White grubs may be the most damaging turf insect pests in the United
States. According to the U.S. Department of Agriculture, Japanese beetle
grubs alone cause an estimated $234 million in damage each year — $78
million for control costs and an additional $156 million for replacement
of damaged turf.
Japanese beetle and masked chafer adults are attracted to turf with
moist soil which means they are especially attracted to lawns that get watered during hot dry spells. During the feeding period, female beetles intermittently leave
plants, burrow about 3" into the ground— usually into
turf— and lay a few eggs. This cycle is repeated until the
female lays 40 to 60 eggs.
soils are certainly easier to dig through than hard, dry soils. Eggs will dry up and die under very dry soil conditions. The eggs also die
when soil temperatures are around 90°F. Higher soil temperatures
are typically associated with drier soils, as well as high air temperatures.
White grubs are the larval stage of many different beetles, including the Japanese
beetle. The grubs live below ground and feed on the roots of tender
grass plants that soon kills the plant. They are most destructive mid-late
summer, but the damage they cause may not show up until early fall and
by then, it's too late.
The best time to control grubs is in early summer,
just after they hatch. At this time they are very susceptible to treatment
and just before they start causing extensive damage to your lawn.
Grub control options
Option 1: Biological white grub control: Bacterial Milky Disease
The bacterial milky diseases, Bacillus popilliae Dutky, has been quite
effective at controlling the grubs in certain areas of the eastern United
States. The spore count must build up for 2 — 3 years to be effective
and during this time you should not use an insecticide against the grubs
that are needed to complete the bacterium cycle. In Ohio and Kentucky,
test trials have not produced satisfactory results. Additional experiments
are needed to determine the lack of efficacy of milky disease in these
Option 2: Biological white grub control: Entomopathogenic Nematodes
Parasitic nematodes have recently become commercially available.
Products containing strains of Steinernema carpocapsae (Biosafe, Biovector,
Exhibit, Scanmask) have been marginally effective against white grubs. Preparations containing Heterorhabditis spp. seem to be more
effective. Apply the nematodes when the white grubs are small. Irrigate
before and after applying the nematodes.
Option 3: Chemical white grub controls: Insecticides
Read also: MERIT
White grubs are best controlled when they are small and actively feeding
near the soil surface, usually late July to mid-August. However, with
the development of new grub control chemistry (e.g., imidacloprid [Merit]
and halofenozide [MACH2]), applications in June and July have sufficient
residual activity to kill the new grub populations as they come to the
soil surface in late July through August.
Control of white grubs in late-fall
or early-spring is difficult, at best, because the grubs are large and
may not be feeding. Only trichlorfon (Dylox) and carbaryl (Sevin) formulations
are available for such rescue treatments. The key to good control is
to make an even application and water thoroughly.
Late summer and early fall white grub damage becomes visible
Approximate 1sq. ft. area
Lawns having numerous white grubs soon will show signs of injury. If browned areas haven't recovered once cool evenings return with adequate moisture check for white grubs 1" — 2" below the surface. Damaged grass areas will typically just peel back when pulled or raked. When the grass is pulled back you'll probably notice one or two white grubs, but with a little scratching, you'll soon uncover quite a few. The threshold for lawn damage is 5 — 6 grubs per sq. ft. which means that if you have more than 5 grubs in a square foot area, you'll see extensive lawn damage.
Repairing white grub damaged areas
Once the damage becomes visible, it's too late to control. Damaged white grub areas will not recover as the plant and root system is dead. Before making repairs the grubs will have to be removed either chemically or by hand. Manually removing the grubs is not hard once the dead grass is removed.
Late summer white grub chemical controls
If you have white grub damage and want to make repairs to those areas in the fall, you'll want to make sure that the grubs are under control before making repairs. Just overseeding these damaged areas without removing the grubs will not be successful as the white grubs will soon eat the new grass seedlings roots.
Products labeled for use earlier in the season (MERIT) won't control white grubs in the fall. Products containing trichlorfon (Dylox) and carbaryl (Sevin) are faster acting insecticides and will kill grubs in 3 - 5 days. Bayer makes 24 Hour Grub Control which contains Dylox. Be sure to read label directions on white grub control products before purchasing. Treated areas should be watered to at least 1" deep before application of the chemicals and then after application another 1/2" of water should be applied. have already reached their full size, but it's not too late to make repairs.
Once the white grubs have been treated or removed you can then proceed with making repairs. If you have large damaged areas, slice-seeding may make sense. If areas are smaller, use a lawn rake or hand claw tool to scratch the surface of the dead grass. Loosen the soil with the claw. If necessary add a little additional soil / peat moss, reseed and keep evenly moist.
White grub prevention
Next year in late June or early July apply an application of MERIT following label directions or contact a local lawn care provider and order a Grub Prevention Treatment.
Threshold: 5-6 per sq. foot