Know tree diseases and ways to avoid them

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Roadside tree nurseries are the major source of tree diseases. Farmers should only buy certified tree seeds and seedlings from licensed tree nurseries and regional centers run by KEFRI and KFS to prevent the transfer of diseases, some of which are difficult to control.

Did you know that just like crops, trees are also prone to diseases? Many farmers may not know it but trees get infected and even die when they get overwhelmed by diseases. Due to climate change and related factors the number of diseases affecting trees has increased. Farmers should remain alert to protect their valuable trees from diseases which threaten our forests and especially the endangered tree species. In this issue we highlight some of the most common diseases including some that may have spread to farms and forests recently and which need urgent measures to control.

Diseased trees produce more seeds

One of the easiest route through which diseased trees are introduced to farms is buying of seeds or seedlings from roadside nurseries. Most roadside nurseries get their seeds from the forest as the owners cannot tell the difference between diseased trees from healthy ones. When the seed collectors visit a forest, they often look for trees with lots of seeds. What they do not know is that some of these trees are already diseased.

According to Dr Jane Njuguna, a plant pathologist at the Kenya Forestry Research Institute (KEFRI), when a tree gets infected by a disease or during periods of stress such as drought, it tends to produce more seeds before it dies. In this way, the tree tries to protect its species from extinction by passing their genetics to the next generation. She advises farmers to avoid trees that produce seeds off-season as they could be diseased and could spread diseases when their seeds are collected and used in nurseries. When such seeds are used in nurseries, they transfer the diseases to other trees in farms or forests.

Common tree diseases in Kenya

A tree disease is defined as any abnormal condition that damages or diminishes a tree’s productivity and usefulness. The most common route for disease transmission is tree seeds. Farmers should, therefore, use high quality seeds and seedlings whose source is known to avoid transferring diseases to their farms. The following are some of the diseases that can affect trees during various growth phases.

Disease type Healthy parts Diseased parts

Diseases affecting seeds and fruits

 

The most common diseases that affect seeds are fungal in nature. These can be avoided by careful selection and storage of seeds before they are planted in nurseries. Seeds and fruits can be affected by seed rot, poor germination and damping off caused by fungi such as Fusarium, Phytopthora, Botryosphaeriaceae, Rhizoctonia or Pythium, among others.

Plant root diseases

Tree diseases that are found in the roots include root rots, change in root color and even rotting of the stem some of which may lead to plant death caused by the above named fungi.

Leaf and branch diseases

Under conducive environments, leaves are prone to diseases such as leaf spots, leaf blights, leaf fall, leaf yellowing, galls, rots and mildews. Branches and shoots can be affected by cankers, diebacks, and tip deaths, among others. Diseases that affect the development of seeds and fruits may sometimes cause fruit rots and falls.

Nematodes and mite

Microscopic (2mm long) round worms that infect plant roots eg. Meloidogyne sp. (root knot) Pratyleachus sp. (root lesion). Exiphenema sp. (corky roots) and Dixylenchus sp. that cause stem lesions.

Prevent tree diseases from your farm

● Seek advice from forest extension staff in your area if you notice any strange sign of disease in your trees.

● Use clean certified seeds and non-contaminated soil.

● Do not collect seeds from diseased trees.

● If in doubt, dust seeds with fungicides before sowing and if necessary spray seedlings with appropriate fungicides.

Cultural methods that can be used to eradicate or prevent the diseases include:

● Pruning and, removal and burning infected plant hosts and parts (cankers, dieback).

● Understand the biologies of both host of the pathogen and take measures to prevent diseases from spreading as soon as signs are noted.

● Practice crop rotation to reduce disease incidence especially in the nursery.

● Improve sanitation to reduce pathogen establishment in tree nurseries.

● Use integrated methods to prevent or control diseases if the infection is high: a combination of cultural, chemical and even physical methods.

>>Tell us how useful this information is to your farming enterprise. Share your experience by email to admin@theorganicfarmer.org,  leave a comment below this article.

 

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