Evaluation of flowering cover crops as an IPM tool in Northeastern hop production

2013 Annual Report for GNE12-033

Project Type: Graduate Student
Funds awarded in 2012: $14,154.00
Projected End Date: 12/31/2014
Grant Recipient: University of Vermont
Region: Northeast
State: Vermont
Graduate Student:
Faculty Advisor:
Dr. Heather Darby
University of Vermont Extension

Evaluation of flowering cover crops as an IPM tool in Northeastern hop production


The demand for locally sourced hops has reached the farming community resulting in a sharp increase in Northeast hop producers from six in 2009 to over 110 in 2013. These growers are small scale and produce anywhere from 0.25 to 10.0 acres of hops. The vast majority of hop growers in the Northeast are new to farming and have limited experience with pest identification and control.  Of the respondents to the UVM Extension 2011 Annual Winter Hops Conference survey, 92% stated that disease, insects and other pests were one of the major constraints to growing hops in the Northeast. The Northeast Hops IPM Working Group identified pest management guidelines for hops in the Northeast that focus on IPM and both organic and conventional agronomic practices.


This new demand has created a niche market potential for many farmers and hopefully more farmers can tap into this growing sector.  A Northeast hopyard can produce between 1,000-2,000 lbs of hops/acre (Darby, 2011).  A price point of $10-15/lb, identified by both brewers and growers as an acceptable price, would allow many farmers to gross between $10,000-30,000/acre (Wilson, 2010). Supporting this burgeoning industry could provide a substantial source of income to farmers, and serve as an agri-tourism opportunity for growers and brewers.


 Pests observed in northeastern hopyards include the two-spotted spider mite (Tetranychus urticae), eastern comma butterfly (Polygonia comma), Japanese beetle (Popillia japonica), potato leafhopper (Empoasca fabae), and hop aphid (Phorodon humuli). It appears that these insects are affecting the quality of hop cones and damaging crop yield.  Our preliminary scouting results before 2012 was the only research conducted on the northeast hop insect community. The Pacific northwest (PNW) is the major hop growing region of the US. Pests from the PNW are also a problem in our northeastern hopyards including, but not limited to, the hop aphid (Phorodon humuli) and two-spotted spider mite (Tetranychus urticae).  The use of integrated pest management practices such as cover cropping in hopyards has only been investigated in the PNW, and suggests that incorporating flowering plants among rows of hops may attract beneficial insects (James et al. 2009). Cover crops have also been shown to decrease erosion and improve soil health as well as aid in the availability of nutrients (Turner 2011, Olmstead 2006).            


The question we ask under this Graduate Student SARE Grant is, “With increasing cover crop plant species diversity and flower, is the number of pest and natural individuals affected?”. Arthropod counts, cover crop, hop yield and quality have now been collected for two seasons (2012 and 2013) with support from this grant. Our larger goal is to develop best management practices for pest control by partnering with farmers and brewers. We intend to ensure that hops grown in the northeast meet brewer expectations and quality requirements so the industry can be sustainable.

Objectives/Performance Targets

A. The first objective of this project is to work collaboratively with growers to identify arthropods among hop plants in the Northeast and create outreach materials to help farmers adopt IPM practices. Steps completed in 2013 included:


1. Two field days where arthropod identification was disseminated (VT and MA)


2. Results shared at Vermont Hop Conference held in Essex, VT and New York Hop Conference held in Morisville, NY


3. A “What Hops in a Hopyard? A Field Guide to Pest and Agronomic Management for Northeastern Hops” was created and distributed. (See appendix A)


B. The second objective is to evaluate the impact of cover cropping on arthropod communities in hop production.


1. Twelve weeks of sticky trap, vacuum, and detail arthropod sampling


2. Identification and sorting of 2012 season samples


3. Half of the 2013 arthropod samples have been sorted


4. Documentation of crop development, hop yield, and hop quality data has been entered, calculated, analyzed.


Approach and Procedures

Cover crops


The cover crops were planted between the rows of hops on May 15, 2012. There were two rows of hops abutting the cover crops. One row consisted of Cascade and the other row of Nugget hops. In each row there were 6 hop hills (2 plants per hill) 5 feet apart and the rows were spaced at 10 feet making each of 9 cover crop plots a 14 by 30 foot block. The experimental design was a randomized complete block with split plots replicated three times. The main plots were cover crops and the split plots hop variety. The objective was to compare the following treatments for their efficacy as an attractant to natural enemies: 1) non-flowering, mowed control, 2) flowering red clover, and 3) flowering mixture of red clover, beebalm (Monarda fistulosa), common yarrow (Achillea millefolium), and sunflower (Helianthus annuus).


