A clandestine attack could be underway in your cannabis garden, hidden beneath the potting mix
Out of sight, phylloxerans and root aphids feast on plant roots. Both of these pestilent creatures wreak havoc, and multiply so fast, by the time you’ve discovered them, their populations could be in the millions. Knowing how to identify these pests, and understanding their lifecycles and potential for crop damage, will help you prevent and treat infestations.
The Great French Wine Blight
In the late 1800’s, the health of Europe’s wine grape vineyards inexplicably began declining. Unbeknownst to grape growers, a North American pest had hitched a ride across the Atlantic, and was spreading rapidly. That pest was D. vitifoliae (grape phylloxera), and for the defenseless Vitis vinifera wine grapes, it spelled disaster. The phylloxera infestation destroyed vineyards across Europe, and decimated France’s wine industry, in what became known as the Great French Wine Blight.
Although present in vast numbers, the tiny insects initially avoided detection.
Eventually, a French botanist named Jules Émile Planchon discovered the cause of the blight to be phylloxera. Working with an American entomologist and a fellow French botanist, Planchon helped develop a remedy for the crisis. The scientists suggested grafting V. vinifera grapes onto rootstocks of North American grape species, which had native resistance through co-evolution with phylloxera. Although many growers disliked the idea, they reluctantly grafted their vines, having no other choice. France’s wine industry was slow to recover, but the rootstocks proved to be a successful solution and are now still used worldwide.
Phylloxera, Aphids, and Cannabis
According to several sources, including a document entitled ‘Legal Pest Management Practices for Cannabis Growers’ by the California Department of Pesticide Regulation, phylloxerans (Daktulosphaira vitifoliae) are a pest of cannabis crops. Contrary to these sources however, D. vitifoliae is known as a monophagous insect, meaning it only feeds on grapes. Also, I came up empty handed after extensively searching online for photographic evidence of phylloxera on cannabis, although I was able to find photos of root aphids on cannabis. Likewise, Lagos-Kutz, Potter, Difonzo, Hartman, and Russell (2018) stated, “Reports of ‘phylloxera’, ‘root aphids’ or ‘red-assed root aphids’ in hydroponic Cannabis culture in the USA are all likely to be R. rufiabdominale (rice root aphid) based on online posted images.”
Future evidence may shed more light on the possibility of phylloxera infesting cannabis. Fortunately, there are very similar protocols for preventing and treating infestations of phylloxerans and root aphids, whose lifecycles are nearly identical.
Wenninger (University of Idaho, 2011) supposed that although the number of root aphid species infesting sugar beets is unknown, they must be similar enough to be treated as a species complex for the purposes of his paper “Sugar beet root aphids: identification biology and management.” Here, I will treat phylloxera and root aphids as a complex, but I’ll discuss their differences.
Phylloxera and Aphid Fossil History and Lifecycles
Insects placed in the infraorder Aphidomorpha include the phylloxerans, aphids and adelgids (wooly, aphid-like insects). From here on, I’ll collectively refer to the phylloxerans and root aphids as aphidomorphs. Aphidomorphs probably evolved from a common ancestor, fossils of which were found from the Triassic period, which was more than 201 million years ago. Angiosperms (flowering plants) like Cannabis sativa don’t emerge in the fossil record until nearly 40 million years later!
Aphidomorphs start their lifecycle as an overwintering egg, attached to grape vine bark or tree bark. In spring, a wingless female emerges from the egg, and begins multiplying parthenogenically (without sex), thereby creating wingless clones of itself. Aphid clones are born live, as opposed to inside an egg, as in phylloxera. Aphid clones are actually pregnant before they’re born— sort of like those Russian nesting dolls. This parthenogenic reproduction occurs all summer, and when populations become crowded on host plants, winged individuals form, and migrate to new plants. In autumn, males are formed, and subsequent mating produces the overwintering egg phase.
According to Colorado State University, the complete lifecycle of rice root aphids does not occur in indoor cannabis cultivation; the egg phase is missing. This is likely due to the relatively consistent environmental conditions of indoor gardens.
At 73℉, rice root aphids can double their population every 1.6 days. Therefore, starting with just one rice root aphid, a population of over 1 million aphids can be produced in 32days.
Differential Identification
Rice root aphids and phylloxerans both produce tiny (< 2mm) asexual individuals that vary in color from translucent to red to dark olive green. One easily observed difference is that all stages of rice root aphids have cornicles, which are absent in phylloxerans. Cornicles are two prominent, needle-like projections found on the upper back-end of aphids, which excrete defensive chemicals, including an alarm pheromone that warns other aphids of predators. Cornicles are one of aphids’ most distinguishing features.
Another striking distinction between root aphids and phylloxerans is how they each hold their wings. When at rest, all aphids hold their wings in a vertical plane in the middle of their back, like the sail of a ship. Contrastingly, phylloxerans hold their wings folded flat over their back, in a horizontal plane.
