This growing season our arborists have been seeing a lot of trees and shrubs. As we visit from property to property we start to see patterns in regards to insects and diseases that are affecting trees and shrubs. Every growing season is a little bit different, with fluctuations in moisture and temperature playing big roles in insect and disease outbreaks. Some problems we see are largely the usually suspects that we see time and time again, and others are relatively new pests that are attacking our trees and shrubs for the first time.
Here are some insects and diseases to be aware of that the Hoppe Tree Service arborists are seeing having an effect on trees and shrubs in the Milwaukee area this year:
Emerald ash borer- Emerald ash borer is now becoming widespread in most Milwaukee area. This invasive insect attacks all species of ash trees and causes damage by burrowing into the trunk and feeding on the cambium tissues that bring water and nutrients through the tree. Protection treatments are available and work best for healthy trees. Treatment consists of a trunk injection around the base of the tree. Treatment dosage lasts for 2 years. Trees experiencing more than 25-33% canopy loss are probably too far gone to treat. If you want to save an ash tree and haven’t treated yet, now is probably the time.
Apple scab- heavy rains during spring has caused one of the worst apple scab disease years in memory. If you are experiencing black spots and discoloration on leaves, along with early leaf drop on your crab trees it is most likely apple scab disease. Pruning the tree to increase air flow throughout the canopy, along with fungicide applications to the leaf surfaces are the most effective methods of minimizing apple scab. There are numerous varieties of crab apple trees and susceptibility to the apple scab fungus varies depending upon the variety.
Boxwood leaf miner- Boxwood bushes are valued for their dense evergreen foliage and ability to be low maintenance plants. Unfortunately this spring we are seeing more boxwood leaf miner than other before. The leaf minor larvae feed between the upper and lower parts of the leaf, causing blisters on the underside of the leaf. The leaves infested by this pest become yellow and smaller than a normal leaf. When the plant is severely infested, it appears completely unhealthy.
Silver maple anthracnose- We’ve gotten a lot of calls regarding black spots and legions on silver maple leafs. This problem is called anthracnose and even though it can look quite troubling it seldom causes real health issues for the tree. The wet weather this spring has caused this disease to be rampant on many silver maples. As with most fungal diseases, the most affected parts of the tree are the lower branches which are more shaded, with less air flow. Typically treatment is not needed. The best course of action is proper pruning to increase air flow through the tree, along with raking up of fallen leaves so fungal spores do not re-infect the tree.
Viburnum leaf beetle- This tenacious feeder of viburnum bushes is a relatively new insect pest in the Milwaukee area. This beetle can defoliate a viburnum bush rapidly. The larvae can skeletonize young leaves by June. This is the first sign of an infestation. Emerging adults continue feeding on viburnum. Plants that have been defoliated for two or three consecutive years may die. Highly susceptible viburnum species include Arrowwood Viburnum and high bush cranberry. Chemical treatments can control this pest and are best applied as soon as damage is noted.
Written by: August Hoppe
Certified Arborist WI-0477A
Hoppe Tree Service