Pests Harming Orchids and Their Control Methods (Part One)

Pests that harm orchids include scale insects, aphids, spider mites, thrips, whiteflies, leaf miners, snails and slugs, nematodes, caterpillars, cockroaches, ants, and others.

1. Scale insects

Scale insects are one of the most common pests harming orchids. There are many species, mainly parasitizing the stems and leaves of orchids, and they can also be seen on the petioles and the membranous sheaths at the base of pseudobulbs, appearing as a white powdery substance. They feed by sucking plant sap with their piercing-sucking mouthparts. In mild infestations, they cause the affected organs to turn yellow and age, affecting the growth of the orchid plant; in severe cases, they cover the leaf surface in patches, consuming nutrients and affecting the orchid's photosynthesis, thereby hindering growth and development, preventing normal flowering and fruiting, and even causing withered leaves, leaf drop, and eventually the death of the whole plant. At the same time, wounds after scale insect infestation are highly susceptible to viral infection, and the secretions of scale insects easily lead to the development of sooty mold. Scale insects have strong reproductive capacity and can reproduce for multiple generations in a year. The adults have a waxy shell, which generally prevents pesticides from penetrating, making control relatively difficult. Once an infestation occurs, it is also not easy to clean up completely.

Control methods:

(1) Prevention first. When purchasing orchids, ensure that the seedlings are free of scale insects. Secondly, since scale insects tend to occur when conditions are too wet and ventilation is poor, special attention should be paid to environmental ventilation in daily management, avoiding excessive humidity.

(2) When there are only a few scale insects, they can be gently brushed off with a soft brush to manually remove the pests, then rinsed clean with water.

(3) When using chemical control, carry it out shortly after the nymphs hatch, before they have formed a waxy shell. Pesticides that can be used include 40% dimethoate or omethoate emulsifiable concentrate at 1000 times dilution, or 50% trichlorfon at 250 times dilution, or 80% dichlorvos emulsifiable concentrate at 1000-1500 times dilution, or 2.5% deltamethrin emulsifiable concentrate at 2000-2500 times dilution. Generally, spraying 1-3 times consecutively with an interval of 7-10 days gives better results. In addition, special attention should be paid to the fact that scale insects easily develop resistance to pesticides, so the use concentration of pesticides should be properly controlled and pesticides should be used alternately.

2. Aphids

They often parasitize orchid plants, mate and lay eggs, and overwinter in leaf axils and crevices, but in greenhouses they can reproduce by parthenogenesis year-round. Adult and nymph aphids harm the leaves, buds, and flower buds and other young organs of orchids, sucking large amounts of sap nutrients, causing malnutrition in the orchid plant; their excrement is honeydew, which leads to mold growth and induces black rot and transmits orchid viruses, etc. Aphids reproduce rapidly, producing from several to dozens of generations in a year.

Control methods:

(1) Control must be timely. From March to April, when the eggs hatch, spray with 40% omethoate emulsifiable concentrate or acephate at 1000 times dilution, or 50% fenitrothion emulsifiable concentrate at 1000 times dilution, or 20% fenvalerate emulsifiable concentrate at 2000-3000 times dilution, etc. Spray once every 7-10 days, 3-4 times consecutively.

(2) When aphids occur sporadically in home orchid growing, they can be brushed off with a writing brush dipped in water, and the brushed-off aphids should be promptly collected and destroyed to prevent spread.

3. Spider mites

There are several species of spider mites that harm orchids, with the red spider mite being the most common. It is small in body size, reddish-brown or orange-yellow. With its sharp mouthparts, it sucks nutrients from the leaves, causing an imbalance in the plant's water and other metabolic processes, affecting the plant's normal growth and development. Red spider mites and others reproduce rapidly and cause serious damage in high-temperature and dry environments.

Control methods:

(1) Maintain environmental ventilation, keep environmental humidity above 40%, and frequently spraying water on the undersides of leaves can control the spread of spider mites.

(2) When using pesticides, since pesticides have difficulty killing the eggs, control is generally carried out during the adult and nymph stages after the eggs hatch. Dicofol 20% emulsifiable concentrate at 1000 times dilution, or omethoate 40% emulsifiable concentrate at 1000 times dilution, or fenpropathrin 20% emulsifiable concentrate at 4000 times dilution can be used, once every 5-7 days, 2-3 times consecutively. Alternating the use of pesticides gives better results. A 600 times dilution of derris extract plus about 1% laundry detergent solution can also be used for spraying.

4. Thrips

Thrips are pests of the family Thripidae in the order Thysanoptera. Because of their small body size and hidden activity, they are difficult to detect in the early stages of damage. They mainly harm the inflorescences, flowers, and leaves of orchids. When harming leaves, they pierce and suck the orchid's sap with their needle-like mouthparts, causing many small white spots or grayish-white spots to appear on the leaf surface, affecting orchid growth and reducing ornamental value. When inflorescences are harmed, growth becomes deformed, making normal flowering difficult or causing flower colors to fade.

Control methods:

(1) Since thrips cause particularly great damage to orchid inflorescences and flowers and are difficult to detect, control should be carried out before the inflorescences emerge.

(2) Spray the whole plant with pesticides 1-2 times a year, which can kill thrips in all parts of the orchid plant.

(3) Before flowering, spray the whole plant again with 50% phoxim emulsion at 1200-1500 times dilution, or 40% omethoate emulsion at 1000-1500 times dilution, etc., generally once a week, repeated 3-5 times.