Greenhouse pest control

I have a few questions about pest control. I have a 48' x 24' greenhouse that I have built myself. Building the monster took a lot more time than I expected (as most projects do). I just did bare minimal upkeep on my plants during this time. I had previously had a plastic hoop greenhouse I had built from plastic PVC water piping, with greenhouse plastic as a covering. We got hit by a hurricane that tore up the plastic on that greenhouse, so my plants got moved into the new greenhouse a little earlier than expected.

I have had an on-again, off-again problem with spider mites, and a slowly growing population of white flies during this winter. I initially used insecticidal soap and horticultural oil, in addition to washing down the leaves of plants that had visible spider mites. So far, my spider mite control plan seems to be working well, with only an occasional plant that shows a few mites which I quickly wash off and treat. The white flies seem to be slowly increasing their population during this time. I have tried spraying with malathion, a systemic poison by Ortho that listed mites and white flies as one of its target controls, and another (nonsystemic) poison by Ortho that also indicated it worked on mites and whiteflies.

None of this seems to be working on the whiteflies. I have been looking at "Dr. Doom" insecticidal spray and foggers, which use pyrethrins. My current plan is to spray and fog every 5 days, 4 different times, over the course of 20 days, then to follow this up a few weeks later with a release of beneficial mites, green lacewings, and ladybugs. If all else fails, this summer I am going to completely empty out the greenhouse, bomb it with insecticide and miticide, leave it empty a few weeks, then move plants back in one at a time making sure each one is pest free.

I am curious if anyone here has any adivce or experience with a persistant pest problem in their greenhouse? I am open to all suggestions.

Okay, a couple of newbie thoughts here....

I'm wondering if Neem oil might not help you? And perhaps the beneficial insects before the chemicals - I would think that the residuals might get them, too.

Someone, I think it was ecrane (?), once said that she'd seal off her GH in the height of summer or August and let the heat decimate all the nasties. So if you're going to empty it out then, you might want to see how that does for you.

Hopefully someone with more experience than I have can give you more help!

Several ideas, but first, what plants do you have in the GH?

A wide assortment of plants. It will typically be for my tropicals, mostly hibiscus, bananas, alocasia, anthurium, bromeliads, amorphophallus, philodendrons, plumeria, etc. If I favor any one type of plant, it would be aroids. When I finish repairing the smaller greenhouse, I will move all of my cacti, succulents, and dry heat lovers into that one, but in the meantime I have an assortment of cacti and succulents in the larger greenhouse as well.

The aroids and a few select other plants seem to be the most affected by the spider mites: colocasia, alocasia, musa, brugsmansia, in particular.

The whiteflies seem to prefer the hibiscus, alamanda, and a few other plants more than the others.

I have some neem oil, just haven't tried it yet. While the soap and horticultural oil would seem like the least toxic approach, they seem detrimental to the leaves of some of the tropicals (I did not spray in midday sun, only in late afternoons when the sun was going down).

I have read that sulfur works well to control spider mites. I know I can get garden sulphur to spread around the greenhouse, or possibly spray from a dry dust applicator. I saw that there are sulfur candles for greenhouses that you burn and the sulfur is spread that way, but I only see them for sale on U.K. sites, not in America. That makes me wonder...

One last note--I saw on several sites that sticky traps are supposed to help with whiteflies, but only to keep their numbers down, not to elimnate them. Just throwing out some of the info I have been reading. I got lucky with my smaller greenhouse. I had a mealy bug problem once that was easily eliminated by consistently using cotton swabs dipped in rubbing alcohol. Got rid of the mealy bugs and never had another problem with pests after that.

If nothing else works, I will definitely try using the heat of the summer. I have prepared garden beds that way for years. In the fall I turn the soil in the site I want to plant in the following spring, then cover it with clear plastic. The heat of the sun over the winter heats up and kills all the bugs and weed seeds in the soil, makes it perfect for planting the following spring.

