Symptoms of Pests and Diseases in Orchids

Orchids get attacked by pests like bacteria, fungus, virus and a variety of insects. But how would you as an orchid grower know that your favourite plant is under attack? A diseased orchid will show symptoms of pest infestation and these symptoms will help you in finding out which pest is troubling your orchid. I will be taking each part of the plant to show you how to see whether your orchid is in any danger.

Let us start with the ‘leaves’:
1. Diseased leaf/leaves will look different from a healthy one. The difference could be in the colour. A normal healthy orchid leaf is generally bright green, any other shade of green which is either lighter or darker, is an indication that all is not well and the plant is trying to cope by producing less/more green pigment. Brighter spots on the leaf that turn black could indicate viral infection. Lighter colouration or yellowish colour could be because of some nutritional deficiency or is under attack of mites (form bright silver spots on the upper surface of the leaf). Yellow leaves could be because the orchid might be getting less of Nitrogen, over exposure to sun or severe scale insect infestation. Calcium deficiency causes margins of the leaves turn black. Bacterial infection produces soft yellow spots on the leaf surface. 
2. Any change in the shape of the leaf is a bad sign again. The leaf can be curled, which points towards virus infection. A slightly curled leaf margins could be because of boron deficiency. Aphids, mealybugs can also cause leaf distortions.
3. Leaf galls are caused by thrips.
4. Upper leaf necrosis can be because of calcium deficiency or due to sun burning. 
5. If the younger softer leaves have been gnawed, it could be the weevils, slugs, snails, caterpillars or rarely even mice at work.

Flowers and fruits
6. Deficiency in the supply of phosphorus will be projected in lacklustre flowering, early fruit fall. Deformed and early bud fall can also be caused by thrips. 
7. Chewed off buds and floral parts indicate presence of pests (insects like weevils, slugs, snails etc.).
8. Deformed flowers emerging from the buds could be because of mites or viruses.
9. Black spots on the flower bud are a possible indication of fungus infection.

Roots
10. If parts of roots are chewed off this means there is some kind of infestation. Roots tips chewed off could be because of springtails or fungus gnats. Sometimes, maggots also eat away the roots.
11. Rotten roots could be due to excessive watering.

General
12. Severe aphid infestation can cause black rot all over the plant.
13. Presence of white threads all over the plant indicates fungal infection.
14. Fungus also attacks roots of orchids, sometimes eating away the older roots. Insects like slugs, snails and sometimes centipede attack the exposed roots.

Sometimes, we get over zealous and supply our orchids with more fertilizer than required, this leads to mineral poisoning. This can have similar symptoms as pest infestation or nutritional deficiency. So, you need to be judicious in fertilizer application also.