Protecting Against Pests and Diseases: Common Tree Problems in Missouri and Their Prevention

Diseases of forest trees and shrubs can be called any abnormality or failure of development caused by a persistent pathogen. For each of the thousands of plant species, there are about a hundred different diseases with individual pathogens.

Causes of Disease Occurrence

There are biotic and abiotic pathogens of disease (wildlife components and climatic conditions). Biotic sources of diseases are divided into groups according to the type of pathogen (bacteria, fungi, viruses, nematodes, etc.).

It is worth noting that in most cases pathogens are parasites. However, not every pathogen is a parasite and not every parasite is a pathogen. Some parasites do not harm plants and, therefore, do not cause any tree disease on the trunk or other parts of the tree. On the contrary, parasites can be beneficial. In addition, some species of bacteria that live on the soil surface do not parasitize plants, but produce harmful toxins that cause tree root diseases.

The most common classification is based on the following parameters:

• The cause is determined by the type of pathogen.
• The host plant – by the type of tree (poplar, conifer, pine, maple, etc.)
• Part of the tree – by the affected area. A distinction is made between diseases of tree leaves, trunk (bark) and roots.
• Age of the tree – the degree of maturity is taken into account. A distinction is made between diseases of trees from the nursery, seedlings, as well as diseases of mature trees.

In determining the disease, signs and symptoms are taken into account. Signs are changes caused by the pathogen’s tissues (e.g. white plaque). Symptoms are the form of disease manifestation (leaf fall, reduction in crown density, rotting, wilting, and others). Using change detection technology, foresters can determine when a forest has been affected by a disease.

Tree Leaf Diseases

From the name, it is clear to us that these diseases affect foliage. The main causative agents of leaf infections are fungi. However, the signs and symptoms of diseases can be similar to the effects of chemical insect damage, making it difficult to identify tree leaf disease and choose an appropriate treatment. Treatments may not be effective when weather conditions are favorable for fungal development, so it doesn’t always make sense to invest in eradicating the problem. The most common method of treating tree leaf disease is to remove and destroy the leaves in the fall. This method will prevent over-wintering of the pathogen and reinfection in the spring.

Conifer Tree Diseases

Diseases of conifers are quite common, but not dangerous. In most cases, these diseases do not need to be treated unless the affected trees are being prepared for sale, such as Christmas spruces and pines. The most popular method of eradicating pathogens that spread needle disease is spraying with chemicals. In large forests, this method is rarely used. Generally, three types of conifer diseases are distinguished: rust fungus, needle drop, and rot.

Fragmentation of Conifers

A fungus that grows inside the needles forms long hysterotetes. They are what causes the needles to fall off. Depending on the pathogen, fungi such as lophodermium, elytroderma and rhabdocline are distinguished. In the United States, about 40 different genera of fungi cause tree diseases.

Conifer rot

Decay is also an internal infection of coniferous needles and causes them to partially die off. The most common fungal species cause white and brown needle spotting in trees, as well as red streaks (needle burns).

Leaf Diseases in Hardwoods

Most infections in hardwoods are also caused by fungi, with no specific treatment. General treatment guidelines in such cases recommend removing and destroying the affected leaves.

The most common methods of preventing and treating tree diseases are

• Prevention. Treating leaves and trunk with fungicides before budding. Freshly cut stumps should also be sprayed to prevent fungal and insect infestation.
• Sanitation and removal. Most foliage diseases are untreated, but fallen foliage should be removed and destroyed in the fall to avoid spreading infection next season.
• Branch thinning. Cutting off damaged parts of the tree is a common way to stop the spread of branch disease. However, this method is only effective if the vital parts of the tree are not damaged. Crown thinning also promotes air circulation.
• Soil improvement. The risk of infectious diseases in plants depends on their overall health. Improve plant health by avoiding excessive watering, increasing soil fatness, and protecting plants from drought. Healthy trees can handle pathogens on their own.
• Biological control. Bark beetles damage trees and carry harmful fungi. Biological control. The emergence of their biological enemies (e.g., birds, flies, mites, wasps).
• Chemical control. Spraying with fungicides, insecticides, and other agents, depending on the type of pathogen.
• Cultivation of resistant species that tolerate exposure to fungi and adapt to pathogens.
• Tight planting at a distance for better isolation from infections.
• Delaying reforestation to confirm no source of infection.

Trees in forests and gardens suffer from thousands of different species-specific diseases. Some of them require immediate treatment, while others are untreatable. The control of any tree disease, regardless of its harmfulness or severity, begins with proper plant health monitoring.