The plant disease diagnostic lab at the University of Kentucky’s Research and Education Center in Princeton received a sample of industrial hemp (Cannabis sativa) in late January from a grower in Christian County. The plants were growing in a greenhouse and were infested with aphids. After a close inspection the aphid species was identified as the cannabis aphid.
Description of Cannabis Aphid and Its Damage
The cannabis aphid or bhang aphid, Phorodon cannabis (above) is a species of Indian origin that initially was misidentified as the green peach aphid (Myzuz persicae) in Oregon by marijuana growers. This aphid species has evolved with plants of the genus Cannabis and is a specialized feeder of hemp. The color of cannabis aphid ranges from light green to pale pink to light brown. In this case we only observed aphids of pale green-yellow color.
This is the most important aphid species affecting hemp because of its ability to vector plant viruses. The cannabis aphids congregate on the underside of leaves, causing leaf wilting and yellowing. Surviving plants might be stunted. Cannabis aphids also infest flowering tops, which may become distorted and hypertrophied. In general, when an aphid feeds, it exudes small drops of a sugary sap from its anus. This substance commonly called “honeydew” attracts ants and can support a heavy growth of black sooty mold that interferes with photosynthesis.
Distinctive characteristics of the cannabis aphid include the horn-like projections at the base of antennae and bulb tipped setae on the head, thorax, and base of antennae.
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The cannabis aphid was identified in North America in 2016 by Dr. Susan Halbert, following its discovery in Colorado in 2015. Since then, additional records have been found in Oregon, Virginia, Minnesota, Illinois, and Quebec.
This is not the first time the cannabis aphid was found in Kentucky. Dr. Bessin from the Department of Entomology at UK confirmed this aphid species in samples of industrial hemp in Fayette County in 2018. It is unknown how widely distributed the species is in the USA and Canada. Prior to the 2018 Farm Bill, hemp research at universities was severely restricted, and as consequence many biological aspects or behavior of the cannabis aphid are unknown.
Pruning, cleaning, and disposing infested plants should be the first steps to manage any insect or disease in hemp. Hosing plants with abundant water may also contribute to reduce aphid populations.
At this time there are no pesticides (herbicides, insecticides, fungicides, nematicides, etc.) registered for use on industrial hemp grown in greenhouses or open fields in Kentucky. Thus, any pesticide applications to industrial hemp are illegal.
A more sustainable approach for control of aphids, especially for greenhouses, should be the use of natural enemies. Ladybeetles, syrphid fly larvae, parasitic wasps, lacewings, minute pirate bugs (Orius sp.), and big eyed bugs (Geocoris sp.) prey on aphids and many other pests (such as spider mites and whiteflies). All of these natural enemies can be purchased by farmers from trustworthy vendors.