Arthropod Sampling in Cover Crops


We preformed three methods of arthropod collection once weekly for 12 consecutive weeks for the second year starting June 5, 2013 and ending August 22, 2013.  The collection methods used in the cover crop study included 1) un-baited 3×5 inch yellow sticky cards hung between hop bines 4ft high on coir rope held with wooden close-pins, 2) suction sampling using a reverse leaf blower vacuum 25cc PoulanPro with mesh bag attachment, and 3) detail hand examination of 3 randomly selected leaves after vacuum samples were taken. First plants were suction sampled for 60 seconds on each of six plants within each plot. After we vacuumed each plant the arthropods held in the mesh bag were transferred to glass jars containing 70% ethyl alcohol. We then proceeded to randomly examine three leaves per plant for remaining arthropods. All sticky traps and vacuum sample jars were then brought to the University of Vermont Crops and Soil Lab to be identified to order and family. Recorded individuals were then pooled into functional groups for data analysis using ANOVA in Version 2.15.1 of R and JMP 9.0 Version 10.




Hop harvest was targeted for when cones were between 20 and 25% dry matter. At harvest, hop bines were cut in the field and brought indoors to be handpicked on a table The number of living bines at the bottom of the coir were counted and recorded, as were bine height, and pre-pick bine weight. Sidearm length was measured on each string at 5’ and 10’, and averaged together. Picked hops were weighed on a per string basis, 100-cone weights were recorded, and moisture was determined using a Koster Tester. Hop cones from each plot were sent to Alpha Analytics in Yakima, WA where they were analyzed for alpha and beta acids using spectrophotometry as per the American Society of Brewing Chemists (ASBC) Method of Analysis entitled Hops 6a. Hop Storage Index (HSI) was also measured using the ASBC Method of Analysis detailed in Hops 12.


The data presented is of three replications. Hop brewing quality data is presented as varietal averages across the trial. Yields are presented at harvest moisture and at 8% moisture on a per hill and per acre basis. Per acre calculations were performed using the spacing in the UVM Extension hopyard of 784 hills per acre.


The hot and dry, yet productive season of 2012 emphasized give and take dynamics of pest and natural enemy insects in addition to the importance of irrigation and air flow in hop production. Cover crop plantings established well in 2012 and matured into the 2013 season. More than 1,000 samples were collected in 2013. There were a total of 16,191 pest individuals and 3,342 natural enemy individuals within hop plant samples through vacuum sampling in the cover crop trial in 2012.On hop plants there was an average ratio of 42:8 pests to natural enemies. In agreement with similar cover cropping studies, our data support an increase of both pest and natural enemy individuals within cover crop plots (Tooker et al 2012, Hummel et al. 2012, Chen et al. 2011, Boucher et al. 2003, and Altieri et al. 1986).  However, we have not yet seen a significant difference between cover crop treatments. We report a significant difference between arthropod functional groups when compared by locations of hop plant and within cover crop treatments. Overall, we conclude from the cover crop trial is at an expected succession of first year phenological stage where pest arthropod populations did not decrease to date, yet yield and quality were not compromised by cover crop presence.



Impacts and Contributions/Outcomes

2012 Arthropod Results

As this grant funded the second season of arthropod pest and natural enemy collection. The 2012 season results are presented here. The following results provide insight into the arthropod groups within the functional groups of pests and natural enemies present in our experimental hopyard. These results also provide insight into the locations within our research hopyard where these functional groups are most abundant.


There were a total of 16,191 pest individuals and 3,342 natural enemy individuals collected from hop plants through suction sampling in the cover crop trial. The most abundant pest arthropods on hop plants in 2012 were two spotted spider mites (42.0%), potato leafhoppers (32.0%), thrips (8.7%), and aphids (4.0%). The most abundant natural enemy groups were parasitoid wasps (53.0%), spiders (19.8%) spider mite destroyers (9.0%), and minute pirate bugs (6.4%). Percentages are among functional group (natural enemy or pest) and depicted in Figure 1 and 2. In 2012 eastern comma butterfly larvae were less pervasive than expected and were not an economically damaging pest. On hop plants there was an average ratio of 42:8, pests to natural enemies. 


It is important to note that figures 1 and 2 are not measures of damage. Different sized arthropods have different impacts on the crop. Feeding method is also a difficult variable to compare between arthropods. The most abundant arthropods are not necessarily the most destructive per individual. This being said, two spotted spider mite and potato leafhopper supported by data here in addition to downy mildew were the most economically damaging to our yield in 2012.


