Thrips can be a major problem in greenhouse, outdoor and indoor horticulture. As more growers switch to artificial substrates, thrips can overwinter more easily and attack younger plants earlier in the season. The western flower thrips ``Frankliniella occidentalis” has become the most troublesome species for cannabis and hemp cultivators to manage.
Juvenile thrips (on the left) and adult thrips (on the right)
Thrips are small insects of 0.5 to 1.4mm.They have a long cylindrical body and adults have two sets of wings. Adults can fly and jump allowing them to quickly move throughout the garden with ease. Thrips prefer to stay on the underside of leaves, but can be found in the soil as well.
Thrips damage looks like silver/gray specks on the leaves and is commonly mistaken for spider mite damage. It indicates damage from the thrips piercing the cells of the surface tissue and sucking out the contents, causing surrounding tissue to die.
Black dots on the leaves are also signs that thrips are present in the crop. They are the excrement produced by thrips.
Thrips cause the reduction of the vigor of the plant, because of the loss of chlorophyll, but they are also responsible for the transmission of viruses.
This pest prefers to feed on developing plant tissue such as growing tips and new flower sites. If the damage occurs to young plants, as the tissue develops further, the leaves can appear severely deformed.
The most important natural enemies of thrips are predatory mites and predatory bugs. Swirskii mites, Cucumeris mites and Californicus mites can feed on larvae stages while Orius can also consume adults. Soil inhabiting predatory mites, Stratiolaelaps scimitus and Macrocheles robutulus predate on thrips pupae and larvae in the root zone. Crops produced in soil, rockwool, and coco can also use nematodes (Steinernema feltiae) to control thrip pupae.