When searching for below-ground pests, a small garden trowel or pocketknife is a handy tool to use. Early season insects can be found attacking the seed (seedcorn maggot, seedcorn beetle), the seed and below-ground parts of the seedling (wireworm, sugarcane beetle), they may be more limited to the roots (white grubs), or attack the under-ground stem (sandhill cutworm). White grub is a generic term for the larval stage of insects like the Japanese beetle, rose or sand chafer, and May or June beetles. True white grubs are the larval stage of May and June beetles. To identify the grubs, the raster pattern, or the setae (hair) pattern on the posterior end is used. Michigan State University has developed an excellent publication, Severe Grub Damage Spotted in Northern Michigan Hay field, that can be used to help identify white grubs in the field. Follow this link, https://www.canr.msu.edu/news/severe-grub-damage-spotted-in-northern-michigan-grass-hay-field to access the Field ID Sheet.
Corn rootworm larvae may be present during the later stages of early season growth but may be too small to readily detect. If detected, they will have a brown to black head and a brown to black anal plate.
Some of these insect pests feed above-ground but can also be found under-ground. The cutworm species feed above-ground at night but spend the day under soil clods.