Metro Area Tree Maintenance Calendar

This calendar is a seasonal planning guide for homeowners, businesses, homeowners associations, planned unit developments, parks, and municipalities in Washington, Ramsey, Hennepin, Anoka, Carver, Dakota, Scott and St. Croix Counties.

This is a summary of the Tree Care that should be considered by month. The information was gathered from our own Certified Arborists, and the University of Minnesota, Wisconsin-Madison, MN Dep of Agriculture, MN Department of Natural Resources, and Wisconsin Dep of Natural Resources.

Because weather patterns vary from year to year, this calendar covers a broadened seasonal window, and all treatments should be approved by a certified arborist from your community, such as those at Green Goddess Trees.

Tree care scheduling will be affected by the following, hence the need to consult a Certified Arborist.

Warm springs or warm falls
Early bud break
Late frost
Wet spring weather
Drought or low water stress
Extended insect activity
Local disease, bug, and fungi outbreaks
Various soil conditions

Seasonal Calendar

Primary purpose: Dormant pruning, sanitation, inspection, removal planning, and spring preparation

Best for:

Oak pruning during the safest oak wilt prevention window
Dormant pruning of many shade trees where appropriate
Fire blight sanitation pruning on apple, crabapple, pear, mountain ash, hawthorn, and serviceberry
Inspecting spruce and pine for cankers, dieback, winter injury, and disease history
Removing or managing infested pine debris where pine bark beetles are a concern
Spongy moth egg-mass inspection and removal where present or suspected
Tree-risk inspections by a certified arborist
Updating the property tree inventory
Building tentative 2 year tree care plans
Scheduling spring plant health care visits

Primary purpose: Early scouting, disease-risk monitoring, spring treatment preparation, and some early preventive care

Best for:
Early disease scouting
Crabapple/apple scab prevention planning
Cedar-apple rust prevention
Fire blight risk monitoring
Pine disease treatment planning
Early pine disease treatment in warm springs
Spongy moth egg-mass or barrier-band work where present
Oak wilt avoidance
Confirming spring treatment schedules for high-value trees
Reviewing the property tree inventory with an arborist before peak season

Important note:
In a warm spring, April can behave like early May. If bud break begins early, disease and insect timing may move earlier too. Oak pruning and oak wounding should generally be avoided once warm spring conditions begin.

Primary purpose: Active treatment season begins for many insects and diseases, unless it is an unusually warm and wet spring.

Best for:

Emerald ash borer treatment startup
Crabapple/apple scab protection
Cedar-apple rust protection
Fire blight bloom-period protection
Rhizosphaera needle cast treatment
Dothistroma needle blight treatment
Diplodia shoot blight treatment
Scale insect systemic treatment where appropriate
Mite scouting
Spongy moth caterpillar management where present
Confirming treatment priorities for high-value trees

Important note:

May is one of the most important months for preventive tree health care. In warm springs, some treatments may need to begin in late April or early May.

Primary purpose: Peak treatment, monitoring, and follow-up month

Best for:

Emerald ash borer treatments
Bronze birch borer monitoring or treatment
Two-lined chestnut borer monitoring or treatment
Spruce needle-cast follow-up
Pine disease follow-up
Scale crawler monitoring or treatment
Japanese beetle monitoring
Spongy moth caterpillar treatment where present
Drought-stress prevention planning
Arborist follow-up on high-risk trees

Important note:

June is a major insect and disease activity month. In wet years, fungal disease pressure can remain high. In warm years, some borer and scale activity may begin earlier.

Primary purpose: Active insect management, stress monitoring, and oak-wilt avoidance

Best for:

Emerald ash borer treatments
Japanese beetle adult management
Grub prevention planning or treatment
Scale insect treatment
Spider mite monitoring
Drought-stress monitoring
Watering plans for stressed trees
Oak wilt avoidance
Follow-up inspections on birch, oak, spruce, pine, and crabapple

Important note:

July remains part of the high-risk oak wilt pruning period. Hot, dry weather increases stress on birch, oak, spruce, pine, and newly planted trees. July should combine treatment, monitoring, and stress reduction.

