Common Fungal Pathogens of Omaha Trees in 2024
As most of you know, the weather in Omaha during the late spring this year was crazy. All the damaging storms that rolled through the metro in May brought historic amounts of rain.
Rain gauges at Eppley Airfield stated that we received 11.14 inches of rainfall in May 2024, the second highest total ever recorded.
All the rain affected many things around us, but one of the most important things that it affected was our native flora and fauna. Specifically, this amount of rainfall, paired with hot, humid temperatures brought trouble in all shapes and forms to our beloved trees. These environmental conditions, that came about due to detrimental storms, brought easy access to pathogens, specifically moisture loving fungi, to the trees around us.
Trees of the great plains can be susceptible to fungal diseases, all of which affect trees in different ways. Some examples of these diseases that you may have heard of are anthracnose, brown rot, and leaf rusts. Although there are thousands of other examples, I want to focus on a few of them that we may be more likely to see due to the current environment.
Example of leaf damage from anthracnose.
Anthracnose of Broadleaf Deciduous Trees
Anthracnose diseases, which can affect many native deciduous trees such as sycamores, maples, ash, oak, and elm, are typically caused by fungi in the family Gnomoniaceae. Fungi in this family are similar in that they need water from rain or fog in order to infect a tree.
This fungal disease affects each of its host trees differently, with the most common sign being leaf blotching and distortion. As the disease worsens over the growing season, other parts of the tree may be affected, such as branches, shoots, and leaf buds. In severe cases, heavy anthracnose damage can defoliate a tree causing instability, and improper growth.
To manage this disease, it’s important to prune the tree when the sap is not flowing (in the dormant season), maintaining the tree via irrigation and proper care, as well as treating the tree with fungicide in extreme cases.
Example of cherries being affected by the fruit rot stage of Brown Rot.
BROWN ROT
Brown rot is caused by several fungi in the genus Monilinia, and it affects many fruit producing ornamentals, typically of the Prunus genus. This genus contains trees such as cherry, plum, peach, and apricot.
Brown rot has two stages, bud and shoot blight in the spring and early summer, and fruit rot. This fungal disease is passed via windblown ascospores, or via insect or rain carried spores from rotted fruit.
An application of fungicide done in the spring and fall, paired with proper removal of infected branches and fruit can help your trees’ chances to fight off this disease.
‘Witches Broom’ gall on juniper branch.
Leaf rust affecting crabapple leaf.
Gall on juniper branch due to cedar apple rust.
LEAF RUSTS
A very common group of fungal diseases for trees in the great plains, are leaf rusts. There are a number of different species of leaf rust fungi, but they are typically in the Gymnosporangium family.
This fungal disease is unique in that in needs two host plants to complete its life cycle. The aecial stage of the disease is carried out on trees in the Rosaceae family, with the telial stage occurring on trees in the genus Juniperus. That is why it is a conventional gardening practice to reduce planting susceptible species together (specifically ornamental crabapples and junipers).
Signs of this disease on rosaceous hosts include orange, and yellow lesions on leaves, whereas the disease presents itself via galls on its juniper host.
Although this disease is rarely deadly to either one of its host species, it can reduce fruit quality, vigor of new growth, and aesthetic value. In extreme cases, if left unmanaged, it can kill branches, which affects the overall shape and function of infected trees.
Management of these diseases can be done via proper pruning, and fungicide applications.
All information gathered from this USFS publication
Riffle, Jerry W.; Peterson, Glenn W., tech. coords. 1986. Diseases of Trees in the Great Plains. *Gen. Tech. Rep. RM-GTR-129*. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station.