Orchid Pests and Diseases: Diagnosis Treatment and Prevention

by Flower El
brown spot on orchid

Orchids are prone to both pests and disease infestations. It is, therefore, important that you should look out for symptoms for diagnosis, treatment and prevention.

1. Scales

These are sucking insects that feed on the underside of orchid leaves. Often they hide under pseudobulb sheaths and old leaves. Severe infestation is likely to cause chlorotic on the leaves and in some cases may cause the leaves to drop off prematurely.

Treatment: For a few scale infestations, you can remove the insects manually by using a Q-tip or a toothbrush dipped in isopropyl alcohol or Malathion. The best way to prevent and treat severe infestations is to spray your plants regularly starting at the crawler stage. Give attention to the leaf axils and undersides of leaves. If you have few plants then you can prevent infestation by removing old floor sheaths and leafs from your plants.

2. Mealybugs

These are other sucking insects that affect most parts of the plant although they are most common at the junction of the stem and the leaf. Mealybugs attack cause chlorotic on the leaves of the plant and sometimes premature dropping of the leaves.

Treatment: If only a few plants are infected then you can manually remove the insects by using a toothbrush or a Q-tip dipped in Safer Soap or isopropyl alcohol. For severe infestation spray using pesticides every two weeks until there is no sign of attack. When applying the pesticide pay greater attention to plant surfaces and particularly the leaf axils and the underside of leaves. Removing old flower sheaths and old leaves helps eliminate the hiding places for the insects.

3. Aphids

Aphids are sucking insects and attack the flowers, new growths, and buds of orchids destroying the plant structure and transmitting diseases to your plants. An aphids attack may cause the flowers and buds of your plants to fail to open or leaves of the orchids to stick together. Aphids sometimes secrete honeydew which may attract ants and causes sooty mold. This affects the general health of the plants and should be attended to immediately they are noticed.

Treatment: The best way to protect your plants from the harmful effects of aphids is to spray with insecticides such as safer soap or Orthene. You may also wash the aphids away with water.

4. Thrips

These are tiny sucking insects that attack plants. In orchids, the thrips are known to feed on floors and the leaves of the plant. They also play a major role in transmitting diseases from one plant to the next. If your orchids are affected by thrips then their buds and likely to have difficult opening and this may lead to deformed flowers. If the leaves are attacked then they are likely to appear bleached or silvery robbing the plants of their natural beauty.

Treatment: Spray your orchids with pesticides such as Safe soap, Malathion or Orthene to kill the insects. Repeat spraying every two weeks until you are sure that the thrips are all gone. If you are growing your orchids outdoors make sure that you also spray nearby plants and flowers as the thrips may be reintroduced from such sources.

5. Whiteflies

These are moth-like insects that feed on the flowers, buds and new growth of orchids. Often you can tell the presence of whiteflies if you see a host of many tiny white insects rising when an affected plant is disturbed. The insects affect the quality of flowers and rob your plants of their natural beauty.

Treatment: To remedy the situation spray your plants with pesticides such as Orthene or Malathion. Repeat the spraying every four days until there is no sign of the insects. Also, ensure that you weed your orchids on time and you practice good sanitation to eliminate chances of infestation.

6. Spider Mites

Spider mites are tiny red-brown pests that feed on the underside of orchid’s leaves. The affected leaves may turn to a silvery sheen and may turn brown. Some leaves may be spotted or streaked due to lack of chlorophyll.

Treatment: Spray your orchids with miticides such as Kelthane with a keen interest to reach all the undersides of the stem and the leaves. Repeat application every 4 days to ensure that you get rid of all the insects.

7. Caterpillars

Caterpillars are known to be voracious feeders and can do great damage to your orchids. They are not common especially if you plant your orchids indoors but you should inspect your plant regularly because they can cause great damage in the shortest time when compared to other insects.

Treatment: You can pick caterpillars and destroy them manually if you see any on your plants. If there is a severe attack then consider spraying your orchids with insect sides such as Bacillus thuringiensis to get rid of the insects. Always remember to inspect the underside of your plants if you see holes or other signs of attack on the leaves of your orchids.

Most of the disease that affects orchids can be classified as bacterial diseases, fungal diseases or viruses. Some of these common diseases include:

8. Bacterial Soft and Brown Rot (Erwinia spp.)

This disease is characterized by small water-soaked spots surrounded by yellow halos on leaves and sometimes on stems. The infection is not checked will rot the leaves than roots and eventually spread into pseudobulbs and rhizomes. Usually, the affected plants will have a water soaked look and will produce a foul odor. This disease spreads rapidly and all your orchids may be completely destroyed in under a week.

