Pests

Over the (few) years with plants I have encountered a number of pests on them. This page shows pictures of them (I warned you!) and reports how I dealt with them.
Of course my suggestions for getting rid of pests don't come with warranty, but if the tricks worked for me, maybe they're worth trying for you, too.

Topics on this page:

Spider mites (Ger.: Spinnmilben)

Springtails (Ger.: Springschwänze)

Thrips (Ger.: Thripse)

Fungus gnats (Ger.: Trauermücken)

Mealybugs (Ger.: Wollläuse)

Scale insects (Ger.: Schildläuse)

Tenthredinidae Larvae (Ger.: Blattwespenlarven)


Spider mites

Spider mites belong, as the name suggests, to the family of mites. They usually sit under leaves and they spin webs that become visible after sprinkling the plants with water. Plants get damaged because spider mites suck the fluid from the plant cells and so complete leaves simply dry out.
Spider mites are very small and can hardly be seen without magnification.

Web with spider mites under an ivy leaf
Web with spider mites under an ivy leaf

Spider mites under an ivy leaf
Spider mites under an ivy leaf

In the two pictures above only the stem of an ivy leaf can be seen. This is a variegated cultivar with smaller leaves than the common ivy. So the whole leaf has the size of a 2€ coin and you can imagine how far this is zoomed in.

Two spider mites in detail
Two spider mites in detail

These pictures were taken with a macro lense and a bellows which enlarges the object even more. Otherwise such detailed pictures are only possible under the microscope.

For countermeasures I must admit that I can't give you any tips. My ivy and I lost the fight against these little monsters. I didn't want to buy an expensive spray, so I tried some home remedies:

I took the ivy out of its pot and cleaned the leaves with a mixture of water, olive-oil and dishwashing liquid. One has to be very careful not to let any of the mixture drop onto the roots.
After the very complicated washing process (the ivy had many branches and each one has to be cleaned carefully) I put the ivy back into its pot and covered the roots with a little Seramis - an inorganic soil.
After two days the procedure has to be repeated because the next generation of spider mites is now mature and it is very likely that quite a few of them survived the first washing.
The ivy survived the procedures... the spider mites too. After two weeks they were back and I gave up. The plant finally showed damages after some more weeks and I threw it out.

The best way to deal with spider mites seems to be not letting them get to your plants in the first place.
Spider mites hate moisture in the air. So sprinkling water onto your plants regularly can help avoid these little monsters.
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Springtails

Springtails are still a riddle to me. They are little white worms that live mainly in the lower parts of pots and that eat dead plant parts. They are pretty useful, especially outside, since they help composting.
I found them first in the pot of my australian fire wheel tree and only in the pot saucer. The fire wheel tree grows in Seramis, so their appearance really surprised me. But aparently they live quite deep inside the pot and live off the roots. It is said that they are dangerous to plants only if they become too many. Then they use up the dead plant parts, find no more food and then start to eat the living parts.

Spring tails at the bottom of a clay pot
Spring tails at the bottom of a clay pot

Somehow no one really knows what actually works against them. The only thing I found was to put the whole pot under water for a few minutes. This will float the springtails up and they can be poured out with the water.
Well, the first problem was the Seramis. It sucks up so much water which can't be good for the plant. The second problem, also in usual soil, are air pockets in the soil where springtails can hide or aren't affected by the flood.

In the end I simply checked the pot saucer every other day and wash the visible tails away. There I could also observe why they are called springtails - they actually jump when confronted with water.
In the meantime I have also had springtails in regular soil of a palm. There they come to the surface when I water the plant, jump out of the soil and make it look like I watered with sparkling water instead of regular tap water.

I didn't get rid of them completely, but my plants are well and don't seem to mind the springtails. So unless they start to really damage my plants they may stay.
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Thrips

I encountered thrips on a citrus seedling that my grandma gave to me. She had put a citrus seed in a pot on her porch an when she gave the little plant to me and I took it inside and put in on my windowsill, a few days later thrips appeared.

