Orchid disease and prevention

There are various types of disease that will damage your plants and nursery. You have to consider the right prevention and elimination method to protect the plants.

Black Rot

This is a major disease that has been found in many orchid varieties such as Vanda, Cattleya, Aranda and Dendrobium.

Causes: Phytophthora palmivora (Butl.) Butler fungi

Symptoms: It can be found in every parts of orchids.

Leaf: At the beginning, the wound is a yellow transparent dot. Then, it turns to light and dark brown. And turns to black at the end. When the environment has high humidity, it can quickly spread to the axillary bud. The fungi will create the fine white filament that can clearly seen at the morning.

Stem: The fungi can enter from the apical or axillary bud. If you touch the black infected bud, it can easily fall off. When you smell it, it is very stinking. And you will see the black line inside the stem.

Root: The root will turn to black and dry. The leaves will be yellow and fall.

Flower: The wound is brown and surrounded by yellow. The stalk will dry. The color look rusty.

The disease will spread when the weather is humid cool. The suitable environment for the fungi is in a raining season with 25-30 degree Celsius, 80 % relative humidity.

Prevention and elimination

A ventilated plastic roof nursery is required. Do not grow the orchids too dense. If you see the infected seedling orchids, burn them immediately.  For the mature orchids, you can cut the wound and observe until it become a good tissue.

Do not water the orchids at the apical bud in the evening when the temperature is 25-30 degree Celsius and 80% relative humidity.

Orchid fungicides

Phosphorous acid: 30 milliliters per 20 liters water. Spray it before noon for a prevention.

Etridiazole: 50 milliliters per 20 liters water. Do not mix with the other chemical. Use it for a prevention.

Metalaxyl: 30 milliliters per 20 liters water. Use this to eliminate the fungi but you should alternate it with Captan or Propineb to prevent drug resistance. If you continually use, the orchids will be stunted.

Fosetyl-Al: 25-50 grams per 20 liters water. Spray 1-2 times a month. Do not mix with the fertilizer. Small amount for prevention. High dose for elimination. You should alternate it with Metalaxyl, Captan and Manozeb.

Flower Rusty Spot

Flower rusty spot

This disease is well-known in a group of cutting flower. It can show the symptom during the transportation especially white flower.

Causes: Curvularia eragrostidis (Hennings) or C. tuberculate Jain fungi in Ocidium

Symptoms: First, it will be a small yellow brown spot on the orchid petals. Then it will be bigger and turn to rusty color. Its diameter is about 0.1-0.3 millimeters. You can clearly see on the red flower. And It quickly spread in raining season.

Prevention and elimination

You must clean your nursery. Remove the flower before it falls. Burn the rusty flower immediately.

Spray Propineb or Captan; 40 grams per 20 liters water. Spray it more frequently in the raining season. Add some surfactants to reduce the strain of the fungicide on the petal. Don’t use it too much, it can make the petals drowning and damage the flower in the summer.

They can live in your water storage. So, you should add some Calcium hypochlorite: 5 grams per 200 liters. Stir and leave it overnight until it doesn’t have the chlorine smell.

Use the right fertilizer would help, Lower the nitrogen amount, and higher the potassium amount. It helps to resist and reduce the damage of disease.

Yellow Leaf Spot

Yellow leaf spot

This is the common disease that has been found in almost of Dendrobium variety,

Causes: Pseudocercospora dendrobii Goh & Hsieh

Symptoms: They are mostly occurred from the bottom of the plant and spread to the top leaves. It is a yellow blot along the leaf. If you flip it, you will see the black dust attach to the leaf’s surface. The leaf will turn to brown, dry, and wither. Finally, the orchids will lose all the leaves. The new bud will not complete. The inflorescence will decrease.

They usually spread during the end of raining season to cold season, when the relative humidity is less than 70% and Temperature is less than 32 degree Celsius. Their spores will spread by wind and water.

Prevention and elimination

Collect all the diseased leaves and burn them outside the nursery.

Before season change, you should spray the fungicide at the end of raining season/the beginning of cold season. And spray under the leaf.

Use the following fungicide,

Systemic fungicide: Carbendazim: 10-20 grams per 20 liters water alternate with Captane: 30 grams per 20 liters water.

Nonsystemic fungicide (contact fungicide): Propineb: 40 grams per 20 liters water or Manozeb in the same ratio.

Leaf Spot

Leaf spot

This disease has been found in Dendrobium, Vanda Cattleya, Oncidium and ground orchid such as Paphiopedilum in mature size.

Causes: Phyllostictina pyriformis Cash & Watson and Phyllosticta capitalensis Henn fungi

Symptoms: The symptom depends on the orchid’s variety. The wound in Vanda has the oval shape. Then it will become the same sheet. The center of the wound is rough embossed dark brown. When it cracks, spores will come out. For Dendrobium orchid, the wound is dark brown to black round spot. The rim is light brown. The size is varied from the pin tip to 1 centimeter large. It can be embosed or dent. Under or over the leaf.

