With the passing of the 2018 Farm Bill, the hemp industry has seen a swift expansion and change mainly due to an array of commercial and medical uses. According to a report by Grand View Research, the global industrial hemp growing market is projected to rapidly surpass $10.6 billion by 2025.

The hemp market’s fast development can be contributed to favorable law changes, as well as, increased consumer awareness and demand for hemp based products, including food, beauty supplies, and health supplements. 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 not a practice that is exclusively reserved to hemp growers, as pest infestations are a primary concern for all types of greenhouses and can cause significant crop losses. There are a number of pests that hemp growers should monitor crops for, including fungus gnats, root aphids, and russet mites. 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. Each crop is vulnerable to different mite species, which can cause different types of damage. It’s important for commercial greenhouses to understand the specific threats of each and how to mitigate crop damage. Here are four common pests hemp growers are likely to 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.

· Twospotted 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 pest species, hemp growers should refer to this fact sheet provided by Colorado State University’s College of Agricultural Sciences.

Key Steps to Hemp Pest Management

Due to hemp’s recent legal status, there is still budding research on the most effective pest controls hemp growers should employ. While there are allowable pesticides approved by some states, there are no pesticides generally labeled for hemp pests currently. Overall, here are some steps hemp growers can take to manage infestations:

· Daily crop monitoring can help prevent an outbreak by scouting for early signs of pest damage.

· Identify the type of damage or species of pest to understand what controls are needed to manage the infestation.

· Be sure to remove or destroy any crop residues or litter after harvesting.

· Are only a select few plants being affected? Isolating the infested plants in a separate area could help prevent the spread of pests to the rest of your hemp crops.

The best and most effective way for hemp growers to manage pests is through prevention. Conducting daily inspections of your crops could help identify an issue before it becomes too big to control. Hemp growers should also refer to the Hemp Diseases and Pests Management and Biological Control for a complete guide to identify and control hemp pests and diseases.

The Link Between Sanitation and Pest Control

According to Greenhouse Grower Magazine, the most effective approach hemp growers should take to avoid pest infestations is proper sanitation. This is because many outbreaks are caused by insects that hitch a ride on hemp growers’ clothing without their knowledge. The best course of action to keeping your greenhouse sanitary is by being proactive. Limiting visitor access to production areas and requiring employees to change their clothing after visiting another growing operation are just a few steps to maintaining a pest free greenhouse. 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.

Source: National Hemp Association