1. EDEMA
Symptoms: Excess water is absorbed by the roots faster than it is lost by the leaves, causing plant cells to swell and form blister-like lesions. This occurs when plants are watered during hot days and cool nights, or during periods of cold weather if the amount and/or frequency of watering is not reduced.
Treatment: No treatment.
Prevention: Water early in the morning when nighttime temperatures drop below 64°F (18°C). Reduce watering in the fall, when plant growth slows.
2. CALCIUM DEFICIENCY
Symptoms: Calcium deficiency resembles bacterial or fungal rot. It affects cattleyas, particularly Guarianthes, especially during periods of rapid growth. Calcium, a secondary macronutrient, is essential for cell wall formation. Deficiencies usually occur in spring and summer, during active growth. New leaves may turn black at the tips, with a yellow band advancing. Bud growth may be inhibited, or the buds may develop abnormally. A calcium deficiency can also cause root tips to die.
Treatment: Provide extra calcium during active plant growth. Use a good-quality calcium-magnesium fertilizer, or add calcium nitrate to the water. You can also make the calcium present in hard water more available by using an acidifying fertilizer such as 20-10-20.
Prevention: Provide extra calcium through a good fertilizer cal mag, calcium nitrate
3. MAGNESIUM DEFICIENCY
Symptoms: Magnesium deficiency can cause curled leaves, reduced growth, and marginal or interveinal chlorosis. Symptoms usually appear in older or middle leaves. When growth resumes in spring, the older leaves of magnesium-deficient plants turn yellow and drop as the plant transfers magnesium to new growth.
Treatment: Provide extra magnesium during active plant growth. Use a good-quality calcium-magnesium fertilizer.
Prevention: Provide extra magnesium through a good cal mag fertilizer.
4. COLD DAMAGE
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Symptoms of Cold Exposure: Growth slows or decreases.
Other symptoms include:
• Superficial lesions, cavities, large sunken areas and discoloration
• Fabrics soaked in water, usually followed by wilting and browning
• Internal discoloration (browning)
• Acceleration of natural tissue death
• Increased susceptibility to fungal and bacterial attacks
Frost Symptoms: Obvious symptoms may not appear immediately, but may appear after the plant has been exposed to warmer temperatures. Signs of frost damage include:
• Dehydration or burning of the foliage
• Fabrics soaked in water, followed by wilting and browning
• Waterlogged areas that develop into necrotic spots on leaves
• Death of parts of the plant or the entire plant
Treatment:
Remove dead tissue to prevent secondary bacterial infections. As a precaution, create a mixture with copper hydroxide and apply it to the damaged areas with a toothbrush.
Prevention:
Know the temperature needs of your orchids and carefully monitor the minimum temperatures expected during the winter.
5. RED POINTS AND LEAVES
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Symptoms : Reddish-purple spots form or the leaves turn reddish-purple when exposed to intense light. This is caused by anthocyanins, natural dyes found throughout the plant, giving it colors ranging from red to blue depending on the pH.
These have several functions:
- They color flowers to attract birds and insects for pollination.
- They protect the plant from the sun's rays, including ultraviolet rays. They absorb a specific wavelength of sunlight, protecting the underlying tissues.
- They increase the plant's resistance to low temperatures
Treatment and Prevention: So, when you see these spots on your orchid or the leaves turning reddish-purple, there's no need to worry! It's just the plant protecting itself from the sun's rays and "tanning." What you can do is shield it from the light or move the plant to a less bright spot.
A slight presence of anthocyanins on the leaves, especially in orchid species like Vanda, Ascocentrum, and some Cattleyas, which prefer bright light, is a sign of a plant's (positive) response to environmental conditions. This doesn't mean they can be kept in full sun during the hot season; they should still be protected from direct sunlight!
Caution: some varieties of orchids, characterized by white flowers, may have a reduced ability to produce anthocyanins even in the leaves, and for this reason they should not be exposed to too much light.
6. SUNBURN
Symptoms: Black spots suddenly appear on leaves when they overheat due to excessive exposure to light. The burn often appears at the top of the leaf, where it receives the most sun. Over time, the damaged area turns into a thin, light brown scar.
Treatment: Sunburn is irreversible and leaf damage can promote secondary infections.
Prevention: Gradually move the plants to brighter light conditions, exposing them progressively to higher brightness over a period of 2-3 weeks, so that they slowly adapt to the new light intensity.
7. DEHYDRATION
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Symptoms:
It is primarily recognized by its leaves, which appear soft, limp, and wrinkled, resembling those of a wilted flower. The leaves may also become dull and yellow, taking on a yellow-brown hue if severely dehydrated. The roots, on the other hand, may appear dry and rotten, or simply soft to the touch, lacking their usual consistency.
