(Editor's Note: This article was originally published on March 27, 2007. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)
Let's face it... We don't grow in a vacuum and we like to get new plants. The more plants we get, the higher the risk of getting new pests and viruses. And the more plants we have, and the smaller/more cramped our growing/propagating space, the higher the risk that a pest outbreak can take out our entire collection. There are
pests and such everywhere (like your yard). Sure, it's worse in some climates than others, but they're there. Most growers would agree that it's pest control, not pest elimination, that we aim for. So we develop methods for isolation, monitoring and treatment (mild preventatives as well, if we're good).
It's difficult to discuss pest control generally when we live in different climates and grow on different scales. Obviously, if you live in a place where it's not unusual to have a hedge infested with mealybugs, then mealy control is going to be difficult. If you want to move plants in and out of the home and not use the "big gun" chemicals, then of course you're more prone to all kinds of pests.
Mites, in particular are really really really difficult to deal with, especially the ones that don't make webs, are not a bright orange, or are otherwise pretty much invisible. Some people, especially folks who live where mealies are all over the yard, may disagree, but I think dealing with mealies and scales is child's play in comparison to mites.
Part of the mite problem is that the infestation isn't visible until you really really have a problem. Several years may pass after the first ones walk into your home before you actually notice a problem. Another big part of the problem is that insecticides generally do not work on mites - mites are arachnids and so a roach killer is more likely to kill mites. (I said "more likely" not "will".... just to be clear.) The insecticides may be killing off the natural predators of the mites. Not even all miticides actually kill off a population; some just suppress it. Not all miticides kill the eggs. Mites develop immunity to miticides. “Systemic” doesn't always mean systemic. And you can pretty much bet that whatever great miticide you have, there are some mites that won't die. Ever look at miticides? Wonder why they're so expensive? Mites are a tough problem to crack.
By the time you have an outbreak across a big collection, it's a pretty daunting task to get things under control. No wonder some people recommend tossing the collection and starting over.
If you have an indoor grow area that you want to keep as pest-free as possible, but you don't want to use a lot of chemicals, then think not only about killing the pests, but also about never letting them in - or at least reducing the influx as much as possible without stressing out totally. This is where we should stop for a moment and think about what we buy and how we bring plants in.
Not to feed paranoia, but... a note about viruses first.
We don't talk much about viruses, but it is a real potential problem. Consider, for example, the reason why the Smithsonian research greenhouses is no longer distributing plants: they discovered Impatiens Necrotic Spot Virus (or something similar) and had to destroy much of the collection. Virus-infected plants do not always show symptoms, so there is no way to tell for sure unless plant material is tested.
Now back to the bug issue...
When I say "what you buy and how you buy", I'm not talking about whether the source (grower and distributor) are reputable or reliable, or if they spray pesticides a lot, etc., although all of these are things you probably want to consider. What I want to point out is that it's easier to debug seeds and rhizomes than leaves, and a couple of leaves are easier than a plant. (Sorry, African Violet chimera fans... this is not very helpful for you.)
Obviously, if you want a particular cultivar, you have to get some plant material. But if you want a species, then could you grow it from seed? One of the reasons I keep recommending that people try growing from seed is that seeds are relatively risk free. (And yes, hybridizing is fun, and perpetuating species is good, and growing weird species is also all good.)
If you want a cultivar, get the plant piece with the least risk. For example, if you are considering getting a Kohleria, do you really need a pot of leaves? Why not just get rhizomes? They are fairly tough to kill, and they sprout and grow quite quickly. Although a cutting might give you flowers faster, a rhizome is one step ahead in maturity anyway.
Selecting what plant piece you get is an easy way to reduce the probability that you'll bring in pests.But of course, we can’t get away with never bringing in foliage. So what do you do when you bring in new cuttings or new plants? Remember, it's safe to assume you can't see pests and eggs, and that they are airborne. They can hitch a ride on pots, bags, clothing, hair, hands, nails, and air.....
