The Diseases & Insects of Green Giant Arborvitae

Bagworm

• The bagworm is a tiny moth that feeds on and takes shelter in the green giant arborvitae. This dark-colored insect produces bags on the tree’s limbs and lays eggs on the tree during the early summer months. Though female bagworms cannot fly, the insect can produce thousands of eggs within the giant thuja to completely infect the tree during one growing season. Bagworm infestations can be controlled and eliminated by pruning away the egg sacs and treating the tree with an insecticide designed for arborvitae bag worm infections.

Shoot Blight

• Shoot blight is a mild fungal disease that infects the needles of the arborvitae. The disease is most aggressive when the giant thuja’s planting location is overcrowded with limited air circulation and sunlight. The weak and injured giant thuja is especially susceptible to this fungal disease. The fungal spores develop in the cool, dark areas of the arborvitae’s canopy and infect the tree. The infected needles turn reddish brown as they wilt, and the stems and branches become weakened and stunted. The infected green giant arborvitae takes on a blight appearance and can experience defoliation during severe infections. Shoot blight infections can be successfully treated with a combination of pruning and chemical treatments. The infected areas should be pruned from the tree with sharp, sterile shears that are sterilized after each cut. The densely foliated interior canopy should be thinned to increase the sunlight and air that flows throughout the tree. The tree should be thoroughly treated with a fungicidal treatment designed for arborvitae blight infections. Always apply the fungicidal spray according to the directions to prevent chemical injury.

Winter Injury

• The established green giant arborvitae is a hardy tree that can withstand cold temperatures and harsh winter elements. However, the young arborvitae, as well as the weakened or injured arborvitae, is easily injured by the winter’s cold temperatures. Winter injury results in brittle, dried out branches and stems, broken branches and stems, and discolored and defoliating foliage. Timely and proper care throughout the growing season helps to reduce the potential for winter injury.

Considerations

• The giant green arborvitae requires little care to maintain its healthy growth. Always keep the western red cedar’s planting area free of debris and defoliation, as this reduces the potential for infectious diseases. Remove weeds and other vegetation from the tree’s planting area to prevent competition for nutrients in the soil. Irrigate the young arborvitae regularly throughout the growing season to promote a good establishment. Place a 2- to 3-inch layer of mulch around the base of the arborvitae to preserve the soil’s moisture levels and protect the tree’s roots from injury during the cold winter months. Keep the mulch about an inch away from the base of the tree, however, to protect its roots from rot. This vigorously growing tree does not require fertilization. However, if you fertilize the green giant arborvitae, cease all fertilization treatments during the mid- to late-summer months to allow the tree’s new growth time to harden before the dormancy period.