Jul 13, 2018

Root Aphids: No! They’re Not Just Fungus Gnats

Of all the pests you may have to deal with in your garden, root aphids or Phylloxera, have the potential to be the costliest and most destructive. Being able to identify the problem as early as possible is key.

Root Aphid Identification

Aphids have a unique and complicated life cycle of up to 18 stages, depending on the species. However, they don’t change much in appearance as they grow or between species, and don’t have a larval/pupal stage to look for. This is good news since even though they are easily mistaken for other problems, they will have a hard time hiding from your watchful eye once you know what to look for.

Root Aphid Life-Cycle


In the aphid’s primary lifecycle, they are commonly called “crawlers,” since they are wingless and crawl through media looking for roots. Once they find a root, they will latch on and multiply. Crawlers don’t lay eggs, instead, they breed and give live birth. This means even a single aphid can start an infestation. Juveniles and adults tend to be under 0.5 millimeters in size, brownish in color, with wide round abdomens and six legs.

Not a Mealybug

Early on, crawlers are very easy to mistake for young mealybugs, since they are about the same size and color. The easiest way to tell them apart is by the many small spines mealybugs have sticking out from the perimeter of their bodies instead of legs. Once mealybugs mature and find a place to feed, though, they exude a waxy substance that makes them much easier to spot.


In their final, reproductive phase, adult crawlers are capable of sprouting wings to help them travel between plants to mate and lay eggs. Their thorax (the part between the head and abdomen) elongates a bit but otherwise, the “fliers” look just like a crawler, but with wings 2-3x the body length. The fliers are particularly dangerous because they can easily spread crawlers to other plants. In this form, aphids lay eggs only and no longer give birth to live young. The eggs are very small, white, and laid in clusters that to the naked eye can easily be mistaken for beneficial soil fungus.

No! They’re Not Just Fungus Gnats…

More than once I’ve heard a grower say to me “I don’t have pests… Well, just some fungus gnats.” More than once I was culling aphid-ridden plants just weeks later. If you cycle plants quickly and apply lots of preventative treatments for pests, you may just think you’ve got some very persistent fungus gnats.

The easiest way to tell them apart is body shape. Fungus gnats have thin abdomens, long legs, and wings about the length of their body, like a small mosquito. Aphids are more squat, round, and stubby-legged. In addition, they have distinguishable “tailpipes” extending off their back-end. A loupe or microscope can be very helpful since both pests are so tiny.

Fungus gnats also behave differently, they seem to fly slowly and aimlessly. Winged root aphids fly higher and farther, seem more “alert” overall, and are better at avoiding being squished. While fungus gnats will fly all over the place, root aphids will fly straight towards your lights. If you are in veg, check above the bulbs in your T5s for root aphid bodies.

It looks like a Nutrient Deficiency

Root aphids cause stunted growth, and droopy or yellow leaves resembling nutrient deficiencies. The yellowing (chlorosis) resembles a magnesium deficiency, and the yellow-brown spotting a calcium deficiency. If you have checked pH (feed and runoff), and know that your plants are being properly fed, you should probably check for root aphids. They feed by sucking nutrients directly from roots before plants can use them, so their damage isn’t obvious at first. Rule out pH problems quickly and carefully inspect any plant with signs of a deficiency.

Summertime Pests

In warmer temperatures, aphids eat voraciously and reproduce more quickly. This means they can be well established, but unnoticed as their eggs over winter and start hatching in the spring. By the time summer rolls around and damage or fliers are noticeable, the infestation may already be in full swing. That’s why it’s so important to check for them early in the spring and often throughout the summer growing season.


Root Aphids are especially easy to spot in hydroponics. Their dark bodies contrast with white roots as they latch on and colonize. Unfortunately, they also spread more quickly. If you use Rockwool, look at the roots that stick out of the cube, and also pull back the plastic wrapper to check the sides. Checking your reservoir and runoff for aphid bodies can help you gauge how effective your treatments have been. Save yourself time and money. Don’t bother transplanting plants that have active and visible root aphids infestation. The plant may survive for a long time but it will likely remain stunted and never successfully root into larger cubes.

Soil & Coco

In soil, soil-less or coco, they are easiest to see when you are watering. They will not drown, but watering does agitate them and you can usually see them crawling up the main stem or sides of the pot from the soil line. If you see crawlers but no fliers, you’ve caught the problem early. Transplanting while fighting aphids is generally more successful in soil or coco than in Rockwool, but it is still best if you can knock them out first.

When to Check for Aphids

Check your room as the lights are coming on, or in the morning outside. Fliers tend to be most active at this time and will buzz around near your lights when they first turn on. Place yellow sticky traps both down low, and up high to monitor their population. Hopefully, this will keep them off of your fruits and flowers. If trimming is essential for your infested crop, doing so around dead aphids makes the job twice as tedious.

Prevention and control

Now that we have a good idea of what they look like and how to find root aphids, let’s talk about what you can do to prevent them from ever entering your growing space.

