The Globe Willow is common in the Grand Valley of Western Colorado, Moab Utah, Farmington, New Mexico and other areas of the Southwest where mild winters are the rule. This round-headed willow is commonly known as the `Globe Willow' in Western Colorado because of its characteristic shape. In other parts of the nation, this tree is known as the `Navajo' willow. In addition to the confusion existing between common names, the scientific names are equally confusing. The J. Frank Schmidt Nursery of Boring, Oregon uses the botanical name, Salix matsudana `Navajo' as its cultivar identification. This tree has also been sold under the name Salix globosa.

Salix matsudana `Navajo' is an Eastern Asian species of willow, closely related to the cork screw willow (Salix matsudana `Tortuosa'. Although it is not truly known how this tree first arrived in Western Colorado, rumor has it that this tree was a selection from a wild willow growing on the Navajo Reservation near Aztec, New Mexico. Years before any commercial nursery began carrying this tree for sale, mass plantings of this tree could be found in the Farmington, New Mexico area. Bob Ludekens, President of L.E. Cooke Co. (www.lecooke.com), informed me years ago this tree was grown and promoted by a Mr. Tom Bolack at his B Square Ranch near Farmington.

This tree is a round-headed upright branching, fast-growing tree that may reach 50 feet or more in height. It has slender green leaves and is said to be a very tough and hardy, and long-lived tree adaptable to a wide range of soil conditions, including deserts. However, the multitude of insect and diseases this tree is susceptible to makes one wonder if that statement is anywhere near correct.

The tree's branching habit results in its globe shape. Multiple branches normally grow from the trunk, often starting at a height of 4 to 5 feet giving the topiary effect desired in many oriental gardens. From a distance it looks like these trees have been sheared into a perfect globe on a slender stem. These trees, however, are genetically designed to produce that shape.

The Globe Willow is well known for its fast growth, its beautiful deep green color, and its characteristic globe shape. It is also know in the nursery industry in the Grand Valley as a very troubled tree. Some of the well-established nurseries guarantee their globes at least as far as the nursery's main entrance. Gardeners should carefully consider if, when, and where to use this tree in the landscape.

Frothy Flux

Frothy Flux is different from the Bacterial wetwood (slime flux) seen afflicting many other hardwood trees. Frothy flux (see image) is contained to the layers of cells immediately adjacent to the cambium, while the true bacterial wet wood, found in elms, ash, hackberry and many other hardwood trees, is in the heartwood of the tree, deeply buried under many years of tissue. The term "froth flux" is used here to avoid any confusion that may occur with the true "slime flux" disease. Dr. Emroy Shannon, Extension Plant Pathologist, New Mexico State University, feels that "frothy flux" is not caused by a true pathogen, but is the result of a yeast or other saprophytic or secondary organism that invades the tree through a wound, causing the fermentation of the plant tissue.

Frothy Flux invades young as well as old trees, killing the cambium and contributing to the tree's death often within a few short years. The organism - - not yet positively identified by researchers at Colorado State University (or any other university to my knowledge) - - in addition to invading the tree through freeze injury, may gain entry through pruning wounds, insect damage, or mechanical injury caused by lawn mowers, weed whips, or other devices. Once gaining entrance to the cambium layer, the fermentation of the bark cambium and inner sapwood layers of the tree occurs. This results in a froth that exudes through cracks in the branches and trunk of the tree at the site of attack.

Frothy flux often invades the tree in a branch crotch that has cracked or split. The growth habit of the Globe Willow is such that these branch attachments are naturally weak and prone to splitting in high winds and during late spring snow storms. Snow damage is increased due to the tree's tendency to leaf out earlier than many other trees.

Early Spring Green-up of the Globe Willow

Globe willow are usually planted in lawn areas where they receive an abundance of water and fertilizer late into the fall. This may keep the tree from properly acclimating for winter, resulting in increased winter damage including the development of cracks. A tree "hardens" from the tips of the branches back toward the trunk. When numerous branches originate at or near the same point on the trunk, it takes an extended period of time before that area properly "hardens". These non-acclimated areas are especially susceptible to winter injury.

The lack of rapid and proper acclimation also may help explain why there are very few successes with the Globe Willow on the Front Range (the Eastern plains of Colorado), and many other parts of the nation. This tree does not appear to be able to withstand sudden changes of temperature, or the limb- breaking storms that are common in many areas.

