Top 10 Insects and Diseases on Trees

Insects and diseases can affect the beauty and long term health of trees and shrubs.  Some pests are minor, while others can be quite serious and can kill trees.  Working with trees day in and day out give our arborists ample experience in understanding which insects and diseases are truly problems that can adversely affect your trees and shrubs.   Below is a list of the most frequently seen insects and diseases that can cause severe damage or death to trees.  This is list is far from exhaustive, please contact an arborist at Hoppe Tree Service if you have questions about insect and diseases for your trees and shrubs.  Hoppe Tree Service offers Plant Health Care programs to protect your trees. 


Emerald ash borer- The emerald ash borer insect attacks and kills all types of ash, healthy and stressed trees alike.  The most concentrated infections are on the southern edge of Milwaukee County.  But the insect has now been found in most municipalities in metro Milwaukee.  There are multiple treatment options available depending upon the situation. 

Bronze birch borer- White birch trees are common landscape trees in the Milwaukee area.  Unfortunately, so is the birch borer insect.  This pest tunnels under the bark, cutting off the flow of water to the top of the tree.  Birch trees with die back at the top of the tree are most likely causalities of the bronze birch borer.  Protection includes keeping your birch tree happy by adequate watering, fertilization and insecticide treatments.  Mature birch trees tend to be more susceptible to the insect.  

Zimmerman Pine Moth- This insect pest attacks Austrian pine trees.  Symptoms include curved dead branch tips, along with yellowish pitch resin on the trunk near the base of limbs.  The pine moth larvae burrow under the bark and cause damage internally in the tree.  The most effective treatments often are trunk sprays timed for the emergence of the larvae either in spring or late summer. 

Japanese Beetle- This insect pest feeds on over 200 types of trees and shrubs. The most susceptible species include roses, linden and birch trees.  Trees usually can withstand some beetle damage, but repeated defoliation can wear down the energy reserves of the tree and cause health issues.  Treatments are wide ranging and include chemical sprays and biological controls such as pheromone traps.  Treatments often need to be repeated throughout the growing season. 

Carpenter ants- Large black ants called carpenter ants, can cause issues for larger mature trees.  They make their homes in decayed areas and can create large elaborate galleries that can weaken the strength of a tree over time.  Look for signs such as sawdust around the base of a tree.  Carpenter ants usually can be controlled with readily available ant killers.  Carpenter ant infested trees should be inspected to determine if the extent of damage poses problem for the tree or not. 


Apple scab disease- Ornamental flowering crab trees and apple trees often experience a fungal disease called apple scab.  This disease causes black spots to develop and premature leaf drop.  Continued infections year in and year out can weaken the health of a tree.  Treatments include preventative fungal sprays to protect leaf surfaces from infection.  Proper pruning can create better air flow through a tree and slow the spread of the apple scab fungus. 

Rhizosphaera needlecast disease- This common fungal disease most often affects large mature spruce trees.  The fungal disease usually starts on the bottom limbs of the tree and works its way up the tree over time.  The branches lose needles from the inside of the tree and the needle loss advances outward to the tips, eventually killing whole branches.  The disease can jump from tree to tree when spruces are all planted in a line close together.  Pruning diseased branches and thinning out of branches/trees can create better air flow and sunlight which can slow the spread of the Rhizosphaera needlecast disease.  Fungicide sprays can also protect new needles from infection.  This needle sprays need to be reapplied throughout the season, and can slow or halt the spread of the disease. 

Fireblight Disease- We have been seeing quite a bit of this disease.  This bacterial disease most often attacks mountain-ash, crab and apple trees.  Signs of this disease include die back in selected branches in a tree.  The leaves shrivel up and stay on the branch and look like there were burnt in a fire.  The bark tends to exfoliate off the infected branch.  Pruning is the best option to combat fireblight.  Chemical treatments are limited and often don’t succeed. 

Dutch Elm Disease-This disease has been killing elms for a long time.  Over the years we have lost most of our large majestic American elm trees to this devastating disease.  However, there are still elm trees around and Dutch elm disease continues to kill them.  Most infections start as “flagging” (wilting) of branches at the extremity of the tree.  If caught very early, infected branches can be pruned out of the elm.  Preventative treatments are available to protect elms and are highly recommended for large important elm trees.  Siberian (Chinese) elms are larger resistant to DED, and nurseries have created a handful of new varieties that are resistant to Dutch Elm Disease. 

Diplodia needleblight- Browning needles, stunted needles and dead branches are signs of this fungal disease on Austrian pines.  Look for small black spots on infected needles.  Like most fungal diseases, Diplodia usually spreads from the bottom of the tree and works its way into the upper canopy.  Fungal sprays are often used to combat this disease along with pruning and raking up of older infected needles on the ground below the tree. 

Landscape trees face unique challenges and stress that forest trees don’t experience.    Competition from turf grass, soil compaction, air pollution, poor pruning and poor nutrient availability cause issues for trees.  Insects and diseases often take advantage of stressed trees.  A Hoppe Tree Service plant health care program can keep your trees and shrubs healthy and ensure that problems are caught early when treatments are most likely to succeed.  

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