• George R. Lee

April Rains Bring May Diseases



Springtime is the mark of new seasonal plant growth which is also the time damaging diseases are infecting your trees, shrubs, ivy, ground cover and even flowers. The cool moist weather of early spring days creates the perfect breeding ground for fungal plant invasions.


In our service area of southeast Michigan there are at least 7 harmful and seasonal plant diseases we deal with. Proactive treatment is key to managing these diseases. We want to identify the plant, the problem and perform active treatments so our trees look healthy, are beautiful and enhance our landscapes each and every year.


1. Sooty Mold

sooty mold
Photograph by Bidgee distributed under a CC-BY 2.0 license.

Sooty mold coats deciduous trees and shrubs restricting their ability to absorb sunlight and thus interfere with the tree's ability to produce nutrients for itself. Without vital nutrients it is unlikely to survive for very long. These are just some of the key plants sooty mold attacks: Roses, Maple, Willow, Elm, Nine Bark and fruit trees.


2. Powdery Mildew


Normally, powdery mildew is carried from a currently infected plant to another by wind, birds or in-flight insects. Powdery mildew coats the leaves of trees and shrubs blocking out the plants ability to produce nutrients. If left untreated, powdery mildew will stunt vital new growth, the tree or shrub will weaken, other insects and diseases add to the trees stress and without corrective action the trees or shrubs will continue to suffer and eventually die. Some of the key plants attacked by powdery mildew include: Dogwood trees and Dogwood shrubs, Peony, Crape, Magnolia, Lilac, Crimson Maple, several varieties of ground covers, Ivy’s and flowers.


3. Cercospora Leaf Spot

leaf spot
Photograph by Scot Nelson distributed under a CC-BY 2.0 license.

Wet, warm conditions in spring create a perfect infection storm for Cercospora Leaf Spot disease, This fungus infects trees as new leaves are starting to develop for the growing season. The fungal spots start out looking very tiny then as the trees complete their leaf expansion for the season the spots become more rampant and larger (these are called spores). The disease stunts plant growth and without corrective, managed care, the disease will eventually cause the tree to become open for more deadly insect and disease invasions. Once the tree can not produce food and energy its decline will continue until the tree is dead. This disease infects many types of shade, fruit and ornamental trees in Southeast Michigan.


4. Phytophthora Root Rot


Generally, Phytophthora Root Rot is likely to develop where the soil is continually moist, there’s very little sunlight and where roots are under stress from “wrong plant, wrong site” choices. The disease impacts the roots thus diminishing root strength. Although Phytophthora Root Rot disease will not immediately kill the plant, the disease will distort its growth and thus the plant will continue to decline and will eventually die. Key plants impacted in Southeast Michigan include: Azalea, Rhododendron, Dogwood, Mountain Laurel, White Pine, Fir trees, Japonica, Yews, and Junipers.


5. Apple Scab Disease

Photograph by Peggy Greb, USDA ARS, Public domain, via Wikimedia Commons

Apple Scab disease is the most aggressive and common disease found in Southeast Michigan. The diseases threatens the health and beauty of several types of fruit and ornamental trees. Scab infects both the the leaves and the fruit. Under certain weather conditions, Apple Scab can effectively invade plants from early spring all the way until winter season. Apple Scab is a more unsightly condition as opposed to immediately life threatening. However, left untreated the tree becomes stressed allowing other concerns such as harmful insects, diseases and nutrient stunting leading to further decline and even total loss of the tree. Key trees infected by Apple Scab disease include: Crab Apple, Apple, Hawthorn, Cotoneaster (shrubs), Mountain Ash, and Pear trees.


6. Needlecast Diseases


Needlecast diseases cause Spruce trees to lose their needles. It’s a fungus that infects the needles of the current year’s shoots. As the disease develops, the needles will die. It typically takes the needles a year after infection to die and begin falling off the branches. There are 2 primary Needlecast diseases found in Southeast Michigan. The most common are Stigmina and Rhizosphaera. Why is needle cast such a problem in Michigan? Blue Spruce are native to Colorado and the Rocky Mountains. The climate in lower Michigan is not nearly as cold or dry. During the summer the humidity here provides the environment which these fungal pathogens thrive in. Needlecast attacks a variety of evergreen trees including Spruce and Pine trees.


7. Anthracanose


Anthracnose disease erupts in trees growing in wet cool areas, when there is lots of spring rain, (even into summer and fall) and where irrigation systems are not properly set and the trees are saturated by over watering. Left untreated the trees stress level goes up while its vigor level goes down. Not only is Anthracnose an ugly looking disease (once developed) it also sets the stage for other harmful insects to become an ongoing problem. Key trees impacted by Anthracnose in Southeast Michigan include: Dogwood (both tree and shrub varieties), Sycamore and London Plane trees, many species of Maple including many varieties of Japanese Maples. Anthracnose makes your tree feel and look stressed and unsightly.


How to Treat Harmful Diseases Invading Your Trees and Shrubs:


  1. Understand planting the right plant in the right location.

  2. Make sure pruning is completed as often as needed to promote air circulation and sunlight.

  3. Be proactive with treatments such as targeted sprays, trunk injections and soil drenching treatments.

  4. Insure tree and shrub vigor by way of proper fertilizing and soil care.

  5. Call a professional tree doctor for help. At Branch Tree Service we specialize in all the treatments just discussed and we're here to help. Call us today at 586-756-7737 or request a quote!