When cover crop trial Nugget and Cascade varieties were compared, no significant difference was seen between the number of arthropod pests or natural enemies by variety. There was also no significant difference between the number of major pests or natural enemy groups by variety. Separately the number of two spotted spider mite, potato leafhopper, thrips, aphid, parasitoid, spider mite destroyer, minute pirate bug, and lady beetle individuals were compared by variety using analysis of variance. No difference by variety was found and therefore further analysis was conducted on pooled Cascade and Nugget samples.


As expected the cover cropped drive rows exhibited a higher abundance of all arthropods than hop plants per 60 second vacuum suction sample. It has been shown that with additional diversity, both pest and natural enemy arthropod groups increase (Tooker et al. 2012).  We found there to be remarkably consistent numbers of natural enemy and pest individuals across treatments and replicates in 2012.  It has been shown by Grasswitz et al. 2009 that a flowering cover crop in hops can take 3 years to mature. The cover crop arthropod community is continually changing given plant development. Although second year perennials were planted, the youth of our cover crop treatments in 2012 may explain the even distribution of arthropods within cover crops and on hop plants between cover crop treatments. 2013 arthropod results will be completed and reported by May 2014. 

2012 and 2013 Harvest Results

Hop yield and quality within the cover crop trial was not affected by cover crop treatment or variety in either 2012 or 2013. We interpret this to mean that our cover crop has not interfered with product yield or quality. Of note however, is the observation of an average higher yield in clover treatments in 2012 and higher yield in diverse cover crop treatments in 2013. This is shown in Figures 6 & 7. The 2013 quality results are depicted in Figures 8 & 9.

As noted earlier in this report, hop plants within the cover crop trail were not sprayed with insecticide yet maintained yield and quality. The natural enemies and pests present kept pest populations in check preventing outbreak of any one pest species. We conclude from visual damage comparisons between variety trial and cover crop trial harvested cones that two spotted spider mite was more injurious to hops in the sprayed variety trial due to secondary outbreak.

Appendix A

Appendix A: “What Hops in a Hopyard?”



Appendix B

Appendix B: Cover crop experimental design

Appendix C: References

Altieri, Miguel, and Linda Schmidt. “Cover Crops Affect Insect and Spider Populations in Apple Orchard; Manipulation of Cover Crops May Improve Biological Control of Some Pests.” California Agriculture (1986): 15-17.




Bugg, Robert, and Carol Waddington. “Using Cover Crops to Manage Arthropod Pests of Orchards: A Review.” Agriculture, Ecosystems & Environment 50.1 (1994): 11-28.




Chappell, Bill. “Small Beer Brewers Hit With ’50 Percent Local’ Rule In Massachusetts.” National Public Radio 5 Aug. 2011.




Frank, Steven, Paula Shrewsbury, and Okemetri Esiekpe. “Spatial and Temporal Variation in Natural Enemy Assemblages on Maryland Native Plant Species.” Community and Ecosystem Ecology 37.2 (2008): 478-86.




Friedlander, Blaine. “For First Time in More than Half a Century, a Brewer Makes Beer Entirely with New York-grown Hops, with Help from Cornell.” Cornell News; New York Hops. Cornell University, 19 Feb. 2004. Web. 1 Oct. 2011. <http://www.news.cornell.edu/releases/Feb04/Hops.bpf.html>.




Fye, R. “Cover Crop Manipulation for Building Pear Psylla (Homoptera: Psyllidae) Predator Populations in Pear Orchards.” Journal of Economic Entomology 76.2 (1983): 306-10.




Grasswitz, T., and D. James. “Influence of Hop Yard Ground Flora on Invertebrate Pests of Hops and Their Natural Enemies.” Journal of Applied Entomology 133 (2009): 210-21.




Ingles, Chuck. “Benefits of Covercropping in Orchards and Vinyards.” Sustainable Agriculture Research & Education Program. University of California Davis. Web. 5 Oct. 2011.




James, David. “Beneficial Arthropods in Washington Hop Yards: Screening the Impact of Pesticides on Impact and Function.” Final Report for Washington State Commission for Pesticide Registration (2004): 1-28.




Kihm, Winship. “A History of Hops.” 2005. Web. 6 Oct. 2011. 




Olmstead, M. “Cover Crops as a Floor Management Strategy for Pacific Northwest Vineyards.” Washington State University Extension 2010 Bulletin (2006 and 2010): 1-12.




Turner, Samuel, Chris Benedict, and Heather Darby. “Challenges and Opportunities for Organic Hop Production in the United States.” Agronomy Journal 103.6 (2011): 1-10. Print.




Heather Darby

Extension Agronomist
278 South Main St.
Burlington , VT 05478
Office Phone: 8027826054