Thrips on a citrus leaf
Thrips on a citrus leaf

Thrips are small insects (a few millimeters long) with horizontal black stripes. They have wings and can fly but they don't seem to like it.
I tried to get rid of them by wiping the citrus leaves with warm water and dishwashing liquid and each time the sponge got near a thrips, it ran away - instead of flying which would have been so much more effective.
I actually got all of them, but didn't think about their eggs and larvae. So a few days later new thrips appeared, sitting happily under my citrus leaves.

Thrips are a danger to plants because they suck the juice out of the leaves' pores. This means that they only attack plants with soft leaf surfaces. Hard leaved plants are fairly safe from thrips.
Since they sit under the leaves one usually doesn't notice them until the leaves show damages on the top. The surface of the leaves slowly turns silvery gray and dry when Thrips are "feeding" on them from the bottom of the leaf.

Fully grown thrips on a citrus leaf
Another fully grown thrips on a citrus leaf. Notice the distinguishing dark stripes on the wings.

Lizetan helps to get rid of thrips. This is a systemic substance that is absorbed into the plant and after a few weeks arrives in the pores of the leaves. So the thrips suck the substance from the leaves and die from it. But this process takes a while and in the meantime they might still do considerable damage to the plant. There are also different sprays that help and might be better suited.

When my mom's citrus plant had thrips I grabbed the oportunity (and my camera) and took a few pictures of them. I even got lucky and found thrips larvae.

Group of thrips larvae on a citrus leaf
Group of thrips larvae on a citrus leaf

Two thrips larvae, one with red eyes
Two thrips larvae, one with red eyes

Thrips larvae, as you can see above, are white. The larger/older ones have red eyes.
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Fungus gnats

Oh gnats, the "favourite" insects of all the people who grow plants. Anyone who has ever sown seeds and then had seedlings standing around, has met them. Some plant lovers have even lost whole boxes of seedlings to a gnat plague.

I had them, too, but fortunately not too many of them. When I discovered the first adult fungus gnats with my lithops, I panicked, googled and then acted - and luckily it was not too late.

What do fungus gnats look like?
Fungus gnats look like fruit flies on the first glance. But if there's no fruit lying around or anywhere near, it is more likely that the little flies zooming around your living room are fungus gnats. Fungus gnats are little black flies that are a little longer than fruit flies.

Fungus gnat with closed wings 
Fungus gnat with closed wings

In this picture their long body can be seen nicely. This gnat is sitting on (well, more like sticking to) a yellow sticker designed to attract, catch and then immobilize them. This picture also demonstrates why they have their German name: Trauermücke (mourning mosquito). It looks as if it has lowered its head in mourning.

The first thing one notices when fungus gnats are present are a few – maybe only one – adult insects. They are looking for a nice moist, warm and nurturing place for their eggs and their larvae. Sometimes one first notices the larvae in the soil. I don't have a picture of the larvae yet, and to be honest I'm glad about it, because it means that I don't have fungus gnats anymore.
The larvae are only a few millimeters long and transparent. One usually doesn't notice the larvae until it is already too late and the plants have started to suffer. If the soil is then inspected closely, many of these little larvae can be seen wiggeling around.
Once these larvae grow they will not stay hidden. Suddenly there is a whole swarm of them flying around and it's obvious what the problem is.

Fungus gnats are very clever, by the way. Sometimes they sit on top of the dark soil and don't move if one looks for them. They can only be seen if their wings reflect the light or if they are blown at, because then they start to run around on the soil.

Where do fungus gnats come from?
Mostly they simply come from outside. But one is not safe from them by leaving the windows shut. No, many people get fungus gnats or their larvae delivered right into their home with their freshly bought soil. And then it is no wonder that they always come back, no matter how often one changes the soil. So, high quality soil should be used with seeds and seedlings. These soils are mostly free of any unwanted guests.

How do fungus gnats damage the plants?
Like I said, fungus gnats place their eggs in the soil, especially the soil of young seedlings. There the larvae hatch and the first thing they eat are the roots of the seedlings. Especially with seedlings the soil is kept moist constantly... a perfect place for fungus gnat larvae.
The roots of older plants seem to be too hard for the larvae so they rather go for the young plants. And the seedlings... well, without their roots they don't have much of a chance of survival.
The adult gnats on the other hand don't seem to do any damage to plants.

