European Corn Borer Detection in Local Hopyards

Final report for FNE19-932

Project Type: Farmer
Funds awarded in 2019: $6,247.00
Projected End Date: 02/29/2020
Grant Recipient: The Hop Yard
Region: Northeast
State: Maine
Project Leader:
ryan houghton
The Hop Yard
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Project Information

Summary:

Our objective was to understand how to accurately detect European Corn Borers (ECBs) in New England hop yards and in turn create standardized scouting and control protocols so that major crop loss from ECB can be reduced or eliminated.Unlike most hop pests which are easily scouted and controlled, the ECB has proven difficult to manage because there is a small window of management opportunity before they bore into the plant rendering controls ineffective.

We compared three different detection methods–pheromone traps, a degree day model, and pest scouting methods to monitor populations of ECB moths to determine which method prompts timely treatment before damage can occur. We used field data to compare what we saw out in the fields to the associated accumulated degree days already established for corn growers.

Overall we were able to reduce crop damage by 65 percent compared to last season. A combination of pheromone traps used to determine the first arrival of ECBs in the yard and calculated accumulated degree days proved an effective means of ECB detection. However, more research must be done to improve the accuracy of site specific degree day calculations and how they correspond to the associate life cycle events for New England Hop yards. 

We found that traps placed within the yard rather on the grassy margins of the field where more effective at trapping ECBs. We observed that the New York strain of ECB is present at the yard as indicated by the preference of lure bait. We also observed that two generations of ECB moths visit the farm throughout the growing season.

Through field observations and pinpointing peak egg hatch through degree day calculations we were able to reduce crop damage by 65 percent and substantially reduce the amount of pesticides sprayed. The expected financial gain in reducing the loss of crops by 65% is significant. At even 100 extra pounds per acre, local hop farms could see a $1,500-$2,000 “gain” per acre. This also suggests that we can reduce the amount of time we spend on scouting practices and rely more on degree day calculations for treatment applications. Relying on a degree day model is easier, saves time and resources and has the potential to be more accurate than field scouting because the egg masses and instar stages are very hard to find due to their small size and instinct to hide among the foliage. Previously control sprays were frequent without the knowledge of EBC lifecycle events. Now we have a better understanding of the pests life cycle and how it corresponds with accumulating MDDs so that spraying can be timed accordingly.

Outreach was completed through a farm tour and a fact sheet promoted by UMaine Extension.

Project Objectives:

This project sought to understand how to accurately detect the European Corn Borer in New England hop yards and in turn create standardized scouting and control protocols. If we can understand the best way to detect ECBs and control damage, hop production in New England will see better yields and a higher quality crop. We aimed to compare three different detection methods–pheromone traps, degree day models, and pest scouting methods–to monitor populations of European corn borer moths and determine an economic threshold for treatment to decrease the amount of spray intervals needed to control this pest. We evaluated these detection techniques to better understand when ECB moths begin moving into hops starting in late spring. This could lead to the creation of the standardized scouting and control protocols, which will be shared and leveraged by farms throughout the region.

Introduction:

Over the last several years, the European Corn Borer (ECB) has caused concern for many hop farms in New England. The ECB is an eastern pest extending west to the rockies. As most hop production has traditionally occurred in the Pacific Northwest, it has not been a major concern for the majority of hop producers in the country. Controlling crop damage caused by ECBs is unique to the Eastern states and has become a major concern with the recent revival of hop farming in the region. Monitoring and control for ECBs is well understood for corn fields but little work has been done for establishing proper monitoring and control methods for hops. Moreover, hops are a perennial plant that stay rooted in the ground for many years and techniques like plowing stalks under to kill overwintering pests and altering spring planting dates used in annual corn production for controls are not applicable. Therefore determining effective control measure is paramount among New England hop yards as multiple yards report significant levels of damage and decreased yields due to this pest. It’s a critical problem for hop farms in the area, as thus far effective control methods have not been established, creating a serious risk to growing hops in the region.

