From the Pests of Ornamental Series
Yew (Taxus) is one of the most popular evergreens used in landscaping. The homeowner can choose, from its many varieties, an upright, hedge, low-lying or a slow-growing type of plant. All forms are free from serious infectious diseases, but certain planting sites and soil types, as well as a few insects may cause trouble.
Dead Branches and Tips
Large or small branches on the yew will not tolerate much injury. Bark removed from as little as one-third of the circumference of a branch may cause the branch to die from that point all the way to the growing tip. Plants growing close to a building are often damaged by snow and ice sliding off the roof. When this occurs, tender bark on smaller branches may be injured. The injured branches and twigs do not die immediately, but dead tips will start to appear the following summer.
A tag attached to a branch with a wire may prove to be a real problem in years to come. If the tag is allowed to remain on the plant, the wire may girdle or constrict the branch after several years. Large sections of plants have been lost in this manner. Therefore, when plants are bought, all tags should be removed from each specimen.
General Yellowing of the Entire Plant
In many cases, yew plants are set out along with members of the heath family, such as laurel, rhododendron and azalea. Yew plants will thrive in a sweet or neutral soil with a relatively high pH of 6.0 to 6.5. Laurel, rhododendron and azalea, however, grow better in a more sour or acid soil with a pH of 4.5 to 5.5. It is difficult to fertilize laurel, rhododendron, and azalea with an acid-type fertilizer, made especially for these evergreens, and prevent it from coming in contact with the yew roots. The best that can be done is the application of the special fertilizer for broad-leaved plants on the entire area and then add ground limestone around the base of yew plants. Three pounds of limestone per 100 square feet of soil area is applied around yew plants and the treatment is repeated every third year.
Normal Needle or Leaf Drop
It is natural for all evergreens to lose inside foliage each year. In late summer or early fall, yew needles that grew 3 to 5 years ago will suddenly yellow and remain on the bush for several weeks before dropping to the ground.
Too much water around yew roots may cause plants to die or grow poorly. If a poorly growing plant is dug up; examine its root ball. If all roots on the lower part of the root ball are dead and the few living roots are those nearest the soil surface-wet feet is the problem. Such plants are usually found in poorly drained soils, at corners of buildings near rainspouts and in areas over-watered by the homeowner.
Corrections can be made by connecting rain spouts to an underground drainpipe. Over-watering of plants should be avoided. Poorly drained soil, however, presents a more difficult problem. If a yew is transplanted into this type of soil, a shallow basin is better than a deep hole. The bottom of the root ball should be placed not more than 8 to 10 inches below the soil surface. The soil around the ball should be mounded up to the lower branches. During an extended drought, water is needed for the plant, but it is easier to do this than eliminating water from soil that is too wet.
When the yew is planted as a hedge on a sloping area, wet feet usually appears first at the lower end of the row.
Shoestring Root Rot
When new home developments are built in areas previously occupied by an apple orchard or by a forest with oak trees, shoestring root rot may develop on yew plants. The fungus that causes this disease may live on the old apple or oak roots for a number of years before attacking yew, rhododendron, or other foundation plants around a building. If a plant dies in such a location, the bark should be peeled off at the soil line, inspecting the larger roots, where they are attached to the stem. Black, rather brittle "shoestrings" may be found. They are somewhat similar to small roots except they maintain the same diameter for their entire length. Also, where the shoestrings cross each other, they fuse or grow together. When one of these shoestrings is split open, the inside appears to be a mass of white cotton pressed together.
If shoestring root rot is found on yew or other plants, they should be replaced with any narrow-leafed evergreen, except yew. Homeowners have been successful in getting rid of this disease by removing all diseased plants and soil to a depth of 8 to 10 inches and then filling in the area with soil free from this fungus and setting out disease-free plants.
Taxus Weevil Injury
The taxus weevil is the most serious insect pest of yew. This insect lives in the soil as a small white grub, feeding on the larger roots. In June, the dark-colored adult beetle comes out of the soil at night and chews notches in the needles, especially near the base of the plant. Feeding by the adult beetle does no serious damage but serves to indicate attack by grubs. Other symptoms of attack are wilting and yellowing of the foliage during hot, dry summer months.
Mealybugs and Scales
Several sucking insects occasionally attack yew or taxus. Mealybugs are small, slow-moving, white insects that gather together on the stems. Scale insects are less conspicuous, brown in color and remain in one place during their entire life.