Disease: soft bacterial rot and brown bacterial rot
Pathogen: Pectobacterium (syn. Erwinia)
Symptoms: small watery spots on leaves, often with yellowish margins. If untreated, the infection will spread rapidly and affect roots and leaves, spreading more slowly in the case of rhizomes and pseudobulbs. An unpleasant odor may be noticed.
Affected taxa: Phalaenopsis, Vanda, Dendrobium, Paphiopedilum, Grammatophyllum, Oncidium, Cambria.
Recommended treatment: Funguran, Champ, Aliette.
Disease: brown bacterial spot
Pathogen: Acidovorax (syn. Pseudomonas)
Symptoms: the most common and dangerous disease of the genus Phalaenopsis, manifests through the appearance of small, soft spots, in the form of swellings filled with liquid, of small size, located anywhere on the leaves, initially green in color; later, as their size increases, the color changes to brown or black, drying out and appearing as sunken areas on the leaf surface. When the infection reaches the leaf tip, it secretes liquid infected with bacteria, which contributes to contaminating other plants. Prevalent in the warm season.
Affected taxa: Phalaenopsis, Cattleya, mainly any species.
Treatment: Aliette, Champ, Funguran.
Disease: brown rot, fungal root rot
Pathogen: Rhizoctonia
Symptoms: root rot occurs when the growing medium decomposes, drainage is insufficient, and plants are overwatered, its onset being favored by mechanical injuries to the roots or due to salt deposits following excessive fertilization. In species of the genus Cattleya, the pathogen establishes more slowly, from older pseudobulbs to newer ones, climbing along the pseudobulbs and causing their browning, followed by their hardening. The roots of older plants, as well as other vegetative organs, will die. Although it is a root disease, symptoms can also be observed on the aerial parts, being similar to those caused by fusarium, namely yellowing of the leaves, drying and shriveling of them, followed by their falling and browning of the pseudobulbs from the lower part towards the tip.
Affected taxa: Phalaenopsis, Paphiopedilum, Miltonia, Oncidium and its hybrids, with extension to the artificial genus Cambria.
Treatment: Folpan, Dithane.
Disease: anthracnose
Pathogens: Colletotrichum, Glomerella
Symptoms: affects the aerial parts of the plant, most often the leaves, whose tips brown from the apex, advancing toward the base. Develops spots, sometimes with the appearance of concentric circles, other times in the form of dark bands, numerous, positioned transversely on the laminar surface. The affected areas are clearly defined, sometimes slightly sunken, while the rest of the leaf appears normal. Sporulating bodies develop in the infected areas. On flowers, watery, black or brown pustules appear, generally taller and preferably on the dorsal parts of older petals and sepals, which can merge and cover the entire flower. The pathogen most frequently associated with anthracnose is Colletotrichum gloeosporioides (in the asexual stage, the sexual stage being known as Glomerella cingulata). Another known pathogen is Colletotrichum theobromicola, which has not been known on orchids until now. It produces chlorotic (greenish) spotting on the upper surface of the leaf, but these spots also correspond on the lower surface, also forming sunken or necrotic spots.
Affected taxa: Paphiopedilum, Masevallia, Phalaenopsis, Stanhopea, Oncidium, Cattleya, Dendrobium.
Treatment: Dithane.
Disease: leaf spotting
Pathogens: Cercospora, Pseudocercospora, Guignardia, Phyllostycta, Septoria.
Symptoms:
Cercospora: the infection initially appears as a yellow spot on the underside of the leaf, and shortly after it becomes visible on the upper side as well. As its surface enlarges, it presents a slightly sunken and necrotic appearance and colors to brown-violet to black-violet. The spots continue to increase in size forming a circular or irregular pattern until they cover the entire leaf. The edges of the spots remain yellow. Heavily infected leaves fall prematurely, especially if the infection started from their base.
Pseudocercospora: causes leaf spots, manifested differently depending on the pathogen species and orchid cultivar, which can have circular to almost circular shapes, reflecting the growth mode of the fungal colony. Sometimes their color is violet-black, with small and numerous brown or black spots toward the interior as the spot size increases. Other species of Pseudocercospora produce smaller, irregularly shaped spots but in greater numbers. When larger leaf areas are affected, a general mosaic pattern is observed on the upper leaf surface, while the lower areas are covered with dots, represented by sporiferous bodies corresponding to the pattern on the upper surface.