Let's assume that you have a spot for isolating new plants. Is this just a separate shelf or room? That may not be enough. Is it a vented humidity dome? That may also not be enough – there are holes in it, after all. It is a sealed container? Not to sound totally pessimistic, but that may also not be enough – after all, you have to open it to water the plants and exchange the air (even if that is once every 2 months like at my place), and when you open the lid – whoosh – a lot of air movement.
It's still possible to reduce your risk. Pause a moment to think about how you get the plant from your car/porch to the isolation area. Each additional step you build in to your plant-welcoming routine helps a little bit to reduce your risk. Take enough steps and you're significantly closer to pest control.
Consider the following....
If you just visited a greenhouse:
Could you possibly have brought bugs or eggs with you on your hair or clothes? I first considered this when I was at an orchid greenhouse with epiphytic cacti hanging from above and there were clumps of mealies on the cacti. I went straight to the shower when I got home.
Did you touch plants while you were there? Should you be washing your hands and cleaning under your nails? Okay, this sounds anal, but you know we should always wash our hands.
As for plants:
Are they covered - like in a plastic bag - when you walk into the house? This would be good practice.
Did you carry an uncovered plant through the living room and past the plant shelves before taking it to the bathroom/kitchen/de-bugging bench?
Do you sterilize your new potting mix? Anyone who has bought a bag of soil only to find it miraculously gave birth to fungus gnats knows that you should never trust those bags. Dried compressed mix is fairly safe though.
Are you cleaning your tools between each plant, pot and soil? Blades should also be sterilized against virus.
What about your hands? Did you just pick up a new plant, dump the soil, and then pick up a clean pot? Or did you just handle a new plant, and then walk over to mix up a batch of potting mix?
Do you wear gloves while re-potting? Are they disposable or are you using gardening gloves?
Do you give your new leaves and cuttings a dip in a treatment bath? Wash them down to physically remove anything that will come off?
When you water, does the tip of your watering can or water bottle touch the plants at all? Are you inadvertently spreading the love?
It's about balancing precautions and the joy of growing. It's about stopping to think about your routine to see if changing a few things might decrease the risk of bringing in an infestation. It makes no sense to continue habits that could contribute to increasing your pest risk level, when you could just as easily have other habits that decrease your pest risk level.
So what does all of this boil down to? For me, it might be something like this:
Always get the least risky plant part.
Get rid of the bug-prone parts as far away from my grow area as possible. If I get a new plant with foliage, this includes removing dead plant material, de-potting if I know I'm going to do that, removing soil or potting medium that might have larvae, eggs, bush snails, etc., spraying or dipping in a pesticide.
Deal with one batch of incoming plants at a time - in other words, the ones from the same source or, better yet, one plant at a time - and replace/clean/disinfect the bench/counter/table/tools after each one.
Keeping the collection down to a manageable size is really good practice, but it's one rule I flaunt all the time.
As far as a virus goes, there's no way to save it or cure it. But some of the same precautions can help prevent the virus from spreading through your collection. Don't share cutting tools or water. Keep your fungus gnats in check (they can carry virus).
When I am starting a plant from a leaf, I dip the leaf first. Everyone who does it probably has their own cocktail. For orchids, my dip mix (possibly in multiple separate dips) would include some or all of the following: a bactericide, such as hydrogen peroxide or Physan20; a pesticide such as Malathion, or a milder one like OrangePlus solution, which is my mildest soap-type pesticide; and Superthrive or some other sugar and B-vitamin type mix. (Physan20 is primarily a bactericide and algaecide; it is not a pesticide. It has some level of toxicity to plants. From discussions I have read, it seems that African Violets are not adversely affected by it. It claims to do a lot of other things and yet be relatively harmless, but it is still a chemical so I wouldn't call it completely harmless. It seems to me that hydrogen peroxide is a fairly good bactericide, and much safer to use.)
It comes down to enjoying growing the plants. If a major pest problem is going to ruin things for you, then put in place as many preventative measures as you can. Monitoring what comes in can drastically reduce the chances that you'll find an outbreak on your hands.