The hemp industry has experienced rapid growth and diversification since the 2018 Farm Bill was passed, owed in part to the plant’s wide range of commercial and medical uses. In fact, the global industrial hemp growing market is projected to reach $10.6 billion by 2025, according to a recent report from Grand View Research. Alongside favorable changes to U.S. laws, the market is also benefiting from increased consumer awareness and demand for hemp-based food, skin care and health supplement products. While this bodes well for greenhouse growers who are just getting into the hemp marketplace, cultivating this crop at scale comes with more than a few challenges.
Identifying Pests in Hemp Greenhouses
Pest control is a top concern for greenhouse operations of all sizes, as a single infestation can significantly impact yields or destroy a full batch of crops. From root aphids and fungus gnats to russet mites, there’s no shortage of hungry insects that hemp growers need to watch for. As pointed out by Greenhouse Grower Magazine, pest control starts with implementing a formal identification system that can help workers recognize signs of a possible outbreak. Since every crop is susceptible to different mite species, it’s important for commercial greenhouses to understand the specific threats they’re likely to face. To that end, here are four common pests hemp growers contend with:
- Hemp russet mites: These near-microscopic mites are host-specific to cannabis plants and are often difficult to detect until crops are already damaged. They typically gain entry to greenhouses by clinging to growers’ clothing and tools, which is why consistent sanitation is crucial. Some of the warning signs include bronzing, blistering and curling leaves.
- Two-spotted spider mites: Spider mites are found in a variety of ornamental and vegetable crops, including hemp, and are often difficult to manage due to their ubiquity. As such, greenhouse operations that manage several different crops are often at a higher risk of an infestation. They typically leave behind a thin webbing on leaf surfaces and thrive in hot, dry conditions.
- Cannabis aphids: Cannabis aphids are a new challenge for U.S. hemp farmers, as they are less widespread than other pests and concentrated in the western portion of the country. In fact, the Oregon Department of Agriculture had to release a pest alert for cannabis aphids in 2018 to ensure outdoor and greenhouse growers were aware of the risks. These pests can severely stress crops and are a potential vector for plant pathogens. Common warning signs include wilting and yellowing leaves, though these bugs are large enough to be spotted without magnification.
- Corn earworms: This species of insect has caused the most damage to hemp growing in Colorado, according to a 2019 article in the Journal of Integrated Pest Management, yet it is widely distributed across all of North America. While corn earworms are primarily an issue for outdoor growers, greenhouse operations can still suffer major losses if they find their way inside. These pests typically appear after hemp plants begin to flower, tunneling their way into buds and developing seeds to lay their larvae.
Keep in mind, different pests are indigenous to different regions, so commercial greenhouses will need to do a bit of research on the insects they’re likely to encounter. For a full list of hemp pest species, check out the University of Colorado’s handy fact sheet.
The Link Between Sanitation and Pest Control
While many hemp growers have started using biological control agents to manage pests, the most direct approach is to practice proper sanitation, according to Greenhouse Grower Magazine. This is because many outbreaks are caused by insects that hitch a ride on hemp growers’ clothing without their knowledge. As such, commercial greenhouses should limit visitors’ access to production areas and require workers to change their clothing after visiting another growing operation. Additionally, all tools should be cleaned with disinfectant before being moved to different crop areas.
When dealing with clones or cuttings, it’s recommended that hemp growers dip their plants in horticultural oil or insecticidal soap to eliminate any lingering pests. Greenhouse growers should also isolate new plants from their main growing area until they can be sure no mites are present. Finally, greenhouses should avoid using their grow facility as a temporary storage space for pet plants and other crops, as this only increases the chances of a cross-host outbreak.