A Root Feeding White Grub Is Eating My Geranium Roots

Identification

• The Fuller rose beetle (Naupactus godmanni) is also known as the Fuller rose weevil and infests a variety of ornamental plants, including geraniums. The larvae of the weevil are white grubs and live within the soil, overwintering and feeding on the roots of the geranium. Both adults and larvae cause damage to the plant, but the adult beetles tend to focus on making a meal out of the foliage while the immature beetles remain true to their affinity for the roots.

Features

• The legless, white grubs have a yellow head and grow to approximately 1/2 inch in length at maturity, while the adult beetle is brownish-gray in color with a patchwork of white scales. It grows to near 1/3 inch long. Gardeners eager to monitor their geraniums for the presence of eggs should look for yellow, cylindrical masses that are covered with a white, sticky material and laid on cracks in the bark or on leaves.

Damage

• Young, white grubs normally feast on the outer surface of young geranium roots, while older grubs are attracted to older roots and stems. The feeding may girdle -- strangle -- the plant, as the roots are unable to properly uptake water and nutrition from the soil. Mature geraniums will suffer a decline in vitality and immature plants may be killed. The damage to the root system is especially problematic if it occurs during a time of drought.

Management

• Management of the Fuller rose beetle begins with closely monitoring the plant for the appearance of eggs and then destroying them. Adults should also be destroyed; they can be removed by simply shaking the plant to force the weevils to drop onto a cloth. As the beetle is not active during the day, this technique should be undertaken late at night or early in the morning. The soil should also inspected for the presence of the white grubs; they may be removed by hand.