Guignardia: the first signs of infection appear as small, dark violet, elongated lesions on any leaf surface, arranged parallel to the laminar venation, taking on an elongated or rhomboid appearance. Sometimes, adjacent lesions fuse, acquiring irregular shapes that can affect large areas of the leaf. With age, the center of the affected areas changes color, darkening, while sporiferous bodies develop inside them, having a rough texture. The disease mainly affects species of the genera Ascocentrum and Vanda, as well as their hybrids. The pathogen is also known as Phyllosticta, the name referring to a different sexual stage of the same fungus.
Phyllosticta: the spots produced can start in any region of the pseudobulbs or leaves, in the form of small lesions, yellow in color and slightly sunken. As they enlarge, they become round or oval, growing in depth, especially if the infection appears on leaves. Over time, they darken in color, becoming gray or dark brown, developing a slightly raised margin, reddish to violet-blackish. Finally, the development of central sporiferous structures is observed. Individual spots are about 6.5 mm in diameter. Leaves with severe infections may fall prematurely. The disease is favored by insufficient light radiation conditions. Phyllostachia represents a different sexual stage of the pathogen Guignardia.
Septoria: small spots can appear on any leaf surface, as small, sunken lesions, yellowish in color, which continue to grow, becoming brown or black, circular or irregular in shape. They can also merge, forming large irregular patterns. Severely infected leaves may fall prematurely.
Affected taxa: Cattleya, Vanda, Oncidium, Phalaenopsis.
Treatment: Dithane.
Disease: flower spotting
Pathogen: Botrytis
Symptoms: small spots, about 1 mm in diameter, on flowers, black or light brown in color. They can enlarge and cover the entire flower. They appear under high humidity conditions, especially if spent flowers are left on the flower stalks or in contact with the growing medium.
Affected taxa: Phalaenopsis, Cattleya, Vanda, Oncidium.
Treatment: Folpan, Dithane, Topsin.
Disease: fusarium wilt
Pathogen: Fusarium
Symptoms: blocks the flow of fluids through the vascular system of plants, leading to their wilting. Infected leaves turn yellow, thin out, wilt, and wrinkle, these symptoms being followed by the death of the plant within 3 - 9 weeks in severely affected plants, or, in moderately affected plants, their decline can last up to a year or more. Diagnosis in species of the genus Cattleya is given by the presence of a ring or a discolored band, purple or purple-pink in color, in the outer layers of the rhizome, visible when it is cut. In severe cases, the entire rhizome may be affected by this coloration, which can also extend into the pseudobulbs. Species of Phalaenopsis and Paphiopedilum can be infected due to too high salt concentration, too low substrate temperatures, excessive watering, or excess fermented peat soil in the substrate. Roots will rot, and the plant's crown will be affected by a dry black rot. Sunken spots on the leaf surface will enlarge over time, while old leaves will become leathery, and young ones will redden. The flower stalk will develop sunken rot spots, eventually leading to flower drop.
Affected taxa: Cattleya, Vanda, Phalaenopsis, Epidendrum, Cochleanthes, and many other species.
Treatment: Topsin, Dithane.
Disease: black rot
Pathogen: Pythium, Phytophthora
Symptoms: initially partially translucent spots, later black, large in size, with a tendency to spread rapidly, affecting any plant organ, especially leaves and new growths. It appears mainly in warm and humid seasons.
Affected taxa: Cattleya, Vanda, Phalaenopsis, Epidendrum, Cochleanthes and many other species.
Treatment: Funguran, Champ, Aliette, Dithane, Curzate Manox, Folpan.
Disease: crown rot
Pathogen: Sclerotinia
Symptoms: the main symptom of crown rot is the rapid falling and rotting of roots, pseudobulbs, and the lower parts of the leaves, which turn yellow-cream, and the tissues later brown due to the invasion of other pathogens. Ultimately, the disease destroys the entire basal portion of the plants. Affected leaves yellow, wither, and die. Small yellow or gray spots, resembling mustard seeds, will be observed on the affected tissues, representing the resistant forms of the fungus.
Affected taxa: Brassidium, Brassia, Oncidium, Cymbidium, Phalaenopsis, Vanda, Cattleya.
Treatment: Topsin.
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