oh my! These guys can really wreck havoc with potted plants and they sneak right up on you. The root aphid is very pernicious and can easily be mistaken for some other problem – worse, it infects your entire production line. Fungus gnats are nearly as bad. Both of these insects, in turn, enable other problems to develop. These can include gray mold, susceptibility to other fungal diseases or the introduction of termites or grub worms.
If very badly infected, you may want to just throw the plants away(and burn the remains). To check for a bad infection of root aphids in potted plants, lift the pot up and look beneath it. If you see many little, scurrying whitish nymphs, you may need to toss that plant. The same with a fungus gnat infestation – if you see many small “gnats” rushing around the top especially coming up along the edges of the pot, then you may be too late and you might consider tossing the thing. You don’t want that plant sitting around as a vector of infection.
Once you have decided what to save and what to toss, you can begin treatment. Considering that the damage you see visible on the plant structure above the soil is the result of the root damage below the soil, you want to not only destroy the insect, but also help the soil and the roots to make a comeback.
Use an IPM (integrated pest management) approach as a way to think about the problem and to overcome these pests. In simple terms, an IPM involves knowing what your insect is, changing your growing environment, helping the plant to defend itself, attacking with biologics and following up with the heavy guns if you need to. All of this needs a calendared step by step application of biologics and pesticide.
First, pay attention to your growing environment – both the gnats and the aphids prefer a moist environment, so don’t let your soil get wet; do not overwater and check your PH – correct with dolomite powder. Too much water creates an insect friendly environment for both fungus gnats and root aphids. They also prefer dense quiet surroundings, so keep your plants clean, add some air circulation, and remove waste. This would also be a good time to put out sticky yellow cards to capture the flying fungus gnats; you do this both to monitor how bad the infection is but also to, simply, catch the things. If they are caught on a card, they can’t lay eggs. Before you start adding any biologics to the soil, apply a soil drench of hydrogen peroxide to contact kill what larve you can. The peroxide must be mixed 1 part peroxide and 4 parts water if you are using ordinary grocery store peroxide.
Now apply non-pesticide products intended to aid your plants against the pests. In this case, we are recommending Regalia, which enables the plant’s immune response system, as well as mycorizia, a soil fungus that symbiotically attaches to the plant’s roots and assists in the roots function.
How to use Regalia, mycorizia and compost tea.
Regalia is an extract of Reynoutria sachalinensis which is a little pricey, but effective. The product activates “a plant’s natural defenses to protect against a variety of fungal and bacterial diseases…” and helps the plant to produce “phytoalexins, cell strengtheners, antioxidants, phenolics and PR proteins” which all hold fungal disease back. Use it as a soil drench – let your soil dry out before application.
Mycorizia has been on the market for quite a while. It is a fungus itself that attaches to the plant’s roots, in effect extending the roots into the soil and increasing their performance. The mycoriza channels nutrients to the roots they attach to. Once an employee accidentally gave some of the nursery’s potted plants too much mycoriza (I think in the form of Dr. Earth) and although green and vigorous, they were stunted. When we pulled the plants out of their pots, we discovered that the roots clustered very close to the plant – no need to go anywhere else. When we re-potted them in fresh soil, they returned to normal, but they were always very large after that.
There is some controversy over the use of compost tea. Some say to brew it one way and some say another. Some say that it has no measurable effect, some say different. We are of the opinion that compost tea, whether anaerobic or aerobic, is a very good enhancer. Foliar spray on the leaves for stronger and greener leaves and soil drench to add more microbes to the soil. Oh, and it is very easy to make. Some people buy air mixing pumps and special ingredients, but you can away with a 55 galleon drum and basic stuff like manure and seaweed power – add some compost enabler to spark things off.
Next apply the biologics –
How to use Gnatrol and nematodes
Gnatrol (bacillus thuringiensis) is alive; don’t let it get hot and use it in a brisk manner. Once it is in the soil, it will hatch and start eating gnat larvae. Add about a 1/2 pound to 100 gals of water. The yellow cards should be cut into pieces so you can better spread them around. When they fill with gnats, remove and replace. Nematodes ( steinernema feltiae) have a delay of about 7 days after application before they become active. They perform very well, but after their food is gone, they will leave – occasional re-application would be appropriate.
Outright pesticides would be last. Bear in mind that pesticides will often kill the good guys in the soil just as they will kill the baddies. Use them last. Having said that, we wouldn’t hesitate to use these pesticides if needed – we are just very careful. A pyrethrum-like pesticide such as bifenthrin works well. We water bifenthrin into the soil around the roots for root aphids and generally in the pot for fungus gnats – the product is a contact killer. We apply for three successive waterings. Use rubber gloves and a mask.
How to use bifithrin
Follow the package directions and the maker’s re-application intervals. Mix it well and drench your soil. Do not mix the bifethrin with other products. The stuff kills on contact.