WHITE GRUBS and FLOWER FEEDING SCARABS: several species, Scarabaeidae

ADULT: White grub adults are robust, oval with rounded backs, and dull reddish-brown (June beetles) to shiny black (sugarcane beetles) in color.  They range from 1/2 to 1 in. long.   Legs often have spines at the end of the fourth segment (tibia) and their last tarsal segment consists of two prominent, curved claws.  Flower feeding scarabs are brightly colored with copper and green with light colored patches along the margins of abdominal segments.  Their bodies are widest at the thorax and are more flattened rather than rounded.

EGG: Eggs are deposited in soil.

LARVA: C-shaped, white, soft bodied larvae have a dark rounded end on their abdomen. They differ from moth larvae by having three pairs of well developed, hardened true legs and no prolegs. They have a hardened brown head with opposing mandibles. They feed in soil on roots. Larvae may take nearly one to several years to complete development.

PUPA: Larvae pupate within a cell below the soil surface. They appear as pale immobile adults. Adults emerge in 3 to 4 wk.

GENERATION TIME: One to several years.

DAMAGE: While white grubs (larvae of June and sugarcane beetles) are the stage attacking corn roots, it is the adult stage of flower feeding scarabs that attack corn ears. White grub populations are usually much greater in fields following green cover crops and sugarcane.  Plants may be severely damaged or stunted by root-feeding white grub larvae. Stand reduction can result from large infestations. Yields may also be reduced by lodging.  Flower feeding scarabs are attracted by milk stage corn.  The beetles push their way into the ear through the silk canal or gain entry through armyworm and earworm entry and exit holes.   They also feed on pollen directly from the anthers or deposited across the plant surface.  These beetles are more of a problem in central and northern Florida, but can cause damage to late spring sweet corn in southern Florida.

CONTROL: White grubs suffer from several fungal diseases.  Birds and disking kill many of the soft-bodied white grubs exposed during field preparation.  Rotation through a cycle of rice has been shown to eliminate the need for white grub treatment in the subsequent crop.  Summer flooding of fields is an effective cultural control, providing it is maintained for at least several weeks.  Birds also feed on the flower-feeding beetles in corn, but this is more of a serendipitous encounter as the birds are usually more interested in feeding on corn kernels.  There are no pesticides specifically labeled for flower feeding scarabs in Florida corn. Pesticides for white grub control are available for pre-plant broadcast and at-plant treatments. Formulations, rates, and pre-harvest intervals of insecticides labeled for white grub control in Florida are listed below for sweet corn (Table 1) and field corn (Table 2).