Primary purpose: Late-season treatment, diagnosis, stress reduction, and planning

Best for:

Emerald ash borer treatment continuation
Japanese beetle follow-up
Scale and mite follow-up
Drought-stress watering plans
Oak wilt caution where disease pressure is nearby
Late-season diagnosis
Identifying trees that need winter pruning, removal, or next-year treatment
Updating the tree inventory based on summer performance

Primary purpose: Late-season monitoring, selected treatment, stress assessment, and fall planning, unless it’s an unusually warm fall.

Best for:

Late emerald ash borer treatments where appropriate
Mite monitoring
Scale follow-up
Tree stress assessment
Fall plant health care planning
Spruce and pine disease assessment
Evaluating treatment success from the current year
Updating the tree inventory
Prioritizing trees for winter pruning, removal, or next spring’s treatment plan

Important note:

In warm falls, monitoring may continue later, especially for mites, scale, and stressed trees. Emerald ash borer treatment may still be appropriate where the tree is healthy enough and product timing allows.

Primary purpose: Monitoring, egg-mass inspection, tree-risk assessment, and winter planning, unless it has been an unusually warm and wet fall.

Best for:

Warm fall treatments
Fall mite monitoring
Spongy moth egg-mass inspection
Tree-risk assessment
Planning removals
Planning winter pruning
Late-season stress evaluation
Identifying trees that failed to respond to treatment
Preparing next year’s treatment calendar
Reviewing the tree inventory with an arborist

Primary purpose: Dormant pruning, sanitation, inspection, removal, tree inventory, and 2-year treatment planning

Best for:

Oak pruning and oak removals during the safest oak wilt prevention window
Elm pruning and sanitation where appropriate
Fire blight sanitation pruning on apple, crabapple, pear, mountain ash, hawthorn, and serviceberry
Pine sanitation and removal or management of infested/high-risk pine debris where appropriate
Spongy moth egg-mass inspection and removal where present or suspected
Winter tree-risk inspections by a certified arborist
Structural pruning
Removal of hazardous, dead, dying, or high-risk trees
Updating the property tree inventory
Building tentative 1–3 year care plans
Budgeting for spring and summer plant health care
Planning spring treatment programs for emerald ash borer, Dutch elm disease, apple scab, fire blight, spruce needle cast, pine needle diseases, scale, mites, and borers

Schedule Treatment

Top Tree Health Risks for the Lake Elmo Area mentioned on the Calendar

Host: Ash
Severity: Extreme
Primary concern: Tree death
Main activity: Trunk injection or other approved treatment, plus inspection and planning
Treatment window: Early May through early October
Best core window: May through late September

Emerald ash borer is one of the most serious tree threats in Minnesota. It kills ash trees and is a major concern for homeowners, municipalities, parks, homeowners' associations, and commercial properties.

Treatment is most effective when the tree has enough healthy canopy to move product through the tree.

Emerald Ash Borer damage on Ash Tree in Lake Elmo MN

Host: Red oak, pin oak, bur oak, white oak
Severity: Extreme
Primary concern: Rapid tree death, especially in red oak group trees
Main activity: Dormant pruning, avoiding high-risk pruning, sanitation, removal, and disease-management planning
Highest-risk pruning window: April through July
Safest pruning window: November through March
Broader caution window: Late March through October in unusually warm years

Oak wilt is one of the most serious diseases affecting oaks in Minnesota. The most important public-facing rule is simple: avoid pruning or wounding oaks during the high-risk April–July period.

Host: American elm, red elm, slippery elm, rock elm
Severity: Extreme
Primary concern: Tree death
Main activity: Preventive treatment where appropriate; dormant pruning, sanitation, and removal planning in winter
Planning/treatment window: April through September
Dormant work window: November through March

Dutch elm disease remains a major concern wherever elms are present. Management may include preventive fungicide injections, sanitation, pruning, root-graft disruption, and rapid removal of infected trees.

