White grubs (Phyllophaga and Polyphylla species)
PDF version of Grubs - Facts at a Glance (with photos)
Where from: Native to US
Host plants: Grasses, many other plants
Symptoms: Seedling decline, death. Loss of small feeder roots.
Life cycle:- How overwinters: As a grub in soil
- Number of generations per year: Depending on species and elevation, one generation can take as long as 3 years. Adult females lay eggs from June through August, depending on species, which starts a new generation.
Cultural practices: Beetles prefer to lay eggs in short grass. Leaving taller grand covers discourages eggs from being lain. Ground covers provide food source for grubs and they do not feed on tree roots.
Scouting: Grubs are C-shaped with dark tip to abdomen. Do pre-plant scouting for grubs in the summer or early fall by digging holes in soil and sifting through the dirt to find grubs. Identify grub using raster patters which are the pattern of hairs on the underside of the tip of the abdomen. Ohio State University has a good website on raster patterns. Grubs that 'crawl' on their backs when put on the soil surface are Green June beetle grubs and don't feed on tree roots.
Control considerations:- Grubs are difficult to control once trees are planted. Scout before planting to determine if grubs are present, especially when planting into old pastures.
- When planting into fields with grubs, dip seedling roots in bifenthrin to prevent grub feeding.
- When apply insecticides in planted fields, apply right before gentle rain. Only treat after soils have warmed and grubs are closer to the surface of the soil.