What can be done against fungus gnats?
The first solution are yellow stickers. These are plastic strips or cards that are covered with a special glue. These cards can be placed in the pots with the most gnats flying around them. The yellow attracts the gnats (that is also one of the main differences between fungus gnats and fruit flies: fruit flies are attracted to fruity smells where fungus gnats go simply for the color yellow), they stick to the card and the more they move, the more they get themselves stuck to the glue.
That may sound mean, but anyone who has ever had a fungus gnat plague will thank God for these stickers.

Fungus gnat with opened wings on a yellow sticker
Fungus gnat with opened wings on a yellow sticker

Unfortunately these stickers only catch the adult, flying insects. The eggs and larvae in the soil are not affected by them.
If larvae are already present, the first order of business should be to change the soil. To be absolutely sure that no larvae stay behind, Neudomück (a solution manufactured by Neudorff) can be used with the next few waterings.

The best long-term strategy, however, is to plan ahead and to keep gnats from even getting into the soil in the first place. My advice for that (tested successfully!) is this:

How to prevent an infestation with gnats:
Build a protective shield into your pots like this:
1. Into an empty pot first put a layer of Seramis (or clay bits, or large grained sand). This also helps drainage.
2. On top of that pour a layer of fine sand. This layer has to be about a centimeter thick so that the drainage layer is covered completely.
3. Now the actual soil with the plant is put into the pot.
4. On top of all that another layer of fine sand is added. Again about a centimeter thick, covering the soil completely and thickly.

Most seedlings won't mind the sand, as their roots are still in the soil. But the gnats won't have a chance to get their eggs into the soil. The only thing they can do is lay them into the sand where it is too dry and the larvae will starve. Even through the holes in the bottom of the pot they can't get into the soil, because there too is a layer of sand.

Now you can relax and watch. Sometimes an adult gnat will come along, land on the sand and walk around irritatedly. It doesn't understand, it seems, that it can't find a place for its eggs... even though there are nice and juicy seedlings present. But since it doesn't find anything it simply leaves.

I have not had more than one or two gnats on my pots since I use the sand-covering method. They come, watch and leave!

By the way: I am not sure the name fungus gnat is correct. In German they are called Trauermücken. Wikipedia only led me to the dark-winged fungus gnats and since "my" gnats do not have dark wings, I decided on the common fungus gnat.
But if anyone knows the correct English name for the Trauermücken on my pics, please let me know!
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Mealybugs

Mealybugs are little but plainly visible white bugs that mostly sit in the junctions of leaves and stems. They spin cocoons that enclose their eggs. These woolly cocoons are often the first thing to be noticed.

Mealybug with cocoon on a passiflora leaf
Mealybug with cocoon on a passiflora leaf

Mealybugs themselves are scale insects and look a little like rough woodlouse. Mealybugs also excrete a sticky fluid that is, next to the cocoons, the most distinctive feature of a mealybug infestation.

Mealybug with sticky excretions on a passiflora leaf showing typical discolorations
Mealybug with sticky excretions on a passiflora leaf showing typical discolorations

I have only had mealybugs once on a Passiflora "Purple Haze" hybrid and I only noticed them because many leaves startet to look strange and fell off. Then I looked more closely and found the mealybugs.

Typical discoloration and deformation of a mealybug-infested passiflora leaf
Typical discoloration and deformation of a mealybug-infested passiflora leaf

The first aid for a mealybug infested plant is to pick the mealybugs off the plant with tweezers one by one and crush them in a tissue or similar. That's pretty gross, but it helps (not only the plant, but also the owners anger...).
However, this does not stop the pest. The mealybugs have already laid eggs in the soil of the infested plant and - they are indeed very thorough - in the soil of the neighbouring plants, too. So, they will come back.

