Tree disease and pest treatment

Diagnosis comes first

Most trees that look sick in Greeley are not infected with anything. They are dealing with alkaline soil, compaction, planting depth, girdling roots, irrigation problems or root damage from construction.

Spraying those trees achieves nothing except cost. So the first visit is a diagnosis, not a treatment, and sometimes the answer is that no pesticide is going to help.

What we actually see here

Emerald ash borer

The big one. Weld County is inside Colorado's quarantine area and untreated infested ash dies. Covered in full on our emerald ash borer page.

Other borers

Bronze birch borer on river birch, lilac-ash borer, and flatheaded appletree borer. Borers overwhelmingly attack trees already stressed by drought, sun scald or root damage — which means the real fix is usually cultural, not chemical.

Fireblight

Bacterial, hits pears, crabapples, apples and mountain ash. Shoot tips blacken and curl into a shepherd's crook, looking scorched. There is no spray cure; management is pruning well below infected tissue in dry dormant conditions and sterilising tools between cuts.

Cytospora canker

Very common on Colorado blue spruce and aspen, and a classic stress disease. Lower branches die back progressively with white resin bleeding on the trunk. No effective chemical control — management is removing affected limbs and fixing whatever is stressing the tree, usually water.

Spider mites

Hot dry summers here are ideal for them. Stippled bronzing on conifers, particularly spruce, and fine webbing. Often made worse by broad-spectrum insecticide use that kills the predatory mites keeping them in check.

Aphids and scale

Rarely a serious threat to tree health, mostly a nuisance from honeydew and sooty mould on cars and patios. Frequently resolves on its own once predators catch up.

Dutch elm disease

Still present in Greeley's older American elms. Wilting and yellowing on individual limbs in early summer, progressing rapidly. Timing restrictions on elm pruning exist specifically to avoid attracting the beetles that spread it.

How we treat

Where treatment is warranted: trunk injection for systemic pests, soil-applied systemics, targeted foliar application, and cultural correction. Pesticide application in Colorado requires a state applicator licence, and anyone applying product on your property should hold one.

Questions we get about this

My tree looks sick. Is it a disease?

Usually not. Most declining trees in Greeley are dealing with alkaline soil, compaction, planting depth, girdling roots or root damage. That is why we diagnose before recommending any treatment.

Do you spray for everything?

No. Many of the most common problems here, including cytospora canker and fireblight, have no effective spray. Management is pruning and fixing the underlying stress.

My spruce is dying from the bottom up. What is that?

Most often cytospora canker, which is very common on Colorado blue spruce and takes hold on trees under stress. Management is removing affected branches and correcting the watering, usually toward deeper and less frequent.

Is my ash worth treating?

If it has lost less than about a third of its canopy and is otherwise sound, possibly, with the understanding that treatment continues for the life of the tree. See our emerald ash borer page for the full picture.

Do you need a licence to apply pesticides?

Yes. Colorado requires a state pesticide applicator licence for commercial application. Ask to see it before anyone sprays anything on your property.