Across the corn belt depending on time of year | A single large size of white grub in late October indicates one of the annual white grub species. It could be Japanese Beetle, European Chafer, Asiatic Garden Beetle or Oriential Beetle. They also could be one of the native June beetle species. To tell them apart, you have to look at the hair pattern on their anus (seriously). You can find images on the web to tell the species apart. According to my former colleagues in Michigan, it is likely Asiatic Garden Beetle.
With all of these annual white grubs, eggs are laid in grassy areas (runout alfalfa field has lots of grass) in August and the larvae feed until cold soil conditions when they go deeper in the soil to overwinter. As the soils warm in the Spring (May), the large larvae move up into the root zone of plants and finish feeding before pupation in late May-early June. Adults emerge in June thus the name "June Beetle". The large larvae in the spring do the most damage due to their large size. Generally speaking, the last larval stage does 80% of the damage.
Seed treatments generally have little impact on the large white grub larvae as do most soil insecticides. So, what do you do? 1) Plant soybeans as late as possible (early June) with the hope that most of the feeding has been finished on the remaining wheat. 2) Plant corn and use a soil insecticide in the row (not bifenthrin, but something like Counter, Aztec). 3) Suffer the damage and hope for the best.
Next time, kill out the alfalfa sod in Mid August and then plant wheat as late as possible.
Edited by Nematotode-guy 10/28/2025 10:37
 (grub hair patterns (full).jpg)
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