Managing Corn Earworm in Hemp Field by Using Sweet Corn as a Trap Crop

Progress report for FNE20-951

Project Type: Farmer
Funds awarded in 2020: $14,895.00
Projected End Date: 03/31/2022
Grant Recipient: Wood Duck Landing Farm
Region: Northeast
State: Maryland
Project Leader:
Kelly Edwards
Wood Duck Landing Farm
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Project Information

Summary:

 Currently, there is no EPA-labeled pesticide or bio-pesticide in the U.S. for industrial hemp, and growers are facing challenges to manage insect pests and diseases. Additionally, Hemp producers indicate that target industrial hemp markets are sensitive to pesticide residue. Our farm has participated in the 2018 hemp pilot program. Dr. Simon Zebelo, from UMES, has identified most of the potential insect pests of hemp in our field. The most abundant and devastating pest was corn earworm (CEW). We had significant damage to the hemp flowers by CEW. CEW mainly dwelled and fed in between the flower buds, and it is difficult to see CEW until it causes visible damage. The CEW larvae contaminate the flowers with frass. We are proposing to develop a sustainable way of controlling CEW by using sweet corn as a trap crop. Moreover, in collaboration with Dr. Zebelo, we will evaluate if heavy insect infestation increases the D9THC beyond the legal limit (0.3%), there is literature that shows insect damage changes plant chemistry. The population of CEW and their damage will be measured by using pheromone traps and visual inspection, respectively. We anticipate that adjusting the ear forming sage of the trap crop with the flowering stage of hemp will significantly reduce damage by CEW. 

Project Objectives:

Objective 1: To develop a sustainable way of controlling CEW by using sweet corn as a trap crop

This project seeks to develop a sustainable way of controlling CEW by using sweet corn as a trap crop. Attractive sweet corn will reduce the insect population in the main hemp crop fields. CEW reported as the main pest of hemp in the northeastern states (Britt et al 2019). This study might benefit hemp growers all over the nation.

Objective 2: To assess the impact of insect herbivore damage in the level of cannabinoids.

This objective seeks to evaluate if the environmental factors such as insect damage increases the level of D9THC. The D9THC level for hemp (i.e. 0.3%) might be spiked up by insect herbivory, as result farmers might loss legal coverage under 2018 Hemp Act. This objective will provide info for educators, farmers and lawmakers.

Introduction:

Hemp and marijuana are both cannabis, but their morphology, chemical makeup, and usages are very different. Hemp has less than 0.3% of delta-9 tetrahydrocannabinol (D9THC) concentration. The recent Agriculture Improvement Act of 2018 includes language that further addressed many issues that had previously hampered the development of the crop. With the passage of the 2018 U. S. Farm Bill that removed hemp from the Federal list of controlled substances and declared it a distinct crop from marijuana, the emergence of hemp (Cannabis sativa) grown for CBD (cannabidiol) products as a potential crop has been sudden and dramatic. Hemp acreage expanded at a rapid pace in Maryland and other Northeastern states in 2019. However, due to the long moratorium on C. sativa in the United States, there is a serious lack of production knowledge for hemp and even less for pest management. Regarding available literature concerning insect pests present in North American hemp, information is dated, not region-specific, and does not address effective management methods.

Pest management in hemp is a serious source of concern and has proven to be challenging in Maryland this year. Because hemp production has been illegal for so long and with the complicated legality surrounding hemp, virtually no pest control products have been registered. Even if products were to be registered, labeling products for a new crop takes years. Consequently, Northeastern hemp growers have very few options for controlling the pests that are damaging their crops. Despite a lack of financial support for hemp-related research, Dr. Zebelo of UMES began research on hemp pest management in Maryland Eastern Shore. Russet mites (Aculops cannabicola) and corn earworm (Helicoverpa zea) have been the most important pests, such as brown marmorated stink bug (Halyomorpha halys), spotted cucumber beetle, and different types aphids have also been found in high densities on hemp. Despite that, the bill passed in 2014, and the recent Agriculture Improvement Act of 2018 includes language that further addressed many issues that had previously hampered the development of the crop. There is no EPA-labeled pesticide or bio-pesticide in the U.S. for industrial hemp, and growers are facing challenges to manage insect pests and diseases. Hemp producers indicate that target industrial hemp markets are sensitive to pesticide residue. Interestingly, the target market sensitivity to a pesticide will remain high even after EP-approved some pesticides because the method used to extract CBD oils will also even extract the trace amount of pesticide used, that may interfere with the quality of the CBD oil and final medicinal use.

Dr. Zebelo, from UMES, has identified most of the potential insect pests of hemp in our field. The most abundant and devastating pest was corn earworm (CEW). We had significant damage to the hemp flowers by CEW (see the attached figure 1). CEW mainly dwelled and fed in between the flower buds, and it is difficult to see CEW until it causes visible damage. The CEW larvae contaminate the flowers with frass . Here, we are proposing to develop a sustainable way of controlling CEW by using sweet corn as a trap crop. Moreover, project focuses on the 0.3% of D9THC in hemp plants that might spiked as a result of various environmental stressors. One of the environmental stressor is insect herbivores. As noted above, hemp cannot contain more than 0.3 percent D9THC, per section 10113 of the Farm Bill 2018. Any cannabis plant that contains more than 0.3 percent D9THC would be considered non-hemp cannabis or marijuana so that under federal law and would thus face no legal protection under this new legislation.

