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Author ORCID Identifier

https://orcid.org/0000-0002-2074-693x

Date Available

5-12-2026

Year of Publication

2026

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Agriculture, Food and Environment

Department/School/Program

Plant and Soil Sciences

Faculty

Robert Pearce

Faculty

Arthur Hunt

Abstract

Cannabis sativa L. is legally defined (U.S.) as hemp if the total tetrahydrocannabinol (THC) concentration remains less than 0.3% on a dry weight basis. Hemp can be produced for cannabinoid extraction, fiber, or grain. Hempseed meal and hempseed oil were approved as feed ingredients for chickens and performance horses in Kentucky. To leverage this opportunity, production requires improvement through an integrated crop management approach. This dissertation (1) reports the main arthropod and disease pests impacting hemp grain; (2) identifies grain yield components and their relationship with corn earworm, Helicoverpa zea (Boddie) (CEW); (3) evaluates Fusarium head blight (FHB) development across hemp reproductive stages and the efficacy of pesticide treatments (4) identifies hemp grain parts infected by Fusarium spp., and the relative incidence of species from Fusarium sambucinum species complex (FSAMSC). A multi-year survey of hemp plots highlighted the consistent incidence of FHB and CEW from early reproductive stage through maturity at two Kentucky research trials located in Fayette and Breathitt counties. Several additional arthropods were reported in abundance; however, further research is required to assess their impact on hemp grain yield and quality. Septoria (Septoria cannabis), Bipolaris (Bipolaris gigantea) and Cercospora (Cercospora cf. flagellaris) leaf spots were consistently observed over the years with a severity remaining below 20% of canopy evaluated. Plants extensively affected by Rhizoctonia web blight (Rhizoctonia solani) were reported only on one location in the 2023 season which was associated with prolongated humidity conditions during the reproductive stage. Grain yield components and CEW impact were studied through a 2 year-field trial with the cultivar Henola. Treatments included were (1) effective control (Coragen®, chlorantraniliprole, 18.4%), (2) natural CEW infestation, (3) high artificial CEW infestation, and CEW damage simulation (50% of inflorescence) performed (4) early (soft immature grain) or (5) late (1-week prior harvest with abundant mature grain). First CEW larvae were observed at the soft grain stage and increased towards harvest with a low overall abundance both years (< 1 larvae/plant). Number of larvae per 20 plants evaluated per plot in 2024 across treatments remained below 1, likewise, damage to inflorescences did not exceed 0.2%. In 2025, high artificial CEW infestation increased the larvae number compared to the natural infestation and effective control, with 9.0, 0.3, 0.01 larvae/plot, respectively, (p-value < 0.001). This increase in number was associated with a higher damage to inflorescences in comparison to the effective control, 3.43 and 0.26%, respectively (p-value: 0.0426). Grain yield was not different between the high and natural CEW infestation, and effective control in 2024 (1473.0, 1552.1, 1738.1 kg/ha) and 2025 (1195.0, 1378.6, 1434.5 kg/ha). Grain yield from the early CEW damage simulation was not different from the effective control, (1213.8 and 1046.8 kg/ha in 2024 and 2025, respectively). Late CEW damage simulation significantly reduced yield (916.3 and 517.0 kg/ha in 2024, and 2025 respectively, p-value < 0.05). Grain proportions of mature, immature and light-weighted grain were not different across treatments. The grain weight per plant was not different across treatments in 2024, nor was the weight of 100 randomly selected grains. In 2025 the late CEW damage simulation resulted in lower grain weight per plant compared to the effective control (1.8 and 4.2 g, respectively, p-value: 0.0276). Therefore, yield compensation in early CEW damage simulation could be explained by the number of grains per area, rather than grain proportions or individual weight. FHB impact on hemp grain and control efficacy was evaluated in a 3-year-long field trial conducted in Fayette County, utilizing cultivar NWG 2730. Treatments tested were four biopesticides with different active ingredients including Double Nickel® LC (Bacillus amyloliquefaciens strain D747), Cease® (Bacillus subtilis strain QST 713) and MilStop® (potassium bicarbonate, 85%) in conjunction, RootShield® WP (Trichoderma harzianum Rifai strain T-22), Lalstop G46® WG (Gliocladium catenulatum strain J1446) and LalStim Osmo® (glycine betaine) (in conjunction), and one conventional fungicide (Miravis Ace®, pydiflumetofen 13.7% and propiconazole 11.4%). Nontreated controls were included under two application schedules in 2023 and 2024 (water sprayed 6 or 2 times), and no water sprayed in 2025 during the flowering period. The FHB incidence and severity on inflorescences were evaluated weekly beginning at flower initiation and area under the disease progress curve (AUDPC) was estimated to compare the effect of treatments. Grain yield was determined, and the incidence of all Fusarium spp. (AFS) in harvested grain was evaluated between treatments, reporting the incidence of FSAMSC due to its recognized pathogenicity and mycotoxin production. Overall, we did not find significant differences between treatments on FHB symptomatology evaluated in field, or AFS or FSAMSC in grain. In 2024 the conventional fungicide applied 6 times resulted in a significant decrease of AFS in grain compared to the nontreated control (2 applications of water). This may suggest the presence of similarities in FHB control strategy between hemp and small grains, with flowering period as the main susceptible stage. Due to the current regulatory limitations for hemp pest management, further research efforts should continue the evaluation of biopesticides treatments to control FHB including the evaluation of spray application technology. Fusarium spp. infection in hemp grain parts was evaluated with grain harvested in 2024 and 2025. Field treatments included a fungicide (Miravis Ace®, pydiflumetofen 13.7% and propiconazole 11.4%) applied (1) 6 or (2) 2-times during flowering; (3) grain inflorescences with visible FHB symptoms; (4) nontreated control. In both years, Fusarium spp. incidence was generally prevalent in whole grains (11.1 to 92.9%) and hulls (14.8 to 92.6%), but significantly lower in hemp hearts (0 to 44.4%). No consistent differences were found between treatments. FSAMSC infections (as a percentage of all Fusarium spp.) ranged from 1.5 to 95.8% in 2024, and 0 to 40.7% in 2025. In 2024 FSAMSC incidence was not different across whole grains, hulls or hearts. In 2025, FSAMSC incidence was not sufficient to allow a reliable statistical analysis. Fusarium graminearum and F. sporotrichioides (FSAMSC), which are primary producers of trichothecene mycotoxins associated with human and livestock toxicosis, were isolated from hemp hearts. Germination rate was overall not different across field treatments, and generally higher than 90%, possibly associated with the lower infestation found in hemp hearts (embryo). Sustained research in hemp pest management is imperative, especially focusing on FHB. Quantifying mycotoxin concentration in hemp hearts relative to whole grains is essential to determining potential markets and regulatory standards of Kentucky hemp grain.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2026.260

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