When Mealybugs Attack!

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Mealybugs tend to seem like white cottony masses, but if you look carefully, you can make out the individual pests. Source: http://www.biocontrol.co.za

Mealybugs are small gray or pink insects, but covered with fuzzy white wax and therefore look like balls of cotton wool. They pierce plant leaves and stems and feed on plant sap, weakening the plant, often causing deformed or yellowed leaves, reduced bloom, stunted growth and, in extreme cases, the death of the affected plant.

The two most common species found on houseplants are the citrus mealybug (Planococcus citri) and the long-tailed mealybug (Pseudococcus longispinus). (There is also a root mealybug [Rhizoecus spp.], but it’s very different in its habits and treatment. Read Root Mealybugs: Death From Below for more information on its control.)

Both aerial species are generalists and will attack almost any plant. Fortunately, they’re of tropical origin and won’t survive winter outdoors in temperate climates, but when it comes to houseplants coddled by warm air year round, there isn’t much to stop them.

Where Do Mealies Come From?

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Succulents are often victims of mealybugs: they tend to congregate at leaf bases. Source: needlesandleaves.net

Discovering mealybugs on a plant is always a shock. How could they possibly have made it to your house? After all, female mealybugs can’t fly, and even the nymphs, the most mobile phase, can only crawl from one plant to another over short distances. You can almost end up believing it’s a case of spontaneous generation!

But it isn’t, of course, the culprit is …you! A mealybug infestation almost always follows the purchase of an infested plant. Of course, once you have one plant with mealybugs, it’s still usually you who transports them from one plant to another on infested hands, clothes or tools (pruning shears, watering cans, etc.).

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Thoroughly check your plants before you bring them home. Source: wshg.net

That’s why the first thing to do to try and prevent a mealybug infestation is to always carefully inspect all plants before you bring them home. Especially if they’re on sale!

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New plants need to be put into quarantine until you can be sure they aren’t harboring pests. Source: ourigny, du livre Les 1500 trucs du jardinier paresseux

And the second thing is …to always put any newly purchased houseplant into quarantine to make sure it doesn’t harbor any enemies. You can set the plant in a room where there are no other plants or even in the same room, but far from others (again, mealybugs don’t fly). Personally, I seal most new arrivals inside a transparent plastic bag and put them with the other plants, since I don’t really have a place where there are no plants. After 40 days, check the plant carefully, especially the leaf axils and underneath the leaves. If no mealybugs are present, you can move it closer to other plants.

The third thing to do is always wash your hands with soapy water after handling any plant and also to sterilize your houseplant tools with isopropyl alcohol (rubbing alcohol) before moving to another plant. And when you water, never let the watering can touch the plant! (Been there, done that!)

Toss Infested Plants

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The best solution is to get rid of the infested plant. Source: chittagongit.com & http://www.flaticon.com, montage: laidbackgardener.blog

Mealybugs are very difficult to control. In fact, nearly impossible. So, if you see one on a plant, the best advice is to …toss it into the trash (tropical climates) or compost (temperate climes) without delay! Then clean the spot where it sat with a soapy cloth, because often the female lays their eggs elsewhere, like in pot saucers and on windowsills.

Another possibility would be to cut the plant back severely, almost to the ground (presuming it’s a plant capable of growing back from the base), and to repot the stump into in a clean pot, replacing most of the old soil (either the potting soil or the old pot could be hiding eggs!). Now, wash the stub well with soapy water … and let it grow back.

In spite of this radical treatment, you still have to put what’s left of the plant into isolation and this time, not just 40 days, but at least 6 months!

For the Brave, the PersistentAnd the Naive

You just can’t convince yourself to toss the plant or cut it back so severely? Well, there is another possibility.

You can try to control mealybugs with rubbing alcohol. It works, because because alcohol melts the insect’s waxy white covering, a protection against dry air, causing the creature to die of dehydration.

