Pests
1. Aphids – Aphids can become a real plague in a very short period of time. Aphids extract nutrients from the plant, which affects plant growth. The secreted honeydew fouls leaves and fruit, which then become unmarketable. Aphids can also transmit viruses and inject toxic substances into the plant that cause malformations. The most widespread species are: green peach aphid (Myzus persicae), cotton (melon) aphid (Aphis gossypii), potato aphid (Macrosiphum euphorbiae) and glasshouse potato (foxglove) aphid (Aulacorthum solani).
2. Whitefly – In greenhouse horticulture, the greenhouse whitefly (Trialeurodes vaporariorum) is a very common pest. The tobacco (silverleaf) whitefly (Bemisia tabaci or B.argentifolii) is increasingly becoming a serious problem in many crops. This species is more difficult to control than the common greenhouse whitefly. Whitefly larvae ingest large amounts of plant sap that they need for their development. Excess plant sap is secreted as honeydew, which fouls leaves and fruit and makes them unmarketable. Moulds that often grow on the honeydew can interfere with plant photosynthesis and respiration, Moreover, whitefly can transmit several viruses.
3. Spider mite – Spider mites are not insects but arachnids (they have eight legs). The most common spider mite in vegetable, ornamental and small fruit crops is the two-spotted spider mite (Tetranychus urticae). Spider mites suck plant sap for food; feeding damage shows as small yellow spots on the leaf upper surface. This reduces photosynthetic area, weakens the plant and decreases yield. Also, webs made by mites reduce the aesthetic value of ornamentals. Other mites commonly found on crops are the carmine spider mite (Tetranychus cinnabarinus), broad mite (Polyphagotarsonemus latus) and cyclamen mite (Tarsonemus pallidus).
4. Thrips – The most common thrips species are the western flower thrips (Frankliniella occidentalis) and the onion thrips (Thrips tabaci). Thrips damage plants by piercing plant cells and emptying their contents. Damage is visible as silver-grey spots with dark dots (thrips excrement). Thrips can also attack flowers, which may result in flower or fruit deformities. Thrips are also vectors of viruses such as the tomato spotted wilt virus (TSWV).
5. Fungus Gnats – Adults are small dark flies with long, slender antennae and long legs. Damage to plants is caused by the long and translucent white larva, which has a distinctive black head. Larvae feed on dead material in the growing media and also on living material such as roots and stalk tissue. Damaged plant tissues are then susceptible to plant diseases such as Pythium, Phytophthora, Botrytis, Fusarium, and Verticillium.
