Pest
Two kind of grubs cause economic damage to Michigan lawns:
European Chafer (Rhizotrogus majalis)
Japanese Beetles (Popillia japonica)
Symptoms
Browning and dying sod causing bare spots on lawn. Maturing grubs feed on grass
roots in the spring and fall reducing water uptake. When pulled the sod comes off
easily without roots. Frequently irrigated turf is able to withstand grub damage to
some extent. Grub damage is often confused with salt damage near walkways and
fertilizer burn. Grubs attracts birds, moles, skunks, and raccoons to lawns.
Grubs undergo complete metamorphosis. The adults lay eggs on the soil surface in
June/July. The Japanese beetle adults prefer to lay eggs in irrigated turf. European
chafer adults lay eggs in both irrigated and dry turf.
Life Cycle
The grubs emerge in July and continuously feed on grass roots until November.
After a brief inactive period in the winter, feeding is resumed in March of the
following year. Grubs complete their feeding in May. After a brief hibernation
period as pupa, adults emerge in June/July. The adult Japanese beetle is a voracious
feeder of foliage of many ornamental plants whereas the European chafer adults are
not a plant pest.
Adult Stage identification is easy
Grubs stage need a magnifying lens.
Pest
Management
Refers to the application of all available strategies that are effective, economical and
environmentally friendly.
Keeping the grass healthy by applying BMP’s, (timely irrigation,
fertilization, mowing and thatch management ) helps the lawn to withstand
grub damage
Scout for grubs and count the number per square foot of sod
For medium to low maintenance lawn the economic threshold is 5
grubs/sq.ft. For irrigated turf, the threshold is 15-20 grubs/sq .ft.
Do not use Japanese beetle traps for control
Grub control does not automatically prevent mole damage.
Tall fescue lawn varieties are less susceptible to white grub damage
Consider options for pesticide use and spot treat.
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