Spider mites
Spider mites attack your plants in droves!
Spider Mites on Trees and Shrubs: Identification, Damage and Treatment Timing
Spider mites are among the smallest—and most frequently misdiagnosed—pests found on landscape trees and shrubs.
A plant affected by spider mites may initially appear drought-stressed, nutrient-deficient or diseased. Leaves or needles begin to look faded, yellow, gray or bronze. As the infestation increases, foliage may turn brown, drop prematurely or become covered in fine webbing.
The mites themselves can be difficult to see without magnification. However, the damage they cause can become highly visible, especially during periods of favorable weather.
Correct identification and treatment timing are essential. Spider mite activity varies by species, host plant, temperature and weather conditions. Growing degree days can help landscape professionals determine when to begin scouting, but treatment decisions should always be based on confirming that mites are present and active.
What Are Spider Mites?
Spider mites are tiny plant-feeding arachnids. They are more closely related to spiders and ticks than to insects.
Adult spider mites generally have eight legs, although their newly hatched larvae have six. Most species are extremely small and may appear as moving dots on the underside of leaves or between plant needles.
Spider mites feed by piercing individual plant cells and removing their contents. The damaged cells lose chlorophyll, creating the pale dots or flecks commonly called stippling.
When enough cells are damaged, the foliage may appear:
Pale green
Yellow
Gray
Silver
Rust-colored
Bronze
Brown or scorched
Heavy infestations can reduce photosynthesis, weaken plants and cause premature leaf or needle drop.
Are Spider Mites Insects?
No. Spider mites are arachnids rather than insects.
This distinction matters when selecting a treatment. A product labeled as an insecticide does not necessarily control mites. Some broad-spectrum insecticides can even make spider mite problems worse by killing predatory mites and beneficial insects that naturally suppress pest populations.
Products designed to control mites are generally called miticides or acaricides. Some horticultural oils and insecticidal soaps may also suppress spider mites when applied correctly and permitted by the product label.
Always confirm the pest before choosing a treatment.
Common Spider Mites on Landscape Plants
There are many species of spider mites, but several are especially important on ornamental trees and shrubs in the Northeast.
Twospotted Spider Mite
The twospotted spider mite, Tetranychus urticae, is one of the most common warm-season spider mites.
It feeds on a very large range of ornamental plants, fruit trees, vegetables, flowers and weeds. Populations frequently increase during hot, dry weather, particularly on plants already experiencing moisture stress.
Under favorable temperatures, twospotted spider mites can develop rapidly. Cornell reports that development from egg to adult may take approximately seven days at 81°F, compared with about 20 days at 64°F.
Common hosts can include:
Hydrangea
Rose
Burning bush
Butterfly bush
Viburnum
Privet
Fruit trees
Perennials
Annual flowers
Many broadleaf ornamental shrubs
Spruce Spider Mite
The spruce spider mite, Oligonychus ununguis, is primarily a cool-season pest of conifers.
It may infest:
Spruce
Dwarf Alberta spruce
Arborvitae
Juniper
Hemlock
Fir
Douglas-fir
Some pines
Leyland cypress
Unlike twospotted spider mites, spruce spider mites are generally most active during cooler periods in spring and fall. Their populations may decline or become inactive during the hottest part of summer.
Damage often begins on older, interior needles and may spread outward as the infestation develops. Affected foliage may become mottled, gray-green, bronze or brown.
Boxwood Spider Mite
The boxwood spider mite, Eurytetranychus buxi, feeds primarily on boxwood.
Damage often appears as fine yellow or white stippling on the upper surfaces of leaves. Heavy feeding may give the foliage a pale, scratched or streaked appearance.
Boxwood spider mites overwinter as eggs on the plant. In regional predictive calendars, egg hatch may begin at approximately 141 growing degree days, although actual timing varies with location, weather conditions and the degree-day model being used.
Southern Red Mite
Southern red mites are another cool-season group that may affect broadleaf evergreens such as:
Azalea
Rhododendron
Holly
Camellia
Laurel
Pieris
Like spruce spider mites, they can become most active during cooler spring and fall weather rather than midsummer heat.
What Does Spider Mite Damage Look Like?
Early spider mite damage is often subtle.
The first symptoms may be scattered pale dots on leaves or needles. These dots are created when mites puncture plant cells and remove their contents.
As feeding continues, the dots merge into larger discolored areas.
