White Grub Management

grub drawing

General Symptoms of White Grub Damage to Turfgrass


White grubs are among the most destructive insect pests of turfgrass. They feed below the soil surface on the roots and rhizomes of all commonly used turfgrass species and cultivars, and are capable of eliminating the entire root system of the plant. Where abundant, white grubs are capable of destroying large areas of turf in a short period of time.
turf damagegrubs
After hatching from eggs, white grubs begin feeding on the roots and underground stems of turfgrasses. The first evidence of injury is localized patches of pale, discolored and dying grass displaying symptoms of moisture stress. Damaged areas are small at first, but rapidly enlarge and coalesce as grubs grow and expand their feeding range. Turf in such areas will have a spongy feel under foot and can be easily lifted from the soil surface or rolled like a carpet, revealing the C-shaped white grubs underneath. Damage is most apparent in mid-August through early September when white grub feeding activity is greatest. Inadequate irrigation and drought stress may compound damage to turf by white grubs. Egg-laying females are generally attracted to vigorous, well-watered turf, and adequate moisture is essential for eggs to complete development. Once eggs have hatched, however, white grubs will feed on either drought stressed or well-irrigated turf. Several animals, especially skunks, raccoons, and moles, are highly attracted to turf insect infestations, and signs of their foraging in an area are strong indications of white grub activity. Flocks of birds, particularly starlings, feeding in the turf provide additional evidence of a possible infestation.
cutting turfcup cutter


Sampling Techniques
Sampling for white grubs should begin early in the predicted grub activity period, and before signs of injury are visible (once damage appears, considerable root injury will already be present). Since white grubs do not distribute themselves evenly throughout the turf, it is essential that the entire turfgrass area be sampled in a consistant, uniform pattern. Enough samples should be taken to assure a reasonably accurate estimate of white grub numbers in the sampled area. At each sample site, cut two 1/4 ft (6" X 6") sections of turf on three sides, peel back the sod and examine the upper 2 inches of root zone for the presence of white grubs. Examination is aided by shaking or breaking the sample, and by probing through the soil and roots with a sharp instrument such as a pocket knife or screwdriver. Turfgrass managers with access to a golf course cup cutter can substitute 4-inch (0.1 ft) diameter turf-soil core samples. If no white grubs are detected but damage is present, examine the turf for other causes of injury such as disease, excessive thatch, moisture stress, heat damage and/or sod webworm or billbug feeding.


Management Strategies
In most years, the first week in August is the optimum time to control white grubs in turf -- if sampling indicates that corrective measures are justified. At this time, most eggs should have hatched, and the small grubs will be feeding near the soil surface where they are more easily controlled. Damage from these grubs will not become apparent until later in the season when grubs are larger and the turf is stressed by hot, dry weather.


Treatment Guidelines
The following thresholds are estimates of the average number of white grubs necessary per unit area of turf to produce visible injury and are provided to assist the turfgrass manager in making treatment decisions. Remember that the condition of the turf, its value, and the damage caused by birds and animals searching for grubs, may alter these thresholds. In general, if white grub numbers exceed these thresholds in non-irrigated turf, an insecticide application is justified. Irrigated areas should be able to withstand substantially more white grub pressure before visual injury occurs. Treatment decisions should be based on average numbers of white grubs detected in the sampled area. If white grub numbers exceed threshold levels in only a few isolated patches, consider controlling these grubs with spot-treatments.

Grub Species Number/Square Foot Number/4-Inch Core
Masked Chafer 8 - 10 1
May/June Beetle 3 - 5 1
Japanese Beetle 8 - 10 1
Black Turfgrass Ataenius 30 - 50 3 - 5


Insecticidal Control
Effective chemical control of white grubs depends on moving the insecticide down to the root zone where the grubs are feeding. This is best accomplished by applying 1/2 to 3/4 inches of water immediately after application. Repeat irrigation every four or five days to continue moving the insecticide into the soil. This also keeps the crown and root area moist to encourage recovery of the turf. If conditions have been very hot and dry and grubs are deeper in the soil, a pretreatment irrigation of 1/2 inches applied 48 hours before the insecticide application should encourage grubs to move closer to the soil surface and enhance the level of white grub control.

Thatch plays an important role in reducing the efficacy of turf insecticides applied for white grub control. If the thatch layer exceeds 1/2 inch, a light aerification and increased post-treatment irrigation will enhance insecticide penetration and should improve white grub control. In many cases, some level of white grub activity will remain even after treatment. However, proper management should minimize damage from reduced infestations. Appropriate fertilization and watering to encourage a healthy turf will enable the grass to recover and reestablish in damaged areas. In some cases, a second insecticide application may be necessary to achieve an acceptible level of white grub control. This can be determined by resampling the area in question.

Entomology News at Nebraska

Breaking Entomological News...

  • Student working with a laptop for online degreeOnline students in the online Master's of Science (MS) degree program will benefit from a reduced credit-hour requirement and a reduced time requirement following changes by the UNL Graduate College and the Entomology Department. Starting next fall, students may earn an online MS degree for 30 credits, instead of 36 credits, under the Option B.  The new degree plan must be completed within five years, instead of 10 years.  More details about this change may be found on the IANR News website.
  • Dr. Gary Brewer
  • Dr. Gary Brewer, professor of Entomology has a new Push-Pull Strategy to manage Stable Flies.  These flies cause billions in economic losses for the US and the world. Brewer explains the Strategy on this YouTube Video. 
  • Annie KruegerAnnie Krueger, Ph.D. candidate in Entomology, was featured in the IANR Student Spotlight this week. Annie is from Stevensville, MD, and plans to graduate this August. She is mentored by Dr. Troy Anderson

  • Dr. Doug GolickDr. Doug Golick, associate professor of Entomology, received a $19,259 grant from the Nebraska Environmental Trust (NET) in April. He received one of 23 grants that were awarded to faculty at the University of Nebraska-Lincoln. Golick will study Milkweed as a teaching tool in the classroom. 
  • Dr. Autumn SmartThe Economics of Honey Bee (Hymenoptera: Apidae) Mgt. & Overwintering Strategies of Colonies Used to Pollinate Almonds,” co-authored by Dr. Autumn Smart, was chosen as a runner-up in the 2019-20 Readers' Choice Award for the Journal of Economic Entomology. Congratulations Autumn!
  • Matthew GreinerMS student Matt Greiner (mentored by Ana Vélez) was awarded 1st place in the student paper competition at the recent Ozark-Prairie SETAC meeting. The victory will provide him with funds to attend the national SETAC meeting in November. Way to go, Matthew!