Final report for OS19-130

Project Type: On-Farm Research
Funds awarded in 2019: $14,913.00
Projected End Date: 03/14/2021
Grant Recipient: University of Kentucky
Region: Southern
State: Kentucky
Principal Investigator:
Jonathan Larson
University of Kentucky
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Project Information

Abstract:

The sugarcane aphid is a severe pest of sweet sorghum that can lead to complete crop failure. $16-25 million of sweet sorghum is grown annually in Kentucky US. Current management practices are limited and more need to be developed to improve the sustainability of sweet sorghum. Growers who practice organic agriculture must rely on insecticidal soap for chemical control, which provides inconsistent control of aphids. We propose the integration of parasitic wasp releases with insecticidal soap spray applications for sugarcane aphid management. Parasitoid releases will give organic growers another option to manage the sugarcane aphid, buffering against the inconsistency of insecticidal soap. Parasitoids deposit their eggs inside aphids, which hatch and kill the aphid as they develop. The parasitoid species Aphidius colemani has been found attacking sugarcane aphids in Mexico, can suppress sugarcane aphid populations in the lab and can be easily purchased by growers in large quantities for releases in their crops.

Project Objectives:
  1. Assess if mass releases of Aphidius colemani can suppress sugarcane aphid populations and reduce insecticidal sprays needed
  2. Improve sweet sorghum grower’s knowledge of effective sugarcane aphid management tactics

Cooperators

Click linked name(s) to expand
  • Kevin Lyons (Educator)

Research

Materials and methods:

Sweet sorghum fields were selected in south central Kentucky, US in 2019. Fields were cultivated and managed by Amish growers for commercial production. Eight fields (0.4 -1.2 ha) were paired and randomly designated as either a control or a parasitoid release field. Fields were surveyed weekly for sugarcane aphids. At the first detection of sugarcane aphids in a parasitoid release field, parasitoids were ordered from the insectary and released 48 hours after delivery along the middle of the field. Parasitoids were released at a rate of 14,800 individuals per hectare. Fields were searched eight days after release for evidence of parasitoid attacks on aphids in the form of parasitoid pupae, called mummies. Insecticidal soap sprays were performed by growers once the sugarcane aphid had crossed the recommended action threshold of 10/40 plants checked having >50 sugarcane aphids on a leaf. Fields were sprayed regardless of treatment to protect grower’s crop. Effectiveness of parasitoids was assessed by reduction in sugarcane aphids and number of insecticidal sprays needed.

2019 Field Season                                                                                                                                                          

8 fields, paired, one of each pair was randomly treated as insecticidal soap or insecticidal soap + parasitoid releases. Pairs were made based on proximity to one another. Growers were to spray insecticidal soap for SCA once the action threshold (10/40 leaves checked with >40 SCA in a field) in all fields.       

Fields monitored weekly for sugarcane aphid, at first sighting in release fields, parasitoids were ordered.        

Upon arrival, parasitoids were allowed to complete emergence in growth chambers and mate. Parasitoids were supplied with a 50/50 honey/water mixture for food.                                                                                                                      

After 48hrs the adults were released, 6,000 parasitoids per acre, along the center row of the sweet sorghum.     

Mummy (parasitized SCA) survey was done 12 days after release, but due to finding no mummies, the next four releases were surveyed for 8 days after release. The initial 12 day time was based on the maximum time it took for mummies to develop in the lab.

Initial plan was to release more parasitoids after the first release if SCA numbers kept increasing, but due to finding no mummies after all the initial releases (over 40,000 parasitoids in total), we didn’t release anymore.

2020 Field Season                                                                                                                                                          

8 fields, paired, one of each pair was randomly treated as insecticidal soap or insecticidal soap + parasitoid releases. Pairs were made based on proximity to one another.                          

Growers were to spray insecticidal soap for SCA once the action threshold (10/40 leaves checked with >40 SCA in a field) in all fields.                          

Fields were monitored weekly for sugarcane aphid, at first sighting in release fields, parasitoids were ordered.             

Upon arrival, parasitoids were released in grower fields in the evening.

Parasitoid adults/mummies were released into plastic containers (250 ml) and capped with mesh screen with holes large enough to allow adult parasitoids to escape. The idea being that parasitoids finish emerging in the field, not in growth chambers and are therefore younger and, hopefully, more likely to parasitize SCA.                 

8 days later surveys were done for mummies and if SCA populations did not decline, a second release of parasitoids was ordered for release.   

Research results and discussion:

Results

In 2019 no aphid mummies were observed in fields following releases. However, in 2020 there were aphid mummies recovered from the field indicating successful use of SCA as a host. Unfortunately, this did not lead to expected reductions in populations or in the need for insecticidal soap use.               

While this is a disappointing result for IPM advocates, it is an important set of findings as growers build an integrated approach to dealing with this emerging pest. These results can be shared with growers to help lead them to other control options and save them time and money for SCA control. It can also help future researchers to focus on other possible biological control agents to use in this agricultural setting. 

It should also be pointed out though, that this project worked with Amish growers in a rural region of Kentucky. They had not previously worked with biological control, despite having an interest in it. This project exposed 4 growers to the methods and possibilities of biological control, and despite its inability to help in this setting, they have expressed interest in utilizing biological control in their other agricultural endeavors. Amish growers are also well connected, and word has spread from this community to others in the state, even in Western Kentucky, about biological control. This could lead to more work in the future with this undeserved group and utilization of methods that have a reduced impact on the environment while being economically sustainable for growers. 