Common symptoms include:
Fine Stippling
Tiny white, cream or yellow dots develop across the foliage. Stippling is often easiest to see on the upper leaf surface even though many mites feed underneath the leaf.
Faded or Dull Foliage
Green foliage may lose its normal color and appear washed out, gray-green or dusty.
Bronzing
Severe feeding can cause leaves or needles to develop a bronze, rusty or scorched appearance.
Premature Leaf or Needle Drop
Heavily damaged foliage may turn brown and drop before the end of the growing season.
Fine Webbing
Some spider mite species produce silk webbing. Webbing may occur between leaves, around stems or across sections of infested foliage.
Prominent webbing usually indicates that the population has already become substantial. However, not every spider mite species produces obvious webbing, and the absence of webbing does not rule out mites.
Reduced Plant Vigor
Repeated or severe infestations may weaken the plant, reduce growth and increase susceptibility to environmental stress and secondary problems.
How to Check a Plant for Spider Mites
Because spider mites are so small, symptoms alone are not enough to confirm a diagnosis.
Several other problems can resemble spider mite injury, including:
Drought stress
Salt injury
Nutrient deficiencies
Lace bug feeding
Leafhopper feeding
Thrips damage
Certain fungal diseases
Herbicide injury
Normal needle shedding on conifers
Use one or more of the following scouting methods before recommending treatment.
The White-Paper Test
The white-paper test is one of the easiest ways to detect active mites.
Hold a sheet of white paper, a white clipboard or a white beating tray beneath an affected branch.
Strike or shake the branch firmly over the surface.
Watch the debris for 10 to 20 seconds.
Look for tiny dots that begin moving across the paper.
Use a hand lens to examine them more closely.
Spider mites may appear green, yellow, orange, red, brown or nearly black, depending on the species, life stage and recent feeding.
Plant debris will not crawl. Mites will.
On conifers, gently smearing a moving speck across the paper may also provide a clue. A dark green streak can indicate a plant-feeding mite, although magnification is preferable for reliable identification.
Inspect the Undersides of Leaves
Use a 10× or greater hand lens to inspect the lower leaf surfaces.
Look for:
Moving adult mites
Smaller immature mites
Round eggs
Cast skins
Fine silk
Predatory mites
Feeding damage
Check both damaged and apparently healthy foliage. Mite populations are often unevenly distributed throughout a plant.
Check Several Areas of the Plant
Do not base a treatment decision on a single leaf or branch.
Inspect:
The sunny side of the plant
Interior foliage
Lower branches
Upper branches
Areas near pavement or reflective walls
Sections exposed to dust
Areas with previous mite damage
Hot, dry and dusty microclimates can support heavier warm-season mite populations.
Spider Mites and Growing Degree Days
Growing degree days measure accumulated heat over time. They provide a more useful biological timeline than calendar dates alone because pest development is strongly influenced by temperature.
GDD data can help professionals determine when a susceptible life stage may begin appearing and when scouting should intensify.
However, there is no single universal spider mite GDD range.
Different mite species have different seasonal patterns.
Approximate GDD Scouting Indicators
Regional pest-predictive resources have reported approximate starting points such as:
Boxwood spider mite egg hatch: around 141 GDD
Spruce spider mite egg hatch: approximately 179 GDD in one Maryland model
Twospotted spider mite egg hatch or increased activity: around 627 GDD in the same regional model
These values should be treated as scouting triggers rather than automatic spray dates.
Degree-day totals can differ because programs may use different:
Starting dates
Base temperatures
Upper temperature cutoffs
Weather stations
Calculation methods
Regional biological observations
The best approach is to combine GDD information with plant phenology, local weather, property history and direct scouting.
Cool-Season Versus Warm-Season Spider Mites
One of the biggest mistakes in spider mite management is assuming that all species behave the same way.
Cool-Season Mites
Spruce spider mites, boxwood spider mites and southern red mites are generally associated with cooler spring and fall conditions.
They may become less active during the hottest summer weather.
Scouting should begin early in the season, especially on plants with a history of infestation.
Warm-Season Mites
Twospotted spider mites thrive during warm and dry conditions.
Populations may increase rapidly in summer, especially on drought-stressed plants or plants growing near:
Pavement
Buildings
Retaining walls
Gravel
Air-conditioning units
Dusty roads
Reflected heat
The University of Minnesota notes that twospotted spider mite activity increases during hot, dry weather.
