Aleppo pines can start to look pretty ragged during the colder parts of the year with brown patches scattered throughout the tree canopy. In most cases, this is a reversible condition that should get better as the weather warms in the spring. The effect can often be minimized by making sure that the tree gets good care.
The Aleppo pine is a good choice for the low desert areas of Southern Arizona because it is well adapted to our harsh climate and alkaline soils. It attracts few, if any insect pests and it has no major diseases to shorten its life. It is a fast-growing tree and it provides good shade for our hot, summer days. It has been, and continues to be, a landscape stalwart in this area.
It does, however, have one disconcerting tendency. The needles close to the tips of some branches during the cool winter months can turn an unsightly brown. Sometimes the needles stay flexible and turn green again as the weather warms. Sometimes the needles will actually die, turn brittle and fall off; but the twigs and branches that support the needles usually stay green and will eventually regrow new needles.
The browning condition is referred to as Aleppo pine blight. The disease is not caused by fungi, bacteria or insects. It is a weather-induced shock to tender, actively growing needles at the tips of the branches. Since not every branch of the tree is affected, the browning effect gives the tree a part-green, part brown appearance that can lead one not familiar with the condition to believe that the tree is dying. In reality trees rarely, if ever, die of Aleppo pine blight.
With all of the recent publicity given to the bark beetle devastation in Northern Arizona pine forests, it is logical to assume that the browning of Aleppo pines is somehow related to these beetles. You can ease your minds on that matter.
First of all, the bark beetles of Northern Arizona do not like the desert climate. It is too hot here for them. Second, if the damage now seen in Aleppo pines were caused by bark beetles, the twigs and branches would not remain green to produce new needles in the spring. Third, the damage would not be spotty on the tree. Bark beetles cause a rapid decline and eventual death of the entire tree.
While the specific cause of Aleppo pine blight is still unclear, there are a couple of theories that have been proposed. One states that the effect develops when there is not enough time between warm and cold weather in the fall and winter to allow sufficient winter dormancy to develop. Certainly, the variable weather that we have been experiencing in past years lends support to this theory. One week, the fall temperatures can be in the eighties and nineties; the next in the low forties and even in the thirties. This transition is hard on plants.
Another theory blames the browning of the needles on a previous stress for water and nutrients. Most plants under stress often shut down part or all of the plant for a time until conditions for growth and development are better. A good example of this is the ocotillo. When warm, dry weather arrives, the ocotillo sheds its tender leaves and goes to sleep. Once the rains come again, the plant reawakens, puts on new leaves and begins a new growth cycle. Aleppo pine blight may be an example of a similar response by the Aleppo pine. The tree may simply not have enough strength to support the many needles on all of the branches of the tree, and the browning may be a move by the tree to cut back to what it can sustain.
Symptoms of Aleppo pine blight are noticeably striking. Affected foliage suddenly dehydrates, turns whitish green, then brown, usually in the cool months of the year. A few green needles or parts of an individual needle may survive in the midst of the blighted ones. Some defoliation may occur and tree sap may sometimes seep from the blighted twigs. In the more severe cases, some twig die-back may actually result.
The blight may be triggered in part by night-day temperature extremes and drying winds, since the symptoms usually show up on the sun-exposed, windward tops and sides of the trees. Most affected branches survive this peculiar affliction and readily replace the brown needles in late spring and early summer as the trees begin their new growing season.
A good way to diagnose this particular problem is to bend the affected needles and twigs. If the needles and twigs are brown beneath the bark and become brittle so that they snap easily, it may be that the tree is experiencing dehydration and death of some of its parts due to severe water stress and heat injury. If the needles are still flexible, or only a few are brittle, the problem may simply be the Blight.
While the symptoms of Aleppo pine blight may never be completely eradicated, there are a few steps that can be taken to ease the problem in most trees. Make sure that the tree gets at least a monthly deep irrigation throughout the entire root zone of the tree and apply a nitrogen fertilizer at least twice a year to support new growth.
There is a slight chance that browning of needles and death of twigs may be related to a more serious disorder, such as root rot generally associated with too much water, but that condition is rare. It is important, whenever there is a condition of which we are not sure, to always be vigilant and watch for signs that the problem is getting worse. The Aleppo, however, is a pretty resilient plant and usually does not give its owners too much to worry about.
If you have questions, you can reach one of the Master Gardeners at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande. The telephone is (520) 836-5221. The author’s email address is gibsonrd@ag.arizona.edu.
The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.
Rick Gibson
Extension Agent, Agriculture
University of Arizona Cooperative Extension
820 E. Cottonwood Lane, Building C
Casa Grande, Arizona 85222
Voice: (520) 836-5221
Fax: (520) 836-1750
email: gibsonrd@ag.arizona.edu
