How do you deal with pests in the greenhouse

I breed oats where I work, and face a huge challenge with aphids. They damage the yield a little, and are quite inconvenient, making the plants all sticky and nasty.
My friend is having a go with fava beans. She’s struggling really bad with thrips. They’ve destroyed all her plants this year.
I’m wondering how people manage pests in their breeding material in the greenhouse.

For the aphids, I’ve tried parasitic wasps (Aphidius colemani, and A. ervi) which seems to work some, but not enough. Ladybugs are insanely expensive.
We can also order lacewing larvae, but they are sort of expensive and they eat the pollen when they grow up. That is often a concern with breeding material.

Does soap really work to prevent these things? Will that destroy the pollen in the fava beans?

I immagine aphids and thrips (and other pests) are a concern in other cultures as well. While I’m mainly looking for tips for the cultures mentioned above, I’m also curious what other people do in other plants

Organic greenhouses tend to fail catastrophically because they lack sufficient genetic diversity to have sufficient predators to deal with herbaceous insects.

Watering with a strong spray of water may dislodge aphids, and they may not find their way back to a plant.  

Also, because greenhouses tend towards overfertilization, that leads to amino-acid poisoning of the leaves, and the plants beg the insects to eat them in order to restore balance.

Hi V,
Welcome to Permies.

When dealing with pests on plants you need to either increase the number of predatory insects (which you have tried), manually pick them off (hard to do with aphids), or make the plants less attractive to the pests in the first place. Like Joseph said (who has way more experience than I do), in a greenhouse it is very hard to get a balance of predators. A stressed out or unhealthy plant is a magnet for pests. There is something called the brix scale, which (to some extent) measures the sugar in the plant, which can (in part) give an idea of the health of the plant. They have found through testing that if a plant has a high enough brix level, pests pretty much leave that plant alone. In a greenhouse setting it is very easy to stress out the plant, because it is not as forgiving as being out in the open. I would try to boost the soil health and make sure you are on top of the watering and temperature regulation, make sure you are not over fertilizing like Joseph said. These things should make the plants less appetizing.

I have a greenhouse attached to my house, which we remove the plastic from for summer and reattach it for winter. In winter it serves 3 functions: it is the primary source of heat for the house, it provides vegetables, and it provides a green space that is really nice to have in winter. I also use it for starting seeds in spring, and for keeping perennials that wouldn't be quite hardy outdoors in my climate (Rosemary and grapes are the big hits), and getting some perennials up early (bulbs in Feb, asparagus in March-April, which are 2 months later outdoors).

The winter produce from the greenhouse is primarily salad greens and herbs. The greenhouse drops below freezing every night for 2-3 months but the arugula, lettuce, spinach, claytonia, brassica/mustard greens, mache, cilantro, parsley, dill, don't mind a bit.

Pests are a constant issue in the greenhouse, especially in the spring when some days get very hot in there but the nights are still too cold to remove the plastic. There's always some aphids (obviously being farmed by ants), sometimes mites, and this past winter some tiny white flies that are smaller than aphids and fly around.

Here are the methods or systems that have worked for me so far:
1) A variety and a succession of things in the greenhouse means that as one thing is getting ruined by a pest, something new is coming up. Each year is different.

2) On some types of plants it's possible to squish aphids with fingertips and wash the plant with a jet from the hose.

3) A couple times I've done ant massacres, which really reduced the aphids. Sometimes with boric acid bait (honey and boric acid powder), and other times by flooding the garden bed they're living under and squishing them all as they come out. Ridiculously time consuming and I was afraid I'd get caught by somebody and disapproved of, so I only really did that once. But reducing the ants clearly reduces the aphids.

4) The permanent mulch on most of the beds in the greenhouse seems to have let populations of small spiders take hold, and that seems to keep the pests down. My theory is when there are lots of ants they stop the spiders from doing their work. Unfortunately the ants are active even in cold months whereas the small spiders don't seem to move around much until everything warms up a bit in spring.

5) Against the mites and the tiny white flies I haven't really found much. I spray the plant with a jet from the hose and that knocks them back temporarily. These pests don't kill the plants outright, and luckily they are mainly on my ornamentals and not much on the edible plants.

I recently sprayed a mix of peppermint (deterrent) castille soap and H2O on my own small garden, they were eating all my cilantro and some of the maters, after two applications they are almost entirely gone. Recommended to do a spot check first to see if it will damage your plants.

Thanks for the replies. Seems like it’s pretty impossible to avoid getting some pests alltogether.

I’m going to try spot spraying some of the plants which different things I’ve seen suggested here and on local websites

I also use a soap spray when i have aphid infestations (it is usually during dry spells) and it works pretty well.

I feel that pests need to be dealt with on a case-to-case basis.

Each pest might have a different treatment.

Some pests are easy as picking them off a plant and dropping in a pail of water.

some are easily removed with a spray of water.

Some can be dealt with soapy water.

I use Irish Spring bar soap to repel chiggers.

Slugs can easily be gotten rid of with salt.

Dear hubby had a method of dealing with cutworms that if I remember correctly used the cardboard roll out of toilet paper.

Ants are said to be the world's number one pest for which I use vinegar.

I see a lot of complaints about squash bugs though I have never had a problem with those.

I am sure there are 100s more pests (bugs) that I have not named.

V Kalsnes wrote:Thanks for the replies. Seems like it’s pretty impossible to avoid getting some pests alltogether.

I think this is an important permaculture principle - if you get rid of the pests you get rid of their predators too....
I'm hoping to have my new polytunnel built for next season, but I'm pretty sure t will take a year or few to get the sort of pest balance I had in the old one.
When I came here the polytunnel (about 14 foot by 35 foot?) was a bit like a desert - someone was growing tomatoes and they survived by the condensation that ran down the plastic and by reaching their roots underneath (I assume). In the first few years I had a lot of problems with spider mite (that like hot dry conditions) I even bought through the mail some of those predatory flies you can buy, although I didn't notice much difference.
Over time I added trickle irrigation to keep the soil moister, a jungle like polyculture and mulched beds, probably breaking every 'this is how to garden in a greenhouse' rule I did chop and drop with the weeds, left salads to self seed and the grape vine leaves made a nice leaf cover in the autumn. The spider mite trouble seeemed to disappear after a few years, the slugs seem to like the algae on the plastic as much as my growing plants, and a toad took up residence.
I think in a small system it would be more difficult to make an acceptable pest/predator balance and birds, for example, fall on both sides of the equation, but it certainly doesn't seem to be impossible in a large enough growing space, you just have to find what works for you and your growing style.

spider in my old tunnel