Quality, organically grown hemp can bring a high level of demand and offer significant economic gain to the organic grower. But tent caterpillars can devastate any crop, especially plump, fresh leaves and buds in a matter of hours when they are in a feeding frenzy. In the eastern U.S. there are several species of tent caterpillars including the Forest Tent Caterpillar, Malacosoma disstria and the Eastern Tent Caterpillar, Malacosoma americanum.
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| Eastern Tent Caterpillars crawling across the pavement in search of host plant material |
The forest tent caterpillar typically weaves silken mats on tree trunks where they congregate after feeding and for protection. Similarly, silky tents observed in the branches of trees are usually constructed by the eastern tent caterpillar.
Does Malacosoma americanum pose a serious threat to hemp? Hemp may not be the first host plant of choice for the eastern tent caterpillar but there are reports in literature (Alexander 1984b) of M. americanum exerting negative pest influence on hemp. It is possible that once a hungry population of tent caterpillars encounters hemp in cultivation, the caterpillars devour much of a crop without a second thought. Moreover, in addition to the defoliation, many caterpillars leave copious amounts of feces in hemp's flower buds.
Regardless, this past year brought significant numbers of tent caterpillars to Arendell Hill's trees. Several of our mature fruit trees were attacked by the caterpillars. Unfortunately, they ate the majority of buds, blossoms and leaves from many of our citrus and fruit trees.
It is easy to see just how many tent caterpillars are in a population once they are in their 'tent'. During their developmental phases, tent caterpillars will crawl out of their nest and feed on the host plant leaves.
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| Caterpillar eggs can survive the winter attached to leaf litter and fallen tent masses |
Worth repeating because of the tremendous potential economic damage a hemp cultivator can suffer is the fact that in addition to tent caterpillars damaging hemp plants by eating their foliage, caterpillars can leave copious amounts of feces as they crawl across and into, eating hemp flower buds. A feces filled flower bud will usually be considered a total loss.
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| Eastern Tent Caterpillar's woven 'tent'. |
The hemp farmer can avoid significant tent caterpillar damage by taking a few common sense pest management steps including; good housekeeping and a focus on cleanliness, support of biodiversity, understanding host plant potential and actual pest identification.
First it is important to be able to correctly identify any potential hemp pest caterpillar. Here in Florida the University of Florida's (UF) agricultural extension program can offer important help to farmers when it comes to growing almost any crop, including hemp.
Most counties in the state have an agricultural agent assigned and if the agent does not personally have the particular pest control experience one needs they will have access to the experts who do.
Here is the link to 'Find Your Local Agricultural Extension Office' website.
Your local agricultural extension agent will be able to assist you in identifying which of the species of tent caterpillars your growing operation may be challenged with. In addition to the tent caterpillar issue, your UF extension agent can help with most any other crop pest issues.
Along with the agricultural extension services discussed above, the internet is another resource to assist with in pest caterpillar identification. One hack I always turn to includes snapping a photo with my phone camera and in turn doing a Google image search. Although not as accurate by any means as the extension expert's identification help, the Google image search usually narrows down pest species choices to family or genus. Many times however, I've been able to successfully identify caterpillar types through the Google image search function.
Once the caterpillar has been identified, in this case we've identified some of our caterpillars as the Eastern Tent Moth Caterpillar rather than the Forest Tent Caterpillar, then the grower must decide what level of attention needs to be aimed at the potential pest caterpillar.
If the ecological, environmental and economic damage potential is great then the hemp farmer may want to consider an eradication or extra strong management approach. Eradication often involves pesticide applications, that though they may be considered 'organic' still possess moderate toxicity and lower the value and quality of the final hemp crop. Additionally, organic pesticides ultimately make a pest problem worse by unbalancing of the farm's long-term, functioning ecosystem dynamics.
