By Beth Berlin, U of M Extension
Many lawns in Minnesota are subject to and will end up seeing damage caused by white grub populations this summer. But, do you know which type of grub you are dealing with? Heavy white grub infestations can destroy grass roots, causing dead patches of grass and allowing the sod to be rolled back like a piece of carpet.
White grub is a general name for the larval stage of beetles in the scarab family, which includes almost 10 different types of beetles whose larvae feed on the roots of turf grass. Larvae in the scarab family are c-shaped, soft-bodied and have six legs located under an orange-black colored head. Size of the grub will vary depending on species and age.
It is important to correctly identify the species of grub found in your yard if you want to implement effective control methods. With minimal differences in the appearance of these grubs, it can be hard to tell which species you will be dealing with. However, the color and form of the adult beetles are distinctive, which makes species identification easy.
The May/June beetle is a very common pest in Minnesota. The adults are usually 1 inch long, chestnut brown in color and they tend to fly near lights in early summer. Adults lay eggs in turf grass in early to mid-summer. Their larvae are the largest grubs found in turf, measuring ½ to 1 inch in length. These larvae will cause irregular patches of yellow or dead grass around the lawn.
Unlike other white grubs with one-year life spans, May/June beetle larvae will grow for three years before reaching adulthood. The damage caused by larvae will become more apparent each year, and is especially apparent in late July through early August. Using an insecticide is an effective way to control this specific species of grub, and is recommended if there are more than 4 grubs/sq. ft.
Northern masked chafers are another beetle in the scarab family that can be found in Minnesota during the summer. Adults are shiny brown with a dark mask around their head and usually measure 1/2 inch in length. Their larvae feed on roots which separates the crown from the roots, causing drought stress later in the summer months. Healthy turf can tolerate over 20 grubs/sq. ft. However, birds, skunks and raccoons commonly dig up dirt around areas with heavy infestations. An insecticide can be used to control this species of grub as well.
The effectiveness of control methods largely depends on the species of white grub you are trying to eradicate. It is also important to note that treatments in the fall will not be effective because grubs move further down in the soil as winter approaches.
For a complete list of lawn and turf insects and specific control methods for multiple root feeding grubs, visit the University of Minnesota Extension website. http://www.extension.umn.edu/garden/insects/find/lawn-and-turf-insects/root-feeding/.