Symptoms:  Excess water is absorbed by the roots quicker than it is lost by the leaves, causing swelling of plant cells and producing a blister-like lesion. Occurs when plants watered during warm days and the nights turn cool or during periods of cool weather when water quantity and/or frequency is not reduced.

Treatment: No treatment.

Prevention:  Water early in the morning when nighttime temperatures drop below 65F. Reduce watering in the fall when plant growth slows.

Read More: Edema (Robert Cating, IFAS Extension, University of Florida)

Symptoms:  Calcium deficiency has a similar appearance to a bacterial or fungal rot, but is really the same problem as blossom end rot in tomatoes. It affects cattleyas, especially the Guarianthe, primarily during periods of rapid growth. Calcium, a lesser macronutrient, is used to build cell walls. Deficiencies usually occur in spring and summer during periods of active growth. New leaves may turn black at the tips. The affected area has an advancing yellow band. Bud growth may be inhibited or buds may develop impoperly. A calcium deficiency may also cause death of root tips. (extracted from Orchid Species Culture by Margaret L. and Charles O. Baker)

Treatment: Supply extra calcium when the plant is in active growth. Use a good cal mag fertilizer, add calcium nitrate at the rate of 1/2 teaspoon per gallon to your water (alternating with Epsom salts) between fertilizations, add 1 tablespoon of dolomitic lime per gallon or top dress with powdered dolomite as a source of calcium and magnesium during the hot months when calcium requirements are high.

Prevention:  Supply extra calcium via a good cal mag fertilizer, calcium nitrate or dolomitic lime. You can also make the calcium present in our well water more available to the plant by using an acidity generating fertilizer like 20-20-20 or one of the fertilizers available from SAOS.

Read More: More Black Tips (Rockhampton Orchid Society)

Symptoms:  Magnesium deficiency can result in cupped leaves, a reduction in growth and marginal or interveinal chlorosis (yellow along leaf edges or between veins) and usually is exhibited in the middle or older leaves (extracted from Orchid Species Culture by Margaret L. and Charles O. Baker). It can also cause an increase in appearance of anthocyanin (red/purple coloration) in leaves, particularly after exposure to cooler temperatures.

Treatment: Supply extra magnesium when the plant is in active growth. Use a good cal mag fertilizer, add epsom salts at the rate of 1 teaspoon per gallon to your water each month (you can add 1 tbsp/gallon as a correction to reddened leaves), add 1 tablespoon of dolomitic lime per gallon or top dress with powdered dolomite.

Prevention:  Supply extra magnesium via a good cal mag fertilizer, epsom salts or dolomitic lime. You can also make the magnesium present in our well water more available to the plant by using an acidity generating fertilizer like 20-20-20 or one of the fertilizers available from SAOS.

Read More: Leaf Reddening from Magnesium Deficiency after Exposure to Cold (Dr. Martin Motes)

Symptoms of Chilling: Slowed growth, or limited growth flush. This may be difficult to detect without non-chilled plants for comparison or a thorough knowledge of the orchid’s normal growth rate. Other symptoms include:
-   Surface lesions, pitting, large, sunken areas and discoloration
-   Water-soaking in tissues, usually followed by wilting and browning
-   Internal discoloration (browning)
-   Accelerated rate of natural death
-   Increased susceptibility to attack by fungi and bacteria

Symptoms of Freezing:  Obvious symptoms may not be present until after the plant has been stressed by warm temperatures. Freeze symptoms include:
-   Desiccation or burning of foliage
-   Water-soaking in tissues, usually followed by wilting and browning
-   Water-soaked areas that progress to necrotic spots on leaves
-   Death of sections of the plant or the entire plant

Treatment:  Remove the dead tissue to prevent secondary bacterial infection. As a precaution, create a slurry with cupric hydroxide (Kocide or Champion) combined in equal parts with mancozeb (Manzate or Dithane M45) and apply to damaged tissue with a toothbrush.

