Cannabis aphid (Phorodon cannabis)
Green peach aphid (Myzus persicae)
Potato aphid (Macrosiphum euphorbiae)
Root aphid (Rhopalosiphum rufiabdominale)
Pest description and crop damage Aphids (Order Hemiptera: Family Aphididae) are soft-bodied insects with a pair of abdominal cornicles that exude sugary droplets. Green peach aphid and potato aphid are common aphid species in hemp west of the Cascades; the cannabis and root aphids are common in west and southern Oregon. Potato aphid is more common in the spring and fall, while green peach aphid is prevalent in July and early August. Cannabis aphid is common mid-season, while root aphid is mostly found early in the season and is usually associated with ants. Large populations of aphids can cause yield reductions through direct feeding. Aphids are good vector for pathogens although none reported affecting hemp.
Biology and life history Winged aphids arrive on hemp from weeds and various crops where they overwintered as nymphs and adults, and from other unknown hosts. Potato aphid and green peach aphid feed on many crops, weeds, and native plants. Throughout the growing season, aphids produce live young, all of which are female and can be either winged or wingless. Winged aphids tend to reproduce more when they become crowded. In the fall, winged males are produced which fly to overwintering hosts and mate with egg-laying females produced on that host. All species may undergo multiple overlapping generations per year. The cannabis aphid is found on the leaves and stems of cannabis; while the root aphid is found below ground. Sometimes root aphids are associated with ants.
Scouting and thresholds Fields should be checked for aphids at least weekly starting shortly after emergence. When plants are upright, the most effective scouting method is to shake plants above beating sheets, beating trays, or white half gallon ice cream buckets. These sampling methods are to evaluate presence of aphids at a single point in time. In some varieties, the vines become very long and bushy and become intertwined, making scouting difficult. In this case, a leaf sampling might be useful. There are no established treatment thresholds for aphids.
Hemp can harbor large numbers of generalist predators that feed on aphids. These include the Hemipteran bugs: Orius pirate bug, Geocoris big-eyed bug, and Nabis damsel bug. Other common aphid predators include lady beetles and their larvae, lacewings, and syrphid flower fly larvae. Aphid-specific parasitoid wasps can also be common since fields are not treated with conventional insecticides.
Purchase transplants from reliable sources.