Dendrobium Cruetum leaves turning yellow with black spots

[csmcguire81]

Help!!! I got this Dendrobium about 2 weeks ago and recently a few leaves have started to develop black spots and the leaves turn yellow then fall off. This happens very quickly, in 1-2 days.

Can anyone tell me what is going on? I am new to this and have no idea what I am doing wrong.

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[titi_bradley]

Maybe this will help, I think it might be one of these two diseases...

Bacterial Brown Spot - Acidovorax (syn. Pseudomonas)

Symptoms: The symptoms may appear anywhere on the leaf as a small, soft, water soaked blister. Initially dirty green in color, the infected spot enlarges, coalesces and eventually becomes brown or black, dried up and sunken. It oozes bacteria-laden liquid, particularly when the disease reaches the tip of the leaf. It is most prevalent during the warmer weather. Attacks all orchid types.

- Phalaenopsis. The blister-like spots may be surrounded with a yellowish or pale green halo. Spots coalesce, and the infection spreads rapidly. If the diseased area invades the crown, the plant will die.
- Cattleya. The infection enters through wounds on older plants and usually affects only older leaves. It advances slowly and is rarely fatal.

Treatment: Immediately remove infected tissue using a sterile instrument, spray bactericides like Physan or copper compounds on infected and adjacent plants following label instructions (copper should not be used on dendrobiums or blooming plants), disinfect growing area with 10% bleach solution. Treat nearby plants as well as those that are diseased.

Prevention: Pseudomonas is a water-borne pathogen that prefers warm, moist conditions. Reduce humidity and temperature (if possible), eliminate overhead watering and increase air circulation.

[titi_bradley]

Leaf Spots - Cercospora, Guignardia & Phyllosticta and Septoria

Cercospora Symptoms: Infection shows first as a yellow spot on the underside of the leaf. Soon after infection occurs, the yellow-green area may be noted on the top surface of the leaf. As the spots enlarge in irregular patterns, they become slightly sunken and necrotic and turn purplish brown to purplish black. The spots continue to enlarge in a circular or irregular pattern and may eventually cover the entire leaf. The advancing margin remains yellow. Heavily infected leaves usually fall from the plant prematurely, especially if the infection started near the base of the leaf.

Guignardia Symptoms: The first signs of Guignardia infection are tiny, dark purple, elongated lesions on either leaf surface. These lesions run parallel to the veins and elongate into purple streaks or diamond-shaped areas. Spots often merge to form large irregular lesions that may affect a large part of the leaf. With age, the center of the lesion turns tan. Raised, black sporing bodies develop in the affected area feeling like sandpaper. Affects mostly ascocentrums and vandas and their hybrids and may indicate insufficient light. This blight is also known as Phyllosticta; the names apply to two different sexual stages of the same fungus.

Phyllosticta Symptoms: Spotting from Phyllosticta may start anywhere on the leaf or pseudobulb. The lesions are tiny, yellow and slightly sunken. As they enlarge, they become round to oval and more sunken, especially if the infection is on the leaves. With age, they turn tan to dark brown and develop a slightly raised, red to purple-black margin. Eventually, tiny black, raised spore structures develop in the center of the spots. Individual spots are about ¼ in across. Severely infected leaves may drop prematurely. Its presence may indicate insufficient light. This blight is also known as Guignardia; the names apply to two different sexual stages of the same fungus.

Septoria Symptoms: The tiny spots may start on either leaf surface as sunken, yellow lesions. They continue to enlarge, becoming dark brown to black, circular or irregular lesions. Spots may merge to form large, irregular patches on the leaf. Heavily infected leaves fall prematurely.

Treatment: Remove infected leaves with a sterile instrument and reduce leaf wetness. Spray with a systemic fungicide such as thiophanate methyl (Cleary's 3336 or Banrot) or a protectant fungicide like Mancozeb, following label instructions. Alternate systemic and protectant fungicides.

Prevention: Good sanitation with good air movement. Reduce leaf wetness, water on the leaves may lead to infection. If the fungus is a continuing problem, monthly fungicide sprays may offer effective prevention.

[titi_bradley]

Microfungus - Microfungus or Phalaenopsis Chlorotic Spot Virus or Tiny Mites?

Fungus or Virus or Mites? I've heard this malady described as all three. Tom Nasser reports that microfungus is an odd life form which is fungal with extra DNA particles, though it is not a virus. Courtney Hackney believes its cause to be tiny mites that require a high powered microscope to see.

Symptoms: In the order of appearance, the leaves display yellow chlorotic spots, then more defined yellow spotting that can grow into elongated yellow streaking, then pitting, and finally large areas of grayish tissue collapse. It can be confused with mesophyllic cell collapse caused by watering with cold water, although this weathers to dark rather than light sunken spots in phals. Paph infections weather to darkish sunken spots. Cattleya may have small black spots on the leaves.

From Bob Gordon Culture of the Phalaenopsis Orchid: "sometimes a condition prevails that is caused by a systemic infection of microfungi. As there are literally hundreds of these, the symptoms vary from plant to plant. Some of the more common are a spotty, ill-defined chlorosis; a streaky chlorosis beginning at the edge of the leaf where it looks as if the leaf edge had been burned with a match or candle; a red-brown coloration appearing at the apical third or half of the lower leaves followed by a dehydrated and senescent (old) appearance and also mesophyll tissue collapse where deep pitting becomes apparent on the surface of the leaves. This latter condition can also be caused by cold water and by virus infections. However, in the latter instance, the pitting is usually dark-brown to black in appearance rather than the white to light fawn caused by fungi."

Treatment: If you believe it is tiny mites, spray with a miticide at the first sign of chlorotic spotting. If you believe it is a fungus, follow the recommendations from Alan Koch of Gold Country Orchids: spray first with Banrot plus Aliette, then Cleary's plus Subdue, then Banrot plus Subdue. These sprays / drenches should be 7 days apart in summer and 10 to 14 days apart in winter, all at label strength. The combination of fungicides results in a synergistic effect. Follow all label instructions and wear protective equipment.

[titi_bradley]

You`ll probably solve the problem using a fungicide on your orchid.
Maybe some of the senior members with more eperience can help out you suggesting which fungicide to use....