There are a lot of myths surrounding hemp, one of them being that the plant is naturally resistant to all diseases and pests. This is simply false. Hemp is like any other plant and is susceptible to certain insects that can drastically damage plants and reduce yield if left unchecked. It’s important to understand the pest pressures that hemp can face, what to look for, and how to treat an infestation. 

The best step you can take in pest management is to start clean and stay clean by working with a reputable grower and scouting for naturally occurring pests that could potentially lay claim to your hemp plants as their new home. Even if you start with clean hemp plants, there is potential for pests to spread to your plants from neighboring hemp fields or other crops. The list of predatory hemp insects is extensive and for time’s sake, we will only go over some common insects (there are many more predators that aren’t, unfortunately, on this list!).

Hemp Aphid: Hemp aphids are small, pale green to yellow insects with piercing mouthparts that penetrate plant tissues and feed on the phloem of the plant. (Phloem is a liquid that transports plant energy/food). These insects can be found along plant stems and on the underside of leaves. In large numbers, hemp aphids can have a significant impact by sucking large amounts of phloem and therefore reducing plant vigor. Symptoms of cannabis aphid are yellowing leaves, stunted plants, and wilting.

Close up of aphids on stem. Photo by W. Cranshaw, CSU, https://bugwood.org/

Thrips: Thrips are historically more of an indoor growing pest but can also impact outdoor crops. These tiny insects also have piercing mouthparts that suck plant fluid and weaken the plant. Thrip damage can be visually detected by detecting small flecking/yellowing on leaves known as a stippling site.

 

 

 

Closeup image of Thrip

 

 

 

Russet Mites: Russet mites are small and invisible to the naked eye; at least 15-20X magnification is needed to view these mites. Russet mites are easily transmittable among greenhouse and field hemp populations. Symptoms can vary and can look like other pests/problems (such as nutrient deficiency), which can make russet mites difficult to detect. Leaf rolling, discoloration, and puckering can all be symptoms of russet mites. Hemp russet mites use their piercing mouthparts to puncture plant tissue and feast on cellular fluid.

Spider Mites (Two Spotted): Spider mites are a ubiquitous and obnoxious pest that can wreak havoc on hemp plants. These mites can be found on the underside of leaves and lay eggs along the nooks and crannies along the midrib and leaf veins. Spider mites use their mouthparts to feed on plant fluids. The first visible symptoms of a spider mite infestation will show signs of discolored marks on top of leaves, where the underside of leaves have been fed from. More extensive infestations may lead to webbing on plant leaves.

Photo Source: Colorado State University 

 

Photo Source: Colorado State University 

Photo Source: Colorado State University 

In Conclusion 

Hemp is a living organism that is cultivated in an outdoor environment where insects and pests are prevalent. As a best management practice, farmers should implement a scouting protocol into their weekly routine. Due to hemp being a new crop and having a very limited list of approved pesticides, pest scouting and integrated pest management should be used to deter/diminish pest populations. By utilizing scouting, IPM, horticultural oils and approved pesticides farmers can be successful in growing and harvesting a clean, legal hemp crop that can be used for processing. 

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