In some instances, frothy flux invades larger branches and trucks, containing itself under the bark and does not cause the typical frothing ooze seen on many of the younger smooth bark trees. The first symptom of infection for these older trees is not the foam, but the yellowing of the leaves and dieback of the branches immediately above the affected site. When tapped with a blunt instrument like the handle of a knife, hammer or screwdriver, one often hears a hollow sound in the affected area. When digging into the area with a heavy knife, one finds the ooze typical of frothy flux just under the bark, often encompassing large areas of the cambium and sapwood.

Larger, reasonably healthy trees seem to outgrow the problem. A weaker tree may have frothy flux for a year or two; the problem may seem to go away for a year or two; and then the problem reappears. Improving the health and vigor of the tree helps reduce the chances of the problem becoming severe.

The common recommendation for eliminating or helping solve the frothy flux problem on Globe Willows is to remove all damaged, decaying tissue down to the wood and as far back as necessary to eliminate any brown or yellowish streaking of the cambium or sapwood. This area is then swabbed with alcohol and a coating of amber shellac put on the wound in hopes of retarding any further `infection' of the area. This treatment is only advised when the disease is in a small area of the tree.

Borers

Quite frequently, gardeners find borers in their Globe Willows, confusing the borer problem with the froth flux problem as both often appear on the tree at the same time. At this stage, no one know which comes first. However, it appears that a wound occurs first, the frothy flux organism colonizes the wound, and borers invade after the tree has been further weakened. The borer found in the Globe Willow is usually the white grub-like larvae of a flat-headed wood borer.

In addition Nitidulid larvae approximately 1/4 inch long are frequently observed feeding or congregating in the flux. These insects are common sap- feeding beetles found on many plants oozing sap.

It is possible that Nitidulids transmit Frothy Flux from tree to tree but this insect is generally considered a problem secondary to Frothy Flux. Due to the presence of Nitidulids, as well as a host of wasps, ants and borers attracted to the ooze, gardeners have the mistaken belief that the problem with their tree can be corrected with the application of an insecticide.

Cytospora Canker

Cytospora canker, a fungus disease troublesome to all members of the willow family, is particularly devastating to Globe Willows that are under stress. Stress may be caused by too little water, too much water, compact soil, plastic over the roots, and many other factors. Cytospora canker (Cytospora chrysosperma) frequently kills the smaller branches and twigs and spreads into the larger branches and even trunks of stressed trees.

To correct a Cytospora canker problem, all the diseased wood needs to be cut out of the tree. Fertilizing the tree at least once each spring with a nitrogen based fertilizer and providing adequate and proper water will help alleviate stress and reduce Cytospora canker problems. Further information on Cytospora canker can be found in the fact sheet on Cytospora Canker.

Aphids

In spring and again in fall, giant willow aphids (see image) are seen congregating on the smaller branches and twigs of Globe Willows. As these insects feed they exude honeydew that drips on leaves and any structures or people unlucky enough to be underneath the aphid-infested tree. The use of an insecticide containing imidicloprid is quite effective on these aphids and should eliminate the honeydew and sticky problems created by these insects.

Other Insects plus Mites

Miscellaneous insects - - such as tent caterpillars, horn worms, katydids, and the occasional grasshopper - - are best controlled with insecticides like Malathion when needed. Kelthane can be used to control the two-spotted spider mite and European Red Mite that in some years are serious on willows.

The use of systemic insecticides, such as disyston, to control aphids, tent caterpillars and other insects in these trees, should be avoided except in those rare instances where recommended and applied by a commercial licensed pesticide applicator.

Culture

When selecting a Globe Willow, purchase one that has a tall, straight center stem. The Globe Willow has a tendency to develop a head that has weak branch attachments (upright), with many branches coming off the trunk at the same spot. Gardeners and nurserymen alike should try and maintain a central leader on their Globe Willows. In other words, the central stem should not be cut, but encouraged to continue its upward growth. This will result in a tree that has branches that originate from the trunk at many points along that central leader, instead of all the branches being at the same level.

The stress of transplanting may result in die-back of the central leader. If that occurs, a branch arising just below the dead portion can often be bent up to serve as the new central leader. Everything possible should be done to maintain a healthy tree. Die-back will be less of a problem on a well-maintained tree.

Globe Willows prefer a well-drained organic soil but are said to tolerate poor soil conditions. This tree appears, however, to need adequate moisture without the problems associated with over-watering or oxygen starvation of the root system. Iron chlorosis due to water-saturated soils is a common problem with the Globe Willow.

Digging a wide hole and breaking through any compacted layers below the planting hole will allow for good drainage and a spreading root system. Planting the tree two to four inches above the finished grade of the surrounding lawn or garden area will allow excess water to drain away from the crown of the tree and help prevent root rots and over watering. Only in an area where hand-watering is to be done should a dish or basin be built around the tree.