Supposedly top dressing your containers with worm castings will help control whiteflies--haven't tried it myself but there were some threads about that in the hibiscus forum a while back. I have to admit that the greenhouse is the one place where I cheat on my no chemicals approach to gardening...things spread so quickly in there since I've got a ton of plants in a small area, so I've taken to using the systemic Bayer 3-in-1 to keep things under control. Even with that treatment though I'm still having horrible problems with mealybugs on my hibiscus this winter--I'm keeping them at a level where they're not doing a huge amount of damage to the plants but they don't completely go away (I've got way too many plants and some of them are hard to reach so the q-tip and alcohol trick won't work).

And I can't take credit for the idea about the August heat treatment...I sort of do it coincidentally because my greenhouse sits empty all summer--I do leave the doors open but since I don't have plants in there during the warmer months I don't bother with cooling, so on days when it gets up to 110 or so outside I'm sure it's considerably hotter in there. But I think it was someone else who suggested it.

You have some whitefly lovers there. Hibiscus, and for that matter most everything you have in your GH, can be effectively treated with systemic imidacloprid (Bayer Tree and Shrub something-or-other, there is also a generic which is cheaper). I put 2T/gal and water thoroughly and retreat about once every 3 months. When used for container plants it doesn't seem to last as long. But it will control your problem and you can use it since you don't have edibles.

Neem is great, that's mostly what I use. There is no resistance to neem, it has several different mechanisms of action. But remember that neem takes 1-2 weeks to see an affect. The bugs won't keel over like they will with other agents. You have to be patient and consistent. I work it into a spray rotation with permethrin.

Beneficials won't like these sprays at all. I have had no luck with a variety of them. Seems like a good idea in theory, but in practice it is easier for me to use neem, permethrin, selected systemics.

This message was edited Jan 29, 2009 7:27 AM

Stressbaby - have you ever used Neem on the soil for (%$$^&%#@) fungus gnats? Someone suggested it, I didn't think much of it but I have some and I don't have mosquito dunks (my next try)... yet....

I've done it but honestly I never really looked hard enough to assess the results.

My neem says that you can add it to the irrigation water; I don't know if that is for pests such as fungus gnats or if it has some sort of systemic effect as well.

Huh... okay, thanks!

Boy, does this sound familiar or what?? I had a serious white fly infestation my first year in the GH BobGoblin, which seemed to center around 3 "Winter Tomato" plants. I have a natural aversion to anything stronger than Safer Soap/Horticultural oil (especially on things I plan to eat) so that's what I used. First weekly, then daily. Always worked outside, so why shouldn't it work inside? The white flies giggled, and multplied. My final solution? Wait for a REALLY cold night (preferably in the teens) and moved those suckers outside. I went out the next morning, whacked those tomato plants with a stick and not one "white cloud" appeared. Not even one white fly. My Safer soap/horticultural oil treatment seemed to keep the rest of the GH under control for the rest of the season. My take-away on this was that once a pest population reaches a certain density in the GH (undefined, but my definition was "out of control"), it can't be reversed short of an atom bomb. Sacrifice the host plants (they're easy to identify), and don't grow them again. Now about them spider mites...they are a perpetual problem for me since I have an affinity for citrus, and so do they. The purists say just "blow them away with a good hosing down", and I've found that works. For about 3 days. Then they're back in greater numbers. And hosing off a hundred citrus plants in the GH isn't really practical (creates a helluvamess!). But I have found one "nasty" pesticide that seems to help maintain control over these things. Don't even know the name of it, but it's produced by Bonide and it's billed as an Insecticide, Fungicide, and Miticide. It's worked for me so far in controlling those ^$7&^@ mites, and fungus on some Salvia's. Key thing is not letting the populations get ahead of you. Move fast and hard at the earliest sign

Have you tried Marathon 1% granular for whiteflies? You couldn't use it on your tomato plants that you're growing in a container for consumption, but you can use it on veggie plugs, and ornamental plants. If you grew your plugs in the late summer using the Marathon, brought "clean" plants into the greenhouse, you would be able to grow them out all winter with little problem since more won't be coming in from outside.
I think the Avid is the best thing I've found for the spider mites on ornamentals like the colocasias and alocasias, brugmansias. Although you have to spray it, when you spray the top sides of the leaves, it goes through the leaves to kill the mites on the bottom sides too.