An Illustrated Analysis of Orchid Leaf Tip Burn and Other Disorders

(1) Main Causes of Orchid Leaf Tip Burn
There are many causes of orchid leaf tip burn. Some are natural factors, some result from improper management, and some are caused 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 inCymbidium faberiwhose leaves are longer; if water cannot be supplied adequately, tip burn is inevitable. The water supply to orchid leaves comes partly from transport by the roots and partly from absorption from the air. Therefore,orchidleaf tip burn is caused not only by potting soil that is too dry, but also has a great deal to do with air humidity being too low. If the air humidity is too low and the air is too dry, transpiration of the orchid plant increases, the water supply and demand of the leaves becomes unbalanced, and tip burn results. Generally speaking, orchids grown indoorsGrowing orchidsexperience higher air humidity, so leaf tip burn is not serious, while orchids grown outdoorsOrchid Growingsuffer more serious leaf tip burn because air humidity is difficult to control.
(2) Sudden climate change: Taking 2007 as an example, people had just moved their orchids out of the relatively humid orchid house when they encountered a drought rarely seen in decades; rivers dried up to their beds, air humidity was extremely low, and orchid tip burn was therefore fairly serious. The plum rain season came late but lasted a long time, about 50 days; leaves that had not seen sunlight for so long were both thin and soft, and just after the plum rain season ended they immediately encountered high temperatures and strong sunlight, so the tip burn became even more serious.
(3) Air pollution: Being near sewage areas or industrial zones, or someone burning harmful substances near the orchid garden, fills the air with harmful gases that damage orchid leaves and cause tip burn.

2. Tip burn caused by improper management
(1) Light too strong: Neglecting shade in summer or providing insufficient shade causes light that is too strong, resulting in orchid leaf tip burn.

(2) Long-term shaded cultivation: If orchids are shaded too much during growth, with light that is too weak, and are kept in shade for a long time, the leaves become thin and weak; if the orchids are then 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 burns the tips. If the water used is polluted, or if the orchids are exposed to acid rain, leaf burn can also result.

(4) Fertilizer damage injuring the leaves: When fertilizing at the roots, if the fertilizer concentration is too high and the frequency too great, orchid roots are burned black, which in turn causes leaf tip burn.
(5) Pesticide too concentrated: Pesticides are formulated according to a certain ratio; if the concentration exceeds the standard and too much is sprayed, the pesticide accumulates at the orchid leaf tips, damaging them and causing tip burn.
(6) Growing medium too dry: Being lazy about watering makes the growing medium in the pot too dry to meet the orchid plant's water needs, forming empty roots; the leaves cannot receive a normal water supply, and dehydration causes leaf tip burn.

The several types of orchid leaf tip burn described above, 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 band at the boundary of the affected area; it does not advance rapidly, its course is relatively slow, and the degree of harm is not great. (Figure 1: Symptoms of physiological tip burn) As long as the cause is identified and management is adjusted accordingly, the damage to orchid leaves can be controlled.

Figure 1: Symptoms of physiological tip burn

3. Tip burn caused by pathogens

(1) Bacterial brown spot disease: OrchidFloralbrown spot disease 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, 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, causing an entire section of the leaf to die. It is extremely contagious, spreads rapidly, and is highly destructive. (Figure 2: Symptoms of brown spot disease)

Figure 2: Symptoms of brown spot disease

(2) Anthracnose: Orchid anthracnose 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 out, there are several wavy transverse black bands. If the burned tip is cut off and no fungicide is applied, it will continue to advance. It is a rather serious tip burn disease. (Figure 3: Symptoms of anthracnose)

Figure 3: Symptoms of anthracnose

(3) Black spot disease: Orchid black spot disease 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 over the leaf surface and leaf margins, and in severe cases they can join together, causing an entire orchid leaf to lose its ornamental value. (Figure 4: Symptoms of black spot disease)

Figure 4: Symptoms of black spot disease

(4) Leaf blight: Orchid leaf blight 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 tissue is dark brown and keeps advancing, even causing the whole leaf to dry up rapidly. It is highly destructive. (Figure 5: Symptoms of leaf blight)

Figure 5: Symptoms of leaf blight

(5) Tip blight: Orchid tip blight 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 with no band-like marks (which distinguishes it from anthracnose), and there are dark brown markings at the junction. (Figure 6: Symptoms of tip blight)

Figure 6: Symptoms of tip blight

The several diseases described above sometimes occur singly and sometimes several occur at the same time. For example, an orchid may suffer from both leaf blight and black spot disease, and after the leaf dies the black spots still remain. (Figure 7: Black spot disease occurring on a leaf blighted leaf).

Figure 7: Black spot disease occurring on a leaf blighted leaf

Another example is when orchid leaves suffer from both anthracnose and black spot disease; after the leaf dies, both symptoms are present at the same time. (Figure 8: Anthracnose and black spot disease causing damage simultaneously)

Figure 8: Anthracnose and black spot disease causing damage simultaneously

Orchid leaf tip burn caused by pathogens is generally quite serious; there is usually a black transverse band at the boundary of the affected area, and this black transverse band lesion keeps advancing (Figure 9: Black transverse band at the junction of diseased and healthy leaf tissue). In severe cases an entire section of the leaf withers, and even if it is cut off it will continue to wither; cut again and it withers again, until the plant is bald. It may even threaten the life of the orchid plant.

Figure 9: Black transverse band at the junction of diseased and healthy leaf tissue

(2) Accurate Diagnosis of Orchid Leaf Tip Burn Diseases
Although the symptoms of the various tip burn diseases have been explained fairly clearly above, ordinary orchid growers still find it difficult at first to tell what cause is behind a given case of tip burn. In fact, as long as one observes carefully, it can still be identified. (Figure 10: Physiological tip burn, brown spot disease, anthracnose, tip blight, leaf blight and black spot disease) From this picture their notable differences can be clearly seen.