If the ecological, environmental and economic damage potential is more moderate but certainly in need of addressing then a focused management approach may be advised. Moderately focused approaches can be taken many times when pest caterpillars first begin to appear and can include; traps, hand removal, facility cleaning, personal protective equipment, soil and container sterilization and more.
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| Caterpillar eggs may be attached to fallen leaves and hatch the next warm season. |
Finally, if the potential pest is a slow reproducing and easy to control organism them monitoring may be all that is necessary. Always keep good notes, including dates, times, events, pest numbers and types and control measures taken.
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| One of the most common vectors of caterpillar and larvae are fallen leaves |
Once the caterpillar has been identified and the level of necessity for adequate response has been decided them control actions can be implemented.Most importantly, it is crucial to understand the best ecological, environmental and economic outcome will be achieved only when the hemp farmer can bring the growing operation into balance with the surrounding ecosystem that itself is functioning within normal ecological variables. What this means from a pest control perspective is that any hemp operation will be mostly affected by pests which are themselves existing in an unbalanced state in the soil, vegetation and air in and around the hemp farm.
An eradication effort on the hemp growing area will be effective only as residual pesticide exists. As soon as the pesticide is degraded additional pests will enter the growing area from the surrounding ecosystem where they are out of balance with respect to excess population numbers. As the caterpillars continue to overwhelm more pesticides must be applied. Eradication and pesticide measures use can easily turn into an unnecessary and damaging repetitive cycle.
In the end, many times eradication efforts do more crop damage than the original pest issue the grower sought to control.
However, once the surrounding ecosystem is balanced with respects to ecological dynamics then hemp crop pest control becomes much more manageable.
The hemp farmer must also consider and strive for ecological balance within the totality of their plot, not just their greenhouse or outdoor hemp garden.
As a hemp farmer I can keep tent caterpillars out of my green house on a consistent basis only if the surrounding land is balanced with normal tent caterpillar population dynamics. If the tent caterpillar populations surrounding the hemp greenhouse are out of balance then eradicating them from the green house will only have momentary benefit. They will crawl right back in once the pesticide level is no longer a deterrent.
Supporting a natural ecological balance in and around the greenhouse or growing plot the farmer should manage the growing areas in a native and natural manner. Area native ecosystems have evolved over the millennia into a harmonious complex system of interacting life forms.
Usually nature has fine tuned native ecosystems to function in a precise balance, one where all forms of life play a part and one where all natural geophysical and climatic conditions help maintain homeostasis.
Once humans become involved though we have a tendency to change an ecosystem's natural variables to suite our plans. Examples of these impacts include; lack of fire, artificial irrigation, replacement of native plant flora with pest prone landscape plants, alteration of natural hydrology, alteration of native soils, change of noise levels, urban heat island effect and much more.
With respect to our tent caterpillars, annual wildfires suppressed for the safety of lives and property, allow a much greater quantity of tent caterpillar eggs to survive in the ground, on bark and on fallen leaves.
Historically, fallen leaves were usually part of the fuel annual lightening fires burned with and much of the egg bank was burned away. However with a lack of fire today potential pest eggs can exponentially accumulate, creating population numbers that are much higher than in fire acclimated ecosystems.
In the hemp greenhouse and across the hemp cultivation area it is important to keep leaf litter cleaned up. Leaves left to lie over the winter, especially those in piles under shrubs or around the base of fences make good incubation areas for next years caterpillars.
In the absence of fire, mowing and raking can help control pest eggs.
Leaf litter control is just one of the many integrated pest management control approaches a hemp grower can take.
I try and visualize my growing area as it would have functioned from a biophysical perspective as it might have before humans arrived.
Of the three pest management approaches mentioned above, an IPM approach to hemp cultivation, based on ecosystem principles consistent with balanced, native communities works best for growing quality, organic hemp products.
We will look at the value of using native plants and avoiding horticultural landscape plantings around the hemp farm, as well wildlife and other IPM tools in upcoming posts.
