What used to be a more prevalent problem on the West Coast has now become a crisis nationwide.
Root aphids are increasingly being found feeding on the root systems of a vast variety of herbaceous perennials. They come in many colors, including pale green, yellow, gray, brown and pink.
They have ovoid bodies and are normally less than an eighth of an inch long. They are almost identical to common, above-ground aphids, except they often have shorter legs and antennae, making them well-adapted for life underground.
Root aphids can be winged or non-winged. The winged variety tend to spawn when a population of aphids has reached such a high density on an existing host plant that they need a new food source to support the burgeoning colony.
The winged root aphid then flies to a new host plant and starts a new colony. As if flying, plant-destroying ninjas were not scary enough for a gardener, root aphids can reproduce parthenogenetically, meaning a female does not need a male to reproduce, she can impregnate herself and multiply.
In the summer, every new aphid is a female and a potential mother. Each female aphid can give birth to 30 or 35 new aphids, and each of these is mature and ready to produce baby aphids of her own in just 10 to 20 days.
Root aphids feed on the root system of various plants, sucking so much sap from the roots that the plants do not receive proper sustenance.
As a result, leaves turn yellow and little new growth occurs. Root aphids tend to congregate en masse, especially on the outer edges of the root ball, forming a white, waxy, snow-like covering over the roots.
This white, waxy coating is an important characteristic gardeners can use to identify a root aphid population.
Plants fed with high doses of nitrogen can be a superfood for aphids. When aphids siphon sap from the phloem of a well-fed plant, the high-nitrogen fertilizer supercharges the plant’s sap and simultaneously the aphids’ reproductive capabilities.
Ways to Control Root Aphids in the Garden
Root aphids can be controlled by several measures. It may be necessary to start heavy-handedly if the population of root aphids has already reached epidemic proportions.
The products listed here are not for use on edible crops and I recommend you read the label of any product before applying it to your garden.
The first step in integrated pest management starts with scouting and monitoring. Paying close attention to your plants is the best way to discover potential insect problems.
Root aphids, living underground, represent a particularly difficult pest to take notice of, but yellow sticky traps are a great way to discover the presence of winged aphids trying to establish new colonies.
One or two yellow sticky traps should be placed for every 1,000 sq. ft. of growing space and monitored weekly to monitor populations and alert a grower to a potential infestation.
The next level of control is the use of beneficial insects. For root aphids, the best beneficial predators are microscopic entomopathogenic nematodes.
Entomopathogenic nematodes are a group of nematodes, or thread worms, that kill insects. Although many other parasitic thread worms cause diseases in living organisms, entomopathogenic nematodes only infect insects and are safe for use around people and pets.
Nematodes make their way into the guts of the root aphid larvae where they multiply until they kill the pests and the nematodes explode out of the stomach of the aphid.
Nematodes are usually sold in a sponge that is placed in a bucket filled with 1-gal. of dechlorinated, pH-neutral water and then rung out repeatedly.
Then the water/nematode mixture is either applied to individual plants or added to a hydroponic reservoir. After that, the nematodes act as a microscopic army with the single goal of killing even more pests. (Read more: Hydroponics: Pros and Cons of Hydroponic Gardening)
Another organic, food-safe level of root aphid control can be achieved with an entomopathogenic fungus called Beauveria bassiana, which is sold as an active ingredient in some specialty gardening products.
The fungus works similarly to the nematodes, killing the aphids from the inside out. Insecticidal soap is also effective against root aphids, provided the root ball is submerged long enough in the soap.
A recent study found submerging the root ball in insecticidal soap for 30 seconds resulted in less than 30% mortality, submersion for 60 seconds yielded close to 70% mortality and submersion for 90 to 120 seconds yielded 95% mortality.
Escalating the arsenal leads one to neem oil, which uses the active ingredient azadirachtin. Azadirachtin is in the limonoid family and is distilled from the neem plant’s seeds.
Azadirachtin has three unique modes of action as a pesticide. It acts as an anti-feedant, a repellant and an insect growth regulator.
As an added bonus, most neem oil products are organic and OMRI certified. Neem oil has been shown to provide some level of systemic protection and is best applied as a soil drench for control of root aphids.
When organic controls are not doing the job, it is time to bring out the big guns. There are new products on the market containing an active ingredient called imidacloprid, which acts as an insect neurotoxin.
Imidacloprid belongs to a class of chemicals called neonicotinoids, which act on the central nervous system of insects but have a low toxicity to mammals. While registered for use on food crops, this is not an organic solution. (Read more: Are Organic Pesticides Always Safer?)
The method is systemic, meaning it is absorbed into the plant tissue and will poison the root aphids if they eat the roots, leaves or any part of the plant.
Bugs outnumber humans 200 million to one, so when fighting an insect army that multiplies faster than you can kill them, an insect growth regulator is a valuable tool.
There are several on the market that are effective on root aphids as well as a host of other garden pests.
One popular insect growth regulator uses the active ingredient fenoxycarb, which blocks the ability of an insect to change into an adult from its juvenile stage. It also interferes with the molting of larvae. Insects have a rigid external covering called an exoskeleton.
To grow and mature, insects must periodically shed or molt their old exoskeleton and produce a new, larger one. By interfering with this process, an IGR prevents an insect from ever becoming sexually mature, thereby eliminating their ability to reproduce.
When all else fails, the no-nonsense nuclear option to eradicating a root aphid infestation is acephate, an organophosphate insecticide that provides a powerful knock down and some level of systemic protection.
It is used as a primary control of aphids, including resistant species and root aphids. Products containing acephate may be sold as powders, liquids, granules, tablets or water-soluble packets.
If you suspect your garden has been invaded by root aphids, there are several options at your disposal to eradicate them before these little ninjas suck the life out of your garden.