Clone Caution

Like spider mites, the easiest way for aphids to spread is by hitching a ride on a cutting or seedling into a new environment. The person selling clones or seedlings likely doesn’t even know they are there. A quarantine procedure for new plants can help. If you do spot root aphids during the quarantine phase the plants should be culled immediately. I have seen clones quarantined (for weeks), treated multiple times with systemic insecticides until there is no evidence of surviving aphids, and they still came back later in the grow.

Watch Over Watering

Aphids and their eggs can be spread between plants via their water runoff. This makes recirculating hydroponic systems especially vulnerable. Over watering also makes roots more susceptible to pests in disease in general.

Cleanliness is next to…..

A clean grow environment helps prevent most pests and is imperative to preventing a comeback once you have gotten an infestation under control. Full cleaning and sterilization of your room and equipment between grows are unavoidable if you want pests to remain gone. Keeping a clean and tidy grow area can help prevent any eggs that do hitch a ride on clothes or plant matter from getting the chance to come in contact with one of your plants.

Natural and Organic Controls

Organic methods are preferred with root aphids since most insecticides are only moderately effective and may just end up making your garden more vulnerable to other pests by removing beneficial insects. Young and/or heavily infested plants should be culled since replacing them will be less costly in the long run.

Botanigard ES & WP

There is a reason this product is at the top of our list. Botanigard is a mycoinsecticide or insect-killing fungus. It can be inoculated in the root zone and kills all stages of crawlers (it kills fliers but they are less likely to come in contact). Aphids are unable to build up an immunity to the mycelium, and it’s perfectly safe to use up to the day of harvest. So while it isn’t cheap, and won’t kill them all in one shot, Botanigard is definitely worth the cost.

OG Biowar Foliar Pack
Another excellent biological control, OG Biowar packs contain beneficial microbes in a pure talc carrier. This means they can be brewed into an activated compost tea and applied as a foliar spray or root drench. The foliar pack is specifically tailored to help plants fight off pests and resist stress, and even includes insecticidal microbe species that work similarly to Botanigard. This product is highly recommended both as a treatment and preventative.

Azadirachtin / AzaMax
Plants treated with a neem foliar spray and root drench will be more resistant to (and may repel) pests and disease. If you are fighting an active infestation, try switching to an Azadirachtin concentrate like AzaMax for a more powerful antifeedant effect.

Insecticidal Soaps / Oils
Essential oils like rosemary, capsaicin from pepper plants, and Insecticidal soaps like Safer 3-in-1 are most effective as a foliar and “spot spray” to kill fliers. However, you can also try an essential oil and capsaicin root drench for an extra punch, just try it on a test plant first. As always, be careful with any kind of foliar spray during the bloom phase when plants are more susceptible to rot and mildew.

Predatory Nematodes
These beneficial parasites attack aphids in the root zone. However, once established root aphids can simply out-breed nematodes. These are best used as a preventative or in conjunction with other methods.

Bonus Tips on Manual Removal
Removing winged adults from the environment can dramatically slow aphids from spreading. If you have vented reflectors, you can try removing the glass (but still keeping them vented). Any winged aphids that fly up towards the light will just get sucked up and out of your room, so be mindful of where the exhaust goes. This was very effective for me in the vegetative phase where I didn’t need to keep the lights/room sealed. Already in bloom or can’t vent your lights without the glass? Grab a shop-vac. Remember that winged aphids will fly up at lights on, suck them up while they’re conveniently in one place before they get a chance to lay eggs or get stuck in your flowers.


Root Aphids are incredibly hardy. Very few pesticides are capable of a “total kill” in one application. They can simply out-breed typical control methods, and quickly build up a resistance to poisons. Many of their natural predators, like nematodes and ladybugs, are also wiped out by pesticide use. Gardens already chemically treated for other problems may be especially vulnerable to root aphids. That is not to say that organic methods are the only choice, just that you should be careful and aware before you start applying any type of poison or insecticide.

If you do choose the synthetic route there are a few things to keep in mind. Ultimately, one or more pesticides may be required to effectively control a root aphid infestation. Be very careful when applying multiple products, it’s a good idea to stagger applications and try each product out on a tester plant first.

Natural and Synthetic Pyrethrin

Contact killers like pyrethrins do kill root aphids. An aerosol or fogger can make short work of fliers. However, they aren’t as effective against the aphids in the root zone since they reproduce so quickly, and can invade all parts of the growing environment. Even synthetic pyrethrins which remain in the environment longer may not achieve a total kill before aphids develop resistance.

Other insecticides

There are a variety of other chemical insecticides which will kill aphids on contact. Bonide Eight is a good options to use in concert with another, preferably systemic insecticide.


Gone, but for good?

Even if all of the root aphids on the existing crop are killed, their eggs can still survive in the environment to infest your next grow. Consider the costs of treating versus culling very carefully. Hopefully, you never have to deal with root aphids, but if you have an experience or method you’d like to share, we’d love to get your feedback, comment below!