Prevention:  Know the temperature requirements of your orchids and watch the projected nighttime lows during winter.

Read More:  Cold Damage (Robert Cating, University of Florida), Treating Cold Damage in Orchids and Leaf Reddening after Exposure to Cold (Dr. Martin Motes), Cold Damage and Mesophyll Cell Collapse (Susan Jones, American Orchid Society).

Symptoms:  Sudden appearance of black spots on leaves when the leaves become overheated from too much light caused by a sudden increase in light during the change in season or moving plants outdoors in the spring. The burn often will occur on the highest point of the leaf where it is exposed to the most sun. Burn fades to thin tannish leaf scar over time.

Treatment:  Sunburn is irreversible and leaf damage could be an invitation to secondary infection.

Prevention:  Move plants slowly into brighter light, moving them into slightly greater light over a 2 to 3 week period so they gradually become acclimated to the higher light conditions.

Symptoms:  Bud blast can take many forms. Buds may wither and fall from an otherwise healthy plant, buds can fail to open into flowers or the buds may rot in the sheath.

Causes:  If you've just brought an orchid home, the most likely reason for bud blast is the damage to the sensitive bud from its being moved or radical changes in the amount of light and water the plant is used to. It can also be caused by too much water: too dry and the moisture can be drawn from the sensitive buds or too much water can cause root rot and the plant can't sustain the emerging flower. Radical temperature changes can also cause it: drafts from an air conditioner or heater can cause bud drop and condensation from day night temperature changes can cause buds in the sheath to rot. Chemicals from fumes and ethylene from combustion engines can cause the buds to age and distort flowers. Insects like aphids and thrips can feed on the buds and cause them to drop or be deformed after opening. Other reasons include drying out from too low of humidity or being too close to grow lights and chemical damage from fertilizers. Sometimes bud blast occurs and there is no obvious reason from it.

Prevention:  The best prevention is good cultural practices maintaining the proper moisutre and temperature for your plants to thrive. If a sheath starts to yellow or darken, carefully peel it back to prevent condensation from rotting the buds. If there is evidence of aphids or thrips, spray the plants with a chemical that won't damage the flower (such as a dilute Orthene).

Read More: Bud Blast (Susan Jones, AOS).

Symptoms:  If you get water soluble fertilizer on your flowers while you are watering, you have the potential for burning the flowers, particularly if you use a full strength rather than dilute fertilizer. The fertilizer salts will burn the flower leaving a water soaked spot. Fertilizing blooming plants may also shorten the blooming time.

Treatment:  After you’re done fertilizing, come back with a plain water spray on the flowers to wash the fertilizer off the flowers to prevent their spoiling.

Prevention:  It is safer to use a more dilute fertilizer more frequently than full strength fertilizer. Try using one quarter to one eighth of the labeled strength weekly (when you water), unless you determine your plant needs a higher fertilizer concentration.

Salt Buildup:  Salts present in your water supply and added by fertilizers accumulate over time. Salt buildup looks like whitish to brownish crusts on the medium and around the pot, or on the surface of the mounting substrate on mounted orchids, and can be a sign of over-fertilizing. If allowed to remain, those salts will negatively impact the health of your plant. Excess fertilizer salts burn and kill orchids

Symptoms:  Lack of root growth may indicate an unhealthy concentration of mineral salts in the medium, on up to full fertilizer burn. If this is suspected, decant the plant and check its roots. Dead root tips, brown roots or salt crust on the potting medium surface are signs of trouble. In later stages, brown leaf tips, leaves and eventually pseudobulbs may appear, indicating burned roots. If allowed to continue, fertilizer burn will eventually kill the plant.

Treatment:  Flush the pot monthly by watering with copious amounts of water to solubilize salts and then watering again an hour later to flush accumulated salts from the pot.

Prevention:  It is preferable to use a dilute fertilizer, say one quarter to one eighth of the labeled strength.