They spread all over the year. Its heavy spreads are during the raining season to cold season. The spores hide inside the black embosed wound and spread by wind and water.

Prevention and elimination

The mother plant should free from the disease.

Collect the diseased leaves and burn them outside the nursery.

Use the following fungicide, Chlorothalonil: 30 grams per 20 liters water with additional surfactant. In the raining season, you should alternate it with Captan in the ratio of 40 grams per 20 liters water or Carbendazim in the ratio of 20 grams per 20 liters water.

Black Spot

Black spot

They are mostly found on Dendrobium orchid.

Causes: Alternaria alternata (Fr.) Keissl. and Drechslera sp. (Helminthosporium sp.)

Symptoms: The leaf front has a dark brown wound. The rim is black and grey. The size is small. They are mostly round and spread all over the leaves.

The leaf front has a white or yellow dot. The center will be black and clearly seen when the leaf is old.

Both leaf front and back have the black dent wound.

They spread all over the year especially Dendrobium variety. Its heavy spread is during the raining season to cold season. They spread by wind and water.

Prevention and elimination

Collect the diseased leaves/stem and planting material, then burn them.

Spray the fungicide. Iprodione: 30 grams per 20 liters water or Prochloraz: 20 grams per 20 liters water alternating with Propineb in the ratio of 40 grams per 20 liters water.

Reduce the fertilizer concentration to the labeled ratio and do not fertilize under the hot noon.

Anthracnose

Anthracnose

This is a common disease in Oncidium orchid.

Causes: Colletotrichum gloeosporioides (Penz.) Penz. & Szcc. Fungi

Symptoms: It can be occurred on the tip or middle of the leaf. The wound is brown and overlap into many layers. The black color fungi will appear on it. The spores are clear oval shape.

They spread very well in the poorly light managed nursery or high humidity in raining season. The exceed light make the plant weak and easy to get the disease. The spores will spread by wind and water.

Prevention and elimination

Collect all the leaves and died stem. Burn them to stop spreading.

Spray the fungicide, Chlorothalonil: 30 grams per 20 liters water or Prochloraz: 20 grams per 20 liters alternating with Captane in the ratio of 40 grams per 20 liters water.

Control the light by using sunshade net and make sure that the light intensity is suitable for the orchids. Too much light can make the leaf burn.

Fusarium Foot Rot/Wilt

Fusarium Foot Rot/Wilt

It occurs when the planting material is old and decay especially the coconut husk. They have been found in Cattleya, Vanda, Aranda and Dendrobium. When the disease is severe, the plant will dry and die in 1-2 months.

Causes: Fusarium oxysporum Schltdl. and Fusarium sp. fungi.

Symptoms: The fungi enter from the root or the stem root, the stem will be rot and slowly dry. For young plants, their leaves will turn to yellow and wilt from bottom to top. The orchid pseudobulb will be stunted and crippled. When you cut the stem, you will see the rot inside.  In humid weather, you will see the orange spores on the wound and the orchid peduncle will be black and broke.

Prevention and elimination

Take the old planting material out from the nursery and burn the infected orchids.

Spray fungicide, Quintozene or Quintozene + Etridiazole: 30 milliliters per 20 liters water.

Take out the weed and moss, then spray Captane 40 grams per 20 liters water. If you double the used ratio, it may make the weed and moss dried or Spray Physan 20: (10% n-alkyl dimethyl benzyl ammonium chloride + 10% n -alkyl dimethyl ethyl benzyl ammonium chloride): 10 milliliters per 20 liters water.

Stem Rot

Stem Rot

This disease has been found in every tropical orchid species.

Causes: Sclerotium rolfsii Sacc. fungi

Symptoms: The fungi will destroy the root and lower stem, then they will spread to the upper parts to the upper leaves. The infected area will turn to yellow and brown respectively. The orchid tissue will decay.

 If the nursery has high humidity, the white filament will be found and covered the stem root. The fungi will generate the white small round sclerotium, then this sclerotium will turn to yellow and brown. The appearance look similar to lettuce seed. Sometimes, the symptoms will show on the leaves. It will make them wilt and brown. Finally, the orchids will die.

They can spread by wind and water and heavy spread in raining season. The sclerotium resist to the chemical fungicide and harshly environment. They can live in the ground and the old plant wreck.

Prevention and elimination

Do not densely grow the orchids in bad air ventilation and high humidity nursery.

Carefully take care the plants, collect the diseased orchid as soon as possible.

Pour the fungicide: Carboxin in a ratio of 20 grams per 20 liters water or Etridiazole in the same ratio. But Etridiazole can damage to some variety of orchids.

When you use Systemic fungicide such as Benomyl for a long time, it can stimulate the stem rot disease. So, you should alternate it with Captan or Manozeb.

Do not lay the planting material on the ground in raining season. Before grow the plants, dip the plants and planting material such as husk in Carboxin: 40 grams per 20 liters water.

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