Cooperators

Click linked name(s) to expand
  • Dr. Simon Zebelo

Research

Materials and methods:

Objective 1: To develop a sustainable way of controlling CEW by using sweet corn as a trap crop

Background: When corn silk emergence was synchronized with tomato flowering and fresh corn silk was present during the tomato flowering stage, CEW infestation was lower in the tomato field with a corn border than in those without a corn border (Rhino et al, 2014), and attractive trap crops may further accentuate this tendency. Then, organically approved insecticides can be applied on the trap crop to arrest the CEW larvae.

Method: Attractive trap crops, sweet corn will be used to reduce corn earworm damage on hemp plots. Three line trap crop will be planted along the borders (perimeter) of the hemp plot (10 inches in the row, with 36 inches between rows). Trap crop study plots will be established on our farm at the beginning of the season (spring). Each test plot (hemp, Cherry blossom variety) will be ~ 200 ft long x 200 ft wide (20 rows 10 ft apart, ~4-6 ft plant spacing) (Figure 2). Similarly the control plots will be designed a mile or two miles apart from the trap crop plots. Hemp planting date will be adjusted with sweet corn, in order to match sweet corn ear production stage with hemp flowering stage. The population of CEW will be monitored using Heliothis mesh traps baited with corn earworm pheromone and monitor them weekly from July to September to determine if adult trap catch correlates with worm/larval presence in the hemp fields. Ten plants will be randomly selected per row, and will be assed for larvae and larvae will be counted per plant. Larval damage will be assessed visually, and the damage ratings will be based on a scale of 1 to 4 (1: no damage; 2: low damage; 3: medium damage and 4: high damage). Our farm topography suites our experimental design because our 40 acres of tillable land distributed over our 104 acres of woodland, so that we can replicate treatment (perimeter crop) and controls at least three times. Data will be analyzed using a general linear model using the SAS software.

Objective 2: To assess the impact of insect herbivore damage in the level of cannabinoids

Background: state and federal law dictated that Taylor do away with the crop. Any hemp plant with more than 0.3 percent D9THC, the psychoactive component, is considered marijuana, not hemp, and is therefore illegal without the licenses required to grow medical or recreational marijuana. The percentage may seem arbitrary, here we test how the D9THC and other cannabinoids might vary with insect herbivory.

Methods: For this experiment we will use cherry blossom, the wife, Sweeten and Hawaiian blossom hemp varieties. The plants first will be grown in a controlled environment and later on will be transplanted to a raised beds covered with black plastics to control the weeds in the Duck Wood Landings farm. When the plant reaches the mature flowering stage, randomly selected hemp plants will be housed in a cage for the insect herbivory test and similarly some plants will be housed in a cage as a control. Twenty pre-starved corn earworm larvae will be introduced to the insect herbivory cage, and the control cages left without insect. The insects will be allowed to feed for 24 hours, and then carefully will be removed from the plants. Flowers will be collected 3-5 inches of the plant from insect herbivore damaged cage (HD), control cage (CC), and from plants without cage (C) in triplicate. The flowers will be dried at 40oC with forced air ventilation for 2 hours, and samples will be extracted and analyzed by Gas Chromatography- Flame Ion Detector (GC-FID), and GCMS following the Drug Enforcement Administration (DEA) protocols.

Hemp produced in conjunction with the SARE grant will not be sold for profit and will either be destroyed or donated to UMES for research purposes.

Research results and discussion:

As per the proposal, attractive trap crops, sweet corn, were used to reduce corn earworm damage on hemp plots. Four lines of trap crop were planted along the borders (perimeter) of the Mountain Mango hemp variety plot (10 inches in the row, with 36 inches between rows). Similarly, the control plot was designed a mile apart from the trap crop plots. Attempts were made to adjust the hemp planting date with sweet corn to match the sweet corn ear production stage with hemp’s flowering stage. Unfortunately, this experiment was progressing well, and then just about the time when the hemp was about to flower in August, we were struck by tropical storm Isaias. The sweet corn plants were swept completely, and they were not able to recover.  We are planning to repeat this experiment next season.

In the United States, industrial hemp is defined as a Cannabis sativa L. plant not containing more than 0.3% delta-9-tetrahydrocannabinol (D9THC) by dry weight. Plants respond to insect herbivore damage by changing their chemistry to counter the effects of herbivore attack. Here, we hypothesized that the corn earworm (Helicoverpa zea) infestation might impact the level of cannabinoids (Cannabidiol (CBD) and D9THC).  

In a laboratory trial, the CBD hemp, Cherry Blossom, and The Wife varieties were subjected to herbivore damage (HD), Mechanical damage (MD), and Control. After 24hrs of the treatments, we found a significant increase in CBD and D9THC in HD plants compared with MD and Control plants. Similar experiments were conducted in the field condition in the wood duck landing farm. A substantial increase in CBD and D9THC observed in herbivore damaged hemp plants compared to the control plants. However, in the field trial, the levels of cannabinoids were not significantly higher in The wife variety. Interestingly, the Corn earworm larvae fed with CBD and D9THC spiked diet showed a significant reduction in body mass than the larvae fed with the control diets.

The level of cannabinoids seems not genetically fixed somewhat; it is affected by insect herbivory.  Our results suggest that CBD hemp plants are exposed to insect herbivory spikes in cannabinoid production and surpass the 0.3 % legal limit of D9THC. The growth and development of Corn earworm, the number one hemp pest in North America affected by cannabinoids. The increased concentration of CBD and D9THC observed in herbivore damaged hemp plants might be associated with the direct deterrence of the corn earworm larvae. Further research underway using different hemp varieties to assess if herbivory and other biotic stressors impact the level of cannabinoids.

Participation Summary

Learning Outcomes

20 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.