Treatment: Once you notice an infection a given plant, act immediately to cut out the affected tissue with a sterile instrument then spray all your plants using bactericides such as copper compounds or physan to curb the spreading of the disease. Using a 10% bleach solution disinfect your growing area. When you notice infection stop overhead watering because splashing water is a major agent that spreads the disease. Also, reduce the temperature, increase air circulation and reduce the humidity of your growing area to kill the pathogens.

9. Bacterial Brown Spot (Acidovorax)

The symptoms of the affected areas start as a small water-soaked blister that enlarges rapidly and eventually becomes a black sunken spot. The disease is more common in warmer weather and infected leaves usually produce a bacteria-laden liquid. The disease enters plants through wounds on plants, spreads much slowly and is not fatal but it affects the quality of your plants.

Treatment: When you notice symptoms of the disease on your plants cut out the affected areas using a sterile object. Then spray your plants with copper compounds to prevent further spreading of the diseases. Disinfect your garden with a ten percent bleach solution to kill the bacteria.

10. Black Rot (Pythium & Phytophthora spp.)

The disease start as small brown watery spots on the underside of orchid leaves. Sometimes the disease may start in other parts of the plant such as roots and new leads. The spots on the leaves may expand and become purplish black or brown in color with an advancing yellowish margin. Sometimes they may ooze water or they dry and become black spots. If not treated on time the disease is likely to kill the plants.

Treatment: The best approach to dealing with the disease is to discard the affected plant altogether. This is because the disease spread easily from one plant to the other especially when you using overhead splashing water. If you notice the infection early and the plant is valuable you should then consider isolating the plant then remove the infected area using a sterile tool. Don’t forget to drench the tissue with a fungicide such as Banrot or subdue. Spray your plants regularly with a fungicide to prevent the spreading of the disease to other plants.

11. Fusarium Wilt (Fusarium sp.)

The disease is characterized by thin plants with yellow leaves that get wrinkled and if not treated die. The Fusarium infection blocks moisture from flowing through a plant’s vascular system thus slowly killing the plant. An infected plant may die within three to nine days.

Treatment: Cut off and discard the affected section of the plant. Sanitize your plants using thiophanate methyl. Disinfect your growing area and make sure you sterilize all your cutting tools.

12. Fungal Root Rot (Rhizoctonia sp.)

This disease occurs when you overwater your orchids. The disease is caused by salt build-up or over fertilization. The disease is contagious and is likely to kill the plant. An infected plant will be thin twisted and will have yellow leaves and pseudobulbs. The roots will have brown rot and brown or white fungal growth.

Treatment: Remove the affected areas of the plant using a sterilized cutting tool. Drench the plant in a fungicide such as thiophanate methyl or subdue. Also, disinfect your planting area to prevent the disease. Don’t over water or fertilize your plant and avoid using hard water when watering your plants.

13. Botrytis Petal Plight (Colletotrichum & Glomerella spp.)

This disease mostly affects the leaves and the aerial section of the plant. The leave turns brown starting from the apex. Sometimes the disease may appear as gray patches or rings across the leaves. Affected flowers develop watery and black pustules. Sometimes the flowers may be covered in brown spots.

Treatment: Increase air circulation in your growing area. Spray your plants with fungicides such as Mancozeb and thiophanate.

14. Cercospora Leaf Spot (Cercospora spp.)

Infection first appears as yellow spots on the underside of leaves. The spots then grow and appear as yellow-green spots on top of the leaf. Infected leaves may fall from the plant before maturity. As the spots grow they may turn purplish brown turning the top of the leaf chlorotic and then necrotic.

15. Guignardia Leaf Spot (Guignardia and Phyllosticta spp.)

When you see small dark purple lesions on the leaves of your orchids, chances are they are infected with Guignardia Leaf Spot. Usually, the tiny lesions will run parallel to veins in the leaves and with time will elongate or form a diamond shape. Sometimes they spots may merge to cover a wider area on the leaf.

Treatment: Maintain good growing environment with emphasis on lighting and air circulation. Spray your orchids regularly with fungicides.

16. Botrytis Petal Blight (Botrytis sp.)

The disease is characterized by small light brown or black spots on flowers. Sometimes the spots may grow to cover large sections of the flowers. If not treated you may note gray fungal growth on dead flowers.

Treatment: Remove affected flowers from your plants. Spray your orchids with fungicides such as Daconil regularly. Check on the growing environment.

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