Honey dew production by aphids is a behavior that distinguishes them from phylloxerans, which don’t produce it. Honey dew is a sugary waste liquid, secreted from the aphid’s anus. It appears as a sheen on the surfaces of leaves, and often has a black fungus called sooty mold growing on it. Ants love to eat honey dew, so they ‘farm’ aphids by transporting them from plant to plant, and by defending aphids from predators.
Growers sometimes mistake root aphid infestations for more common fungus gnats (Bradysia spp). Unlike the Aphidomorpha, which only produce adult-like nymphs, fungus gnats have a larval stage. The larva is a translucent worm with a black head capsule, and is found in the growing medium. Adult fungus gnats look like small mosquitos. Fungus gnats’ wings are approximately the length of their own bodies, whereas aphidomorphs have wings nearly twice their own body length. Fungus gnats also have more slender, elongated bodies, longer legs, and have only two wings instead of four like most insects.
Scouting
Aphidomorphs feed on plant liquids using syringe-like mouthparts, thus weakening plants. They release chemicals into feeding wounds which inhibit healing, thereby aiding continued feeding. Feeding wounds are susceptible to secondary infections such as root rots and vascular wilts, which compound the damage. Look for inexplicably weakened plants in your garden, and examine their roots for pests.
Symptoms may include stunting, yellowing from nutrient deficiencies, and wilting.
The feeding activity of these insects also transmits plant viruses from plant to plant. In some cases, virus infection is the worst consequence of an infestation. Plant viruses cause symptoms such as stunting, mosaic yellowing patterns on leaves, and deformation.
Use yellow sticky cards to monitor for aphidomorphs, and examine the cards frequently and carefully for prompt, proper identification of trapped insects. Hang sticky cards above plants and at pot level. You can easily make custom stakes or supports for sticky cards by bending heavy gauge wire. Sticky cards can provide an early warning for fungus gnat infestations; however, if winged aphids or phylloxerans make their way to your sticky cards, a large population is already established.
Frequently examining root zones for aphidomorphs is therefore crucial for early detection, which could greatly increase your chances of successfully controlling a problem. An illuminated magnification loupe is helpful for examining roots.
Keep an eye out for ants, since they may transport various species of aphids into your garden. If you find ants, eliminate them using sealants and baited traps.
Prevention and Treatment
The most likely way for aphidomorphs to invade gardens is by growers bringing in infested plants. The best policy is to start all of your new strains from seeds. If you have to start from clones, try to buy unrooted clones, and dip them in a neem solution, before rooting them in a quarantined area. Only introduce clones to the main garden(s) once you’re confident they’re pest free.
In Australia, vineyard machinery is given mandatory heat treatments to prevent transporting phylloxera from one vineyard to the next. 113℉ (45℃) for 75 minutes or 104℉ (40℃) for 120 minutes of dry heat in a controlled atmosphere room is sufficient for 100% phylloxera mortality. Avoid borrowing equipment for plowing or cultivating your cannabis garden, or consider heat treatment. One way of achieving heat treatment could be via solarization: enclose the equipment in a sheet of clear plastic and leave it outside on a hot sunny day. Monitor the internal temperature to determine effectiveness.
Hot water treatments are frequently used in Hawaii for disinfesting exported plant products. Dr. Arnold Hara at the University of Hawaii at Manoa found that a 120℉ (49℃) hot water dip, for 5.5 minutes, was able to achieve 100% mortality of taro root aphid. Experimentation is needed to determine hot water protocols for disinfesting cannabis. A balance must be struck between water temperature and duration, to achieve pest mortality without damaging plants.
Other measures to prevent aphidomorphs from entering your garden include air showers and foot baths at entryways, keeping pets out of the garden, proper filtration for incoming air, and never entering the garden after outdoor activity.
In grapes, phylloxera is not a pest of vines grown in sandy soil. Sand’s sharp texture damages phylloxerans’ soft bodies, and prevents their movement. Experts in California recommend incorporating sharp amendments like diatomaceous earth into potting mix for preventing cannabis infestations of phylloxerans and rice root aphids.
Treating root aphid and phylloxera infestations is challenging. If these pests infest flowering plants, you may be able to hold them back until harvest, by rotating treatments of Beauveria bassiana, Metarhizium anisopilae, Lecanicillium lecanii, and Chromobacterium subtsugae beneficial microbes, and additions of predatory nematodes, rove beetles, and H. miles predatory mites. Where allowed, azadirachtin- based drenches of the root zone may also be effective, albeit incompatible with the aforementioned treatments.
When infestations occur in mother plant rooms, your best bet for total eradication is to take cuttings, dip the unrooted cuttings in an azadirachtin drench, and root them in a quarantined area. Next, dispose of the mother plants and sanitize the room(s), and then start over with the newly rooted clones.
Don’t let sneaky phylloxerans or root aphids ruin your medicinal crop. Careful prevention, vigilant scouting, and prompt treatment can give you the upper hand.
by Joe Bender, Cannabis Crop Solutions, LLC
Originally published in Weed World Magazine issue 139
