Extended drought killing and damaging trees from northern to southern Arizona
After questions from the public, University of Arizona Cooperative Extension experts examined trees and tested for diseases. The verdict? It's from a lack of water.
These juniper trees in Yavapai County near Prescott are suffering from Arizona's extended drought.
Cooperative Extension
In recent weeks, University of Arizona Cooperative Extension has received a flurry of questions through our Ask an Expert portal about dying trees – native trees and non-native landscaping varieties – from several parts of Arizona.
After examining trees at several sites across the state and testing some samples in our plant pathology lab, our experts agree the likely main culprit is drought. The trees simply aren’t getting enough water.
Alex Hu, an Extension plant pathologist and assistant professor in the School of Plant Sciences checked dying pine trees in Bonita, Willcox and Pearce. He took samples to the main campus Extension Plant Pathology Lab and found no pathogens that would cause the problems, he said.
“One common denominator is watering. If the owner is watering the pine trees, they are doing OK, exhibiting less stress. However, for those trees receiving little or no supplemental water, the majority of them are struggling,” Hu said.
Those stressed trees can also be susceptible to secondary problems like sooty canker and bark beetles, he said.
Dying trees have also been reported in central Arizona, said Beth Reidhead, Extension’s Maricopa County Master Gardener program coordinator.
“We have had issues with both eldarica and Aleppo (pine trees) for quite some time in Phoenix. With increased and extreme temperatures and low rainfall, more and more of our landscape trees are showing signs of stress without proper supplemental irrigation,” Reidhead said.
Bark beetles leave these distinctive channels under tree bark.
Adobe Stock
Similar problems existed in Phoenix last year, when the valley saw a record stretch of 110-plus degree days and one stretch in late September. Landscape pines have suffered near Globe for the same reasons, said Chris Jones, an Extension Agriculture and Natural Resources agent and interim director of Coconino County Extension.
“I recall quite a bit of roadside mortality last year in the Phoenix area in August and September. These were mature, and many were moderate water use species. This provides an opportunity to replace the trees with even more drought-tolerate species as the 21st century continues to heat up,” Jones said.
There have been a few reports of juniper trees dying in Yavapai County, said Yavapai Extension Director Matt Halldorson, an Extension Agriculture and Natural Resources area agent. Halldorson attributed the problem to drought after examining stricken trees and finding no signs of insects or disease.
“I have no doubt, however, that as the summer proceeds we will begin to get more calls on non-irrigated trees that are suffering from drought, as well as secondary problems such as bark beetles,” he said.
Hu has also investigated deaths of screwbean mesquite trees in riparian areas. The cause of that problem, which has existed for two decades and has resulted in mass die-offs, is unknown, but drought, insects and disease appear to be working in concert, he said.
What To Do
How much water trees need varies depending on the species, weather, soil type and other factors, but some general guidelines can be helpful.
Watering should cover a large portion of the root zone, which extends out from the trunk varying distances depending on size and species. For mesquites, oaks and pines this zone is two to three times the width of the canopy and 2-3 feet deep. Palm trees only need water 2-3 feet from the trunk to a depth of a foot.
As trees get larger, the roots next to the trunk will not need irrigation. Instead, water soil under the outer circumference of the tree canopy, where it will be taken up by the fine roots.
During the hottest time of summer, irrigation may be needed every four to seven days. Some native plants may be able to survive without irrigation once they are established. Irrigation amount and frequency will depend on soil type, plant species and size as well as rainfall at the site.
For more information about managing landscaping during drought, see this Extension publication: Drought and Extreme Heat: Plant Responses and Landscape Maintenance Practices
Bark beetle site assessments
The Arizona Department of Forestry and Fire Management's Forest Health team is scheduling free site assessments for property owners who believe they may have bark beetles or damage from them. The invasive Mediterranean pine engraver was recently confirmed in Sedona and Cottonwood. Email foresthealth@dffm.az.gov to schedule a free assessment.
To learn more
Signs of Bark Beetle Infestation