Figure 10: Physiological tip burn, brown spot disease, anthracnose, tip blight, leaf blight and black spot disease

1. Physiological tip burn: (water damage, fertilizer damage, pesticide damage, etc.) The damaged area is entirely black, with no black stripes at the junction; with pathological tip burn, after the leaf dries out it is not black, and there are black stripe lesions at the junction.
2. Lesions caused by bacteria: In the early stage there are water-soaked brown patches that look as if scalded by boiling water; whereas tip blight caused by fungi has no yellowish-brown patches.
3. Diseases caused by fungi: Generally there are black transverse bands at the junction. On tips damaged by anthracnose there are several transverse wavy black lines, while other diseases do not have this wavy pattern; leaves damaged by leaf blight are grayish white; leaves damaged by tip blight are grayish yellow.
To sum up: the damaged area of physiological tip burn is entirely black, with no black transverse band at the junction of diseased and healthy leaf tissue; the damaged area of bacterial brown spot disease begins as brown patches and later the lesions turn black, with a black transverse band at the junction of diseased and healthy leaf tissue; leaves damaged by anthracnose have several transverse wavy black lines, with a black transverse band at the junction of diseased and healthy leaf tissue; the damaged area of leaf blight is grayish white, with a black transverse band at the junction of diseased and healthy leaf tissue; the damaged area of tip blight is grayish yellow, with a black transverse band at the junction of diseased and healthy leaf tissue.
Only by accurately grasping the symptoms of each kind of tip burn disease can one have a clear understanding and take targeted action when treating tip burn. Therefore one must put effort into studying it and truly treat the disease according to its cause.

(3) Measures to Eradicate Tip Burn Diseases
It is fairly difficult to fundamentally eliminate orchid leaf tip burn caused by disease, but as long as one deals with it actively, manages carefully and uses integrated control, notable results will certainly be achieved.

1. Diseased leaves must be cut off: Once a leaf tip has burned, there is no point in being reluctant to cut it off; it must be resolutely cut away with no hesitation. Diseased leaves must be removed thoroughly, and the cut should be more than 1 cm away from the lesion. If an old plant is severely affected, the entire plant can be cut away without mercy. (Figure 11: Cutting off diseased leaves) Then spray with thiophanate-methyl. After cutting off diseased leaves, they must be burned or buried deep; on no account should the cut diseased leaves be left in the orchid garden, and any diseased leaves that fall to the ground during pruning must also be picked up, to prevent them from becoming a source of infection again.

Figure 11: Cutting off diseased leaves

2. Medication must match the cause: Once orchid leaf tips have burned, one must find out what caused it. If it is physiological tip burn caused by improper management, then strengthen management accordingly. If it is tip burn caused by disease, then first distinguish whether it is caused by bacteria or fungi. This is very easy to distinguish: bacterial brown spot disease has an obvious symptom, namely that in the early stage the lesions look water-soaked as if scalded by boiling water. Diseases caused by bacteria are controlled with agricultural streptomycin, yekuning and copper hydroxide; diseases caused by fungi are controlled with thiophanate-methyl, chlorothalonil, Score and similar fungicides. If it is difficult for a time to distinguish which disease it is, then mix a bactericide and a fungicide and use them together, which can also achieve twice the result with half the effort.
3. Treatment must be timely: Once disease is discovered, medication must be applied promptly for treatment. One must absolutely not have the numbing attitude that “it does not matter if orchid leaf tips burn,” and even less the mistaken idea that “orchid leaf tip burn is normal,” thereby delaying treatment and causing the disease to worsen and spread. One must clearly recognize that diseases of orchid leaves spread very quickly; although they may not be fatal, they cause the plant to lose its ornamental value.
4. Prevention must be carried out consistently: “Prevention is more important than treatment.” Preventive work must be carried out consistently without slackening. Spray pesticide solution regularly; preventive medication should begin in early spring, with bactericides and fungicides used together, once every 10 to 15 days. Even if no disease is found, medication should still be applied, to take preventive measures and eliminate the disease in the bud.
5. Water spraying must be strictly prohibited: Once tip burn caused by pathogens appears on orchid leaves, spraying water must be strictly prohibited. This is because spraying water moistens the leaf surface and accelerates pathogen reproduction, and at the same time spraying water accelerates the spread of pathogens, causing vicious transmission. If there is too much dust on the leaf surface, affecting the orchid's photosynthesis and respiration, then after spraying water and once the leaf surface is dry, immediately spray copper hydroxide together with other fungicides, to prevent the spread and transmission of pathogens.
6. Management must be strengthened: Not only is physiological tip burn of orchid leaves related to management; tip burn caused by bacteria is, in the final analysis, also closely related to management. Therefore we must think more and study more where management is concerned, do a good job of managing orchids, and do as much as possible to eliminate human-caused orchid leaf tip burn.
7. Buying plants must be done with care: Re-exported plants and greenhouse seedlings, having grown for years in high-temperature, high-humidity environments, are almost raised soaking in chemical solutions. Once transplanted into a natural environment, because of stronger light, lower humidity and other reasons, they will rapidly develop burned tips and shrunken leaves.
8. Pesticides must be rotated: Any pesticide used for a long time will produce resistance, so one must never use one pesticide for a long time to control disease. Pesticides should be rotated frequently; generally speaking, each pesticide can be used three times in a row before switching, which can achieve fairly good control results.