Giulio Celandroni Orchidee

1. Bacterial Soft and Brown Rot

Symptoms by species:

• Phalaenopsis: Small water-soaked spots on leaves, often with yellow halos. The infection rapidly rots leaves and roots with an unpleasant odor. Plants can completely rot in 2–3 days.
• Dendrobium: Yellow and water-soaked leaves, then black and sunken. In pseudobulbs, the infection progresses more slowly.
• Paphiopedilum: Small round spots near the central part of the leaf, initially yellow and water-soaked, then reddish-brown and sunken. Can reach the growing point before the leaf tip.
• Grammatophyllum: Water-soaked spots that turn brown, black, and sunken.

Treatment: Immediately remove infected tissue with a sterile tool. Spray bactericides with quaternary ammonium or copper compounds on infected and adjacent plants (copper should not be used on Dendrobiums or flowering plants).

Prevention: Avoid overhead watering if infection is present. Keep leaves dry, increase air circulation, and reduce temperature and humidity. Periodic preventative sprays with copper compounds help, especially during hot and humid weather.

2. Bacterial Brown Spot

Symptoms: The most common and severe disease of Phalaenopsis. Begins as a small, soft, water-filled blister, dirty green in color, which enlarges, merges with other spots, and turns brown or black, dry, and sunken. More frequent during the hot season.

• Phalaenopsis: Blister-like spots with a yellowish or pale green halo. If it reaches the growing point, the plant dies.
• Cattleya: Well-defined, sunken black spots, progresses slowly and is rarely lethal in mature plants.

Treatment: Immediately remove infected tissue with a sterile tool. Spray bactericides with quaternary ammonium or copper compounds (not on Dendrobiums or flowering plants). Also treat nearby plants.

Prevention: Reduce humidity and temperature, avoid overhead watering, and increase air circulation.

3. Black Rot

Symptoms: Infection usually starts in the roots or the basal part of the pseudobulb. It spreads rapidly under conditions of high temperature and humidity.

• Pseudobulbs, roots or rhizomes: Purplish-black areas, often well-defined. The infection can travel up to the base of the pseudobulb or leaf, causing it to fall off at the slightest touch.
• Cattleya: Creamy yellow discoloration on one or both sides of the pseudobulbs, which then turns black or brown and leads to bulb decay.

Treatment: If the plant is valuable, isolate it, remove infected tissue with a sterile tool, and treat with an appropriate fungicide.

Prevention: During particularly humid or rainy periods, carry out preventative treatments with suitable fungicides.

4. Fusarium Wilt

Symptoms: Fusarium blocks the flow of moisture through the plant's vascular system.

• Cattleya: Leaves turn yellow, thin, wrinkled, and eventually die. The diagnostic symptom is a purple or pinkish-purple ring or band on the outer layers of the rhizome, visible when cut. Severely infected plants can die in 3–9 weeks.
• Phalaenopsis and Paphiopedilum: Roots begin to rot, and the base of the plant develops a dry, black rot. Older leaves become leathery, younger ones may take on a reddish hue. The flower stem may develop rotten spots with premature bud drop.

Cattleya Treatment: Eliminate infected parts of the rhizome and pseudobulbs with the purple band. Repot only the healthy part. Soak in an appropriate fungicide and thoroughly disinfect the area and tools.

Phalaenopsis/Paphiopedilum Treatment: Eliminate severely infected plants, remove damaged tissue and all infected roots, treat with fungicide.

Prevention: Sterilize cutting tools after each use (preferably by flaming). For Phalaenopsis, maintain an adequate balance of temperature, substrate humidity, and fertilization.

5. Collar Rot

Symptoms: Rapid collapse and decomposition of roots, pseudobulbs, and lower parts of leaves. Infected tissue turns creamy yellow, then brown, collapses, and quickly rots. Leaves yellow, wilt, and die. Small yellow or light brown sclerotia (similar to mustard seeds) form on infected tissue: this is the dormant form of the fungus.

Treatment: Remove infected parts with a sterile tool. Immerse the remaining plant in an appropriate fungicide.

Prevention: Proper hygiene, good air circulation, and lower temperatures. The pathogen is most active in warm, high-humidity seasons.

6. Root Rot

Symptoms: Appears when the substrate degrades, drainage is poor, and/or plants are overwatered. Infection develops when roots are damaged by wounds, salt buildup, or excessive fertilization.

• Cattleya: Rhizoctonia spreads slowly from older pseudobulbs to younger ones. Infected pseudobulbs become brown, hard, and fibrous. Leaves turn yellow, wrinkle, and fall off, while older pseudobulbs yellow and brown from the base upwards.

Treatment: Remove infected parts with a sterile tool. Immerse the remaining plant in an appropriate fungicide.

Prevention: Use well-draining substrates, avoid overwatering, and maintain proper hygiene.

7. Anthracnose

Symptoms: Dark brown or light gray spots on leaves, sometimes arranged in concentric rings or dark bands. The infected area is usually well-defined and slightly sunken. Watery, black or brown pustules appear on flowers, usually raised on older sepals and petals.

Treatment: Spray an appropriate copper-containing fungicide, carefully following label instructions.

Prevention: Proper hygiene, good air circulation, lower temperatures, and increased light. The pathogen is most active in warm weather, low light, and high humidity.

8. Leaf Spots

Cercospora

Infection begins with a yellow spot on the underside of the leaf, then visible on the upper surface. Spots enlarge into irregular shapes, become slightly sunken and necrotic, taking on a purplish-brown color. Severely infected leaves fall prematurely.

Pseudocercospora

Causes irregular leaf spots and blemishes. Spots can be circular, purple or black with brownish-black specks as they expand. On the upper surface, the infection can appear as a mosaic pattern, while on the underside, corresponding specks of fungal spore structures form.

Guignardia

First signs are tiny, elongated dark purple lesions on both leaf surfaces, developing parallel to the veins. Spots merge to form large, irregular lesions. Over time, the center becomes leathery, and black fruiting bodies with a sandpaper-like texture appear. Also known as Phyllosticta.

Phyllosticta

Initial lesions are small, yellow, and slightly sunken. Over time, they become round or oval, light or dark brown, with a slightly raised red or purplish-black margin. Small black spore structures appear in the center. Severely infected leaves fall prematurely. Also known as Guignardia.

Septoria

Initial spots are small, yellow, and slightly sunken on both leaf surfaces. As the infection progresses, spots enlarge, becoming dark brown or black, with circular or irregular shapes. Severely infected leaves fall prematurely.

Treatment (all leaf spots): Spray a suitable fungicide containing copper or quaternary ammonium compounds, following label instructions.

Prevention: Maintain good hygiene and ensure proper air circulation. Reduce leaf wetness. If the fungus is a recurring problem, apply preventative fungicides monthly.

9. Botrytis

Symptoms: Small black or light brown spots on flower petals, which can enlarge to cover the entire flower. Under conditions of high humidity, a gray mold may appear on the surface of severely infected flowers.

Treatment: Remove infected flowers, then spray an appropriate fungicide. This fungus is widespread in the environment and cannot be completely eliminated.

Prevention: Remove infected flowers (they act as a reservoir for infection). Maintain adequate hygiene, increase air circulation, reduce humidity, and maintain warmer night temperatures (>20°C).