This difference is critical. Brown needles on a spruce during July may be old damage from a spring spruce spider mite infestation rather than evidence that mites are currently active.
Always check for living mites before treating.
Why Hot, Dry Weather Can Increase Spider Mites
Warm-season spider mites frequently become more damaging during periods of drought and high temperatures.
Several factors may contribute:
Mites reproduce and develop more rapidly in warm conditions.
Water-stressed plants may be less able to tolerate feeding.
Dry weather can reduce fungal pathogens that naturally affect mites.
Dust can interfere with natural predators.
Some beneficial mites perform better under more humid conditions.
Broad-spectrum pesticide applications may eliminate predators.
Adequate irrigation can reduce plant stress, but watering alone may not eliminate an established infestation.
Natural Enemies of Spider Mites
Landscape plants support many organisms that feed on spider mites.
Important natural enemies include:
Predatory mites
Minute pirate bugs
Lacewing larvae
Lady beetles
Predatory thrips
Certain small predatory beetles
Predatory mites can feed on spider mite eggs, nymphs and adults. Their presence may prevent a small population from becoming damaging.
Before applying a pesticide, inspect the plant for predators. A low spider mite population accompanied by numerous predatory mites may not require treatment.
Unnecessary broad-spectrum insecticide applications can remove these beneficial organisms and allow the spider mite population to rebound.
Can Insecticides Make Spider Mites Worse?
Yes. Certain insecticide applications can contribute to a spider mite outbreak.
This can happen when the product:
Kills predatory mites and beneficial insects
Fails to control the target spider mite
Reduces competition from other arthropods
Causes the spider mite population to rebound
Leads to repeated applications that further disrupt biological control
Some pyrethroid insecticides are particularly associated with mite flare-ups in certain crops and landscape situations.
Never assume that a general insecticide will control mites. Read the entire pesticide label and verify that the target mite, host plant and application site are listed.
How to Manage Spider Mites
Effective spider mite management begins with proper diagnosis and early detection.
1. Reduce Plant Stress
Keep susceptible plants adequately irrigated during dry periods.
Correct problems involving:
Poor irrigation coverage
Compacted soil
Root damage
Excessive mulch
Improper planting depth
Heat exposure
Drought stress
A healthy plant is generally better able to tolerate moderate mite feeding.
2. Wash Mites From Foliage
A strong stream of water can physically dislodge mites and remove some of their webbing.
Direct the water toward leaf undersides and interior foliage. Repeated washing may help suppress small populations on accessible plants.
3. Preserve Beneficial Predators
Avoid unnecessary broad-spectrum pesticide use.
When treatment is necessary, consider options that are less disruptive to predatory mites and other natural enemies, provided they are appropriate for the site and allowed by the label.
4. Consider Horticultural Oil or Insecticidal Soap
Horticultural oils and insecticidal soaps can suppress spider mites through direct contact.
Thorough coverage is essential, especially on the undersides of leaves. These products generally have limited residual activity and may require repeat applications.
Do not apply oils or soaps to drought-stressed plants, during excessive heat or to plant species listed as sensitive on the label. Certain oils may temporarily alter the blue color of glaucous conifers such as blue spruce.
The University of California IPM program recommends confirming that mites are present and avoiding treatment when plants are water-stressed or conditions are very hot.
5. Use a Labeled Miticide When Necessary
Professional miticides may be appropriate when:
Mites are confirmed
Populations are increasing
Damage is progressing
The plant is valuable or highly susceptible
Cultural and mechanical measures are insufficient
Different miticides may target different life stages, including eggs, immature mites or adults.
Coverage, timing and resistance management are critical. Repeated use of the same mode-of-action group can select for resistant mite populations.
Always follow the product label regarding:
Target species
Host plants
Application rate
Spray interval
Maximum number of applications
Temperature restrictions
Personal protective equipment
Pollinator precautions
Reentry requirements
Resistance-management instructions
Pesticide registrations vary by state and can change. Applicators in New York should verify that a product is currently registered for the intended use before application.
When Should Spider Mites Be Treated?
There is no universal threshold for every tree or shrub.
A treatment decision should consider:
The spider mite species
The number of mites detected
Whether the population is increasing
The amount of existing damage
The presence of eggs and immature mites
The number of beneficial predators
Plant health
Plant value
Weather conditions
The likelihood of natural population decline
The treatment history of the property
Finding one or two mites does not automatically justify treatment.