Treatment:
If an orchid is dehydrated, it needs to be rehydrated. This can be done in several ways, depending on the severity of the dehydration and the condition of the roots.
I would make two main distinctions: if the plant hasn't been watered for a long time, that's probably the cause, and the roots will be gray, wilted, wrinkled, but still hard. In this case, simply soak the orchid in water (only) until the roots turn green again. And then remember to water it every time the roots turn gray or otherwise light in color.
If, however, you water it regularly and the orchid appears dehydrated, there will certainly be root problems. It's therefore important to check the condition of the roots, which are likely rotten. I refer you to the diseases page, where you'll find root rot at number 6.
Prevention:
water regularly.
8. FALL OF THE BUDS
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Symptoms:
Bud drop can manifest itself in various ways. Buds may wilt and fall from an otherwise healthy plant, fail to open into flowers, or rot inside the sheath.
Causes:
If you have just purchased an orchid, the most likely cause is damage to the sensitive buds due to moving or sudden changes in the light and water conditions to which the plant was accustomed.
Other causes may be:
• Water can be a determining factor: if the substrate is too dry, moisture can be drawn from sensitive buds; if it is too wet, it can cause root rot, preventing the plant from sustaining flowering.
• Sudden temperature changes can cause buds to drop.
• Chemicals in the air, such as fumes or ethylene from combustion engines, can accelerate the aging of buds and deform flowers.
• Insects such as aphids and thrips can feed on the buds, causing them to fall off or become deformed after opening.
• Too low humidity, excessive exposure to grow lights, and chemical damage from fertilizers can also cause bud drop.
• Sometimes, bud drop occurs without any apparent cause.
Prevention:
The best prevention is to adopt good cultural practices, maintaining adequate humidity and temperature levels for the plant to thrive. If a sheath begins to yellow or darken, carefully remove it to prevent condensation from rotting the buds. If there are signs of aphids or thrips, treat the plants with a flower-safe insecticide.
9. WEEDS AND FERNS
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Symptoms:
When ferns begin to grow in an orchid pot, their sturdy rhizomes and fibrous roots quickly fill the pot, suffocating the orchid's roots. The orchid will slowly decline, as the decaying roots can no longer support the plant's growth.
Treatment:
Remove ferns and weeds as soon as they begin to emerge from the pot. If you wait too long, you'll need to remove the plant from the pot, remove all growing material and any remaining ferns around the roots, and then repot with fresh, sterile soil.
Prevention:
Avoid growing ferns near orchids and keep the growing area free of weeds. Spores spread easily through the air and always find a way to take root in orchid substrate.
10. MOLD IN THE SUBSTRATE
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Mold is usually caused by the fungus Ptychogaster.
This powdery fungus, with white filaments, grows on decaying organic matter, but does not feed directly on the plant.
Symptoms:
The first sign of snow mold is a fluffy white growth on the surface and inside the growing medium. As the infection progresses, the fungus permeates the substrate and eventually covers the roots. Being water-repellent, it prevents the orchid's roots from absorbing water, causing poor growth and, in severe cases, the death of the plant.
Treatment:
Repot the orchid in fresh, new substrate, making sure to remove all decaying material harboring the fungus.
Prevention:
Coarser substrates with a certain amount of inorganic material are less conducive to fungal growth than substrates based solely on bark. It's advisable to use high-quality bark and repot the plants before the substrate begins to degrade.
11. FERTILIZER BURNS
Accumulation of Salts:
Salts in irrigation water and those added with fertilizers accumulate over time. Salt buildup appears as whitish or brownish crusts on the substrate and around the pot, or on the surface of the substrate in mounted orchids. This phenomenon can also be a sign of overfertilization. Excess fertilizer salts can burn and kill orchids.
Symptoms:
Lack of root growth may indicate a harmful concentration of mineral salts in the substrate, potentially causing actual fertilizer burn. If you suspect a problem, remove the plant from the pot and inspect the roots. Dead root tips, brown roots, or salt crusts on the substrate surface are warning signs. In advanced stages, brown leaf tips, damaged leaves, and eventually damaged pseudobulbs may appear, indicating burned roots.
Treatment:
Rinse the pot thoroughly once a month, watering generously to dissolve the salts. After an hour, repeat the watering process to completely remove the accumulated salts.
Prevention:
It is preferable to use a diluted fertilizer, with a concentration equal to one-quarter or one-eighth of the dose indicated on the label, rather than using the full-strength fertilizer.
Collaboration between Criplant and Giulio Celandroni Orchids
Info: St. Augustine Orchid Society
