In this article we will discuss about the various plant diseases and disorders.
Plant Diseases:
Plant diseases are caused by one of three organisms: bacteria, fungi or viruses. All groups may trouble from time to time, however bacterial and viral diseases are relatively rare. Diseases usually affect the growth or health of the plant visible by distortion, discoloration or wilting.
It may ultimately lead to its death. Good garden hygiene is the key to disease prevention. Keeping the garden or greenhouse clear of decaying, diseased or dead material, trays, canes and other equipment at the end of each season can get rid of potential sources of infection. Choosing disease-resistant plant species will keep plants vigorous and healthy.
1. Bacterial Diseases:
Many foliage plants are sensitive to bacterial diseases showing typical symptoms of leaf spots, blights, and wilting. Bacteria are found on the surface of all plant surfaces. Certain conditions such as high humidity, crowding and poor air circulation may lead them to multiply out of control. Misting plants also provide a film of water on the leaves where bacteria can multiply. Unhealthy plants often become weak making them prone to bacterial infection.
To reduce plant weakness, avoid the following conditions:
i. Too much, too little, or irregular watering.
ii. Fluctuating temperatures.
iii. Low light intensity.
iv. Poor soil drainage.
v. Too large or too small a pot.
vi. A deficiency or an excess of nutrients.
The most severe diseases of foliage plants are caused by bacteria belonging to the genera Erwinia and Pseudomonas, which can cause infections such as fireblight and bacterial canker.
Fireblight is one of the most dangerous bacterial plant diseases. It may affect members of the rose family. The term ‘fireblight’ describes the appearance of the disease, which can make affected areas appear blackened, shrunken and cracked. Fireblight is caused by bacteria, which is produced from the cankers and spread by wind, rain, birds and insects.
The first sign is the browning and withering of foliage. Oozing cankers appear on the branches, and the whole tree may eventually die within a few years. Infected areas should be removed by pruning. Any cuts are approximately 60 cm (2 ft) into healthy wood. Any pruning equipment should be disinfected between each cut. If the plant is small or the infection is severe, it is necessary to dig it up and destroy it.
Bacterial canker is a serious disease usually seen on plum and cherry trees. The leaves develop brown spots, which may be surrounded by a yellow halo. The spotted areas then fall out, giving a ‘shot-hole’ appearance. Lesions (cankers) begin to form on the bark and exude a sticky gum. Control may be carried out by pruning away the affected branches. Any pruning equipment should be thoroughly disinfected between each cut to reduce the risk of spreading the disease. The plants may also be sprayed with copper fungicide once a month.
2. Fungal Diseases:
The most common diseases in the garden and greenhouse are caused by fungus. The most important are honey fungus, mildews and grey mould because they have many susceptible hosts.
3. Viral Diseases:
All plants can be affected by viruses, which can cause a variety of symptoms depending on the disease. The leaves of infected plants may become yellow and distorted. The whole plant may show growth distortions such as stunting or abnormalities in flower formation. Viruses may spread horizontally between plants, by wind, insects or basic injury or vertically passed down from a parent plant.
There is usually no cure for plant viruses, so prevention is the cure. Reduce the risk of horizontal transmission between plants by keeping tools and equipment clean. Greenhouse sap-sucking pests are a major carrier of viruses. Introduce suitable pest control measures to reduce their numbers. Always wash hands and tools after handling any suspect plants.
Any plants badly infected by virus should be burned. Replacements should be planted in a new site in the garden. Always consider buying certified virus-free stock. These plants may be more expensive to buy, but they are more vigorous and worth any extra money.
Plant Disorders:
Plant disorder means nutritional deficiency or a physiological disorder. Unsuitable growing conditions such as too much or too little water or an inappropriate temperature range can also cause plants to show a range of symptoms like yellowing of foliage and wilting stems. Plants receiving unsatisfactory water, food, light or minerals will look unhealthy. They may not be able to resist attack from pests or diseases caused by bacteria, fungi or viruses.
Plants become unhealthy and vulnerable to pest and disease damage, if placed in unsuitable conditions. Plants should always be positioned in growing conditions suitable for their needs. Care should be taken that they get enough water, but not excessive water. They may also need to be protected during very hot weather to prevent scorching and in very cold weather to avoid damage by frost.
Nutrient deficiencies in plants are most commonly seen in light and free-draining soils. Foliage is most often affected becoming discoloured. Growth also usually becomes stunted. Nutrient deficiencies are relatively easy to treat.
1. Chemical Damage:
Chemical damage to plants may arise in three major ways:
(a) Careless application of a chemical.
(b) Using the wrong chemicals for a particular problem.
(c) Applying the right chemicals at the wrong rate or interval.
Weed-killer damage can affect plants, which are unknowingly sprayed with weed-killer through careless application or by spray drift in windy conditions. Contamination may also occur if equipment used for weed-killer is used to water plants. Bleached patches appear on the affected foliage turning them brown. If the plant is severely contaminated, its growth may be affected leading to its death. Use a watering can instead of a sprayer and keep all equipment separately for use with weed-killers.
Plants may also be damaged by fungicides or insecticides if they are applied at the wrong rate or during hot conditions. Never treat plants in bright sunlight. It may lead to scorching. Make sure that the manufacturer’s guidelines for application rates are followed carefully. Young plants are more vulnerable to damage. They may be injured by the application of some chemical treatments.
2. Mechanical Damage:
Mechanical damage involves injuries to plants from the careless use of garden machinery and tools. One of the most common forms is the removal of bark from trees by lawn mowers. Consider altering the shape of the lawn or have a wider area of longer grass around trees if this happens on a regular basis.
Tree, shrub and other plants ties can cause choking. Point tight ties may be loosened by regular checks. One of the most serious forms of damage is from ragged and badly placed pruning cuts. This can provide entry points for disease weakening the plant. In severe cases they may lead to its death. Keep pruning equipment sharp. Make sure that any cuts are made in the right position.