Thrips – Pest

Pests & Diseases: Thrips

Thrips – Pests & Diseases

Thrips are recognizable by their small size and long flat shape. The adult thrips has four feathery wings. They can vary in color from gray to yellow or brown. Thrips are carriers of viruses, mainly of the genus Tospovirus. These viruses cause significant crop loss and are incurable.
 

About the pest in brief

 

What are Thrips?
When we use the term thrips, we are referring to a wide group of insects of the order Thysanoptera.
What can you see?
Because certain toxic substances are present in the saliva of thrips, you may see some deformations in the shoots or flowers of the affected plants.
What can you do?
Spray plants with ecological insecticides like potassium soap or plant extracts with pyrethrum.

Biological cycle of thrips

 

The first stage of the thrips’ life cycle is the egg, which will hatch much more quickly when temperatures are higher. The females lay eggs in plant tissues. The larvae that emerge from the eggs feed on the surrounding tissues. One of the characteristics of these insects is that they make the transition from pupa to adult in the soil or in the lower leaves. The larvae live in the leaves, but as soon as they reach the right stage of development, they fall to the ground or lower leaves where they live during the pre-pupal and pupal stages until a reproductive adult appears with fully developed wings. The whole life cycle lasts only a few weeks.

 

Thrips

 

Symptoms of the pest

The adult thrips eats a varied diet based mainly on pollen, but the larvae feed on plant tissues and it is the larvae that are responsible for the majority of plant damage. The larvae suck the liquid from plant cells, mainly from the leaves, but also the petals, shoots and fruits. Early symptoms include an almost transparent or clear discoloration of the leaf with black dots (which are caused by fecal secretions). They have rasping, sucking mouthparts that look like combs and make a soup from the tissue which is then sucked up. Usually the top layer of the tissue is undisturbed and a window of clear tissue is seen in the middle of the area of discoloration.

 

Because certain toxic substances are present in the saliva of thrips, some deformations may occur in the shoots or flowers of affected plants. In cases of very severe infestation, the leaves may dry up entirely. At the same time, some thrips like Frankliniella occidentalis secrete a few drops of a substance when they are threatened by predators. These excretions contain decyl acetate and dodecyl acetate – pheromones that serve as a warning signal for other nearby thrips.

 

How to prevent the pest?

 

Because of the thrips’ ability to transmit viruses, it is important to monitor our crops for thrips and detect them as early as possible. The classic method for doing this is by using adhesive traps. These traps are blue in color, because thrips are strongly attracted to blue. The traps should be examined every few days using a magnifying glass to see if any thrips (usually winged adults) have gotten stuck to them.

 

Thrips

 

Solutions for controlling the pest

 

If you detect thrips, appropriate treatments need to be administered to minimize the risk of an infestation. These treatments include ecological insecticides such as potassium soap or plant extracts with pyrethrum, in places where these are allowed by law. Plants must be sprayed thoroughly all over because the thrips will take refuge under the veins of the leaves, making it difficult for the insecticide to come into contact with all the insects.

 

It is also possible to use entomophagous fungi to combat thrips. Beauveria bassiana is one fungi that is typically used to combat thrips. It is also important to make sure that you clean up and remove any plant or soil residues from the floor or worktops.

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Spider Mite – Pest

Spider Mite – Pests & Diseases

Spider mites affect many crops worldwide. There are well over 1200 species of spider mite, of which more than a hundred can be considered a pest, and about 10 are major pests. The most well known and problematic spider mite is Tetranychus urticae (common names include red spider mite and two-spotted spider mite). Their ability to reproduce extremely rapidly enables them to cause enormous damage in a short period of time. Spider mites have needle-like sucking mouthparts. They feed by penetrating the plant tissue with their mouth parts. Large populations can even cover entire plants with their web. These webs are used to move around. Because spider mites are so small, they can easily move through ventilators. 

About the pest in brief

What are spider mites?
Spider mites are not insects and are in fact more closely related to spiders. They belong to a class called Arachnida.
What can you see?
Spider mites usually spin a silk webbing. When spider mites infest plant leaves, they damage the plant tissue, leaving yellowing and dead spots that coalesce until the entire leaf is eventually affected. The leaf will turn yellow, wilt and finally be shed. Some varieties of mites do not spin webs and live in the plants bud terminals, where the damage cannot be seen until the tip expands.
What can you do?
Spider mites have several natural enemies that can be used to control the population.

Biological cycle of spider mites

Each female two-spotted spider mite lays 10-20 eggs per day and 80-120 in total during its life cycle of up to four weeks. These eggs are mostly attached to the silk webbing. The six-legged larvae hatch after 3-15 days. Newly hatched larvae are almost colorless and have bright red eyes. They moult three times within 4-5 days, becoming a protonymph, then a deutonymph and finally the adult form. Both adults and nymphs have eight legs.

Spider mite

 

Symptoms of the pest

The first visible symptoms will be small yellowish or whitish specks, mainly around the midrib and larger veins of the leaves. If these spots grow bigger and merge, the empty cells give some areas of the leaf a whitish or silvery-transparent appearance.

How to prevent the pest?

To minimize the risk and rapid spread of spider mite infestations, try to keep the temperature lower (60 %), since this will slow the reproduction rate. Higher humidity is also needed for the predators of the spider mite. Keep your growing areas clean and remove all leaf litter. Adequate irrigation is important because water-stressed plants are more likely to suffer damage.

Spider mite

 

Solutions for controlling the pest

When you see spider mites (recognizable from silk webbing on top of the leaves), remove the affected leaves. Spray the plant thoroughly with a mixture of alcohol and soap. Repeat this treatment several times a week.

You can also use natural enemies: predatory mites, ladybirds, predatory bugs and lacewings.

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