This summary is based on a variety of available sources (thank you all who unknowingly contributed) and covers the most common orchid pests, specifying for each how to recognize their presence (Symptoms), who or what is the cause (Description), under which circumstances they occur (Conditions) and how to handle the problem (Treatment). Pests covered in Part 1 are Snails & Slugs, Caterpillars & Weevils, Cockroaches & Crickets.
GENERAL COMMENT: Spread of Diseases. All sap-sucking and plant-eating pests bring the danger of spreading various diseases, in addition to the direct damage they do, making it even more important to control them. Biological Control of insect pests constitutes a subject by itself and is therefore ignored in the descriptions below. Pressure Packs: when using pressure packs to spray pests, remember to keep the nozzle at least 30 or 40 cm from the plant, to avoid frost damage from evaporative cooling or chemical burning from drops of fluid. Safety Precautions: when using poison sprays (especially systemic insecticides), make sure to follow the safety instructions (protective clothing, gas mask and gloves), and to spray in windless conditions. After applying toxic sprays, shower and put on fresh clothing.
SNAILS & SLUGS – Symptoms: Slime trails and damaged young growth (holes in pseudobulbs, flower spikes and buds). Description: Slugs and garlic snails attack mostly young root tips, often causing considerable damage before being noticed, while snails dine on visible young growth and flower buds. They can spread diseases. Nightly inspections can reveal the culprits (< 10% of slugs only) and continuous treatment is the only way of control. Conditions: Slugs and snails like humid conditions; they prefer to hide in the mix or under cover and feel generally at home with orchids. Treatment: Liquid Metaldehyde is the only certain way of killing the inhabitants of the mix, while snail pellets can control the snails (in humid conditions pellets may become mouldy, with some danger of the mould spreading). Garlic snails and also slugs may also be controlled using “traps” (slices of apple or lemon on the mix) which can be turned over in the morning to remove the catch hiding under there. Beer in a can or jar is also suggested to trap/drown slugs.
WEEVILS & CATERPILLARS – Symptoms: Chunks eaten from leaves, buds and flowers (mainly flowers) without signs of snails or their trails. Description: Weevils burrow into the mix and come out at night (the time to spot them). Many of the caterpillars blend in and are difficult to spot. Both attack leaves and the weevil grubs can attack the root tips. Conditions: most active in warm weather. Treatment: Watering with a solution of insecticidal soap will kill the weevil grubs, while the caterpillars can be removed by hand or killed with an insecticide such as carbaryl.
COCKROACHES & CRICKETS – Symptoms: Damaged cattleya flowers, plants deteriorating. Description: Cockroaches and crickets feed at night and hide during day. They can seriously damage the root tips (although crickets less often) and cattleya flowers. A flashlight at night may reveal the cockroaches scurrying away. Conditions: Cockroaches like warm, dry conditions. Cold winters will help in their control. Treatment: Both insects can be controlled by trapping them with potato slices slightly hollowed at bottom (check traps in morning) or with commercially available poisoned bait, contact poisons like Roach & Ant Killer (Yates) sprayed on pots, benches and walls or by using pybuthrin powder or pyrethrum.