- What Are Root Aphids?
- Nymphs
- Wingless Adults (Aptera)
- Winged Adults (Alate)
- Handling Root Aphids
What Are Root Aphids?
Root aphids that commonly affect indoor cannabis plants are rice root aphids (Rhapolosiphum rufiabdominalis). They appear slightly pear-shaped and can be brown, dark green, or have dark red and yellow tints. The color depends on the color of the roots or the part of the plant they are feeding on. Just as the name suggests you can find root aphids on or around your plant’s roots. Besides clustering and feeding on roots, root aphids excrete a white wax in later life stages which can increase the likelihood of infested plants getting pythium or root rot.
Rice root aphids feed on several different kinds of plants including herbaceous plants. When infestations get bad you can find them crawling around the top of the soil, find some on the bottom leaves, or you can observe flying root aphids in the air. Root aphids feed like all aphids do by using their piercing-sucking mouthparts to pierce into the plant tissue and extract sugar-rich sap from the roots. In order to prevent root aphid infestations and the damage that it brings it is important to understand their life cycle to provide the ability to accurately identify and eradicate them.
Nymphs
Root aphid nymphs will generally mature in about 9-10 days in a total lifespan lasting approximately 30 days. They have antennas and 6-8 legs depending on what nymph stage they are on and are about 1-2mm in length. There are technically four nymphal stages for rice root aphids, but the slight differences are not too important. They tend to cluster in concentrated areas on a plant’s root system which means you will find them in your grow medium. Root aphid nymphs are not fast crawlers, but can accidentally be transferred from plant to plant through grow medium debris, dirty grow equipment, or even water passing through drainage holes on plant pots.
Wingless Adults (Aptera)
Wingless adults of root aphids will develop on the roots of plants and generally measure about 3mm in length. Adult root aphids reproduce asexually in enclosed cultivation spaces being able to produce several new offspring everyday. No males are produced and females give live birth to genetically similar daughter aphids. At approximately 74F, root aphid populations can double every 1.6 days. Wingless adults produce a white, waxy secretion that covers them and everything around them. It is especially noticeable on rockwool where you can flip them upside down in the cannabis veg phase and observe the root system. Cannabis growers often describe this white secretion as appearing as a white mold. These are the more common forms of root aphid adults, but occasionally a winged adult will emerge from the soil or hydroponic medium in order to disperse to other plants.
Winged Adults (Alate)
Root aphids can grow wings during their life cycle which is why some cannabis growers mistake them for fungus gnats or vice versa. Winged root aphids have longer and more slender wings compared to fungus gnats and are generally considered weak fliers. Scientists are not entirely sure how rice root aphids infest indoor growing facilities, but it is commonly believed that winged females enter facilities through either the vents or any open doors. When a plant is infested with root aphids, the plant can become chlorotic and wilt easier under stress. Cannabis plants will have stunted growth and in extreme cases will die.
Handling Root Aphids
It is important to identify and disrupt the life cycle of root aphids early for indoor cannabis cultivation. Early detection, like with all pests, is crucial to your success of eradication. Roots can be examined of clones and of larger plants when transplanting which provides several opportunities for growers to inspect the roots of plants throughout the plant’s life cycle. When infested plants are spotted, they should be killed and removed from the facility to prevent the infestation from spreading. Chemical applications of biopesticides including beauveria bassiana, bacillus subtilis, pyrethrum, insecticidal soaps, and azadirachtin are all effective in breaking the life cycle of root aphids which will eventually lead to their eradication. It is important to apply these biopesticides as drenches and sprays on a regular cycle for prevention and reducing infestations. Depending on your grow medium, there may be difficulty applying chemical drenches to plants. Peat moss can inhibit the activity by binding to many active ingredients of biopesticides. This is why it is important to find biopesticides formulated and designed to be used for chemigation. There are some additional techniques, besides chemical applications that are beneficial to the eradication of root aphids such as sand at the bottoms and tops of your potted plants. Of course many other cultural and mechanical controls should be followed as a part of your integrated pest management program.
Resources
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Whitney S. Cranshaw. (2018). “Phorodon cannabis Passerini (Hemiptera: Aphididae), a newly recognized pest in North America found on industrial hemp”. Insecta Mundi, A Journal of World Insect Systematics. 0662: 1–12. Online ISSN 1942-1354.
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