Controlling ECBs is a two part problem– first you have to establish a scouting protocol and then you have to determine how to treat the pest once it arrives. There is no standard scouting protocol for detecting ECBs in hop yards and while pesticides exist to control ECBs, there are no economic thresholds for determining when treatment is recommended. If there was more information about how to monitor the moths arrival and when to treat, there is a possibility of reducing damage caused by ECBs in New England. Understanding what protocols work the best and when treatment should be initiated would also help reduce the amount of pesticides used to control this pest. Timing is everything and rather than blanketing the fields as a precautionary measure, farmers could know exactly when to target the ECB. Reducing the amount of pesticides used on site will decrease environmental risks associated with these chemicals and lower farm inputs required for a profitable crop. 

The ECB prefers corn, especially sweet corn, but also attacks other vegetable crops like peppers, beans and tomatoes as well as many other herbaceous plants like some weeds. The damage in hops is from internal bine feeding where larvae enter the center of the bine, usually at a leaf node or between bines that are tightly wound around the trellis string. Weakened bines are susceptible to breakage from wind or high powered mechanical sprays used for treatment applications, or results in a secondary bacterial infection. Once bines break hops quickly dry up and do not mature properly, dramatically reducing yields. Damaged hops can easily be mistaken for downy mildew damage.

Regional farms have thus far attempted various controls with both organic (such as spraying Bacillus thuringiensis (Bt) and covering plants with diatomaceous earth) and non-organic (several pesticides) practices. These attempts have proved mostly ineffective, however, as proper scouting methods and best practices to determine timing are not available. 

So far, we know the moths life cycle and have developed trapping methods used in corn fields. ECB adults are hard to detect because of their nighttime flight patterns. Determining when the moth is active is crucial for controlling the larvae because this pest is the most susceptible to insecticides after the eggs first hatch. The initial generation in the spring is the most critical and compact in terms of flight and egg-laying, making them the ideal target. Moths begin to emerge in late May and early June (David Handley, U. Maine Extension, 2018).

Only larvae that have not bore into the plant can be killed so the treatment window is very tight. In other words, between the time the eggs hatch and the larvae bore into the plant, there is a specific period, or window, when pesticides must be applied to be effective. Egg deposition in a given field may last three weeks (David Handley, U. Maine Extension, 2018). Insecticides kill larvae over a relatively short period of time; therefore, they must be applied before all eggs are deposited. If the treatment is delayed, larvae from eggs deposited early in the egg-laying period will enter the plant and will not be controlled effectively by the insecticide. This makes early detection of early emerging moths critical to properly timing applications.

Description of farm operation:

The Hop Yard has been in business since 2011 and has grown to over 10 acres of hops spanning five different varieties. The Hop Yard is a full time operations that provides fresh (wet) hops and pelletized hops all year long to local breweries.

Cooperators

Click linked name(s) to expand
  • David Handley - Technical Advisor (Educator and Researcher)
  • Ryan Houghton (Researcher)
  • Acadia Tucker (Researcher)

Research

Materials and methods:

In order to determine best practices for detecting ECBs in hops yards we adapted pheromone trapping methods, degree day models and scouting protocols typically used for corn. 

Pheromone traps

We used wire mesh cone traps with a baited lure because research suggests these traps are the most efficient at catching ECB males compared to delta sticky traps and bucket traps. We settled on the Heliothis-type traps and bait them with two different pheromones targeting the two races of ECB known to reside in Maine (a New York strain and and Iowa strain). Traps were initially baited on May 20th and the lures swapped out each week. A total of four traps (two per pheromone type) were placed within the yard next to hops and four traps (two per pheromone type) along the grassy margins of the yard where these moths are known to prefer. 

The traps were initially hung just below the plant canopy because this location has the most accurate population count compared to traps placed just above the plant canopy. As the hops started to grow, traps were raised to keep up with the growth until plants reached overhead. This decision was made because, unlike corn, hops grow over 25 feet tall making it unrealistic to empty traps that were so far off the ground. Traps were checked weekly for the presence of ECBs and the number of moths were recorded for each trap. 

