Common Insect & Disease Problems

See American Tree Experts for prevention & treatment

Many trees are susceptible to a variety of regional diseases and insect infestations, which often require a tree health specialist like those on our staff to make a diagnosis. See our certified arborists who can identify common insect and disease problems. We can offer preventive, long-term measures to help protect your trees. Some of the insects and diseases which affect trees and shrubs in our area:



  • Anthracnose

    This fungal disease attacks the foliage of trees, especially maple, white oak and ash. Anthracnose can also affect the twigs of some species of sycamores. Symptoms include tan or brown dead spots on leaves. Good control can be achieved through fungicide applications in the spring.



  • Bark Invaders or Borers

    Many favorite trees suffer from small wood-boring insects that bore into the trees in search of food and shelter, inhibiting the tree’s ability to transport food and nutrients. Borer infestations in our area have been on the rise and the trend is expected to continue. The good news is there are effective treatments available for preventing and stopping these infestations.



  • Diplodia Tip Blight/Dothistroma Needle Cast

    These two fungal diseases can be very problematic on Austrian pines but may also affect Scots and mugo pine. Diplodia tip blight causes a browning of branch tips that eventually die. The first signs of dothistroma needle cast are scattered yellowish spots on older needles. These needles eventually turn brown and die. Both diseases can be fatal if allowed to spread. Fungicide applications made in the spring have proven to be a good control for both diseases, along with removing diseased tree parts.



  • Gypsy Moth

    This destructive insect reached Wisconsin in the late 1980s. Gypsy moths feed on about 500 different species of trees and shrubs found in North America. When populations are high, gypsy moths can defoliate an entire neighborhood or forest in May and June.



  • Oak Wilt

    This fungal disease affects red and white oaks. It interferes with a tree’s ability to pass water throughout the canopy to roots. It is spread by sap-feeding beetles that fly from infected trees to healthier oak trees. It can also be spread from moving firewood infected with oak wilt.



  • Powdery Mildew

    This fungal disease affects the above ground portion of many trees, especially the leaves. Infection can occur on deciduous trees and shrubs but does not infect coniferous species. Powdery mildew is commonly found on maples, lilacs and roses. Symptoms include a white or gray colored powder on upper leaf surfaces and stems.



  • Rhizosphaera Needle Cast

    This is another fungal disease that can cause deterioration of the appearance of pines and spruces—especially Colorado blue spruce. This disease starts with innermost needles on the lower branches becoming infected. The disease can then spread outwards, killing entire branches and then move its way upwards throughout the tree. Fungicide applications can be effective in combating the disease; however, the best defense is to plant resistant trees



  • Scab

    If your crabapple is losing leaves by mid-summer, there is a high probability it has scab. Ornamental and fruit trees in the rose family are affected by this disease. Small circular brown lesions first appear on the upper side of leaves. These lesions expand and coalesce leading to defoliation. Trees with minimal defoliation do not need treatment. If heavy defoliation occurs in consecutive years, fungicide applications should be made.



  • Tar Spot

    Primarily a cosmetic disease, tar spot is found on maple trees. This disease is common on Norway and silver maples and is easy to identify by the large round black spots on the leaves. This is not a serious disease and treatment is often not necessary.