My next step was to buy Lizetan sticks and put the recomended amount into the soil. With Lizetan you should be careful. Even though it comes with a plastic stick for application without touching the Lizetan, you should wash your hands after using it, anyway. And - by God - keep it away from children: the Lizetan sticks look like normal vitamin pills (at least like some vitamin pills in Germany).
The Lizetan gets into the plant with every watering and finally the mealybugs ingest the plant and with it the poison and they simply die and fall off the plant.
This takes up to three weeks and in order to keep the bugs from harming your plant in the meantime, you're back with the tweezers and a tissue after a few days.
But, don't panic! I only had to pick them off the plant twice and after that the Lizetan seem to take effect and no more mealybugs appeared.
Since they lay their eggs in all pots they can reach, the guy in the hardware store who sold me the Lizetan said that it's best to treat all plants on the same windowsill.
Positive side effects are that Lizetan is also a fertilizer and after a few weeks my passiflora had recovered and even startet to blossom.

To avoid mealybug infestations plants can be sprayed with water regularly. Mealybugs don't like moist environments.

Oh, and another thing that seems to help against mealybugs (and I'm sure against many other pests) are spiders.
I had three pots with different passiflora hybrids on my windowsill. The left one was the "Purple Haze" that had the main infestation. The right one (a beautiful "Sapphire") had some mealybugs on it but not as many damages as the left one.
And the one in the middle (a "Petra" - yes, I mainly bought it because of its name) had not a single mealybug on it... but a small spider that was busily running over the leaves and apparently was having regular feasts of mealybug.
I don't know if that's really the reason, but it is curious that the plant right next to the infested one had nothing on it, don't you think?
So whenever you find a spider in your home (well the smaller ones anyway - I have no idea how big common spiders are where you live and I wouldn't put a tarantula on my passiflora), put it on your plants. You'll be happy without pests and it will be thankful for the free snacks.
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Scale insects

Scale insects are small but plainly visible brown to black insects that mainly appear on the stems of a plant. They are roughly the size of mealybugs, but they do not leave woolly cocoons or webs behind. Instead scale insects hide under a shield, hence the German name Schildlaus (shield lice).

Scale insects mostly look like little lumps and they appear to belong to the plant or to be just a thicker part of the plant. The damage they do to the plants becomes apparent much later.
The scale insects on my plants didn't survive long enough to actually do any damage, so I don't have a description or pictures of typical damages.
Pictures of scale insects on the other hand I do have:

Three adult scale insects on the stem of a young jacaranda plant
Three adult scale insects on the stem of a young jacaranda plant

Adult scale insect (under the stem), young scale insect (larger, orange one above) and babies (little ones on top of the larger orange insect)
Adult scale insect (under the stem), young scale insect (larger, orange one above) and babies (little ones on top of the larger orange insect). On the larger orange scale insect the white legs are visible.

Adult scale insect with white spots on its back, that look like vertebrae
Adult scale insect with white spots on its back, that look like vertebrae

Two scale insects on top of each other
Not an unusually large scale insect, but two on top of each other...
well, somehow they have to reproduce...

What can be done against scale insects?
If the infestation is not too bad and if the plant has only a few large leaves (e.g. monstera, strelitzia, musa...), the scale insects can be picked off the leaves or scrubbed off carefully with warm water. But a little pressure is needed to get them off the plant.
If the infestation is bad or the plant has too many leaves to treat them individually, Lizetan can be used. It is a combination of different chemicals, that acutally helps against many pests at once.
It takes a few weeks to work but untill then the insects can be picked off the plant manually (the ones that can be seen/found easily anyway).
Also an infested plant should be put in quarantene to avoid the scale insects to infest other plants, too.
Three scale insects in a row
Scale insect procession
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Tenthredinidae larvae

Tenthredinidae are a family of sawflies. Their larvae can sometimes be encountered on plants in spring.
I found some of them on one of my passion flowers.

Tenthredinidae larvae with typical excrement and damages done to a passion flower leaf

The larvae are several inches long and clearly visible. They sit under the leaves of soft leaved plants and eat whole layers of the leaf, leaving only the thin top layer behind.
The larvae I had were present for a few weeks and then vanished without me having to do anything about it. The few damaged leaves died, but there was no other damage to the plant.

If these larvae appear in bigger numbers, they can simply be plucked off the leaves. Other than that they shouldn't do much damage since they're only present for a short time.

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2 comments:

  1. Fantastic post Petra!! Very helpful, and the photos are great in identifying these pesky pests. Thank you. :-)

    ReplyDelete