Last post we discussed how Eastern Tent Caterpillars, Malacosoma spp., lay their eggs on the branches, twigs and leaves of hardwood trees. Once deciduous leaves fall and autumn winds blow twigs to the ground, caterpillar eggs can overwinter in accumulated biomass, groundcover vegetation and the dirt.
Until humans began the suppression of seasonal lightning fires, heat generated by combustion of dry biomass served to control population numbers of many pest organisms including caterpillars.
Natural seasonal fires served to cap population numbers of many pest insects.
Many farming operations today have reintroduced the practice of land fire management with prescribed burning. Prescribed burning involves the intentional application of fire to plots for the purpose of weed and invasive plant control, pest management, biomass fuel reduction (safety), hunting plantation management and many other purposes.
Often times though, prescribed fire may not be practical for safety sake and sometimes burning is simply impossible, say in a greenhouse for example. In the event a hemp cultivation area is located in an area where burning is not practical then leaf litter and grounds cleaning becomes a pest management tool of utmost importance.
Pest organisms take advantage of many transportation mechanisms referred to as vectors, to increase, sustain and spread their population numbers.
Leaves and twigs are subject to seasonal winds. Once deciduous leaves fall from a branch they may be blown hundreds of feet from the tree from which they grew. Over time these leaves can be carried significant distances via strong breezes.
Moth laid caterpillar eggs attached to wind blown leaves and twigs can stay viable through winter months and hatch when appropriate weather conditions develop during spring months, increasing hemp pest population numbers.
Leaf litter management will not cause moths or caterpillars to go extinct. On the contrary, managing tree leaf and twig drop can benefit the moth and caterpillar populations. Excess caterpillar population numbers and overgrowth may lead to weakened individuals, spread diseases and lead to larval food shortages. Good leaf management mimics nature's own way of managing insect populations.
As mentioned above, wildfires and lightning fires historically served as a limiting control on caterpillars and other insect egg spread. As fire frequency diminished, pest pressure increased. It is not really a big surprise that as the natural complexities of ecology change, a result of human actions, caterpillar and pest overpopulation occurrences are becoming more commonplace.
Today, because of the lack of seasonal wildfires it is important to 'simulate' fire's pest destruction effects by mechanically removing leaves that fall across the hemp cultivation areas. Importantly, the grower should not only remove tree, leaf and twig litter from active cultivation areas but also from adjacent areas of the cultivation plot or greenhouse area. Caterpillars and other leaf borne pests can crawl long distances.
Backpack blowers, rakes, lawn mower debris collection bags and other equipment can be employed to collect tree drop biomass (litter).
Once the twigs and leaves are gathered it is necessary to burn, compost or mechanically degrade the biomass to actually destroy pest eggs. A big pile of leaves in the corner of the property can serve as a giant pest incubator.
Today, understanding and managing the leaf-twig-wind vector complex is just one of many important factors comprising an organic hemp growing ecosystem.
Seasonal fire is always helpful, but not always practical. Therefore an organic hemp growing IPM program is benefited from simulated fire practices.
Predictable management of pest occurrences is a goal of organic pest IPM. Keeping leaf litter under control can help keep hemp crops pesticide and toxicity free, and avoid diseases, leaf destruction or bud feces damage.
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