Winter is not the main injection season. It is mainly a time for pruning, sanitation, inspection, and spring-treatment planning.

Dutch Elm disease on a tree, found in Stillwater MN

Host: Birch, especially stressed white birch and paper birch
Severity: Very high
Primary concern: Decline and death of susceptible birch
Main activity: Monitoring, treatment where appropriate, watering, mulching, and stress reduction
Monitoring/treatment window: May–July

Bronze birch borer is a serious pest of stressed birch trees. Many ornamental birches in residential and commercial landscapes are vulnerable, especially in hot, dry, compacted, or exposed sites.

Bronze Birch Borer damage on Birch tree in Stillwater MN

Host: Colorado blue spruce and other spruce
Severity: High
Primary concern: Long-term thinning, decline, and possible loss of spruce trees
Main activity: Preventive fungicide treatment, diagnosis, inspection, and long-term spruce-health planning
Treatment window: Mid-May through early July
Best timing: When new needles are about half their mature length, with a possible second application 3–4 weeks later if needed

Rhizosphaera needle cast is a major landscape problem, especially on Colorado blue spruce. Treatment protects new growth; it does not restore already infected needles.

rhizosphaera Needle Cast disease found on pines

Host: Spruce, especially Colorado blue spruce
Severity: High
Primary concern: Branch dieback, decline, and long-term loss of spruce
Main activity: Inspection, pruning, stress reduction, watering, mulching, and removal planning where needed
Management window: Year-round inspection; pruning during dry weather

Cytospora canker is not a simple spray-calendar disease. Management focuses on reducing stress and pruning infected branches during dry conditions.

Cytospora Canker found on spruce trees in MN

Host: Austrian pine, ponderosa pine, and some other pines
Severity: High
Primary concern: Needle loss, decline, and long-term weakening of pines
Main activity: Preventive fungicide treatment, inspection, and pine-health planning
Treatment window: Late April through mid-July

Dothistroma needle blight can be serious on susceptible pines. Treatment timing follows bud break and needle development, not a fixed date.

Dothistroma Needle Blight disease found on pine trees in New Richmond MN

Host: Pine, especially stressed Austrian pine, red pine, and other susceptible pines
Severity: High
Primary concern: Shoot death, cankers, branch decline, and tree weakening
Main activity: Preventive fungicide treatment, inspection, pruning where appropriate, and stress reduction
Treatment window: Late April through June

Preventive fungicides can help protect new growth but do not reverse established cankers. Stress reduction is critical.

Diplodia Shoot Blight found in Minnetoka MN

Host: Stressed pine
Severity: High in drought-stressed or damaged sites
Primary concern: Decline or death of stressed pines
Main activity: Monitoring, sanitation, removal or management of infested material, and stress reduction
Monitoring window: April through September
Best sanitation window: Fall through winter

Pine bark beetles are most concerning where pines are stressed by drought, storm damage, overcrowding, construction, or fresh pine debris.

Winter work is mainly sanitation, debris management, inspection, and removal planning — not routine spraying.

Pine bark beetle problem on a tree in Woodbury MN

Host: Crabapple and apple
Severity: Moderate to high
Primary concern: Defoliation, weakening, poor appearance, and recurring decline
Main activity: Preventive fungicide treatment, spring monitoring, and tree-health planning
Treatment window: Mid-April through early June

Apple scab is very common on apple and crabapple trees. It is usually not an immediate tree killer, but repeated defoliation can weaken trees and impact appearance.

Apple Scab fungis wilting apple tree leaf in Lake Elmo MN

Host: Crabapple, apple, mountain ash, hawthorn, serviceberry, and related plants
Severity: Moderate to high
Primary concern: Branch death, disfigurement, and possible tree death in severe cases
Main activity: Bloom-period prevention, storm-response treatment where appropriate, and dormant sanitation pruning
Treatment window: Late April through June; storm response as needed
Dormant pruning window: Late winter, generally February–March depending on weather

Fire blight is favored by warm, wet weather, especially during bloom and rapid shoot growth. Hail, wind damage, pruning wounds, and other injuries can increase risk.