In many cases, the best decision is to record the infestation, correct plant stress, preserve predators and recheck the plant several days later.
Why Spider Mite Treatments Sometimes Fail
Spider mite control can be difficult even when the correct product is selected.
Common reasons for treatment failure include:
Poor Coverage
Spider mites frequently feed on leaf undersides, interior foliage and protected areas. Spraying only the outer canopy may miss much of the population.
Treating Old Damage
Bronzed or stippled foliage will not turn green after mites are controlled. Evaluate success by checking for living mites and healthy new growth, not by expecting old damage to disappear.
Incorrect Pest Identification
Lace bugs, thrips, leafhoppers, drought stress and several diseases can resemble spider mite feeding.
Wrong Treatment Timing
The product may not control the life stage currently present.
Eggs Survive the Application
Some products control active mites but provide limited egg control. Newly hatched mites may make it appear that the treatment failed.
Resistance
Spider mites reproduce quickly and can develop resistance when the same mode of action is used repeatedly.
Continued Plant Stress
A plant exposed to heat, drought or root problems may continue declining after the mite population has been reduced.
Spider Mite Prevention
Spider mites cannot always be prevented, but damaging outbreaks can often be reduced through routine monitoring.
Recommended practices include:
Inspect susceptible plants regularly.
Begin scouting before symptoms become severe.
Track properties with a history of mites.
Use growing degree days to anticipate activity.
Maintain appropriate irrigation.
Minimize dust on foliage.
Avoid unnecessary broad-spectrum insecticides.
Preserve predatory mites and beneficial insects.
Recheck plants after treatment.
Record pest activity, weather conditions and treatment results.
The earlier an infestation is detected, the more management options are generally available.
Frequently Asked Questions About Spider Mites
What is the fastest way to check for spider mites?
Hold white paper beneath an affected branch and strike the branch firmly. Watch for tiny moving dots. Confirm them with a hand lens.
Does webbing always mean spider mites?
No. Spiders and some caterpillars also produce webbing. Spider mite webbing is usually very fine and may contain numerous tiny moving mites. Some mite species produce little visible webbing.
Can spider mites kill a tree or shrub?
Spider mites usually cause discoloration, leaf drop and stress rather than rapidly killing a mature tree. However, severe or repeated infestations can contribute to decline, particularly on young, newly planted, drought-stressed or otherwise weakened plants.
Will rain eliminate spider mites?
Heavy rain may reduce exposed populations, wash mites from foliage and disrupt webbing. It does not guarantee complete control, particularly when eggs and mites remain in protected areas.
Do spider mites prefer hot weather?
Some do. Twospotted spider mites often thrive in hot, dry conditions. Spruce spider mites and southern red mites are generally more active during cooler spring and fall weather.
Can spider mites live on arborvitae?
Yes. Arborvitae can be affected by spider mites, including cool-season species such as spruce spider mites. Confirm active mites before treating because arborvitae browning can also be caused by drought, winter injury, root problems, bagworms and several other conditions.
What plants are most susceptible to spider mites?
Spider mites can feed on hundreds of plant species. Common landscape hosts include spruce, arborvitae, juniper, boxwood, rose, hydrangea, viburnum, burning bush, privet and many fruit trees.
Should I spray as soon as the GDD range begins?
No. A GDD range indicates when scouting should begin or when a susceptible life stage may be present. It does not confirm that a damaging infestation exists on a specific property.
Use Growing Degree Days to Improve Spider Mite Timing
Spider mite management is most successful when weather data, plant development and field scouting are used together.
Calendar-based treatments can miss the target life stage because seasonal development changes from year to year. Growing degree days provide a more precise way to estimate when pest activity may begin in a particular location.
GDDIntel helps arborists, landscapers, plant health care companies and property managers track growing degree days by ZIP code and anticipate important pest and disease windows.
Use GDD data to know when to start scouting—but use direct observation to decide whether treatment is actually needed.
References
Cornell Cooperative Extension, Ornamental Crops Integrated Pest Management
University of Maryland Extension, Mites in Home Gardens
University of Maryland Extension, Pest Predictive Calendar
University of Minnesota Extension, Twospotted Spider Mites
Colorado State University Extension, Spider Mites
University of California Integrated Pest Management, Spider Mites