<p>Agronomic
management decisions are made to maximize plant growth and crop yields but can
also be used as tools to manage insect pests. Different management practices,
such as nitrogen fertilization, cultivar selection, and planting date choice
can influence the foliar traits of a crop. Plant foliar traits play important
roles in mediating plant-herbivore interactions. Herbivores balance consumption
of plant tissue for nutritional gains while contending with plant traits that
may deter herbivory or are toxic. Agronomic management practices have been
widely studied in many crops, however, for a new or re-emerging crop, there is
less information on the influence management has on insect herbivory.
Industrial hemp (<i>Cannabis sativa</i> L.)
is a re-emerging crop in the United States that is gaining interest, but the current
literature has not clearly defined the influence different management practices
can have on hemp foliar traits and the role foliar traits play on hemp-insect
interactions. The goal of this study was to understand the influence management
strategies and temporal changes have on hemp morphological and chemical foliar
traits and how these differences alter herbivore performance. </p>
<p>To understand the influence of
management practices on hemp foliar traits and insect performance, I conducted
both greenhouse and field herbivory studies using field grown hemp in both
cases. In 2017 leaves from three different field-grown hemp cultivars, were planted
on two different dates, and received two different rates of nitrogenous
fertilizer and were then used for a no-choice feeding bioassay using fall
armyworm (<i>Spodoptera frugiperda</i>). Foliar
nitrogen, C:N, LMA, THC, and CBD were determined and insect performance was measured
as growth, consumption, and frass production. Management practices influenced
the foliar traits of hemp, specifically fertilization rate, cultivar, and the
interaction of fertilization rate with cultivar and with planting date altered
foliar traits. Fertilization rate had the greatest influence on herbivore
performance, driven by higher foliar nitrogen. Foliar nitrogen had a strong positive
influence on insect performance and the ratios of carbon to nitrogen and total
cannabinoids to nitrogen had strong negative influences on insect performance. </p>
<p>To measure foliar trait changes
over the course of a growing season in different cultivars and to determine
herbivore damage, three hemp cultivars were planted in 2018, and leaves were
collected at five time points to measure changes in foliar traits. To measure
herbivory, leaves were collected at the end of the 2018 growing season and percentage
of tissue removed by herbivores was calculated. Foliar traits changed across
the growing season, with a decrease in foliar nitrogen and an increase in the
ratio of carbon to nitrogen, leaf thickness, THC, and CBD. The foliar trait
that had the strongest positive influence on herbivore damage was foliar
nitrogen, and higher nitrogen was associated with more herbivore damage. C:N,
LMA, and ratio of total cannabinoids to nitrogen had strong negative influences
on herbivore damage. Both studies can give us insight into the foliar traits that
are driving hemp-insect interactions. Because foliar nitrogen had the greatest positive
influence, while the ratios of carbon to nitrogen and total cannabinoid to
nitrogen had the greatest negative influence on both performance and field herbivory,
focusing on management that affects these three foliar traits is important for
pest control. Since foliar nitrogen, C:N and total cannabinoids:N were all
affected by nitrogen fertilization, reducing the amount of nitrogenous
fertilizer applied while still considering yield could be and important
management tool to reduce insect pests. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8044646 |
| Date | 14 May 2019 |
| Creators | Marguerite Bolt (6636275) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Influence_of_Agronomic_Management_Strategies_on_Hemp-Insect_Interactions/8044646 |
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