Common Pests Affecting Industrial Hemp: Identification, Prevention, and Impact

As industrial hemp gains traction as a novel crop, the realm of potential pests remains largely unexplored. The journey of cultivating hemp brings with it the challenge of safeguarding the crop against a variety of diseases and arthropod pests that could potentially impact its growth and yield. While these pests might not be posing significant problems currently, the trajectory of hemp’s prevalence hints at the possibility of issues arising in the future.

The Importance of Vigilant Scouting

One of the critical components in managing pest-related challenges in industrial hemp lies in vigilant scouting. Regularly monitoring hemp plants provides invaluable insights into the populations of pests and potential issues that might emerge. To effectively scout hemp plants, experts advise a comprehensive examination of both the upper and lower leaf surfaces. This exploration should encompass not only the high portions of the plant stems but also the lower segments. Random sampling across the field ensures a comprehensive assessment, enabling a nuanced understanding of the entire plantation’s health.

Navigating the Pest Landscape

At present, industrial hemp is classified as a minor use crop, a status that limits the availability of registered pesticides for its cultivation. Consequently, the emphasis is placed on preventive measures and integrated pest management strategies to mitigate the impact of potential pests.

Understanding Disease Dynamics

Among the challenges that hemp growers encounter, white mold (Sclerotinia sclerotiorum) emerges as a notable disease. This ailment is not unique to hemp; it can afflict a range of broadleaf crops and weeds, from sunflowers and mustards to edible beans and soybeans. The disease spreads via spores carried by wind and insects, targeting the stem and grain head of the hemp plant.

The fungus responsible for white mold, known as Sclerotinia, is known for its remarkable endurance. Sclerotia, its resting structures, can survive in the soil over several winters, maintaining their viability for over five years. Under specific environmental conditions—characterized by moisture, high humidity, and optimal temperatures between 68 to 77⁰F—spore survival and growth are encouraged.

Seedling blights, particularly prevalent during cool and wet conditions early in the growing season, pose another concern. These blights can lead to seedling rot and stunted growth, resulting in compromised establishment and reduced yields. Various pathogens, including pythium root rot and rhizoctonia, contribute to this issue. One of the most effective strategies for mitigating the risk of white mold is implementing a four-year crop rotation away from host crops.

Arthropod Pests on the Radar

In the realm of insects, several species have made appearances in Vermont’s hemp fields. Tarnished plant bugs, aphids, Japanese beetles, leafhoppers, European corn borers, and grasshoppers have all been documented. While the damage caused by these insects is minimal for now, understanding their behavior and lifecycle is essential for preemptive measures in the future.

Leafhoppers, Aphids, and European Corn Borers

Leafhoppers, known for their piercing, sucking mouthparts, tend to target the phloem of plants during June and July. However, their effects on hemp growth are negligible, with most leafhoppers causing minimal symptoms. Similarly, aphids, which appear most commonly in August, extract fluids from the phloem, potentially leading to stunted growth and wilting. Natural predators, including lady beetles, green lacewings, and parasitic wasps, play a role in controlling aphid populations.

The European corn borer, a pest familiar to many, has been observed weakening hemp stalks by feeding on them. This could ultimately lead to breakage and reduced yields, making it a concern for hemp plantations located near corn fields. The moth’s life cycle, involving overwintering as caterpillars, pupating, and emerging as moths in spring, contributes to its lifecycle and potential impact on hemp.

Grasshoppers and Other Pests

While grasshoppers may nibble on hemp stems and leaves, their impact is generally limited by the plant’s rapid growth. Grasshoppers are more likely to target the larger outer leaves of the hemp head, and if damage is severe, seed development could be hindered, impacting yields. The grasshopper lifecycle, involving eggs laid in late summer and hatching in mid-to-late spring, adds a seasonal dynamic to their potential impact.

In addition to the aforementioned pests, other challenges arise from birds, such as blackbirds, sparrows, and starlings. These avian creatures target protruding hemp seeds from the seed head, leading to potential harvest losses.

The Road Ahead: Navigating Pest Challenges

As the landscape of industrial hemp continues to evolve, so does our understanding of its potential pests and diseases. By adopting proactive scouting, integrated pest management strategies, and a keen eye for emerging challenges, hemp growers can ensure the health and resilience of their crops. While some pests might currently pose minimal threats, the cultivation of hemp demands a forward-thinking approach to safeguard its growth and potential as a valuable crop in the Northwest and beyond.

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