Gardeners should avoid the use of:

• soil sterilants anywhere within the vicinity of the tree
• plastic over the root system
• the digging of trenches around the base of an established tree (in the ground more than one year) for any purpose
• tilling around the tree to control weeds or to plant flowers.

All of the above tasks can cause damage to the roots of the tree resulting in stress, increased insect and disease problems and the yellowing and dropping of leaves and branches.

The Globe Willow, like many other members of the willow family, will drop leaves and branches even when the tree is healthy. When the tree is under stress, even more branches are likely to be shed. This is a natural process called Cladoptosis (Kladoptosis). and can be an aggravating and messy problem and one that is seldom corrected. The dropping of branches can occur year-round. Any dead branches that do not drop, however, should be pruned out to avoid problems with Cytospora canker.

Established Globe Willows should be watered once every 1 1/2 to 2 1/2 weeks, based on the moisture content of the soil. Young trees may have to be watered once a week until their root systems become extensive enough to supply the needs of the top of the tree. If planting a container-grown or balled and burlapped (B and B) tree, it would be wise to irrigate the first few times with a soil needle or root watering device. This implement attaches to the hose and is inserted into the soil to depths of two feet. This device can be successfully used to probe through the soil ball into the surrounding native or amended soil. This not only waters the root ball and surrounding soil, but also helps break the interface (barrier) that often results when two different soils are against each other.

To determine when to water, the soil ball technique should be utilized. Dig three to four inches into the soil within the drip line of the tree and collect a handful of soil. If the soil is sandy, and you can feel moisture within the soil, the soil has adequate water. If the soil has a clay component, soil with adequate moisture can be squeezed into a ball and will retain its shape when the pressure on the fist is released. If the soil ball breaks apart or you can not mold this soil into a compact shape, watering is needed. This same technique should be used to determine the moisture content of the soil within the original root ball itself. It is possible that the root ball may be saturated while the surrounding soil is dry, and vice versa. Check both soils for moisture content and be sure to water both areas to allow for the proper development of roots.

The biggest cultural problem of the Globe Willow in Western Colorado is over-watering even though this tree is said to be a high water using plant. While willows are tolerant of moist soils, they still need an abundance of oxygen in the soil for root respiration to take place. Respiration is the process of burning food by the plant cells to produce the energy necessary for cell growth. Without adequate air, root growth slows, roots die and leaves yellow and drop. As this condition becomes more advanced, a problem commonly referred to as iron chlorosis results.

Yellow leaves with green veins at the tips of the branches is the first symptom of iron chlorosis. As this condition becomes more severe, the die back of the tips of the branches may occur. An application of an EDDHA chelated iron, such as Sequestrene 138 Fe may help.

The Globe Willow is naturally shallow-rooted and consequently benefits from a monthly watering during the winter in those areas where snow cover is sparse. As the upper layers of the soil dry out during such dry and open winters, moisture is pulled from the fine roots of the willow causing root death. This results in a stressed tree the following year. Watering during such winters helps prevent this damage.

Young Globe Willows have tender bark and guying should be done with a wide material such as nylon strapping or indoor/outdoor carpeting. When attached to a single stake, the guying material should be in the form of an eight (8) with the tree in one loop, and the stake in the other loop of the eight. Attach the guy to the stake with a nail or staple to hold the guy in place. The loop used to encircle the trunk should be loose enough to allow the tree freedom of movement to permit the proper development of taper and girth.

If a wire, hose or other narrow guy is used around the trunk, girdling can result that marks the tree for life and creates a weak area where the tree can be broken off, crack, or be invaded by disease or insect pests at some later time.

Young or newly planted Globe Willows should be wrapped for at least the first two winters to protect the trunk tissue from the devastating effects of `sunscald'. This condition occurs on the south or southwest side of trees due to the heating and freezing of the bark tissue by the winter sun. A commercial tree wrap available from most nurseries and garden centers should be used to prevent this problem. With those tree wraps that are black on one side and white on the other, always be sure to wrap the tree with the white side OUT. Do not use burlap, plastic sheeting, or other material not specifically designed for preventing `sun scald' as increased burning may occur.

The wrap should be applied about the first of November and removed by the first of April. If left on during the summer, the wrap will provide an excellent habitat for disease and insect pests to congregate under and feed on the bark of the trunk. The wrap should be applied starting at the base of the trunk and spiraled up the trunk, overlapping the wrap in the process. The wrap can be attached to the trunk with a single tack or staple. Masking tape can also be used to hold the wrap in place but the use of duct-tape is not recommended as this does not stretch and may result in trunk injury. The use of twist-ties, wire, or string to hold on the wrap also may result in girdling.

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