Field Scouting

We sampled 100 plants (20 plants per row in five different locations across the yard) every week for evidence of ECB eggs and/or larval infestations starting in the spring. Three leaves per plant where inspected for eggs and worms and the bine of the plant was inspected for bore holes. We considered a plant damaged when bore holes were present. 

We also looked at infestation rates at the end of the season during harvest. At the time of harvest plants are cut and removed from the field to be processed and picked. At this time, entire plants are easily inspected for damage and a simple count of infested plants vs. unharmed plants were tallied for each of the five varieties on the farm. A total of 100 plants were inspected and the percentage of infested to healthy plants was recorded.

Degree-Day Model

We used a standard predictive degree day model for ECB moth emergence presently used in corn, to determine if it can be applied to hops. Basic degree day models take the average between the maximum and the minimum daily temperature. Daily degree days (DD) accumulate throughout the season and correspond to relevant ECB life cycle events. For more accuracy we calculated modified degree days (MDD) by integrating the developmental threshold for ECB growth which is 50 degrees F.   

[(maximum temp. + minimum temp.)/2]-developmental threshold =MDD

Table 1. Historic degree day life cycle events for ECB. Source: a 2017 Iowa State University of Science and Technology report by Marlin E. Rice, affiliate professor, and Erin W. Hodgson.

We installed a Davis Vantage Pro II weather station in the yard to measure accumulated MDDs and compare this data to actual moth trap captures and field scouting described above. We used Table 1. to predict life cycle stages, originally developed for corn growers in the midwest because similar data for Maine hop yards does not exist. MDDs started to accumulate after the first moths was captured in a trap. Degree days continued to accumulate until the crop was harvested in early September.

Parasitic wasps

The use of biological controls like parasitic wasps was not part of the originally proposed study. However we felt that testing novel controls for ECBs would be useful information for New England hop growers. We purchased 3 million Trichogramma ostriniae wasp eggs that arrived on paper tabs. During the time when we believed moths were laying eggs as indicated by the number of accumulated MDDs, we stapled the paper tabs to the yards cedar poles, about two feet from the ground. To protect the eggs from the rain and slugs, we placed paper cups over the eggs as a barrier. Eggs hatched within three days of arrival. In order to see if the parasitic wasps destroyed ECB eggs, we scouted the yard for evidence of parasitized egg masses.

 

Research results and discussion:

Pheromone Traps

Two different pheromone lures were used to see which strain of ECB was more prevalent in the hop yard (NY vs IA). Over 98% of the total moths trapped where collected from traps with the NY lure. We also compared the difference in the volume of moth captures between traps in the yard with those placed in the grassy margins of the yard. The yard margin traps caught the first to arrive moths but the in yard traps accounted for 85% of the total moths captured, suggesting that we could reduce the number of traps we place along the border of the yard. Throughout the growing season we observed that two generations of ECB visit the yard (Figure 1). The first to arrive came in mid June with a peak in population occurring in early July where 71 moths were collected from traps in one week. The second generation arrived in mid August but the ECB population was much smaller when compared to the first generation.

Figure 1. The presence and population count for European Corn Borers in Gorham, Maine. ECBs were trapped using New York stain baited lures in Heliothis-type traps.

Field Scouting 

Field scouting proved to be a successful means of detecting the arrival of ECBs to the yard. Egg masses, leaf damage and bore holes were able to be found throughout the season but searching for them was time intensive and difficult to spot. None the less, we found some good examples of ECB presence in the yard that was instrumental in fine tuning a site specific degree day model going into next season.

 

ECB egg mass on the bottom of a hop leaf
Mature eggs have a distinctive black color just before they hatch
Since its difficult to find newly hatched ECBs on hop plants, egg masses were collected from leaves and monitored until they hatched to get a better understanding of the corresponding MDDs associated with this event.
An adult ECB found inside a hop bine
An example of pinhole feeding common of first and second ECB instars
Hop bine damage from ECBs
ECB pupate ready to overwinter in a hop bine

Using the information we gathered from scouting, we were able to determine corresponding MDDs to better help us predict when to spray for ECB in the future (Table 2). On average 17.7 MDDs accumulated each 24 hour period. 

