Thrips damage and symptoms

Thrips cause damage to crops and ornamentals. Symptoms depend on the species of both plant and thrips.

Key thrips damage symptoms

Sunken streaks, patches → leaves
Colored spots on leaves → white
Stunted growth → buds (flower/leaf)
Curly, waffled, crumpled → leaves

Carrier/vector for – plant virus, fungal diseases (tomato spotted wilt virus)

Read also:

• Learn all about thrips
• Thrips lifecycle

Read on to discover what type of problems that result from thrips on plants. Included are images of thrips damage on fruit trees, flowers, and trees/shrubs. Damage can appear on leaves, stems, buds, fruits and flowers.

What parts of plants do thrips attack?

Usually, soft, young tissue is attacked first.

Also, buds, junctions and bends that are protected from wind, rain and predators are colonized early on.

Some species of thrips even attack roots underground.

• Not all thrips are bad, however. There are some beneficial thrips that help eat up other pests and fungus!
• Learn more about the various thrips species

Damage to the whole plant

With a magnifying glass, you can see the small insects crawling around.

• Shake a leaf over a sheet of white paper.
• Tiny specks will fall down on it.
• If they’re a bit oval and long, shaped like a small grain of rice, they’re thrips!
• They come in different colors, but usually brown, gray or yellow.

The main symptoms of a thrips infestation on a plant are the following:

• leaves with spots that are silver-white or yellow, then turn to brown or rusty-red
• leaf losing its thickness
• as the entire leaf is infected, it curls up
• leaf drop is rare

In some cases, thrips will trigger leaf galls (usually as part of the nesting/egg-laying process).

Damage to leaves

Flattened silver-white spots and lines on leaves

Telltale symptoms on leaves are that these spots often turn a silvery-white color. This may turn brown in time.

• Thrips feeding spots turn white because the space below is hollowed-out. Contents like green chlorophyll are sucked out.
• The skin and walls between groups of cells remain intact though. They form a kind of window that lets light through!
• The botanical term is skeletonization – only the skeleton or structure of the plant leaf is left.

Typically, portions of leaves are flattened and aren’t as thick as the rest of the leaves.

• This is because thrips feed on the content of cells. Like mosquitoes, they drill beneath the surface or skin of the plant.
• Thrips release enzymes that dissolve the inside of the plant into a nutrient-rich soup.
• Afterwards, they suck the content up. This flattens the leaf in the area.

Patterns of damage are more like short burrows or trenches dug into the leaf and young stem.

• They aren’t as long and twisted as leaf-miner damage, though.
• As an individual or a colony advances, this can either resemble a line or a widening spot.

Black dots or tiny pellets are actually what’s left after thrips have digested everything. It’s their poo!

• These black dots look a lot like the pycnidia spore-sacs on a plant that is suffering from leaf septoria.

Thrips egg-laying and larva damage

Lastly, depending on which species of thrips is attacking your plant, you may find damage due to “thrips nesting“.

• As part of the thrips lifecycle, the female will lay eggs in a cut or on a leaf or stem.
• These eggs hatch and the larvae secrete special chemicals to the plant around them.
• Chemicals disrupt neighboring cells, making it easier for thrips to feed.
• Sometimes damaged cells proliferate and form galls.

Symptoms of thrips on stems

On stems and on leaf veins, the damage has the same causes but may look a bit different.

Thrips feeding damage on stems

• There are still trench-like structures where the thrips are feeding.
• Usually the color is brown instead of silver-white.

Thrips nesting in stems

• Egg-nests resemble dots that are white or light in color.
• These spots are the size of the prick of a needle.
• Learn more about thrips eggs and what they look like.

Symptoms of thrips on flowers and fruits

Fruits contaminated by thrips

In citrus, banana, and other fruits, thrips will feed on the outer skin.

• The skin will also turn silvery-white. This is the cause for “silver banana” disease.

• Citrus fruits are also vulnerable to this. The skin is marked with white-gray patterns.

It’s still perfectly safe to eat the fruits, though.

• Shown here is thrips on a young orange tree fruit.

Thrips on flowers

Usually, these thrips simply feed on the pollen and also help pollinate the plant. However, sometimes, they also attack flower petals.

• Damaged wet spots or discolored blotches appear on petals, similar to when you crease or fold them.
• Flower buds stunt and grow deformed if too many thrips are present.
• Shown here, thrips on fairy-like aster flowers.

Diseases and pests that look like thrips damage

How to tell Septoria damage and thrips damage apart

Mentioned above is Septoria, a fungus that infects many different types of plants.

• Both have black spots, but those of Septoria are clustered together. They’re on the oldest spots. These spore-sacs don’t move when you rub your finger along.
• Oppositely, black dots of thrips are their waste. They’re distributed more randomly, not only on the spots. They’ll fall off if rubbed or shaken.

Lastly, both Septoria and thrips result in flattened leaf portions.

• However, edges around Septoria spots seem to swell and appear colored. This is because the plant is fighting the fungus back with an inflammation.
• With thrips, portions of leaves that touch flattened spots seem very healthy. There is no swelling or change in color.

Another check you can do is verify whether your plant is prone to septoria infection or not.

Other small insects that attack plants

Much more common and slightly larger are aphids and scale insects.

About the same size as thrips is the red spider mite. However, its bright red color gives it away: not many thrips are as red!

---