I need you all to put your thinking caps on, lol. I’m at the point where I’m maxed out on seedlings in the house under lights and they have to go outside NOW. So I’ve made some little greenhouses from cardboard boxes with the sides cut out and covered them with shadecloth to keep out the fungus gnats and aphids. Problem is, the shadecloth reduces the sun too much. I’ve also tried cheesecloth, which works well but deteriorates too quickly. Anyone have any thoughts on what else I can use?
Plain old vinyl window screen? You can buy it at most home improvement stores and cut it with a plain old pair of scissors. Kim
If the top layer of your seed trays is sand and not potting soil you will see almost no fungus gnats.
Please don’t shoot me. I didn’t know that’s what they’re called, but I love 'em. I can’t prove it, but I believe they spread the beneficial fungi around my yard. Thanks to them I can almost call it a garden - a gutsy statement in Florida. Now the aphids, even though I apologize to the ants every time I destroy their aphid farms I kill them ALL.
Don’t feel badly sandandsun, fungus gnats are a prime protein source for hummingbirds.
As a practical matter, fungus gnats do not do well if things are kept a bit drier. It’s a problem with growth chambers in labs and that’s the solution for them. Or yellow sticky traps or nasty pyrethroids.
Aphids you can kill with 1% Murphy oil soap spray. But never all of them, just most of them, so every threee days you have to do it again. The soap also kills fungus gnats if it hits them. Also paper wasps, squash beetles, bees etc.
More toward your question, Judith. I’d consider cold frames. Me, I’m very slow when it comes to construction. Maybe an option for next year?
Chris
Adam, if I don’t protect the young seedlings from the gnats, I lose up to 75% of my seedlings to them. A coldframe will not do it unless I cover the cold frame with shadecloth or screening, which is essentially what I’m doing now with the boxes. Also, when open (which would be most of the time or the seedlings would fry) pack rats would get them. I don’t use seedtrays. Each seedling is potted and sand on top makes it hard to see if they need water.
Larry, it doesn’t get much drier than here in Tucson. The good thing about that is I never lose seedlings to damping off. On the flip side, the seedlings MUST be watered almost daily as they dry out so fast. And sticky traps won’t help outside. As for pesticides of any type, I’d rather not use them when the seedlings are so young and need to be taken into the house at night when it’s freezing. I’ve been reluctant to use soap because spraying the seedlings means the soap will drip into the pots. Years when I don’t have too many seedlings I knock off the aphids daily, but that’s a lot of work when you have a big crop. Up to 160 now and many are blooming already. And the season has barely begun. I’ve only processed about 20% of my hips, but the rest are open pollinated, so I may not get to those at all.
Hybridizing here in the desert presents different challenges from other places. All a learning experience.
Judith, Have you ever tried AzaMax? It is a botanical, it repels, stops the insect from feeding (really works fast with rose slugs and spider mites), and is a growth regulator-meaning it prevents the insect from maturing and reproducing the next generation. This has done wonders in reducing the year 'round reproduction here in the San Diego area. It is an Azadiractin-which is a product of the Neem tree. The packaging reads as if it is highly poisonous, but my daughter took Neem pills to ward off intestinal ‘bugs’ for the year she was in India, and there, they treat Neem as if it was the drug store.
The only thing with AzaMax is that I had to make sure that I was covering both the top and bottom side of the leaves when it came to the rose slugs and mites. But it totally eliminated them, which I checked quite closely to see if they continued feeding.
Judith,
I meant old fashioned English cold frames which are usually bottomless constructed like boxes with boards using old windows, for example hinged to the top - i.e. glass.
The construction required is why I said maybe for next year.
Sorry for the frustrating confusion,
Chris
I think sticky will work anywhere, but you have to have it down in amongst the plants. If those really are fungus gnats it is usually a sign that the surface of the medium is damp. They actually live largely on fungus which grows only at high humidity. But I know the larvae can really damage roots.
If you are already watering, try using a more vigorous force on the sprayer and just knock the aphids off. The force of the water also stimulates the plants to produce strong inhibitors of herbivory. It simulates the effects of leaf munching without the damage.
Maybe if your pots were up on a slatted table, with a frame and hardware cloth above you’d have better air circulation, and the aphids would have to crawl much further to get back up. I’ve had good luck growing young roses up on a rough table so long as they are protected from the wind blowing them off. I usually set flats of six-packs or pots up that way in a partially shaded place.