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Don’t waste your time chasing down mealybugs with a cotton swab dipped in alcohol. You never get them all and soon the infestation is back again! Source: onlinepharmacynoprescription.co

But touching each individual insect with a cotton swab dipped in alcohol as recommended on so many websites is just an exercise in frustration, because you’ll only be treating the adults and the fluffy egg clusters, both of which are white and fairly visible. The nymphs, tiny and yellowish, are rarely seen, not only because of their diminutive size, but because they tend to hide in leaf axils and clefts in stems. Thus, they survive the cotton swab treatments and then the infestation starts up all over again.

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Spraying with alcohol can get at even the best hidden mealybugs. Source: http://www.walmart.ca, montage: laidbackgardener.blog

Instead, try spraying the entire plant with 70% rubbing alcohol. Or a solution of 1 cup (250 ml) of rubbing alcohol and 1 cup (250 ml) of water, adding a teaspoon (10 ml) of concentrated insecticidal soap so the solution sticks better. Apply in a well-aerated room and repeat every 3 days as needed.

If, after a month or two of regular sprays, mealybugs keep coming back, however, resign yourself to throwing the plant away. Sometimes that’s the only logical solution!

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Scale Insects on Houseplants: A Nasty Surprise!

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Scale insects are quite visible on a green leaf, but often blend in with bark when they’re on a branch or trunk.

You find a strange growth on one of your houseplants, a sort of small brown bump. In fact, not just one brown bump, but several. Even many? Unfortunately, there’s a very good chance that what you’re seeing is an insect, a very sneaky one called a scale insect or just “scale”. If so, the faster you react, the faster than you can regain control!

Well Camouflaged

Detection of scale insects is difficult because they are so well camouflaged. The mature insect is covered with a shield-shaped shell that can be rounded or almost flat; brown, gray, green or transparent; or oval, comma-shaped or resembling an oyster shell. They often seem to be part of the plant’s bark or you may take them to be drops of dried sap. They can be especially confusing on ferns as the latter produce sporangia (spore-producing organs) that some scale insects are able to imitate!

Not sure if that small bump is part of the plant or not? Give it a flick with your finger. If it stays put, it’s part of the plant; if it comes off, it’s a scale insect.

Infestation usually begins out of sight on less visible parts of the plant (under leaves, at leaf axils, etc.) before spreading to cover much of the plant.

Often the first symptom you’ll notice is a clear, sticky substance that drips onto lower leaves and nearby objects. This is called honeydew and is excreted by scale insects. It is even more obvious when the honeydew becomes covered with sooty mold, looking much like black powder, and that can happen over time.

The infested plant usually continues to grow normally at first, but possibly with less vigor, then as the scale population increases, the leaves gradually turn yellow. It not treated, the plant will likely die.

Personal experience

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Cute, n’est-ce pas? But this little cycad caused me years of trouble!

A few years back, I found an adorable little cycad (Cycas revoluta) at a very reasonable price and I brought home without thinking too much about it. It seemed healthy and I placed it among my other houseplants. A few months later, I noticed some fronds turning yellow, then saw that the lower leaves were abnormally shiny and that there was a sticky substance in the saucer below. Upon closer inspection, I discovered it was full of scale insects: literally hundreds of them! And other plants in the area were too. After repeated treatments, I was able to save most of my plants, but I had to admit defeat and tossed the cycad and five other plants into the garbage: despite treatment after treatment, the scale insects kept coming back.

And now I have to inspect all my houseplants regularly because even 3 years later, I still occasionally find a plant I need to treat or toss. All because I brought home one plant without isolating it!

A Truly Weird Insect

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Brown soft scale (Coccus hesperidium).

Scale insects don’t look like insects. They have no antennae, wings or visible legs and live permanently attached to their host plant. The species most commonly seen on indoor plants is brown soft scale (Coccus hesperidium) which produces a brown to tan domed shell from 2.5 to 4 mm in length… and it’s one of the larger ones! This scale insect has a wide host range and can attack almost any houseplant. Other scale insects are specific to a single group of plants. Some are only found on orchids, others only on bromeliads, others only on ferns, etc.

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Mealybugs are close relatives of scale insects, but unlike the latter, are mobile.

