Commercial Cannabis Pests
Two-Spotted Spider Mite
Nymphs, adult males, and reproductive adult females are oval and generally yellow or greenish in color and may or may not have one or more dark spots on each side of their bodies. Two-spotted spider mite eggs are about 0.14 mm in diameter and are usually laid on the undersides of leaves. They are spherical, clear, and colorless when laid but become pearly white as hatch approaches.
Powdery Mildew of Cannabis
Rice Root Aphid
(Rhopalosiphum abdominalis or rufiabdominalis)
Infestations generally begin with a pear-shaped wingless form of the rice root aphid, which are dark purplish, with tints of orange, dwelling on the root ball. When populations exceed capacity in the rhizosphere (root zone), root aphids can be seen crawling on the surface of the substrate and winged adults are produced, which fly to look for more host plants to feed on. Winged root aphids are attracted to light, so they are often found dead on grow light fixtures. The winged version can also be caught on yellow sticky cards. To the naked eye, they look much like fungus gnats, but with magnification, they have shorter, hairy antennae while aphids have a longer filament type antennae. Also, fungus gnats have one pair of wings while aphids have two.
Root aphids suck plant sap from the roots, these 1mm tiny aphids feed on plant roots and appear in a color range from yellow to green to brownish-orange some people confuse them with Fungus Gnats as some adults grow wings when their populations reach critical mass.
Plant roots begin to show a yellowing when infected, then swell and then harden as root aphids feed. This leads to secondary fungal infections with dead spots. Severe infestations will stunt plants and diminish the quality drastically.
Dark Winged Fungus Gnat
Western Flower Thrips
Thrips are often found in the flower buds. These flowers may be tapped or lightly shaken over a white sheet of paper (a drop cloth, of sorts) where you will be able to see their slender, small bodies racing around. The adult male is about 1 mm long; the female is slightly larger, about 1.4 mm in length. Western flower thrips are go through five stages egg, larval, prepupal, pupal and adult. Female adult thrips live for about 30 days and lay 2 to 10 eggs per day. From Egg to Adult in a 77 degree environment takes about 13 days so each generation is a problem for a total of about 43 days. Males are rare, and are always pale yellow, while females vary in color, often by season, from red to yellow to dark brown. Each adult is elongated and thin, with two pairs of long wings. At first glance they resemble a Fungus Gnat but have two pairs of wings versus one pair present on Gnats. The eggs are oval or kidney-shaped, white, and about 0.2 mm long. The nymph is yellowish in color with red eyes.
Hemp Russet Mite
A single russet mite is too tiny to be seen by the human eye without magnification of 15x and higher. Their near invisibility makes these mites a significant threat to become established in your commercial grow before you realize it. These voracious plant pests leave no webbing or other secretions when present. Visible damage to the plant is usually the first indication of their presence. Their life cycle is a three-stage cycle including egg, followed a couple days later by the larva stage then a few more days to a larger nymph and a couple more there is a final molt to an adult. One early warning sign is a curling of the leaf on the edges, just above the petiole. Another sign when in flower is that of a general dulling of the leaves (russeting). as infestations grow, some areas on leaves will show a visible yellow or brown spotting. Russet mites tend to start at the bottom of a plant and work their way up. Heavy infestations can lead to smaller bud growth but more importantly they reduce Quality as they feed on the THC in flower, usually noted when the bud takes on a beige appearance. Seen through a lens or microscope, russet mites are torpedo-shaped, translucent/yellow-tinted, maggot-looking creatures, especially in groups. Unlike most varieties of mites, eriophyid, including russet mites, have only two pairs of legs.