Common Tree Problems in Arizona

Most tree problems in the desert come down to a handful of culprits: alkaline soil, intense sun, watering mistakes, and a few specific pests and pathogens that thrive here. Learning to read the symptoms helps you catch problems early, when they're still fixable. Here are the ones we diagnose most often across the West Valley.

Iron Chlorosis (Yellow Leaves, Green Veins)

If your tree's leaves are turning yellow but the veins stay green, that's classic iron chlorosis. It's extremely common here because Arizona's high-pH, alkaline soil chemically "locks up" iron so roots can't absorb it, even when iron is present in the soil.

• Most affected: non-desert species like citrus, ash, and many ornamentals; rarely desert natives.
• Made worse by: overwatering and poor drainage.
• Treatment: chelated iron (look for the EDDHA form, which works best in alkaline soil) and soil sulfur to gradually lower pH. Correcting overwatering is often half the cure.

Sunburn and Sunscald

Our sun is strong enough to literally cook exposed bark. Sunscald shows up as cracked, peeling, or dead bark on the trunk and upper sides of limbs, usually on the south and west faces. It most often appears after a tree has been over-pruned, when bark that was shaded for years is suddenly exposed.

• Prevention: don't over-thin or lion-tail the canopy that shades the trunk.
• Protection: young or newly exposed trunks can be painted with diluted (50/50) white latex paint or wrapped to reflect sun.

Overwatering Damage

Because everyone knows the desert is dry, overwatering is the most under-diagnosed problem of all. Symptoms include yellowing leaves, leaf drop, weak fast growth, constantly wet soil, and fungal issues. The fix is almost always to water deeper but far less often, see our desert watering guide.

Sooty Canker

A fungal disease that attacks ash, mulberry, citrus, and other thin-barked trees. Look for dieback of branches and black, sooty spores under cracked or peeling bark. It spreads through pruning wounds, especially in hot weather.

• Management: prune out infected wood well below the canker, in cooler dry conditions, and sterilize tools between every cut.

Texas Root Rot (Cotton Root Rot)

One of the desert's most dramatic killers. *Phymatotrichopsis omnivora* is a soil-borne fungus that thrives in our alkaline soils and strikes in the heat of summer: a tree wilts and the leaves turn brown but stay attached, often over just a few days, and the tree dies.

• There's no reliable cure once it takes a susceptible tree.
• Defense: plant resistant species. Desert natives, palms, and many monocots resist it; lush non-natives are most vulnerable.

Palo Verde Borer

If you see large exit holes and a wilting, declining palo verde, the palo verde root borer (a big beetle whose grubs feed on roots) may be involved. The key insight: these beetles target stressed, over- or under-watered trees. A healthy, deeply watered tree is far more resistant. Vigor is the best defense.

Other Pests to Know

• Aphids and whiteflies, sticky "honeydew" on leaves and surfaces below, often with black sooty mold growing on it. Usually cosmetic; healthy trees tolerate them.
• Spider mites, fine stippling and webbing in hot, dusty conditions.
• Bark beetles, more a concern for stressed pines; pitch tubes on the trunk are a warning sign.

Mistletoe

Desert mistletoe is a parasitic plant that takes hold in mesquite, palo verde, and acacia, appearing as dense clumps of leafless green or reddish stems hanging in the canopy. Heavy infestations sap a tree's vigor. Pruning out affected branches helps, but established mistletoe is persistent.

Girdling From Stakes and Ties

Not a disease, but a frequent killer of younger trees: stakes and ties left on too long bite into the expanding trunk, cutting off the tree's "plumbing." Always remove staking after a season, more in our planting guide.

When in Doubt, Get a Diagnosis

Many of these problems look alike, yellow leaves alone could mean iron chlorosis, overwatering, or several other things. Misdiagnosis wastes time and money, and some conditions (like Texas root rot or advanced borer damage) are far easier to manage early. If a tree is declining and you're not sure why, a certified arborist can identify the cause and give you a realistic plan. Here's how to know when it's time to call one, or reach out through our tree care services.

This guide is part of the TCGS Tree Care Wiki. Need hands-on help? Book a tree care assessment with our certified arborists.