First Generation

Stage

Activity

Accumulated MDD

Date of occurrence

egg hatch

pinhole leaf feeding

242

6/30

second instar

shothole leaf feeding

390

7/8

third instar

midrib and stalk boring

N/A

 

fourth instar

stalk boring

N/A

 

fifth instar

stalk boring

829

7/29

pupa

changing to adult

982

8/6

adult

mating and egg laying

1110

8/8

Second Generation

egg hatch

pinhole leaf feeding

1219

8/18

second instar

shothole leaf feeding

1335

8/25

third instar

midrib boring

N/A

 

fourth/fifth instar

stalk boring

1471

9/2

Table 2. The type of ECB damage that was observed during interval scouting and the corresponding date and accumulated MDD 

We also compared what we observed at the Yard to the published degree day predictions already established for corn growers in the midwest (Table 3). At the beginning of the season our observations more or less matched what was predicted from documented degree day calculations. In general the Gorham yard was 1 to 4 days behind what was expected from previous studies. However our observed MDDs for the second generation where 16 to 29 days ahead of what was expected from the historic data. This suggests that ECB behavior in the midwest is widely different from that of Maine and that we need to continue to observe MDDs and the corresponding life cycle events specific to Maine for more accurate treatment windows. 

 

Documented accumulated MDD

 

Number of days behind or ahead of the documented target

First Generation:

Stage

Activity

 

212

egg hatch

pinhole leaf feeding

-1.7 days

318

second instar

shothole leaf feeding

-4.1 days

435

third instar

midrib and stalk boring

N/A

567

fourth instar

stalk boring

N/A

792

fifth instar

stalk boring

-2.1 days

1002

pupa

changing to adult

1.1 days

1192

adult

mating and egg laying

4.6 days

Second Generation:

     

1510

egg hatch

egg hatch

16.4 days

1627

second instar

leaf feeding

16.5 days

1759

third instar

midrib boring

N/A

1984

fourth/fifth instar

stalk boring

29.0 days

Table 3. The difference between historic degree day predictions used by corn growers and observed degree days and the corresponding life cycle for the Gorham hop yard. Negative numbers indicate where observed MDDs are behind what was expected and positive numbers indicate when observed MDDs occurred faster than what was expected. 

Parasitic Wasps

In addition to controlling ECBs with the organic pesticide Bt, we also tried a biological control of Trichogramma ostriniae wasps which feed on ECB egg masses. We wanted to release these predators into the yard in an effort to cut back on spraying. While we have no conclusive data on the effectiveness of the wasps we feel that they did help based on scouting observations of parasitized egg masses and the presence of Trichogramma ostriniae wasps captured in our pheromone traps. 

What we believe to be a parasitized ECB egg mass

Harvest Data

At the end of the season each five varieties of hops were scoured for ECB damage. On average we saw a 35% damage rate across all varieties. Willamette, however, was observed at a 100% damage. It is unclear whether ECBs favor this variety over others or if it was purely based on this hops location in the yard. These final numbers are encouraging because last season we saw a 90% to 100%.damage rate for all varieties suggesting that our control efforts, on average, reduce crop damage by 65%. 

 

Research conclusions:

We aimed to accurately detect the arrival and presence of the European Corn Borer in order to control this pest efficiently and effectively. We used a combination of pheromone traps, degree day models and scouting data to determine an accurate treatment window to combat ECBs in New England hop yards, reducing pesticide use and farm expenses. We also tried using biological controls like Trichogramma ostriniae wasps to naturally reduce ECB populations without the use of pesticides.   

We found that traps placed within the yard rather on the grassy margins of the field where more effective at trapping ECBs. We observed that the New York strain of ECB is present at the yard as indicated by the preference of lure bait. We also observed that two generations of ECB moths visit the farm throughout the growing season.

Through field observations and pinpointing peak egg hatch through degree day calculations we were able to reduce crop damage by 65 percent and substantially reduce the amount of pesticides sprayed. This suggests that we can reduce the amount of time we spend on scouting practices and rely more on degree day calculations for treatment applications. Relying on a degree day model is easier, saves time and resources and has the potential to be more accurate than field scouting because the egg masses and instar stages are very hard to find due to their small size and instinct to hide amongst the foliage. 

