KNOW YOUR ENEMY!

Aphids are small sap-sucking insects that are usually found on the underside of leaves and/or close to the growing tips of the plant. They may be winged or wingless, depending on age and environmental conditions. Their presence may cause leaf curling, distorted plant growth, and a loss of plant vigor. They can also secrete a sticky 'honeydew' that drips onto the leaf below and which may attract ants. Some species transmit plant viruses.

For more information on aphid biology and identification, please see this page.

Thrips are very small, slender-bodied insects that, like aphids, can transmit some plant viruses. Most species of thrips feed on plants (although some are predatory) . The plant-feeding species rasp through the surface cells of the leaf and suck out the sap. This causes a characteristic 'silvering' or 'flecking' of the damaged leaf (or petal, in the case of flower-feeding species).  Adult thrips have wings that appear to have a 'fringe' of fine hairs when viewed under a microscope. Body color varies with species. The immature stages are wingless and are often paler than the adults.

For more information on thrips biology and identification, please see this page.

Adult whiteflies look somewhat like minute moths and are typically found on the underside of leaves; they fly readily when disturbed. The immature stages superficially resemble scale insects. After hatching from the egg, they disperse to feeding sites elsewhere on the host plant, where they settle and remain motionless until they pupate and eventually emerge as winged adults. All stages feed by sucking sap from the host plant, and some species can transmit plant viruses.

For more information on whitefly biology and identification, please see this page.

Fungus gnats are typically associated with growing media that is high in organic matter and that remains damp for prolonged periods. Such conditions may occur when plants are over-watered, and/or when they are growing only slowly (e.g. under cooler temperatures and shorter daylengths). The adult flies are approximately 1.5 to 3 mm long and fly only weakly, often close to the surface of the soil. The larval stages develop in the growing media and may damage plant roots.

For more information on fungus gnat biology and identification, please see this page.

Mites are not insects but arachnids (i.e., they are more closely related to spiders than to insects). Several families of mites include species that can be plant pests.

Spider mites, for example, often form dense colonies on infested leaves that can eventually become covered with a webbing of fine silken threads. Initial feeding damage by spider mites may resemble the silvery flecking caused by thrips, but if left untreated, affected leaves can rapidly dry out, become bronzed and brittle, and may eventually die.

Other mite pests include Tarsonemid mites (e.g. broad mites and cyclamen mites) and Eriophyid mites (e.g. russet mites).

For more information on the biology and identification of different mite pests, please see this page.

Caterpillars

Most pest caterpillars* found on commercial crops are the larval stages of moths (*commonly called 'worms' by US growers).  They have chewing mouthparts and feed by consuming plant tissues (leaves, buds, or fruits) rather than by sucking sap. They may cause holes in leaves or fruits, create ragged edges around feeding sites, and typically leave small but noticeable 'pellets' of frass (excrement). Although they are occasionally a problem in indoor crops, it is unusual to find large numbers in such environments.

Leafminers

The most common leafminers found in indoor crops are the larval stages of various fly species. Their eggs are inserted into the leaf and the larvae feed between the upper and lower leaf surfaces, creating visible white or silvery lines (‘mines’) that reduce the photosynthetic area of affected leaves.

For more information on these pests, please see this section for caterpillars and this section for leafminers.