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 on warm days and the nights turn cool, or during periods of cold weather if watering is not reduced.
Treatment: No treatment available.
Prevention: Water in the early morning when nighttime temperatures drop below 18°C. Reduce watering in autumn when plant growth slows down.
2. Calcium deficiency
Symptoms: Has a similar appearance to bacterial or fungal rot. Affects Cattleyas (especially Guarianthe) during periods of rapid growth. New leaves may turn black at the tips with an advancing yellow band, bud growth may be inhibited, and root tips may die back. Symptoms usually occur in spring and summer.
Treatment: Provide extra calcium during active growth. Use a good quality calcium-magnesium fertilizer, or add calcium nitrate to the water. You can also make calcium in hard water more available by using an acidifying fertilizer like 20-10-20.
Prevention: Provide extra calcium through a good cal-mag fertilizer or calcium nitrate.
3. Magnesium deficiency
Symptoms: Can cause cupped leaves, reduced growth, and marginal or interveinal chlorosis. Symptoms usually appear on older or middle leaves. In spring, older leaves turn yellow and drop as the plant translocates magnesium to new growth.
Treatment: Provide extra magnesium during active growth. Use a good quality calcium-magnesium fertilizer.
Prevention: Provide extra magnesium through a good cal-mag fertilizer.
4. Cold damage
Cold exposure symptoms: Growth slows down. Other symptoms include:
- Superficial lesions, pitting, sunken areas, and discoloration
- Water-soaked tissues, followed by wilting and browning
- Internal discoloration (browning)
- Accelerated natural tissue death
- Increased susceptibility to fungal and bacterial attacks
Frost damage symptoms: Symptoms may not appear immediately but may develop after exposure to warmer temperatures. Signs include dehydration or burning of foliage, necrotic spots on leaves, leading to the death of parts of the plant or the entire plant.
Treatment: Remove dead tissue to prevent secondary bacterial infections. As a precaution, apply a mixture with copper hydroxide to damaged areas with a toothbrush.
Prevention: Know your orchids' temperature requirements and closely monitor predicted minimum temperatures during winter.
5. Red spots and leaves
Symptoms: Red-violet spots form or leaves turn red-violet when exposed to intense light. This is due to anthocyanins, natural pigments present in all parts of the plant, with colors ranging from red to blue depending on pH.
Anthocyanins have several functions:
- Color flowers to attract birds and insects for pollination
- Protect the plant from ultraviolet rays by absorbing specific wavelengths of sunlight
- Increase the plant's resistance to low temperatures
6. Sunburn
Symptoms: Black spots suddenly appear on leaves when they overheat due to excessive light exposure. The burn often appears at the highest point of the leaf and eventually turns into a light brown scar.
Treatment: Sunburn is irreversible and leaf damage can promote secondary infections.
Prevention: Gradually move plants to brighter light conditions, progressively exposing them over a period of 2–3 weeks, so they slowly adapt to the new light intensity.
7. Dehydration
Symptoms: Primarily recognized by leaves that appear soft, limp, and wrinkled, similar to a withered flower. Leaves may become dull and yellow. Roots may appear dry, rotten, or soft to the touch.
Treatment: Two main cases:
- Plant not watered for a long time: roots will be gray, withered, and wrinkled but hard. Submerge the orchid in plain water until the roots turn green again. Then water whenever the roots turn gray or light in color.
- Plant watered regularly but still dehydrated: there are likely root problems. Check the condition of the roots — they are probably rotten. See the root rot section on the diseases page.
Prevention: Water regularly.
8. Bud drop
Symptoms: Buds wither and fall from an otherwise healthy plant, do not open into flowers, or rot inside the sheath.
Causes: If you have just bought an orchid, the most likely cause is bud damage due to relocation or abrupt changes in light and water. Other causes may include:
- Substrate too dry (drains moisture from buds) or too wet (root rot)
- Sudden temperature changes
- Chemical substances in the air (fumes, ethylene from combustion engines)
- Insects such as aphids and thrips feeding on buds
- Too low humidity, excessive exposure to lamps, fertilizer damage
- Sometimes with no apparent cause
Prevention: Adopt good cultural practices, maintaining adequate humidity and temperature levels. If a sheath starts to yellow or darken, gently remove it to prevent condensation from rotting the buds. In case of aphids or thrips, treat with an insecticide safe for flowers.
9. Weeds and ferns
Symptoms: When ferns begin to grow in an orchid pot, their robust rhizomes and fibrous roots quickly fill the pot, suffocating the orchid's roots. The plant will go into a slow decline as the rotting roots can no longer support its growth.
Treatment: Remove ferns and weeds as soon as they begin to emerge in the pot. If you wait too long, you will need to take the plant out, remove all growing material and ferns from around the roots, then repot with new, sterile substrate.
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 the substrate.
10. Substrate mold
Mold is usually caused by the fungus Ptychogaster. This powdery fungus, with white filaments, grows on decomposing organic matter but does not directly feed on the plant.
Symptoms: The first sign is a white, fluffy growth on the surface and within the substrate. As the infection progresses, the fungus permeates the substrate and eventually covers the roots. Being water repellent, it prevents the roots from absorbing water, leading to poor growth and, in severe cases, plant death.
Treatment: Repot the orchid into a new, fresh substrate, making sure to remove all decaying material hosting the fungus.
Prevention: Coarser substrates with a certain amount of inorganic material are less favorable for fungal growth than bark-only substrates. It is advisable to use high-quality bark and repot plants before the substrate begins to degrade.
11. Fertilizer burn
Salt accumulation: Salts present in irrigation water and those added with fertilizers accumulate over time. The accumulation appears as whitish or brownish crusts on the substrate and around the pot. Excess fertilizer salts can burn and kill orchids.
Symptoms: Lack of root growth can indicate a harmful concentration of mineral salts in the substrate. If a problem is suspected, remove the plant from the pot and check 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 compromised pseudobulbs appear.
Treatment: Rinse the pot thoroughly once a month, watering with large amounts of water to dissolve the salts. After one hour, repeat watering to completely eliminate accumulated salts.
Prevention: It is preferable to use a diluted fertilizer, with a concentration of one-quarter or one-eighth of the dose indicated on the label, rather than using full-strength fertilizer.
