Grubs on the march

White grubs may be the most damaging turf insect pests in the United States. According to the U.S. Department of Agriculture, Japanese beetle grubs alone cause an estimated $234 million in damage each year - $78 million for control costs and an additional $156 million for replacement of damaged turf.

White grubs are the larval stage of a group of beetles that includes hundreds of species. However, less than a dozen of these account for nearly all the significant damage to turf. When grubs are present, the population may consist of just one species, though frequently two or three are present.

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The damaging grub species include a mix of introduced "alien" types and native types. The native types tend to be more widespread, but the introduced species, where they occur, are often more damaging. The introduced species are spreading, but slowly. The exception is the Japanese beetle, which has now invaded large parts of the Midwest from its Northeast stronghold. Because of its destructiveness and ability to spread, the Japanese beetle is the target of substantial regulatory efforts to stem its expansion.

Native species Native grub species include such well-known types as Northern and Southern masked chafers, May and June beetles, and the black turfgrass aetenius (BTA). These are widespread and damaging in many regions. The BTA seems to have become a more serious problem since the 1970s, for reasons that aren't entirely clear.

Introduced species Introduced grubs include the notorious Japanese beetle, as well as the Oriental beetle and the European chafer. The ranges of these species are gradually expanding, but all remain primarily pests of the Northeast. Only the Japanese beetle has significantly extended its range westward.

Mole crickets are not grubs, obviously, but they are the most important turf soil pest of the Southeast and Gulf Coast states. And like some grub species, they (at least the damaging species) are non-natives. The two most important species, the tawny mole cricket and the Southern mole cricket, are now present in all coastal states from Texas to North Carolina, and now even southern Virginia. Both were intially introduced to Georgia. They damage all warm-season turfgrasses, but especially bermudagrass and bahiagrass.

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