Wildfire Implications for Integrated Pest Management

Burnout 2020

Tens of thousands of firefighting responders aided by helicopters, tankers, and logistical support have descended upon the now record-breaking 4.1 million acres (~16,592 km² or almost 4 % of the total area) of California land that has been enveloped in a blazing inferno. Across the United States of America, closer to 6 million acres of land have been desolated by wildfire. Weeks of high heat weather and tumultuous resource supply have made for a perfect storm, with ecological impact that will span decades. The wildfires of the United States and especially California wreaked great agricultural havoc specifically, mainly through direct damage to agricultural sites or supply lines, threatening areas with evacuation which included vegetable, ornamental, and Cannabis cultivation areas.

Even those sites that were not directly burned would meet additional challenges regarding air quality and migration of pests. These times of extreme environmental stress have important impacts for integrated pest management and the greater ecological dynamics at play and will continue to exert influence years after the fires have been controlled. It will take time for unique environments to grow back, supporting a more complex ecosystem rife with natural biocontrol agents, as well as sinks for pests to inhabit that aren’t well-manicured sites of human plant cultivation.

A Frenetic Plague Incoming

Undoubtedly many pests of Cannabis like immobile or non-aerial life stages of insects, will perish in the fire while those that can become airborne like the Hemp Russet Mite, Silverleaf Whitefly, Western Flower Thrips, Two-Spotted Spider Mite, as well as various species of aphids, beetles, and moths may be able to outrun the fires on air currents. So-called aerobiota like small insects, as well as viruses attached to larger particles, fungal, and bacterial spores can waft through the air after a fire though this is an understudied aspect of fire ecology and agricultural phytopathology. Relatedly, various phytopathogens and insect herbivores contribute to wildfires by increasing population stress and overall death rate, ultimately leading to more wildfire fuel and a propensity for more concentration. For this reason, Integrated Pest Management must include not only the direct cultivation space, but the general environment, in a multifaceted holistic approach: fire ecology and the presence or absence of fire-fighting resources influenced the outcome of many agricultural crops.

Extensive research regarding pest dispersal during and after wildfires serves as an important reference for Cannabis cultivators planning for future pursuits. As in the co-evolution of plants and their various herbivores and pathogens, refugia play a significant role in the agri-ecological interface. Forces such as wildfires may not touch certain parts of the landscape for geographical reasons, there can be patches where certain plant populations reside that are generally not disrupted, becoming refuge for pest species as well as their natural enemies, and those populations may seed the recolonization of the land. However, the dynamics of this coming repopulation from the larger wildfires will be dramatically different than in in decades past (for which there is comprehensive data), as less refugia has been spared in recent years, colonization has not matched the environment of a half-century ago, and now there will be less plant life to accommodate a larger diaspora of herbivores which will likely compound with other environmental stressors like higher air temperature and lower humidity. As farming increases, so too does the human transportation into more remote forested areas for cultivation and logistical accommodations to support population increase like housing and markets which can also have a disruptive effect on present forested landscapes as well as those that are currently burned as they grow.

Since the most recent wildfire is close to quadruple the size of the previous record of 1.67 million acres, and within a five-year period, the larger ecological context can be understood. Many more early-succession plants which are often herbaceous, will be colonizing these areas, which may be more suitable for some of the generalist pests common in cannaculture than the stolid trees that populate western North America and the rest of the continent. Some of these plants are not only suitable hosts for pest like whiteflies, thrips, and spider mites, but they are also suitable reservoirs for pathogens like various viruses, bacteria, and fungi, with pathogen load likely to increase. The Cannabis microbiome is understudied, especially its virome, though a few viruses have been confirmed to infect Cannabis like the Lettuce Chlorosis Virus, as well as the Beet Curly Top Virus, both of which have had long histories as agricultural plagues and can remain in the ambient environment, sometimes asymptomatically in wild plant populations. Viruliferous pests like the Silverleaf Whitefly and the Beet Leafhopper are known in California as well as other parts of the world, and population migration may inoculate a vast and different pattern of plants than previously. When combined with the challenges mitigating pathogen biosecurity and increase in cultivation acreage already experienced in Cannabis cultivation, there is potential for a greater epidemic event as larger populations of insect vectors take their microbiome and influence their surroundings with it. While many populations of viruliferous plants succumbed to the wildfires, those vectors that escape will congregate and concentrate viruses as well as other microbes in a smaller space.