A quick word about mealybugs, another houseplant insect. Scale and mealybugs are closely related, but the mealybugs are white and appear covered with cotton. Even more obviously, they have legs and move when disturbed, while a scale insect will not move when you touch it.

For more information on mealybugs, read Just Toss Plants Infested with Mealybugs.

How Can a Legless, Wingless Insect Get Around?

You must be wondering how an immobile, legless, wingless insect is capable of spreading from plant to plant. The secret is that scale insects are mobile… in their youth. Nymphs, called “crawlers”, are born from eggs hidden under their mother’s shell. Crawlers are so tiny they are rarely seen. In most species, they wander about for just two or three days, then settle down for the rest of their life on a new stem or leaf. Nymphs readily crawl from one plant to another and thus start a new colony. And there are several generations per year. One scale insect that escapes your treatment can result in to 20,000 scale insects in a single year!

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Outdoors, scale insects can be spread by ants.

In nature, as well as by wandering on their own, nymphs are often carried from plant to plant by the wind, by birds or by ants. In fact, some ant species even raise scale insects in order to harvest their sweet honeydew and carefully move them from one plant to another.

In our homes, though, we can’t blame wind, birds or ants. Scale insects inevitably arrive on infested plants we bring home. Then crawlers move on to new plants or the plant owner inadvertently carries them from plant to plant when watering or pruning or when he moves an infested plant.

If scale insect nymphs crawl, the males fly. They too are tiny and rarely seen. With no mouthparts, they live only a few days and their only role is to fecundate females. But they’re pretty much redundant, as the females of most species can produce eggs without fecundation through a process called parthenogenesis.

Controlling Scale Insects

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Always, always, always put new plants in quarantine.

It’s important to understand that, unless you live in the Tropics, the scale insects that infest your houseplants did not come from outdoors. The species of scale insects that infest houseplants are of tropical origin and can’t survive outdoors in temperate climates, at least not over the winter. Nor do scale insects spontaneously generate (although they may seem to!). The source of just about every infestation is always a plant that was already infested, brought home from somewhere else, often a nursery, but maybe too as a cutting offered by a friend.

Don’t do like I did: inspect every new houseplant before you buy it and then put it in isolation for a good month once you do bring it home. Did you know the word quarantine means 40 days? And that’s just about right as an isolation period for new houseplants.

If you have no separate room in which you can put your new purchase, just put it 6 feet (2 m) away from other plants or isolate it inside a transparent plastic bag.

If you do find scale insects, isolate the infested plant immediately if you already haven’t done so… and ask yourself seriously if it wouldn’t be better for you to simply discard it. Sometimes you can nip the infestation in the bud by cutting the plant right to the ground… but if so, do clean your pruning shears before using them on any other plant! Of course, not all plants will tolerate such a heavy pruning, so you’ll need other methods.

Insecticide sprays are not very useful. Adult scale insects are essentially immune to insecticides due to their protective shell. Moreover, even if the insecticide treatment did kill them, how would you know? The shell of a dead scale insect can remain on the plant for years, making you think the plant is still infested. The best treatment is to go over the whole plant with an old toothbrush dipped in an insecticidal soap solution to remove any shells. Yes, it’s tedious, but if it works, it may well be worthwhile! Then rinse the plant thoroughly to knock off any crawlers that may  be present… and watch it for a few weeks. If new shells appear, repeat the treatment… or toss the plant!

Outdoors

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There are literally hundreds of species of scale insects that can infest outdoor plants.

There are also many species of scale insects that attack outdoor plants, mostly woody plants like trees, shrubs and evergreens, but they are not the same ones that live on houseplants (again, if you live in a temperate climate).

The initial treatment for scale insects outdoors remains essentially the same: clean the trunk and branches with a brush dipped in a solution of insecticidal soap. Then spray the plant all over with insecticidal soap or horticultural oil. Also, a dormant oil treatment can be very helpful in reducing the population if you apply it at just the right time, and that is almost always just before the buds open in early spring, as that is when crawlers are active or when they have just settled down and therefore before their protective shell is fully formed. Even so, as with indoor plants, the shells of dead scale insects can remain attached to the bark for ages, so you still have go over the infested plant with a brush to be absolutely certain whatever treatment you used was effective.