I don’t think there’s much evidence that a potassium salt of fatty acids such as Murphy’s soap hurts anything plantish even when it gets on the soil. There are bacteria just waiting to consume it really fast. Short-chain F.A.s are herbicidal but that’s things like are found in goat’s milk. And it would kill the gnat larvae that came into contact with enough of it. Detergents are a different issue, some of them may be toxic to roots, but again I don’t know of much published evidence of that. I’ll look.
Chris, yes, I understand the cold frame thing. I have made them before. But they would not prevent bugs from getting in. And when closed, the heat would build up to very high levels here in the desert.
Larry, I only keep the soil damp enough as to not have the plants dehydrate, which happens quickly here. A hard water spray when the plants are 2 inches tall is risky. I’ve done it with a spray bottle, but having flying aphids, which we do have here, means they come back pretty quickly.
I’ll give the Murphy’s a try. what dilution do you use?
Have you considered trying tobacco water/juice? I have used it in the past to treat insect infestation and the pests always seem to go away. I’m not sure it would work on fungus gnats as I’m not sure what they are. It will work on aphids though. I usually use a diluted solution (don’t have a specific ratio but the water is slightly discolored) and lightly water the plants with it. I have tried both watering it directly into the soil and onto the leaves and both work - I prefer into the soil just in case it has the potential to burn the seedling. Just a thought I had.
FWIW I’m not sure that a coldframe would work either unless you can completely seal it up. But if overheating is a problem, and you wanted to have one, I might have a solution for that. What I did was dig a trench in a shady area and line it with cinder blocks (the skinny ones are best). I then placed an old Patio door over that which completely covers the opening. Currently I am sealing it with the some rolled up bedsheets but I plan on making a wood/metal frame to place on top of the cinder blocks and using foam to make the seal next year.
When we were in the high 90s (not tripple digits but still hot) I took several temperature readings and there was about a 15-20 degree difference from inside the cold frame versus outside. I’ll take some reading this spring to see what the difference is in reverse.
I think the three reasons why this setup might regulate better than the wood coldframe is 1) the ground insulates, 2) the door is double paned, and 3) it is located in a shady spot. It took me lees than an hour to build and the only tool you need is a good shovel which, given the nature of this forum, I’m assuming you might have lying around somewhere.
Nicotine is toxic to roses.
Thanks Don. I did not know that. I guess its a good thing the solution I used was highly dilluted.
Also, I don’t want it in a shady area. I want it in FULL sun since I’m breeding for hot weather climates. Of course, I don’t want to fry them, either which I think a cold frame will do in this climate.
I spent the day updating my shadecloth covered boxes with fiberglass screening bought at the hardware store as Kim suggested. It’s PERFECT! My seedlings will get the full brunt of the sun tomorrow and they will be so happy. Thanks for the suggestion, Kim!
Here’s typical link to and Extension service brochure on insecticidal soap.
http://www.ext.colostate.edu/pubs/insect/05547.html
I personally would use a lower concentration like 1 %. I would also check the label. Last I looked at my bottle of Murphy oil soap it was pure potassium salt (softsoap) of long chain fatty acids. In the late 1980s we did a lot of experimentation with different vegetable oils converting them to soaps. We did F.A. analysis on many oils from castor to walnut. All seem to make a decent soap. Bar soap such as Ivory which is the sodium salt is not anywhere near as good or easy to use. Beware of the dispensers of so-called soft soap. Mostly they are actually detergents masquerading as soap. I don’t know why the FDA allows it, but they do. Detergents are cheaper to prepare and process, but as the CO State bulletin says, they may be toxic to plants.
Best results with distilled water. Or perhaps a little vinegar to lower pH which helps keep the calcium from precipitating the soap.
I do spray the plants with plain water every few days to rinse off excess soap.
I hope this helps.
Thanks Larry. I will pursue this.
I did find a paper on greenhouse tomatoes treated for whiteflies (Bemesia) where a detergent was subtly phytotoxic even at the lowest concentration of 0.25 %. Yield and fruit quality were adversely affected. Probably not something you’d be able to notice with heterogenous seedlings, but a warning. Effect was bad at 1%. Paper was an on-line version of something around 1995 from Am Soc Hort Sci but I didn’t save the ref.
Never had a problem with either of these out doors, but there are products for the gnats having Bt in them. Bacillus thuringiensis (sp?) kills fly and mosquito larvae, and will destroy the gnats’ larvae in the ground. In theory, you could use “mosquito bits” (available at most hardware stores) in the soil if you use early enough to allow to dissolve adequately. Also, I know folk who swear by diatomaceous earth, if you want to avoid pesticides.
As for aphids, soap is a very good option if you can’t rustle up any of their predators.