Wednesday, September 12, 2012

Spruce Trees Giving You Worries?


This is about the time of year when we at Trees "R" Us, Inc. start to get calls from homeowners that are concerned with their browning spruce trees.  Spruce trees are a very popular landscape feature, whether they are large specimens or shrub-sized dwarf cultivars in a garden. However, when the foliage starts to turn brown, it can cause some concern.

The questions we seem to get the most of are:
~Is some browning normal? 
~Will it spread to other parts of the tree or to other spruces nearby? 
~Will my spruce die? 
~More importantly, if it does have a disease or insect problem and what can I do about it?

There are a number of pests and diseases that can cause trouble for spruce. Here I’ll describe some of the most common problems. Pests that will be covered include spruce spider mite, spruce gall adelgids and white pine weevil. I"ll also touch on two common diseases for spruce trees, Rhizosphaera needle cast and Cytospora canker.
Browning of tender new growth in the spring can be caused by a hard overnight frost. Winter injury can cause browning when there is a loss of moisture from the needles on windy sites or during a mild spell. To prevent winter injury, water deeply late in the fall if it has been dry. Small spruces near buildings that reflect heat can be protected by wrapping them loosely in burlap or placing a screen between the tree and the building.
Spruce spider mites feed on needles by inserting piercing and sucking mouthparts (like tiny straws) into the tissue and withdrawing cell fluids. This results in tiny yellow to brown spots on the needles that create a “stippled” look. From a distance, the foliage may look bronze to brown.
Damage is more severe on drought-stressed trees. Spruce spider mites are most active during cooler weather in spring and fall, but the browning may not occur until weeks or even months later. By mid-summer, the mites are inactive but you can look for signs of their activity which include webbing or tiny black bits of frass (excrement) on the needles. These are most easily seen with a good magnifying lens.
To check for spider mites when they are active - and this is a highly scientific method;) - hold a stiff white paper (a paper plate works well) below a branch and firmly tap on it a few times. If mites are present, they will fall onto the paper and be visible as very tiny, slow-moving dots. If you check several branches and find 10 or more mites per branch, treatment is recommended.
A strong stream of water or even a heavy rain will dislodge many mites. Horticultural oil can be applied as a dormant oil to target the eggs or as a summer oil in early May and/or early September. Horticultural oils can diminish the blue color of Colorado blue spruce.
Several insects cause interesting galls to form on spruce. These are usually just a curiosity or aesthetic problem and seldom affect the health of the tree. Symptoms include curled or deformed older twigs and dead needles beyond the gall. Adelgids cause swellings that include the needle bases; after adult adelgids emerge they look like tiny brown pineapples. Midges cause similar galls but they do not include the needle bases.
If control is desired, remove young green galls by pruning. Bag and dispose of them in the trash because the insects will continue to develop on the clipped twigs. A dormant oil can be applied in late fall.
If the terminals shoot up to a few adjacent whorls of branches that wilted, drooping or dead and no other branches are affected, the white pine weevil is a likely suspect.
Spruces less than 20 feet tall and growing in an open, sunny location are most susceptible. Larvae feed under the bark of the stem during May through early July then form cocoons on the host tree. Clip off and dispose of the attacked shoot(s) before mid July when the adults emerge. Remove any larvae by pruning just below the junction of live and dead stem tissue.
Insecticides are not usually recommended. When the terminal shoot is removed from a young spruce, one or more of the lateral branches will take over as the new main stem.
Browning or dying lower branches on spruce can be caused by Rhizosphaera and other needle cast diseases. Colorado blue spruce is most susceptible to Rhizosphaera.
Symptoms typically begin on the lower branches and the older needles will become brown first, while the current year’s needles remain green. The interior of the tree may be sparse or bare. The older infected needles may have a purplish cast. Check browning needles for tiny black fungal fruiting bodies in the rows of white stomates (pores) on the needles with a magnifying lens to confirm this disease.
Management recommendations include promoting good airflow around the lower branches by allowing for plenty of space around the tree as it grows, mowing under the tree, and pruning lower branches.
Good airflow promotes rapid drying of the needles after rain or dew formation which reduces fungal infection. Infection can only occur when a film of water is present on the needles. Prune diseased branches to remove sources of spores that will cause new infections on adjacent branches. Fungicides can be used preventively and should be applied in the spring when new growth is half elongated and again when fully elongated. When using pesticides, always read and follow the label instructions carefully.
If browning and dying branches are occurring at various locations on the tree, the problem may be Cytospora canker. Look for cankers at the base of dead twigs and branches by checking for whitish, resinous sap. Colorado blue spruce is very susceptible.
To prevent Cytospora canker, minimize tree stress by using good cultural practices. Plant spruces in sunny sites with a well-drained soil and avoid crowding. Avoid wounding the branches and trunk. Prune any infected branches during dry weather in late fall. Sterilize the cutting tool between each cut by dipping or swabbing with 10 percent household bleach, 70 percent alcohol, household disinfectant or a product made for this purpose to avoid spreading the disease.
While nothing is foolproof, the best thing you can do to help minimize losses due to insect and disease problems is to maintain healthy trees and shrubs and avoid wounding them, both above and below ground. Plant them in a site they are well suited for and have the soil tested if there is a concern about the soil pH or fertility.
New spruces should be planted at the same depth they were in the nursery. Planting too deeply is a common cause of failure or stress in newly transplanted trees and shrubs. Water regularly to supply one inch of water per week (including rain) for the first two seasons. It is better to water deeply a couple of times a week than light watering daily to promote healthy root development.
Success in controlling pest and disease problems once they occur is much more likely if the problem is discovered early. With this in mind, keep an eye on your landscape plants and try to notice wilting, browning or dieback in its early stages. This minimizes damage and can reduce the need for chemical pesticides.
For more information on the care of your spruce trees or other plants contact Trees "R" Us, Inc. at 847-913-0669.


Trees "R" Us, Inc. is a professional tree service in the Chicagoland area.  We service the north shore, north suburbs and northwest suburbs of Chicago.  Trees "R" Us, Inc. has 4 certified arborists on staff ready to assess your plants and tree care needs in a timely manner.  Our services include tree trimming, pruning, stump grinding, emergency tree services, tree removal, cabling and bracing, fertilization and plant health care.

Trees "R" Us, Inc. can be contacted at 847-913-9069 or through our online forms at www.treesrusinc.com.

Thanks for reading,
Nick
nick@treesrusinc.com

No comments:

Post a Comment