The Marred Environment Heals Slowly

Smoke which blanketed the air had a cooling effect on ground temperatures in some places, and the pyrolysis of various substances natural and artificial created myriad compounds of hazardous effect, many of which undoubtedly volatized and settled across the environment, including outdoor areas of Cannabis cultivation. Particulate matter both coarse (~2.4-9 micrometers in size according to the Environmental Protection Agency) and fine (less than 2.5 micrometers in size) are expulsed, and depending on the temperature of the fire, contaminants like furan, sulfur dioxide (the major contaminant of burning sulfur practices that is toxic to inhale), methanol, acetic acid and acetone from foliage according to some laboratory analyses of both flame combustion and glowing combustion that resides after (1, 2). Besides these and other harmful substances created by foliage burning, carbon monoxide, carbon dioxide, nitrous oxide, and oxygenated volatile organic compounds (OVOCs) make up a large proportion of fire byproduct, which are variously problematic for the local and greater atmosphere, particularly as greenhouse gases. Although smoldering combustion that occurs long after the blaze continues to create smoke, it is much less volatile and smoke generally stays lower to the ground (3).

All of these chemistries are from the burning of only plant material, and does not account for the many volatile compounds produced during the burning of materials like rubber, plastic, metal, and paints, which choke the air in a toxic haze and both settle into Cannabis foliage and inflorescences as well as interact with the greater ecological area, influencing the diaspora of organisms displaced by such fires such as those animals that are pests. Mammals and birds fleeing from the fire can still become contaminated lethally by these noxious compounds; insects, being the first animals to develop powered flight, can still generally escape danger (as adults at least since other forms rarely have good transportation capacity). However, the various chemical agents and particulates swirling in the air will offset the navigation of some, sometimes attracting them, confusing them, and causing extirpation events that while beneficial to cultivators in that many herbivorous pests may succumb, a great amount will be simply displaced, with an increased incentive to seek unaffected plant life, especially managed lands like farms. With their natural predators displaced or killed as well, particularly larger insectivores like birds, it is possible for a cascade-event to occur whereby pest insect pressure rises to greater ambient levels than typical in the remaining places with vegetation until natural enemy dynamics normalize, if they ever do.

In order to be successful in cultivating salubrious, verdant Cannabis during this time of heightened contaminants, it is imperative to be able to assess exactly what impurities may be lingering, and may have beset the crop. Producing Cannabis that is healthful and desirable has been a great challenge among the myriad other factors influencing the world. As a facet of Integrated Pest Management, testing plants for such compounds that could harm those that consume the material is imperative. The results of analyses like CannaSafe’s Heavy Metals and Foreign Materials tests inform this nature of the crop, and its suitability for human consumption as well as other uses like composting and similar processes. As a hyperaccumulator of heavy metals that is known for its bioaccumulation and bioremediation capacity in that realm (4), there is incentive to conduct such tests to maintain the safety of the end product under these current environmental contexts.

About the Author

Matthew Gates

Matthew Gates

Born and raised in San Diego, California, Matthew is an Integrated Pest Management Specialist that provides a multidomain holistic ecological perspective to planning and implementing pest mitigation strategy for the past 10 years as Zenthanol Consulting. Focusing on Cannabis for most of this time, Matthew provides advice on a number of related topics of cultivation on his science science-communication YouTube channel Zenthanol as well as Instagram and Twitter (@Synchangel) sharing useful pest prevention and curative strategies alongside academically-sourced information.

Matthew is an advisory board member of the Cannabis Horticultural Association based in Humboldt, and regularly travels across the USA to evaluate cultivation sites for improved readiness against biosecurity threats. He has written articles for magazines such as Terpenes and Testing and 1000 Watts, is cited as a contributing editor in Ed Rosenthal’s “Marijuana Garden Saver: A field guide to identifying and correcting cannabis problems” and has written a chapter about Integrated Pest Management in Cannabis for the upcoming agricultural book, “Biopesticides in Organic Farming: Recent Advances”. Additionally, he has spoken about rare and newly documented pests in the Cannabis cultivation industry, as well as novel treatments, using hundreds of academic sources composed in a personal database.