Winter work is mostly pruning infected branches and cankers, not spraying.

Fire Blight disease found on trees in Woodbury MN

Host: Maple, oak, ash, sycamore, and other hardwoods
Severity: Moderate
Primary concern: Leaf damage, defoliation, and stress after repeated infections
Main activity: Preventive fungicide treatment only for high-value or repeatedly affected trees; otherwise monitoring and stress reduction
Treatment window: Mid-April through early June

Anthracnose and other leaf spot diseases are often worse in cool, wet spring weather. They usually do not kill healthy mature trees by themselves, but repeated defoliation can weaken trees.

Anthracnose disease found on a tree in Eagan MN

Host: Magnolia, pine, spruce, fir, maple, oak, and many ornamentals
Severity: Moderate to high
Primary concern: Branch dieback, decline, honeydew, sooty mold, and stress
Main activity: Crawler-stage treatment, systemic treatment where appropriate, and monitoring
Treatment window: May through August

Scale insects are timing-sensitive because many treatments work best during the crawler stage. Different scale species have different timing, so diagnosis is important.

Scale Insects found on trees in Shakopee Area MN

Host: Spruce, arborvitae, juniper, and many ornamentals
Severity: Moderate to high
Primary concern: Needle discoloration, bronzing, thinning, and decline
Main activity: Monitoring and treatment where mite pressure is confirmed
Treatment window: April through June; July–August in hot/dry periods; September through October

Spruce spider mite is often most active in spring and fall. Two-spotted spider mite can become worse during hot, dry summer weather.

Spider Mites on a tree in minneapolis MN

Host: Linden, birch, crabapple, rose, grape, turf near trees, and many ornamentals
Severity: Moderate
Primary concern: Defoliation, stress, turf grub damage, and homeowner concern
Main activity: Adult beetle management, grub management where appropriate, and plant stress reduction
Treatment window: Early June through August

Japanese beetles rarely kill mature healthy trees by themselves, but repeated heavy defoliation can weaken trees and create high customer concern.

Japanese Beetle that distroys 300 varieties of trees, plangts and grass, found in the Lake Elmo, MN area.

Host: Oak, aspen, birch, and many hardwoods
Severity: Emerging / high watch-list
Primary concern: Defoliation, stress, and secondary pest/disease vulnerability
Main activity: Egg-mass inspection/removal, caterpillar treatment where present, and outbreak monitoring
Treatment window: Mid-April through June for caterpillar activity; October through April for egg-mass work

Spongy moth is more of a monitoring and outbreak-management concern than a routine treatment item for every Lake Elmo property.

Egg-mass work is inspection and removal, not routine spraying.

Schedule Treatment

Why a Tree Health Plan Matters

Trees are long-term living assets. Many landscape and shade trees take 15 to 80 years to reach meaningful maturity, but some can be severely damaged or killed in 1-2 seasons without proper maintenance.

Property owners and managers should work with a certified arborist to maintain a basic tree inventory and a tentative 1–3 year care plan for important trees.

A good tree plan may include:

Tree species
Location on the property
General size or age class
Tree condition
Known insect or disease risks
Pruning needs
Treatment schedule for the next two years
Watering, mulching, or soil-care needs
Removal or replacement concerns

Not every tree needs treatment every year. The goal is to identify high-value or vulnerable trees before problems become severe.

Important Distinction: Treatment vs. Maintenance

Not every calendar item is a spray or injection.

Generally, April through October is best for active treatment, such as:

Fungicide applications
Insect treatments
Trunk injections
Mite or scale treatments
Disease-prevention treatments

Other months, especially November through March, are mostly for:

Dormant pruning
Sanitation pruning
Inspection
Tree-risk assessment
Removal planning
Tree inventory updates and 2-year treatment scheduling
Spring treatment planning