Aleppo pine blight is the most serious disorder of established, mature Aleppo pine (Pinus halepensis) trees in the low elevation desert of the southwestern U.S. The disorder has been particularly severe in the Phoenix metropolitan area. Aleppo pine blight occurs primarily on large, mature trees that tend to have high landscape values. The cause of the disorder has primarily been attributed to abiotic stress from excessive heat, dry winds and dry soil conditions. In some cases mites and aphids can cause further stress on Aleppo pines. Aleppo pines are among the most commonly planted landscape trees in arid regions of the desert southwest and treatments that can reduce the severity of the disorder are needed.
Promoting tree health through proper cultural practices is extremely important with this disorder. Deep watering of trees to meet the seasonal needs for pines in the southwest is important. Less frequent deep watering during winter months and more frequent watering in summer months. Alleviate compaction in soils by using the Airspade and incorporate in soil amendments and prescribe fertilizer as needed. Do not over-fertilize, especially trees that are subject to moisture stress.
Cambistat has shown to improve Aleppo pine’s ability to withstand drought stress and improve root:crown ratios, while also improving fibrous root production. Apply Cambistat every 3 years. Manage secondary pests such as Aphids with systemic applications of Transtect, which has been shown to NOT induce secondary mite flare-ups as seen with systemic imidacloprid formulations. Monitor for spider mite outbreaks in the summer and treat with soil applied Lepitect or conventional miticide sprays of Binfenimite or Lucid.
Other Treatment Practices
- Plant Aleppo pines in full sun and ensure that shade is minimized from competition from other trees/plants.
- Avoid high soluble salt concentration fertilizers and be cognizant to reduce impact of wind salt damage.
- Aleppo pines do well with flooding-style irrigation, but do not tolerate long-term soil saturation.
- Mulch trees with organic mulch 2-4 inches deep as far out to the dripline as possible, taking care to prevent mulch from being on trunk and root flare.
Strategies should be aimed at proactive management of tree health using a combination of cultural and chemical controls prescribed in this protocol. Once trees are showing symptoms of Aleppo pine blight it is extremely difficult to preserve these trees. Target preventive management as there is no cure once symptoms are found throughout the canopy.
Cambistat has shown good results in improving the root:crown ratio and improving fine root development in conifers, however, if soil compaction is an issue using the air spade to decompact the soil is necessary to maximize the benefits of Cambistat.
- Use Cambistat as a tool in combination with other tree health care treatments that promote overall tree health.
- Cambistat treatments result in only moderate growth regulation of many pine species (20-30%) which can also be desirable in areas where growth reduction is needed.
Signs of Damage
- Needles typically turn yellow colored to brown and dehydrate and die and symptoms usually occur in the upper part of the tree in November through February/March. This is a result of hot dry conditions earlier in the summer
- Symptoms can also be seen in the summer months as well
- Needles turn brownish/grey then brown but continue to cling to plump healthy branches until normal seasonal needle drop in the summer.
- Twigs and branches may die
- Sun-exposed sides are most affected and water-soaked cankers can appear on branches, which may split
- Aphids can feed on trees and produce sticky honeydew and sooty mold
- Spider mites can also feed on Aleppo pine causing stippling on needles and turning needles yellow
- Other diseases such as Fusarium may cause cankers and tip blight
Trees At Risk
- Aleppo pine (Pinus halepensis)
- Afghan pine (Pinus eldarica)
- A healthy spruce will retain its needles 5 to 7 years, whereas a spruce severely infected with Rhizosphaera needlecast may hold only the current year's needles.
- Rhizosphaera needle cast infects needles on the lower branches first and gradually progresses up the tree.
- This pattern holds true for most needle diseases on conifers and is the result of more favorable conditions for disease development near the ground.
- Under epidemic conditions, lower branches may be killed by this fungus.
- Although needles on new growth become infected in May and June, symptoms are not visible until late fall or the following spring, when infected needles turn purple to brown and begin to drop.
- Tiny fruiting bodies of the Rhizosphaera fungus protrude through the stomata of the infected needles.
- During wet weather in late spring, spores are released from these fruiting bodies and are rain splashed onto newly developing needles where infection occurs and the disease cycle is repeated.
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.