What causes webs to form on evergreen shrubs?

1 ANSWERS

1. jane
   

   Evergreen shrubs are often used in residential landscape. They are different than trees in that they tend to be lower in height and have multiple stems. Evergreens include pine, spruce and juniper. Trees and shrubs are susceptible to many diseases. Conifers are especially susceptible to canker, needle cast, wilt and blight. Descriptions of each of these diseases are provided below
   
   Spruce Canker
   Spruce can be attacked by three types of canker with Cytospora sp. being the one that does the most damage. It is the number one killer of the Colorado blue spruce. It only occurs on a spruce when it is not grown in its native range. All branches must be cut back without injuring the bark. Shrubs should not be pruned, and adequate water and drainage should be available. Fertilizing the shrubs may help.
   Pine Canker
   Pine can be attacked by several cankers, including Botryosphaeria dothidea, Sphaeropsis sapineas, Leucostoma sp., Valsa sp. and Scleroderris. These all tend to form on stressed plants. Some of the canker types will cause the plant to bleed heavily and some will not. To control canker, the plant should be kept growing well and long-term stress factors should be minimized. Long-term stress factors can be controlled by pruning dying and dead limbs, making sure that the plant receives enough water during a drought and feeding the plant in the fall.
   Needle Cast of Spruce
   Needle cast is caused by a fungus and usually occurs on a spruce that is grown outside its natural habitat. Of the spruce, the Colorado blue is the most susceptible and the Norway spruce the least. The fungus may attack any size plant but the smaller plants are most likely to be attacked and die from infection. To control the disease, the use of fungicide may be needed. When fungicide is needed, the treatment will need to be done two years in a row. Otherwise, providing good air circulation, avoiding overhead and night watering, and removing and destroying all infected needles will help control the disease.
   Blight
   This disease occurs on many pines and other conifers. The fungus tends to attack trees 30 years and older. However, seriously stressed young trees can also be attacked. This disease causes needles to die prior to reaching full length and can cause cankers. All affected twigs and cones have to be removed. Fertilizer should be given to stunted trees and fungicide use is recommended.
   Pine Wilt
   This disease is caused by the pine wood nematode. The nematode by itself can cause a tree to die, and in association with bacteria, will cause the vascular tissue to plug, also killing the tree. Scots pine is the most susceptible and eastern white pine the least. Diseased and dead evergreens must be removed as fast as possible to control wilt.

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