Common Tree Pests & Diseases

Trees are the longest living organisms on the planet and one of the Earth’s greatest natural resources, and in order to survive they require light, water, air and nutrients. Just like any living organisms, trees can be susceptible to pests and diseases due to the weather and other environmental conditions.

These pests and diseases pose a great threat to the City of Johannesburg’s (CoJ’s) green canopy. However, they can never be fully eradicated but can be managed. Johannesburg City Parks and Zoo (JCPZ) has put measures in place to minimise the impact of infestation throughout the CoJ.

Here are some of the most common tree pests and diseases to look out for in your garden and how to manage them:

Euwallaceae fornicatus – polyphagus shothole borer/Invasive shothole borer

The Polyphagous Shot Hole Borer (PHSB) is an ambrosia beetle native to Southeast Asia. Female beetle bores into the wood and form galleries, which it inoculates Fusarium euwallaceae and Graphium euwallaceae fungi into the tree; and results on die back diseases. The beetle attack wide range of trees.

Control Method: Chemicals not recommended, especially on reproductive host. It is recommended to prune highly affected branches or remove highly affected trees, then solarise or incinerate the wood.

Aphis spp– aphids

They are small, delicate insects which occur in colonies on the growth tips, flower heads and leaves of the most plants especially during spring and summer months. They vary in colour and sizes. Sucks sap out of the plant causing slowed down growth and wilting in the case of severe attack and excretes honeydew as a by-product. Severe attack causes yellowing, leaf curl and death of plant tips. It is a major vector of plant diseases.

Chemical control: Systemic/contact pesticides

Biological control: Ladybird feeds on aphid

Boisea trivittata – Box elder bug

Boxelder bugs feed mainly on boxelder (Acer negundo) tree seeds and newly developing leaves, which may result in discoloration of the foliage and it also feeds on Brachychiton spp, shrubs and fruit trees such as plum and apple.

Chemical control: cypermethrin

Biological control: box elder bug has natural predator called gladiator bug

Glomerella cingulate – Anthracnose

Anthracnose is a fungal disease that affects primarily the leaves but also sometimes the stems of hardwood trees. Symptom of these diseases is dead areas or blotches on the leaves. Because of the scorched appearance of the leaves, the diseases are sometimes called leaf blight.

Attack various tree species

Armillaria fuscipes – armillaria root rot

Armillaria is a soil-borne fungus that causes a root and trunk rot of trees. The fungus establishes in roots and the root crown before symptoms visible. Infected trees usually die prematurely, and young trees often die quickly after infection. Some of the symptoms of the fungal disease is mushrooms on the trunk.

The fungus can be managed by removing infested trees.

Fusarium oxysporum – fusarium wilt disease

Fusarium is widespread and can infect wide range of plants. The fusarium is soil borne and air borne, thus can affect the tree through the wound. The symptoms include vascular wilt, root rot, stem rot, leaves turn yellow and dry. Eventually the tree will die.