What are the main causes of tip burn on orchid leaves?

There are many causes of tip burn in orchid leaves. Some are caused by natural factors, some by improper management, and some by disease. Among these, tip burn caused by disease is the most serious.

1. Tip burn caused by natural factors

(1) Humidity too low. Orchid leaf tip burn is closely related to water supply, especially in Cymbidium faberi, whose leaves are relatively long; if water supply cannot keep up, tip burn is inevitable. Water supply to orchid leaves comes first from transport by the roots, and second from absorption from the air. Therefore, besides excessively dry potting medium, the cause of orchid tip burn is greatly related to low air humidity. If air humidity is too low and the air is too dry, transpiration of the orchid plant increases, water supply and demand in the leaves become imbalanced, and tip burn results. Generally speaking, orchids grown indoors have higher air humidity, so tip burn is not serious; orchids grown outdoors, where air humidity is difficult to control, suffer more serious tip burn.

(2) Sudden climate change. Taking 2007 as an example, just after people moved orchids out of the relatively humid orchid house, they encountered a drought rarely seen in decades. Rivers dried up to the bottom, air humidity was extremely low, and orchid tip burn was therefore relatively serious. Although the plum rain season came late, it lasted a long time, about 50 days. Leaves that had not seen sunlight for a long time were thin and soft, and right after the plum rain season ended, high temperatures and strong sun followed, making tip burn even more serious. The author visited several outdoor orchid gardens, and tip burn in Cymbidium faberi was relatively serious in all of them.

(3) Air pollution. If an orchid garden is near a sewage area or industrial zone, or if someone burns harmful substances near the orchid garden, harmful gases fill the air, damage orchid leaves, and cause tip burn.

2. Tip burn caused by improper management

(1) Light too strong. Neglecting shading in summer or providing insufficient shade causes light that is too strong, resulting in orchid leaf tip burn.

(2) Long-term growing in shade. During growth, if orchids are shaded too much, receive too little light, and are grown in shade for a long time, the leaves become thin and weak. If the orchids are suddenly exposed to strong light, tip burn and leaf shrinkage are easily caused.

(3) Water damage injuring the plant. Watering too frequently causes root rot, which leads to tip burn. Spraying water in sunlight causes water to collect at the leaf tips, and strong light then causes tip burn. If the water quality is polluted, or if the orchids are exposed to acid rain, leaf burn can also be caused.

(4) Fertilizer damage injuring leaves. When fertilizing at the roots, if the fertilizer concentration is too high and the frequency too great, orchid roots become scorched black, which in turn causes orchid leaf tip burn.

(5) Pesticide applied too concentrated. Pesticides are mixed in a certain ratio; if the concentration exceeds the standard and too much is sprayed, the pesticide accumulates at orchid leaf tips, injuring the tips and causing tip burn.

(6) Growing medium too dry. Being too lazy to water causes the medium in the pot to become too dry, unable to meet the orchid plant's water needs, forming empty roots. Orchid leaves cannot receive a normal water supply, and water loss causes tip burn.

The above cases of orchid leaf tip burn caused by natural factors or improper management are usually called physiological tip burn. This kind of tip burn is usually black, and there is no black transverse line at the edge of the affected area. It does not advance rapidly, its course is relatively slow, and the degree of harm is not great. As long as the cause is identified and management is targeted accordingly, the damage to orchid leaves can be controlled.

2. Tip burn caused by pathogens

(1) Bacterial brown spot disease. Brown spot disease of orchids is caused by bacteria infecting orchid leaves. It is the most vicious tip burn disease among orchid leaf diseases and is relatively easy to identify. Its lesions are brown. In the early stage of the disease, the leaves have water-soaked, faded spots that look as if they have been scalded by boiling water, and these rapidly join together and advance forward, causing an entire section of the leaf to die. It is extremely contagious, spreads rapidly, and is highly harmful.

(2) Anthracnose. Anthracnose of orchids is caused by fungi and is the most common tip burn disease of orchid leaves. It is relatively easy to identify. Its notable feature is that after the leaf tip is damaged and dries up, there are several wavy transverse black bands. If the burned tip leaf is cut off and no fungicide is applied, it will continue to advance forward. It is a relatively serious tip burn disease.

(3) Black spot disease. Black spot disease of orchids is caused by fungi and is one of the most common tip burn diseases of orchid leaves. It is relatively easy to identify. Its notable feature is that the lesions are round and scattered on the leaf surface and leaf margins. In severe cases, they can also join together, causing an entire orchid leaf to lose its ornamental value.

(4) Leaf blight. Leaf blight of orchids is caused by fungi and is one of the more vicious tip burn diseases. It is relatively easy to identify. Its notable feature is that in the later stage the leaf tip turns grayish white and an entire section dies, while the junction between diseased and healthy leaf tissue is dark brown and continually advances forward, even causing the entire leaf to dry up rapidly. It is highly harmful.

(5) Tip blight. Tip blight of orchids is caused by fungi and is the most common tip burn disease. It is relatively easy to identify. Its notable feature is that the dead portion is grayish yellow and has no band-like marks (which distinguishes it from anthracnose), and there are dark brown markings at the junction.

The above diseases sometimes occur singly and sometimes several occur at the same time. For example, if an orchid has both leaf blight and black spot disease, the black spots still remain after the leaf dies. Another example is if an orchid leaf has both anthracnose and black spot disease, both symptoms are present at the same time after the leaf dies.

Orchid leaf tip burn caused by pathogens is generally relatively serious in terms of damage. There is usually a black transverse line at the edge of the diseased area, and this black transverse line and lesion continually advance forward. In severe cases, an entire section of the leaf scorches and dies; even if it is cut off, it will continue to scorch and die, and if cut again it will scorch again, until the plant is bald. It can even threaten the life of the orchid plant, and must never be taken lightly.