The expected financial gain in reducing the loss of crops by 65% is significant. At even 100 extra pounds per acre, local hop farms could see a $1,500-$2,000 “gain” per acre. In addition, we expect the new ECB management plan to greatly reduce labor costs/effort in scouting. While scouting for ECB will still be required to some extent, the degree day model, at least for the first generation, has proven to be a reliable measure to dictate when controls are needed. Additionally, we expected measurable reductions in spray applications and costs for ECB control. Previously control sprays were frequent without the knowledge of EBC lifecycle events. Now we have a better understanding of the pests life cycle and how it corresponds with accumulating MDDs so that spraying can be timed accordingly.

 

Participation Summary
1 Farmer participating in research

Education & Outreach Activities and Participation Summary

1 Curricula, factsheets or educational tools
1 On-farm demonstrations
10 Tours
1 Email hop growers about our findings and what we specifically did to reduce ECB populations in our yard.

Participation Summary

3 Farmers
2 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

Regular farm tours and on farm demonstrations occurred at the farm during the harvest season. Those seeking more information of the impact of ECB and how our researched helped where given the attached factsheet and a full explanation of our new protocols. 

Prominent hop farmers in the region were also emailed and given updates about how our research and new understanding of ECB behavior was improving our ability to control this destructive pest. 

Finally an in depth factsheet was created to spread the word about ECBs because many hop yards could be mistaking borer damage for something else all together. This fact sheet is freely accessible on the cooperative extensions website and by request. ECB factsheet

Learning Outcomes

10 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

Scouting of ECB, identification of ECB eggs, weather pattern/degree day model for predicting ECB behavior, new control methods both biological and conventional.

Project Outcomes

2 Farmers changed or adopted a practice
Project outcomes:

The original goal of this project was to create a structured management plan around control of European Corn Borers (ECB) on hop farms in the Northeast. While much of our work was to determine how to create a management plan to implement and build upon in future years, we were lucky enough to also experience an obvious improvement in ECB control this year. We expect this benefit to grow even further as we continue to collect more data, build upon the plan, and share with other farms over the coming years.

In 2018, we saw significant crop yield loss in our hops due to ECB. There was also major damage from ECB reported in both Michigan and New York in 2019. This validated our need to come up with a trusted management plan, and thankfully in working on this on our farm this year we achieved this added benefit of much less yield loss. While we do not have exact qualitative numbers (as we were not tracking specific ECB pressure prior to this grant), we estimate that we saw 60% less yield loss in 2019 while testing some new techniques related to the ECB management plan. We are very encouraged by this, and expect to continue to reduce this as we further build out the plan and implement our new management practices. Prior to this summer, this pest was our largest concern regarding the ability to successfully grow hops in the Northeast in the long term.

Assessment of Project Approach and Areas of Further Study:

The project was a success because we accomplished our goal of determining the best detection method for ECBs, recognizing a valid window for control and successfully reducing crop damage. Much of this success was due to our partnership with David Handley at the Cooperative Extension. His knowledge about ECBs in other crops like corn and beans was valuable in adapting existing information to hops. We have more confidence going into next season that we can mitigate the damage and reduce population numbers go the yards most destructive pest with the ground work we accomplished this season.

But we still have more work to do. Our key challenge, this season and going into the next, is that our observations of ECB behavior are not exactly what the historical data suggests. This is understandable given that we relied on degree day information for a different location and crop because that’s what was available. Going forward we need to record more degree day information as it relates to ECB life cycle events for our specific crop and climate.  Another challenge was assessing whether or not the investment of parasitic wasps was worth the time or money. Using biological controls rather than spraying is a better treatment option but only if it works.  

Next season we will continue to work on our site/crop specific degree day model to determine the best treatment windows and better asses the parasitic wasps as a biological control. We think that more accurate degree day models and investigating alternative control methods like biological controls for ECBs can benefit all New England hop yards. 

 

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.