True White Grub & June Beetle Update Back »

Written collaboratively by Adam Varenhorst, Mike Dunbar, Patrick Wagner, and Amanda Bachmann.


Throughout South Dakota, there are continued reports of grub injury in pastures and rangeland. After visiting additional sites, we observed that nearly all of the true white grub populations are currently in their adult form (May or June beetles). June beetles normally move from the lower soil horizon towards the surface as air and soil temperatures warm up. We found beetles in the root zone of the grasses, just below the soil surface. Within the next couple of weeks, adults will emerge, mate, and females will lay eggs in areas with grassy cover.

Life Stage Determination & Identification

To determine the life stage of any true white grubs presently in your pasture or range, dig up a one square foot area approximately 6 inches deep. Sift through the removed soil to determine if grubs are present. At this point in the season focus on the grass matt, especially the roots. Break the roots apart gently and carefully search for beetles or grubs (Figure 1).


Figure 1. To scout for true white grubs or June beetles, use a spade or shovel to dig a one square foot hole. Remove the soil and grass mat and search for grubs and adults. Photo by Adam Varenhorst.

For identification guidelines please refer to a previous article on true white grubs.

Species observed so far this year are large and vary in color from light to dark red-brown (Figure 2). Their legs tend to be a slightly lighter brown color, and the underside of adult beetles have light brown legs and a tan layer of hairs on their lighter colored undersides. Emerging adults are nocurnal but are still attracted to yard lights and porch lights. Due to their large size they are clumsy fliers, and often inadvertenlty come into contact with humans around these areas.


Figure 2. Adult June beetle. Photo by Adam Varenhorst.

Fall Scouting & Assessing Future Risks

Due to the majority of samples being composed of adult beetles, scouting efforts this fall will be critical to determine the population of first year true white grubs in pasture and rangeland, including previously injured areas. To address this potential problem, SDSU Extension personnel will continue to monitor June beetle and true white grub populations. To assist us with these efforts, please contact Adam Varenhorst 605.688.6854 if you have grub issues in your pasture or rangeland, or if you are observing large numbers of June beetles.


References:

  • Varenhorst, A., M. Dunbar, and E. Hodgson. 2015. True white grub identification and management. Integrated Crop Management News. Iowa State University Extension.
  • Chirumamilla, A., A. Bachmann, and P. Bauman. 2015. Grubs in pastures. iGrow. South Dakota State University Extension.
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