surface. This transformation takes place in early summer, lasting for about a month. After the beetle has crawled out of the soil it spends 2-3 weeks mating before laying eggs. The eggs (up to 60 eggs) are buried in the soil during the summer (June – early August). The Adult beetle is the final stage in the life cycle of the white grub.
Signs & Symptoms you have Grubs
A grub infestation will cause patches of thinning turf, and these patches will gradually increase in size. Often grub damaged grass will pull out very easily at the roots. When your yard is under attack by grubs, grass will thin and turn brown. This leads to visible larger brown patch areas in your yard. It is common to notice these odd-shaped brown patches in late summer or early fall. Does your grass have a spongy or loose feel when you walk on it? The damage that grubs cause is quite unique and leads to some rather unusual symptoms. Grubs feed on the roots of grass, and so the damage they inflict occurs underground. As the grubs feed on the root structure, the connection between the root base and the green turf is weakened. Meaning you can pull out tufts quite easily.
Grub Damage Skunk or Racoon damage
Animals like skunks and raccoons love to dig up grubby lawns looking for their next meal. Birds will similarly feed on grubs and leave behind pencil-sized holes. This damage can be just as unsightly and expensive to fix as the grub damage itself.
To check for grubs, use a shovel to dig up a few small spots in the suspicious parts of your yard. Grub worms are off-white in color with brown heads, chubby bodies, and three pairs of legs. They usually lay in a c-shape when they are exposed. If you see more than five grubs per square foot, you may have an infestation. If you have found larger numbers of grubs in each hole, then at this point, it’s time to do something.
What can I do?
In Ontario cosmetic pesticides have been banned for over a decade which has greatly improved our water table. So that leaves us with only natural options for grub control. By far and away the best choice is nematodes. Beneficial Nematodes are microscopic worms that occur naturally in all soils. Like people, there are good nematodes and bad nematodes. The bad nematodes eat and destroy plant roots, whereas the good nematodes seek out and destroy lawn grubs.
How to apply Nematodes?
Nematodes are super easy to use, require very little work. You can apply them using a watering can, sprayer and hose attachment or misting system. You get a whopping 10 million nematodes in an individual package. That will cover an area between 2000-3000 square feet (based on a heavy or light application rates. Application of nematodes is an easy process, simply add water to create a nematode solution then watering said solution down and applying it to your lawn via hose end sprayer or watering can.
How to apply Nematodes?
Here is a link to a short “How to video”
Best time for an application is as soon as the ground temperature reaches 10 degrees.
Best practice is to
- Cut lawn prior to application
- Water lawn pre application
- Choose a rainy or overcast day
- Use entire solution and finish application with in a couple of hours DO NOT leave nematodes solution sitting as nematodes will drown
- Average Canadian size lawn should take roughly an hour
- Water lawn post application
- Sit back and let the nematodes do their stuff