Yes, scale insects are sneaky and hard to control, but if you’re persistent, you can succeed. Still, do remember they are much easier to prevent than cure… and prevention starts wit isolation!

Longer Days Awaken Pests

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Whiteflies may be in diapause in mid-January, but by March they’ll be wide awake and hungry!

You may not have noticed, but if you live in the Northern Hemisphere, many houseplant pests have been less visible of late than usual. That’s because many of them enter into diapause, a kind of semi-dormancy, starting in the fall. This is due to the influence of shorter day lengths. In fact, they are often so inconspicuous in late fall and early winter that you may even have thought you’d gotten rid of them entirely.

Other insects continue to remain active even when the days are short, but develop at a much lower rate than in summer and likewise may go sight unseen for a while. But when the days start to get longer and the increasing sun heats up your home or greenhouse just a bit more, the two groups are re-energized and begin to reproduce abundantly.

Even as early as late January, although it still feels like the middle of winter outdoors, days are getting perceptibly longer and gradually, depending on the species, the enemies of your plants will start get back to work. By early March, they are all active… and hungry.

The Culprits

Insects that are quiescent during short days (or almost so), but awaken as days lengthen include:

Aphids, fungus gnats and thrips, however, don’t seem to slow down much in winter. They are just about as active in January as in July! You have to keep your an eye open for these insects throughout the year.

What to Do?

  • 20160128C.jpgInspect your plants at the end of January, looking especially at leaf axils and leaf undersides. A magnifying glass may be needed to see red spider mites, as they are very tiny. Subsequently, an inspection every two weeks is never a bad idea.
  • Set out yellow sticky traps: often flying pests like whiteflies, fungus gnats and winged aphids will be caught before the infestation even begins, nipping it in the bud.
  • Isolate infested plants so the pests can’t spread.
  • Treat infested plants.

Treatments

20160129BInsecticidal soaps and horticultural oils are almost universal treatments against these creatures. Just follow the application details explained on their packaging. You can also spray infested plants with solutions of dishwashing liquid or other soaps, but make sure you test a few leaves first: they can be toxic de certain plants.

Another possible treatment is to spray a solution of 1 cup (250 ml) of rubbing alcohol in 1 quart (1 liter) of water to control scale insects, mealybugs, aphids and whiteflies. Warning: for your own protection, ventilate the room when applying rubbing alcohol on anything more than a limited scale. Its fumes can be toxic.

Keep an eye open and your finger on the spray bottle’s trigger. That way you ought to be able to stop pests in their tracks… and allow your plants to take full advantage of the lengthening days!

 

Laidback Gardener Tip of the Day

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Just Toss Plants Infested with Mealybugs

décembre 20Mealybugs, those little “cotton balls” that collect in the leaf axils of your houseplants, are very difficult to control. So if you see any on one of your plants, the best advice is to… simply toss it in the garbage! Next, thoroughly clean the spot where the pot was located with a cloth soaked in soapy water, because often the female lays her eggs elsewhere than on the plant. Even if you want to keep the pot, it’s best it to place the dishwasher where the intense heat of the water jets will eliminate any hidden mealybug eggs.

You find yourself unable to throw out a living plant? First, try to get over this: it’s not a good habit if you want to be a successful gardener. If not, you can try to control them with rubbing alcohol. But not by dabbing every insect individually with a cotton swab dipped in rubbing alcohol, which is the usual trick you hear. That is simply a waste of time because you’ll only see the adults; the tiny larvae, barely visible even when in exposed spots, survive these treatments by hiding in cracks and leaf axils. Next thing you know, the mealybugs are back again.

Instead, try spraying the entire plant with a solution of 3 tsp (15 mL) rubbing alcohol, 2 tsp (10 ml) of concentrated insecticide soap and 2 cups (500 ml) of warm water. Be thorough: you need to get the solution into every nook and cranny.  Repeat every 3 days as needed. That might work. But tossing the plant is still the safest bet.