The experiences and results of this project are also being included in a 5 part Zoom Based “biological control certification” program for Kentucky Extension agents. Mercer is one of the presenters for this effort and as a result of this SARE grant is able to share helpful insights in this train the trainer program.                                                                                                                                       

 

Participation Summary
4 Farmers participating in research

Educational & Outreach Activities

10 Consultations
1 Curricula, factsheets or educational tools
1 On-farm demonstrations
1 Online trainings
2 Webinars / talks / presentations

Participation Summary

5 Farmers
2 Ag professionals participated
Education/outreach description:

The efforts and results of this project were featured in a Kentucky Pest News article and as part of a 5 part series on biological control for county extension agents. This training is focused on increasing the recommendation of biocontrol as a pest management strategy by agents and Nathan was one of the speakers, as am I. This project is ongoing, with 2 of the 5 classes complete.

Learning Outcomes

4 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation

Project Outcomes

2 New working collaborations
Project outcomes:

This project was designed and conducted by Nathan Mercer, now at UC-Berkely as a post-doc. To help him to be able to submit everything he needed as he left I agreed to submit his final findings on his behalf.

Mercer’s aims with this project were to help learn if there were options for biological control in sweet sorghum. Mercer implemented releases of parasitoid wasps across 2019 and 2020 with follow up assessments to determine if the wasps had utilized the sugarcane aphids (SCA) present in the field as hosts and reduced damage from the pest.

Materials and Methods

2019 Field Season                                                                                                                                                          

8 fields, paired, one of each pair was randomly treated as insecticidal soap or insecticidal soap + parasitoid releases. Pairs were made based on proximity to one another. Growers were to spray insecticidal soap for SCA once the action threshold (10/40 leaves checked with >40 SCA in a field) in all fields.       

Fields monitored weekly for sugarcane aphid, at first sighting in release fields, parasitoids were ordered.        

Upon arrival, parasitoids were allowed to complete emergence in growth chambers and mate. Parasitoids were supplied with a 50/50 honey/water mixture for food.                                                                                                                                                            

 After 48hrs the adults were released, 6,000 parasitoids per acre, along the center row of the sweet sorghum.     

Mummy (parasitized SCA)survey was done 12 days after releases, but due to finding no mummies, the next four releases were surveyed for 8 days after release. The initial 12 day time was based on the maximum time it took for mummies to develop in the lab.

Initial plan was to release more parasitoids after the first release if SCA numbers kept increasing, but due to finding no mummies after all the initial releases (over 40,000 parasitoids in total), we didn’t release anymore.

2020 Field Season                                                                                                                                                          

8 fields, paired, one of each pair was randomly treated as insecticidal soap or insecticidal soap + parasitoid releases. Pairs were made based on proximity to one another.                          

Growers were to spray insecticidal soap for SCA once the action threshold (10/40 leaves checked with >40 SCA in a field) in all fields.                          

Fields were monitored weekly for sugarcane aphid, at first sighting in release fields, parasitoids were ordered.             

Upon arrival, parasitoids were released in grower fields in the evening

Parasitoids adults/mummies were released into plastic containers (250 ml) and capped with mesh screen with holes large enough to allow adult parasitoids to escape. The idea being that parasitoids finish emerging in the field, not in growth chambers and are therefore younger and, hopefully, more likely to parasitize SCA.                 

8 days later surveys were done for mummies and if SCA populations did not decline, a second release of parasitoids was ordered for release.   

Results

In 2019 no aphid mummies were observed in fields following releases. However, in 2020 there were aphid mummies recovered from the field indicating successful use of SCA as a host. Unfortunately, this did not lead to expected reductions in populations or in the need for insecticidal soap use.               

While this is a disappointing result for IPM advocates, it is an important set of findings as growers build an integrated approach to dealing with this emerging pest. These results can be shared with growers to help lead them to other control options and save them time and money for SCA control. It can also help future researchers to focus on other possible biological control agents to use in this agricultural setting. 

It should also be pointed out though, that this project worked with Amish growers in a rural region of Kentucky. They had not previously worked with biological control, despite having an interest in it. This project exposed 4 growers to the methods and possibilities of biological control, and despite its inability to help in this setting, they have expressed interest in utilizing biological control in their other agricultural endeavors. Amish growers are also well connected, and word has spread from this community to others in the state, even in Western Kentucky, about biological control. This could lead to more work in the future with this underserved group and utilization of methods that have a reduced impact on the environment while being economically sustainable for growers. 

The experiences and results of this project are also being included in a 5 part Zoom Based “biological control certification” program for Kentucky Extension agents. Mercer is one of the presenters for this effort and as a result of this SARE grant is able to share helpful insights in this train the trainer program.                                                                                                                                       

 

Recommendations:

Future work that looks at sugar cane aphid in sweet sorghum should focus more on the use of insecticidal soaps. While control has been obtained with soaps and conventional insecticide applications of Sivanto Prime applied by growers, there is needed data that focuses on better calibrating the spray rate of the soap, the timing of application, and fine-tuning the threshold at which the soaps are applied. 

 

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.